NASA Design Guide for High Pressure Oxygen Systems

7/18/2019 NASA Design Guide for High Pressure Oxygen Systems

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NASA.ReferencePublication1113

Design Guidefor High Pressure

Oxygen ystems

Aleck C. Bond Henry 0 Fohl

Norman H. Chaffee Walter W. Guy

Charles S. Allton Robert L. Johnston

i and Willard L. Caetner

Lyndon B. Johnson Space Center

Houston Texas

Jack S. Stradling

JS Whi te Sands Test Facility

Laa Cruces New Mexico

.A . 1- - . __ _ _. . ._

NASA-BP- 1 13 E S I G GUIDE PCR HIGH ~83-32990

PRESSURE O X Y G E N SYSTEMS NASA ) 8 3 pHC A05/11F A01 S L 3

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NASA RP-11134 T~t le nd SuM~tle

DESIGt4 GUIDE FOR H I G H PRESSURE O X Y G E N SYSTEHS

7. Aurhorlsl

Aleck C Bond, Henry 0. Pohl Norman H Chaffee, Walter W GUY,Char1 es S A1 1ton, Robert L Joh nston , Will ard L. Castnerand Jack 5 . S t r a d l i n g

9 Paformrng Orpn~zattonName and ddreo

Lyndon B Johnson Space CenterHouston, f X 77058

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Xational Aeronautics a n d Space A dmin is tra t ionWashington, DC 29546

953-36-00-00-72

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13 T y p of Repon and P n ~ dov a e d

Reference Pub1 ic at io n14 Sponmr~ngA-Y code

5 Supplementary Notn

Aleck C Bond, Henry 0 Pohl, Normal H Chaffee, Walter W Guy, Charles S. All ton ,Robert L Johnston, and Willard L Castner: Lyndon B Johnson Space Center,Houston, Texas.

Jack S S t r a d l i n g : JSC White Sands Tes t F a c i l i t y , Las Cr uce s, New Mexico.

16. A b m m

The design of a succ essfu l high pres sur e oxygen system req ui re s sp ec ial knowledge of ma erialdesign prac t ic es , and manufactur ing and operat ional techniques. The current 1 te ra tu re ' on thsub je c t a reas i s indeed use fu l in p rov id ing a guide to the des igner f o r se lec t ion of ma te r ia land f o r deter mi ning general ized d esi gn ap proache s fo r oxygen system and components. However,many of the design subtle t ies , techniques, and re la ted knowledge, present ly i n use i n aerospaappl ic at io ns , have not been reported in the 1i t e r a t u r e . Consequen t ly , to a ssu re the a va i l ab i

o f th i s impor tan t in fo rmat ion to des igners o f fu tu re sys tems , the re sea rch , exper ience , andpr ac ti ca l know1 edge gained from desig ning systems fo r the nianned space f l ig ht program duri ng p a s t 20 years i s incorporated in to t h is document. The engineers from JSC and White Sands TesFacility have compiled and fornlatted this document to provide a ready and easy reference for

designers of any high pressure oxygen system.

17 ey Words 1Sug9arcd by Authoris) 1

High p ressu re Mate r ia l s t e s t sOxygen R el ia bi l i ty engineeringGases Nonfl amnable m at er ia l sFi re Preventio n Sys erns eng ineer ingOxygen sy s erns l a m a b i 1 i t ySpark ig ni t io n Accident prevention

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ACKNOWLEDGMENTS

This document i s a comp i la t ion o f te s t data knowledge des ign in fo r -mat ion and other re la te d technology f o r the des lgn of h ig h pressure oxygensystems drawn from several or ga ni za t i on al elements o f t h e Johnson SpaceCenter. I t was assembled and prepared through the e f f o r t s o f many i n d i -v i du a ls of the Crew Systems Pr op uls ion and Power and St ruc tur es and Me-chanics D iv is ions of the Engineer ing and Development D i rec torate and theMa ter ia l s Tes t Labora to ry o f the White Sands Tes t F a c i l i t y . The severalauthors o f t h i s document w ish t o acknowledge and thank the many in d iv id -ua ls o f these o rgan iza t ions who have con t r ibu ted ma te r i a l l y t o the p rep-a r a t i o n o f t h i s document.

NOTE

Whi le NASA does not endorse commercial products t h i s document i n r e -p o r t i n g t h e r e s u l t s o f m teri ls t e s t i n g of nec es s i t y uses s pe c i f i c t r ade

names o f the mater ia l s tes ted . This use does not i mpl y tha t t her e are nos u i t a b l e s u bs t i t u t es av a i l ab l e ; how eve r t he reade r i s cau t ioned t ha t sub-s t i t u t e m a t e r i a l s s houl d be s ubj ec ted t o t he same s t r i n ge n t t e s t r equ i r e -ments th a t the repor te d ma ter ia l s have undergone. The gu ide l ines i n t h i sdocument a r e p r es ent ed i n t he s p i r i t o f r es pons i b l e c om un i c a t i on o f t here su l t s o f research and development . Ne i the r the U S Government nor anype r s on ac t i ng f o r t he U S Government assumes any l i a b i l i t y re su l t i n grom t h e use o f t he i n f o r m a t i on c on t a ined i n t h i s document.

Preceding page bl nk



CONTENTS

Page

. . . . . . . . . . . . . . . . . . . . . . .NTRODUCTION 1-1

. . . . . . . . . . . . . . . . . . .GNITION MECHANISMS 2 -1

. . . . . . . . . . . . . . . . . . . .ATERIAL SELECTION 3 -1MATERIAL TESTS . . . . . . . . . . . . . . . . . . . . . 3-1BATCH/LOT TESTING . . . . . . . . . . . . . . . . . . . 3-5

. . . . . . . . . . . . . . . . .ONFIGURATION TESTING 3-10. . . . . . . . . . . . . . . .ATERIAL RECOMMENDATIONS 3-10

COMPONENT DESIGN . . . . . . . . . . . . . . . . . .COMPONENT HOUSINGS . . . . . . . . . . . . . . . . .

T h i n w a l l s . . . . . . . . . . . . . . . . . . . . .. . . . . . .l i n d Passages o r Dead End Cav it ie s

Sharp Feathered Edges . . . . . . . . . . . . . .B u r rR e mo v a l . . . . . . . . . . . . . . . . . . .. . . . . .lowImpingementonAluminumHousings. . . . . . . . . . . . . . . . . . . . . . .ALVESStat ic and Impact Loads on Submin ia ture Par ts .Check Valve Chatter . . . . . . . . . . . . . . .. . . . . .o p p e t O s c i l l a t i o n ( A s y m n e t r i c a l F l o w )Ac tua t ion Ra tes . . . . . . . . . . . . . . . . .S i ng le B a r r i e r F a i l u r e . . . . . . . . . . . . . .R o t a t i ng Stem Valves . . . . . . . . . . . . . . .

SEALS . . . . . . . . . . . . . . . . . . . . . . .Flow Impingement . . . . . . . . . . . . . . . . .

. . . . . .l t e r na t i ng P ressu re (Redundan t Sea l )

Seal Extrus ion (Backup R ings) . . . . . . . . . .Seal Squeeze . . . . . . . . . . . . . . . . . . .R o t a t i o n o f S e a l s . . . . . . . . . . . . . . . .Seat Shape . . . . . . . . . . . . . . . . . . . .Dynamic Seals . . . . . . . . . . . . . . . . . .Meta l - t o-Meta l Rubbing Seals . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . .ILTERS. . . . .i l t e r s a t I n l e t s and O u t l e t s o f M odules. . . . . . . . .i l t e r s U ps trea m o f V a lv e S e ats

F i l t e r s I s o l a t i n g U n av oi da b ly " D i r t y " PassagewaysANCILLARY EQUIPMENT . . . . . . . . . . . . . . . .

Bootstrap Oxygen Turbopump . . . . . . . . . . . .Heaters . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . .ensors

.. . . . . . . . . . . . . . .YSTEMS DESIGY'J? . '&: ; ...... . 5-1..... . . . . . . . . . . . . . . . . . .Y STEM ARCHITECTURE 5 2. . . . . . . . . . . .ro te ct io n o f System Redundancy 5-2Loca t ion o f Oxygen Sys tem Re l ie f Po r ts . . . . . . . . . 5-3

SYSTEM FLOW DYNAMICS . . . . . . . . . . . . . . . . . . . 5-4System Eros ion . . . . . . . . . . . . . . . . . . . . . 5-4. . . . . . . . . . . .a v i t a t i o n i n R o ta t i n g E qu ip me nt 5-4



Page

F l ow I nduc ed V i b r a t i on i n B e l l ow s and F l ex i b l eJ o i n t s . . . . . . . . . . . . . . . . . . . . . . . . 5 5

Geyser i ng i n C ryogen ic L iq u id Oxygen P ropu ls ion. . . . . . . . . . . . . . . . . . . . .eed Systems 5 5

. . . . . . . . . . . . . . . . . .YSTEM THERMAL DESIGN 5 6S t a r t up M a l f unc t i ons i n R o t a t i ng E quipment and. . . . . . . . . . . . . .ynamic System Components 5 6. . . . . . . .ondensat ion on External System Surfaces 5 6. . . . .ockup o f Cryo gen ic Oxygen i n System Segments 5 7

Condensa t i o n o f Contam inan ts w i t h in C ryogen ic. . . . . . . . . . . . . . . .ystems Du r in g Loadin g 5 7. . . . . . . . . . . . . . . . . . . .YSTEM CLEANLINESS 5 8. . . . . . . . . . . . . . . . . .y s t e m L e v e l F i l t e r s 5 8. . . . . . . . . . . .ys tem F lush and Purge F i t t i ngs 5 8

. . . . . . . . . . . . . .CLEAN ASSEMBLY AND INSPECTION 6 1. . . . . . . . . . . . . . . .L tA N ASSEMBLY TECHNIQUES 6 1. . . . . . . . . . . . . . . . . . . .ssembl ingS ea ls 6 3

. . . . . . . . . . . . . . . . . . .hreaded Assembly 6 3. . . . . . . . . . . . . . . . . . . .efonnable Pa r ts 6 3. . . . . . . . . . . . . . . . . . . . . . .r es s F i t s 6 3elded. Soldered. and Braz ed Jo in ts 6 3. . . . . . . . . . . . . . . . . . . . . . . . .urr s 6 5. . . . . . . . . . . . . . . . . . . . . . .ub r i c an t s 6 5. . . . . . . . . . . . . . . . .NSPECTION REQUIREMENTS 6 6. . . . . . . . . . . . . . . . . . . . . . .h i n W a l l s 6 6

. . . . . . . . . .l i n d Passages or Dead End C a vi t i es 6 6eathered Edges and Machine Burrs 6 6

. . . . . . . . . . . . . . .ea l and F i l t e r P lacement 6 8. . . . . . . . . . . . . . . . . . . . . . . . .ebr i s 6 8. . . . . . . . . . . . . . .EINSPECTION RECOMMENDATIONS 6 9

. . . . . . .EMENTS. . . . . . . . . . .

TYPES OF TESTINGEng inee r ing Deve 1opment Tests

. . . . .u a l i f i c a t i o n Te sts. . . . . . .cceptance TestsGENERAL SYSTEM TEST REQUIREMENTS

EST PROGRAM CONTENTEngi ne er l ng Development Tes t s

. . . . .u a l i f i c a t i o n T e s tsAcceptance Tests . . . . . . .

TEST PROGRAM EVALUATION . . . .

. . . . . . . . . . . . . . . . . .LEANING REQUIREMENTS 8 1

SUMM RY . . . . . . . . . . . . . . . . . . . . . . . . . 9 1

. . . . . . . . . . . . . . . . . . . . . . . .EFERENCES 10 1



1 INTRODUCTION

Oxygen i s a r e l a t i v e l y en e r ge t i c r ea c t an t a t nor ma l amb ient cond i -t i on s and becomes m ore h i g h l y r e ac t i v e w i t h i nc r eases i n p r essu r e. A t

ve r y h i gh p r essu r es i t becomes ext remely react ive. The successful design,

development and op era t ion o f h i gh pressu re oxygen systems re qu i re s sp ec ia lknow?edge o f m a t e r i a s des i gn pr ac t ic es , t e s t phenomena, and ma nufa ctur in gand opera t i ona l t echn iques .

Dur in g the course o f the manned space f l i g h t programs, a gre at dealo f rese arch and te s t i n g has been conducted by th e Government and i t s con-t r a c t o r s t o develop h igh pressure oxygen systems used i n the propu ls ion ,power, and l i f e suppo r t systems o f manned ve hic les . To suppor t such va r ie dap p l i c a t i o ns , t e s t i n g has covered a b road spect rum o f env i ronmenta l ando p e r a t i n g c o n d it i o n s . As a r e s u l t o f t h i s r e s e a rc h and t e s t i n g , a w e a lt hof t e s t data and knowledge has been amassed on the r e a c t i v i t y o f a wide va-r i e t y o f m e t a l l i c and n o n m e t a l l ic m a t e r i a l s i n h i g h p r es s ur e e nv iro nm en ts .For example, r e f . 3, JSC-02681.) Another cur ren t da ta base on the prop-

e r t i e s a nd b e h av io r o f ox yg en i n i t s v a r i o u s s t a t e s has been co m pi le d i nt h e n i e -v ol ume Oxygen Techno1 ogy Survey, spo nso red by NASA s AerospaceSa fety Research and Data I n s t i t u t e ASRDI) 1972-1 975 re f . 1 . A d d i t i o n -a l l y , i n re fe re nc e 2, Clark and Hust have pro v ided a thorough re v iew o f al a r g e number o f r e p o r t s o n t h e o xyge n c o m p a t i b i l i t y o f b o t h m e t a l l i c a ndnonmetal 1 c mat er ia l s . These and oth er re1a t ed sou rces pub1 shed i n t hec u r r e n t l i t e r a t u r e a re in de ed us e f ul i n p r o v i d i n g a g u id e t o t h e d e s ig n e rf o r t h e s e l e c t i o n o f m a t e r i a l s and f o r d e t e rm i n in g g e n e r a l i z e d d e s ig napproaches f o r oxygen components and systems. However, many of th e de sig nsu bt l e t i e s , t echn iques , and re1a t ed know ledge, p r e se n t l y i n use i n aer o-space app l ca t i o ns , have no t been adequa te t y r e po r t ed i n t he 1 t e r a t u r e .

Our exper iences have proved th a t a succ ess fu l h i gh pres sure oxygen

sys tem i s no t nece ssa r i l y ach ieved m ere l y by se l ec t i n g t h e m ost oxygenc o m p a ti b le m a t e r i a l s a v a i l a b l e . Because, even the be st m at er ia ls have1 m i t a t i o n s , i nn ova t i ve des ign fea ture s and techn iques must be employed t omake up f o r ma te r ia l def ic ie nc es . Space program engineers have gained con-s i de r ab l e unde r s t and i ng o f t he e f f ec t s o f geom e t r y on t he des i gn o f oxygensystem components and have developed des ign fea tu re s d i r e c te d a t overcom-i n g some o f t h e phys i c a l l i m i t a t i on s o f m a t e r i a l s . Much has been l ea r nedabout unsafe and undes i rab le des ign prac t i ces . Advancing technology, w i t hth e a t te nda nt demand f o r s to rag e and use o f oxygen a t i nc rea s in g pressuresand f l o w rate s, makes i t i m pe r a t i ve t ha t t h i s des i gn expe r t i se and know l -edge be w e l l unders tood and documented fo r ap p l i c a t i o n by the fu tu re deve l -ope rs o f space f l i g h t hardware .

There fore , t he pr imary purpose o f t h i s handbook i s t o document andp r o v i d e a r e p o s i t o r y f o r c r i t i c a l and i m p o rt a n t d e t a i l e d d e si g n d a t a andi n f o rm a t i on , h i t he r t o unpub li shed , a l ong w i t h s i g n i f i c an t da t a on oxygenr e a c t i v i t y phenomena w i t h m e t a l 1 c and nonm eta l 1 c m a t e r i a l s i n m ode ra tet o very h ig h pressure envi ronments. The au thors , repre sen t i ng severa l d i -v i s i on s o f t h e Eng ine er ing and Deve lopment D i re c t o r a t e o f t he JohnsonSpace Center and i t s Whi te Sands Test Fa c i l i t y , have compi led and forma t -t ed t h i s da t a and i n f o r m a t i on t o p r ov i de a r eady and easy t o use r e fe r encef o r t h e g u id an ce o f d e s ig n e rs o f f u t u r e p r o p u l s i o n , power and l i f e s u pp o rt



sys tems f o r use i n space f l i g h t . Th i s document whi ch ve ry c l e a r l y l u s -t r a t e s bo th good and bad des ign prac t i ces i s app l i cab le no t on ly t o aero-space d es ig ns b u t a ls o t o d e si gn s f o r i n d u s t r i a l and c i v i l i a n uses o fh i gh press ure oxygen systems. The inf orm at io n presented he rei n are er

r i ve d f rom data and des ign pra c t i ce s in vo lv in g oxygen usage a t p ressures

rang ing f rom about 20 ps ia t o 8000 ps ia equa l w i th thermal con d i t io nsra ng ing from room temp eratu res up t o 500° F.



2 I G N T O N MECH N SMS

The number o f p o te n t i a l i g n i t i o n s ou rc es t h a t c o u ld be p re s e n t i neven a s imp le component in tended f o r h ig h p ressu re oxygen se rv ice i s qu i te

la r ge and va r ied . Fo r example , e l e c t r i c a l sensors o r hea te rs can f a i l andcause a r c in g , s p a rk i n g o r o v e rh e a t in g wh ic h l e a d t o i g n i t i o n . Small con-t a m i n a t io n p a r t i c l e s , b o t h m e t a l l i c o r n o n m e ta l li c , can be a c ce l er a te d t os o n ic v e lo c i t i e s i n h i g h f l o w re g io n s o f t h e c omponent a nd l e a d t o imp ac ti g n i t i o n o f s u sc e pt ib le m a t e ri a ls . C on ta m in at io n c an a l s o c o l l e c t i n s t ag -nant re g ions o f a component and be heated t o i g n i t i o n by pneumatic shockor ad iaba t ic compress ion .

A c tu a t i o n c an cause imp ac t l o a d in g o f v a l v e s e a t s o r o th e r d e ta i lp a r t s r e s u l t i n g i n f a i l u r e o f t he p a r t s o r m e ch an ic al ly i nd uce d i g n i t i o n .F a i 1u re t o c o ns id e r m a t e r i a l h ard ne ss d i f f e r e n c e s c an r e s u l t i n g a l i n go f r u b b i n g s u rf ac e s wh ic h ca n cause b ot h f u n c t i o n a l f a i l u r e o r i g n i t i o n .C h a t t e r and s ub se qu en t f r e t t i n g c a n re s u l t f r o m u nb alan ce d a i r l o a d s ,

C a v i t y r es on an ce l e a d in g t o i g n i t i o n o f t r ap p e d c o nta m in a nts c an o c cu ri n b l i n d passages upon system a c tua t i on . F lo w in du ce d v i b r a t i o n l e a d i n g t os ys te m f a i l u r e c an a l s o o c cu r i n b e ll o w s a nd l i n e s where s ys te m d e s ig n o fs u p p or t s t r u c tu re i s n o t a de qu ate . Flow i nd uc ed c a v i t a t i o n i n LO2 systemsmay r e s u l t i n f or m at i o n o f i g n i t i o n s u s c e p ti b l e f r e s h s ur fa ce s.

C o n s id e r at i on o f i g n i t i o n mechanisms s h o ul d i n c l u d e a l l o f t ho se f a c -t o r s l i s t e d above a nd s h o uld be covered dur ing des ign o f both componentsand systems. W h i le t h i s 1 s t i n g c o v ers t h e most f r e q u e n t l y ob se rv ed i g n i -t i o n s ou rc es , t i s n o t c on si de re d t o be e x ha u st iv e . c a r e f u l f a i l u r emodes and e f f ec ts ana lys is wh ich inc ludes i g n i t i o n as a f a i l u r e mechan ismshou ld be conducted as a p a r t o f each new design.



3. MATER L SELECT ON

Materials currently used in high pressure oxygen systems range from

ignition-resistant materials like Monel 400 to materials of widely varying,ignitability like butyl rubber and the silicones. The range of ignitabil-

ity as a function of pressure is illustrated in figure 1 for nonmetallicsand in figure 2 for metals.

The material selection process has historically been guided by consid-erations of functional acceptabi ity and 1 ight weight, with only secondaryconsideration being given to the possibility or ease of ignition.Many currently used materials appear to work primarily because the designin some way protects the ignition-susceptible material or because no parti-cle with sufficient energy to ignite the system has yet impacted it.While functional performance is obviously a very important requirement inthe design of high pressure oxygen systems, the incidence and severity offires indicates that selection based on ignition resistance is at leastequally important.

M i l e material selection a1 one cannot precl ude igni tion from thesemechanisms, proper choices can markedly reduce the probabil ty of ignition. For example, ignition induced by mechanical impact can be minimizedby selecting valve seats and balls that do not shatter under normal load-ing. Gall ing can be largely el iminated if potential rubbing surfaces aremade from materials with widely differing hardnesses. For all types of ig-nition mechanisms, selecting materials that have relatively small exother-mic heats o combustion I ike Monel 400 and Inconel 718) will reduce notonly the probability of ignition but also the probability of propagation.Materials with high heats of combustion (stainless steels) or very highheats of combustion (a1 minum alloys) should be avoided wherever possible.A summary of typical heats of combustion as well as other properties forsome currently used materials is given in table 1

MATERlAl TESTS

Over the past 20 years a large number of different types of tests(ref. 2 ASRDI, Vol. IX, 1975 have been developed and evaluated by vari-ous groups, both public and private, in an attempt to find test methodsthat would predict materials behavior in planned applications. For non-metall ic materials, both mechanical and pneumatic impact tests have beenstudied. For metals, tests studied have included promoted ignition, me-chanical and particle impacts, rubbing or rotating friction, and arc orspark ignition, with a number of variations on each type. To date, no sin-gle test has been developed that can be applied to all materials, both

metals and nonmetals, to produce either consistent relative rankings or ab-solute ignition limits as a function of oxygen pressure alone. The teststhat appear to show the greatest predictive ability are as follows.

1. Nonmetals Test No. 13 in NHB-8060.JB, Ambient Liquid Oxygen andPressurized Liquid and Gaseous Oxygen Mechanical Impact Tests (ref. 4



ORIQW L P GE IS

O POOR QU LITY

Pressure, 1000 lb li n 2Material 0 1 2 3 4 5 6 7 8

Alumina

Teflon, PTFE

Tef Ion, g ass-f lled

Asbestos

Viton Rubber 1502

Viton Rubber

Parker Seal V747-70)

KEL-F

Teflon, FEP

Silicone rubber

Parco Seal 1235-70)

Vespel SP-21

Nylon

Tecfiuorfil B

Vespel SP-21

Vespel SP- I

Sllastic 675

Ty-Ply-3 adhesive

Neoprene RubberChloroprene

Parker Seal C-557)

Loctite 222

EPR Parker Seal E-529)

Butyl rubber

Epoxy glass laminate

Eccobond 104

M-Bond 61

Noryl plastic

1 Not ignitable 0 10 2 30 50

f A Igni tion varies wi th lot Pressure, M N I ~ ~

Always ignites

Figure 1. Range o f ignitability or nonmetallics.



CRlO ? AL EGE f

O POOR QUALITY

Pressure, 1000 lblin2

2 3 4 5 6 7 8

7 ot Ignitable0 10 20 30 40 50

Pressure, ~ ~ l r n ~m f l gnltlon varies with lot

Always Ignites

Material

Gold

Silver

Nickel

Monel

lnconel

MP35N alloy

Beryllium copper

Aluminum bronze or

Phosphor bronze

Copper

ElgiloyHastelloy

Ni-Span C

Brazing alloys

A-286 alloy

PH stainless steels

Stainless steels

Aluminum alloys

StellHe or Stoody 2

Tungsten carbide

with 10 cobaltBrass

Molybdenum/rhenlum

Permendur 2 V

Samarium cobalt

Magnesium

Solder

Carbon steel

K-601 Kennametal alloy)

Figure 2 . Range o f ignit bility or metals

3 3



ORIGlN L

O POOR



T h i s t e s t i s a m o d i f i ed form o f t h e Army B a l l i s t i c M i s s i l e AgencyABMA) impac t te s t , wh ich has been i n use fo r ove r 20 years. A schematic

o f t he t e s t f i x t u r e i s shown i n f i g u r e 3. I n ssence, samples o f the mate-r i a l b e i ng t e s t e d a re i m pa cte d a t 368 f t - l b / i n (772 kd/m2) w i t h oxygen a tth e pres sure and tempera ture o f in ten ded use. Twenty specimens a r e t e s t e df r om each l o t o f m a t e r i a l . I f two o r more specimens reac t , the l o t i s

r e j e c t e d . I f on ly spec imen o f 20 react s , an ad d i t i on a l 40 specimens aretested and, i f no more rea c t io ns occu r , the l o t i s accep ted. Thousands o fma ter ia ls have been tes ted and, t o date, no component ig n i t io n s have beena t t r i b u t a b l e t o m a t e r i a l s t h a t h ave passed t h i s t e s t when used w i t h i n t h el i m i t s ( temperatu re, impac t energy, and p ressu re ) o f the te s t enve lope. A

com preh ensive l i s t i n g o f t e s t r e s u l t s o bt ai ne d f o r a wid e v a r i e t y o f m ate-r i a l s i s g i v e n i n JSC-02681.

2. Metals - Whi te Sands Tes t F a c i l i t y (WSTF) P a r t i c le Impact -TR-277-001 - Meta ls I g n i t i o n Study i n Gaseous Oxygen

T h i s r e c e n t l y d ev el op ed t e s t has d em on str at ed t h e a b i l i t y t o d i s c r i m i -na te between ig n i t a b l e and non - ign i tab le me ta ls a t p ressu res up t o 6000 l b / i n 2

(41 M N / ~ ) . The t e s t f i x t u r e i n f i g u r e 4 i nvo lv es impac t o f cand ida te me ta l -l i c specimens w i t h t y p i c a l p a r t i c l e s i n t he 1 00 t o 1000 micron range a t son icve lo c i t i es w i t h oxygen a t th e temperatu re and p ressu re o f in tended use . Ex-p e r i e n c e t o d a te i n d i c a te s t h a t t h i s t e s t c o u ld b e a do pted as a me a n in g fulmethod fo r se lec t in g me ta ls f o r use i n oxygen systems.

The p a r t i c l e i g n i i o n p r e ss u r e i s d e f in e d as t h e p r e ss u re be lo wwhich the maximum s ized p a r t i c l e which can pen etra te th e components filt e r s and m oving a t s o n i c v e l o c i t y w i l l g n i t e t h e m a t e r i a l .

BATCH LOT TESTING

As i s r e a d i l y a p pa re nt f r o m t h e d a ta shown i n f i g u r e 1 many nonmetal-l i c m a t e r i a l s show a s i g n i f i c a n t r an ge o f r e a c t i o n p re s su re s when d i f f e r -e n t l o t s o f m a t e r i a l f r om t h e same s ou rc e a re t e s t e d u s i n g i d e n t i c a lm ethods. The re as on s f o r t h i s v a r i a b i l i t y a re n o t u nd er st oo d i n d e t a i land a r e p r o b a b ly d i f f e r e n t f o r each m a t e r i a l t e s t e d . As a r e s u l t , p r e d i c -

' t l o n o f t h e t e s t b eh av io r o f a g i ve n l o t o f m a t e ri a l i s p o s si b l e i n o n lya l i m i t e d number o f cases . Excep t f o r ma te r i a ls th a t have been p roved ac-cep tab le by t e s t s o f a t l e a s t 1 0 l o t s o f m a t e r i a l w i th o ut a s in g l e f a i l -u re, each new l o t o f m a t e r ia l mus t be expe r ime n ta l l y p roved accep table .Ma te r ia ls tha t have passed the necessary tes t ing and have been found to bei n s e n s i t i v e t o b a t c h / l o t v a r i a t i o n a r e shown i n t a b l e 2.

When t h e materials t h a t w i l l f u n c t i o n i n a d e s i gn r an ge f r o m t h os et h a t d o n o t r e q u i r e b a tc h c o n t r o l t o t ho se t h a t a lw ays i g n i t e a t t h e de-

s i g n pr es su re , t h e s e l e c t i o n l o g i c v a r i e s w i t h t h e s e n s i t i v i t y o f t he mate-r i a l . F i g u re 5 i l l u s t r a t e s t h e s e l e c t i o n and c o n t r o l l o g i c we have d ev e l-oped f o r h i gh p ressu re oxygen systems. It shou ld be no ted tha t us ingb a t c h / l o t i n s e n s i t i v e and b a t c h / l o t t e s t e d m a t e r i a ls be lo w t h e i r i g n i t i o np r e s s u r e s i g n i f i c a n t l y s i m p 1ife s th e t e s t requ irements , documentation, andrev iew



ORIGINAL PAGE i

OF POOR QUALITY

Pneu matic amp lifier Equa lizer pln anvilchamber N cavlty

Pneumaticampli f ier cham ber

High pressure seal

Pressurization

High pressure seal

Figure 3. Pressurized mechanical impact test chamber drawing.

3 6



ORIWAL PAGE 8

OF POOR QUALIV

Inlet

port

specimen)

Figure 4. White Sands T e s t F a c i l i t y hlgh veloc i ty sonlc) impactpla te t e s t f i x t u r e



OR lGlN L PAGE ffO POOR QiJALI Y

Not batchllot sensitiveimpact data show at intended-use conditions.

failures for 10 or more Use and refurbish

without further approval.

r

some lots \ yes r

Review material mechanical

impact test data

368 ft-lblin2 772 k. lm2).

pass at intended-useUse lots that passed

conditkns? - without further approval.

Conduct configuration test

ononditknsrticl~l~;nded-useor 4 times the k ls basis for waiver.expected number of cycles.

Board review and approval.

yes <n 'deq~ate>ubstltute materbl

available?

Use identical components

for 114 the number of cycles

passed in configuration test.

material equal to or better than

material used In configuration

Find new design. test.

Figure 5. Nonmetallic materials control logic.



TABLE 2.- MATERIALS THAT NOT REQUIRE BATCH CONTROL

M a t e r i a1 Type of Ma te r i a l F l u i d Max. temp., Max. pressure,

OF K ) 1b / i n2 ( ~ ~ / r n 2 )

E v e r l ube 812 D r y f i l m l u b r i cant OX 530 (550 ) 5500 (38 )LOX -297 (90) 1000 (6.9)

*Mi croseal 100-1 D r y rn l u br l c a n t GOX 200 (366) 1000 (6 .9 )LOX -297 (9 0) Amb ient

*Mi c ro se al 200-1 D r y f i l m l u b r i c a n t GOX 200 ( 36 6) 3300 (23)

LOX -297 (9 0) 1000 (6. 9)

* T r i o l u b e 1175 D r y f i l m 1u b ri can t GOX 350 (450 ) 3300 (2 3)LOX -297 (9 0) 1000 (6. 9)

K r y t o x 240 AB Grease GOX 250 (394) 1000 (6 .9)LOX -297 (90 ) 1000 (6 .9 )

K r y to x 240 AC Grease O 150 (339) 6000 (41 )

Br ay co te 3L-38RP Grease

T e f l on , PTFE P l a s t i c GO 250 (394) 1000 (6.9)LOX -297 90) 1000 (6.9)

25 g l a s s - f i l l e d P l a s t i c GOX 150 (339) 1000 (6.9)T e f 1on LOX -297 90) 1000 (6.9)

Rulo n A P la s t i c LOX -297 (90) 600 (4 .1)

KEL F P l a s t i c GOX 150 (339) 500 (3.4)LOX -297 (9 0) 400 (2. 8)

V to n Rubber 1542/1441 E l a st an er GOX 250 (394) 135 (0 .93)

T ec f 1u o r f B P l a s t i c OX 200 (366 ) 200 (1.4)LOX -297 (9 0) 275 (1. 9)

V e sp e l SP-1 P l a s t i c GOX 150 (339 ) 250 (1.7 )

V i o n Rubber (Parke r El a s t m e r

Seal V747-70)

Armal on TG-4060 Fa b ri c O X 275 (40 8) 400 (2.8)

Maximum use p ressu re on t hese d ry f i l m l u b r i ca n t s i s t h e m ximm pressu re whe e

1 0 - b a t c h d a t a a r e a v a i l a b l e . T hese l ub r i can ts m ay be accep tab l e a t h i ghe r p ressu res , 'b u t a d d i t io n a l t e s t i n g i s r e q u i r ed f o r p r oo f.



CONFIGURATION TESTING

f i t i s n o t p o s s i b l e t o fi nd , even w i t h b a t c h / l o t t e s t in g , m a t e r i a l st ha t m ee t t he f unc t i ona l r equ i r em en t s o f a des i gn , i t may be po ss ib le t op r o v id e s u f f i c i e n t p r o t e c t i o n from i g n i t i o n t o p e r m it use o f a suscep t i t j l e

m a t e r i a l .f

t h i s des ign approach i s used, t heni t

i s m a nd ato ry t h a t t h eadequacy o f t he des ign be demonstrated by con f i g ur a t i on t e s t i n g a t cond i -t i o n s more severe than th e expected worst-case use environment f o r th e com-ponen t i n ques t ion .

F o r c o n f i g u r a t i o n t e s t i n g t o be c o ns id e re d v a l i d , t h e t e s t s s h o ul d beconducted on hardware ident ica l to the proposed use hardware. S u b s t i t u t enonmeta l1 c s shou ld be ba t ch / l o t t es te d t o p rov id e a rep lacement base1 eeven though the ma te r i a l w i l l no t pass t he s t anda rd i mpact t e s t s i n t heexpected use environment. On ly nonmeta l l i cs tha t equa l o r exceed theb a t ch / lo t r a t i n g o f t he o r i g i n a l m a t e ri a l used i n t he c o n f i g u r a t i o n t e s t sshou ld be used t o re fu rb i s h the components.

The co n f i g u r a t i on t es t s shoul d use oxygen p r essu res a t l ea s t 10 pe r -cent above th e worst-case use co nd i t io n. Expected temperature 1 m i sshould be exceeded by at least 500 F 24 K . And, i f t he m at er ia l i s t obe s ub j e c te d t o r a p i d l y c ha ng in g pr es su re s, t h e p r e s s ur e r i s e r a t e u se d i nt he con f i gu r a t i on t es t s shou l d be a t l eas t t w i ce t ha t wh i ch t he com ponen ti s e x p e ct ed t o e x p er ie n c e i n o p e r a t io n .

f c y c l i n g o r m u l t i p l e r eu se o f t h e component i s a d e s ig n r e q u i r e -m ent, t hen t he con f i gu r a t i o n t es t i n g shou ld exceed by a f a c t o r o f 4 t h eexpec ted num ber of cyc l es o r reuses . Fa i l u r e o f t he co n f i gu r a t i o n t e s ta r t i c l e b e f o re c o m p l et io n o f t h e r e q u i r e d number o f c y c l e s w o uld l i m i tt he use l i f e o f t he com ponen t t o 114 t he number o f cyc l es ac t u a l l y com-p l e t e d b e f o r e f a i l u r e .

MATER IAL RECOMMENDAT IONS

The m a t e r ia l s l i s t e d i n t a b l e 3 have demonst ra ted super io r res i s tancet o i g n i t i o n and f i r e p r o p a g a ti o n i n h i g h pr e ss u re oxy ge n system s. V a lv eand pressure vesse l m at er i a l s a re examples. The s t a i n l es s s t ee l s norm al l yused f o r va lv e stems, bodies, and s p ri ng s a re p o t e n t i a l l y c om b us ti bl e i nh igh press ure oxygen sys tems. Monel a1 oys , wh ich a re s e l f ex t i ng u i s h in gi n oxygen f i r e s , a re av a i l ab le i n t he necessary range o f hardnesses. KM n e l can be used f o r t he v a l ve s tem and 400 -se ri es M onel f o r t h e va l vebody. S pr in g s can be wound from Monel wire . Though sm all diam ete r Monelw i r e i s n o t c u r r e n t l y a v a i l a b l e , m i n i a t u r e s p r in g s c an be made o f E l g i l o y .Sapphi re poppet b a l l s shou l d rep l ace tungs ten ca r b i de o r s t ee l b a l l s be-

cause s a pp h i re h as a lo w e r l e v e l o f r e a c t i v i t y a nd t h e r e f o r e i s l e s scom bus t ib l e ) t han e i t h e r t ungs t en ca r b i de o r s t e e l and i t i s more r e s i s t -an t t han tun gs te n carb id e t o b reakup under a mechan ica l impact . T i t an iumand i t s a l lo y s , n o r m a l l y a t t r a c t i v e as c a n di da t e m a t e r i a l s f o r p re s s u revesse ls because o f t h e i r h i g h s t r eng t h -t o - we i gh t r a t i o s , canno t be usedf o r oxygen vesse l s because they a re impact se ns i t i v e n oxygen. Inconeli s a good cho i ce f o r t1.e vesse l s t o con t a i n h i gh p r essu r e oxygen . U t i l i z a -t i o n o f t h es e m a t e ri a l s , p a r t i c u l a r l y when t h e y a r e use d i n c o n j u n c t i o n



T BLE 3 RECOMMENDED MATERIALS

Application

Component bodies

Materi a1

Mone 1Inconel 7 8

T u b i n g and f i t t i n g s MoneInconel 7 8

Internal par ts

Springs

Valve seats

MonelInconel 7 8Beryllium copper

Beryl 1 um copperElgiloyMone 1

Gold or silver overMonel or Inconel 718

Valve b a ll s Sapphire

Lubricants Batc h/lot tes ted Braycote 3L 38RP

Ba tchl lo t te ste d Ever1 ube 812Krytox 240 AC

0-seal s and backup r in g s Batch/lot tested VitonBat chllo t tested Teflon

Pressure ve sse ls Inconel 7 8

Usage should be limited to temperatures less than or equal to thosel i s t e d i n t ab le 2.

Note: Titanium and i t s all oy s ar e impact-sensit ive i n oxygen atmos-pheres and therefore may not be used i n oxygen systems.



with the design, manufacturing inspect ion, and test techni ues recom-mended in other sections of this document, should result in componentswith the lowest risk of fire possible in today's state o f the art.

In no case should an alloy be used at an oxygen pressure above its

particle ignition pressure. This criterion would limit the u e of alumi-un alloys and stainless steels to pressures below 105 0 b/in (7.24 M N / ~ ~to allow some margin for error in test results and impact predictions.

Only those nonmetallic materials which have been found to bebatch/lot insensitive or have been batch/lot tested should be used fororiginal or replacement component parts. Even in cases where the designis justified by configura tion testing, only those materials which ha vebeen shown y test to be at least as good as those used in the configura-tion tests should be used.

Off-the-shelf equipment or slightly modified current designs shouldnot be used in high pressure oxygen systems to save money, time, orweight, unless it can be shown that at the operating pressure limit the ma-teria ls used are not ignitable in accordance with the values given (withsome margin) in figures 1 and 2.



4 OMPONENT DES IGN

The pu rpose o f t h i s se c t i on i s t o document improved h igh p ressu re oxy -gen component des ign tec hn iqu es wh ich have been developed. The examplest h a t fo l l o w are drawn f rom act ua l oxygen systems. Most o f the prob lems

i l l u s t r a t e d w ere d i s c o ve r e d i n ha rd wa re t e s t s o r use a nd t h e s o l u t i o n sshown are, f o r t he most pa rt , tho se wh ich we have succ essfu 1ly implemented.I n these examples, we o f f e r s pe c i f i c sugges t ions f o r th e des ign o f compo-n en t h o us in g s and v a l v e p a r t s , f o r t h e us e o f s e a ls and f i l t e r s , and f o rt h e d e s ig n o f a n c i l l a r y e q u ip me n t . The major problems addressed includeig n i t i o n o f me ta l l i c s a nd n o n me ta l l ic s , a d ia b a t i c co mp re ss io n, me ch an ic alove rs t r ess , sea l eros i on, and cont amin at ion gene rat ion and co nt ro l . Someo f th e gu id e l ines a re in tended fo r use i n o r ig in a l des ign , where maximumbene f i t can be ob ta ined . O the rs a re examp les o f les s - than - idea l co n f ig -u ra t i o n s , each o f w hi ch p ro v e d t o be t h e b e s t a c h ie v ab le f i x t o a p ro b le mth a t o c c u rre d i n a n e x i s t i n g component.

The d e s ig n er i s c a u t i on e d t h a t i n a d d i t i o n t o t h e s ta n da r d a na ly se s

re la t i n g t o component o r sy stem fu n c t i o n ( s t r e s s , t hro ug h pu t, e t c . ) t h e rea re c e r t a i n a d d i t i o n a l s p e c ia l a n a ly s es t h a t a re co n s id e red man da to ry t oth e prop er de s ign o f oxygen systems and which must be cons idered i n the de-s i gn process. These are as fo l lo ws .

1 E x am i na ti on o f r e g i o n s f o r t h e g e ne r a ti o n o f p o t e n t i a l a c o u s t icre so n an t c o n d i t i o n s and a l s o where p a r t i c u l a te c o n ta m in a t i onc o u l d be a c c e l e ra t e d t o h i g h v e l o c i t i e s .

2. C a l c u l a t i o n o f me ch an ic al imp ac t en e rgie s f o r mo ving p a r t s , p a r -t i c u l a r l y v a l v e s e a t s and po pp et s. The impact en erg ies sh u l d bek e p t as l o w as p o s s ib l e , w i t h v a lu e s l e s s th a n 1 0 f t - l b / i nc l e a r l y b e in g s a fe .

3. Pressure r i se ra tes caused by ac tua t ion shou ld be de te rmined .Values be low 2000 p s i second are cons idered acceptab le .

4. Resonant fre qu en ci es o f l i n e s and components sho uld be comparedt o f lo w induced componen t f requenc ies t o insu re t h a t f low cond i -t i o n s d o n o t g en e ra te d e s t r u c t i v e v i b r a t i o n s .

5. Fa i l u r e modes and e f f e c ts analyses shou ld cons ide r no t o n ly t heknown and potent ia l i g n i t i o n mechanisms b u t a l s o t h e e f f e c t s o fc o mp o n e n t f u n c t i o n a l f a i l u re s .

6. S in g le b a r r i e r f a i l u r e a na ly se s s h o uld be co nd uc te d t o d e te rm in ew h e t h e r b a r r i e r f a i u r e s o r l e a ks c an expose s u s c e p t i b l e m a t e r i a l s

t o h ig h p ress u re oxygen .

7. To p re v e n t c a v i t a t i o n i n l i q u id o xy ge n (LO2) sy ste ms a n a n a l y s i sshou ld be conduc ted t o insu re t ha t the sys tem p ressu res exceedthe LO v a p o r p r e s s u r e b y a t l e a s t 2 p s i f o r a l l f l o w c o nd i t io n swhich he system i s expected t o see.



COMPONENT HOUSINGS

The h o us in g g e n e r a l l y c o n t r i b u t e s t h e g r e a t e s t p r o p o r t i o n of w e i gh tand com usti le mat te r t o the component assembly . Th is mass i s due t o i t sfu nc t i on as the enve lop ing s t ru c t u r e and as a p ressure con tainment vesse lw h ic h r e q u i r e s s u b s t a n t i a l m a t e r i a l t h i c k ne s s t o ke ep s tr e s s e s a c c e p t a b l y

low. S ince hous ings do co ns t i tu te so much o f the mass the se le c t io n o fh ou si ng m a t e r i a l i s e s p e c i a l l y i m p or ta n t i n f i r e - s e n s i t i v e o xy ge n sy ste ms.

H igh p ressure oxygen sys tem components f o r p o r ta b le o r f l i g h t usemust be l ig htw eig ht so t may ap pe ar t o b e d e s t r a b l e t o b u i l d t h e i r h ou s-ing s from such l i g ht w e ig h t me tals as aluminum. Such metals however havel i m i t e d f i r e r e s i s t a n c e and t h e i r use r e s u l t s i n an i n cr ea s ed co m bu st io nhazard. Aluminum may be used f o r an oxygen system o n ly when pr es su ref l o w v e l o c i t y and p r e s s u r i z a t i o n r a t e s a r e lo w. I n such a p p l i c a t i o n s ana n a l y s i s o f a d i a b a t i c h e a t i n g s h ou ld be p e r fo rm e d t o a ss ur e a c c e p t a b i 1 t y .F o r h i g h e r p re ss ur es h i g h e r f l o w v e l o c i t i e s o r h i g h e r p r e s s u r i z a t i o nra tes Monel and s i m i l a r a l l oy s which have much g re a te r f i r e to le ran cemust be used and th e ad d i t io n a l weight p en al ty accepted as necessary f o r

system safety .

To o f f s e t t h i s a d d i t i o n a l w ei gh t some w e i gh t r e d u c t i o n t e c h n iq u e scan be used such as t r im n i ng the ex te r i o r su r faces i n a reas where s t res sle v e ls are low. However th e des ign er should use cau t ion . Some guid e-l i n e s o n u s i n g t h i s t e ch n iq u e and o n a v o i d i n g h az ar do us t h i n w a l l s b l i n dpassages feat her ed edges bur rs and f l ow impingements are inc lude d i nthe fo l l o w in g d iscu ss ion o f component hous ing prob lems and so l u t i on s t othem.



Thin Wal ls

P rob 1em:

ORIQWAL P GE TS

O POOR QUALITY

The wa l l s between inner ca v i t i e s o r passageways and the o u te r sur face o fcomponent housings may become so t h i n th a t s t re ss conc ent rat ions re s u l twhen pressu re i s in t roduced. Since geometr ies both in s i d e and ou ts i de canbe complex i t may not be obvious f rom drawings or even f rom d i r e c t inspec-t i o n t h a t such t h i n h i g h l y s t re s s e d a re as e x i s t . f such walls becometoo th in they may rup ture under press ure loading . This sudden rup tur e re -su l t s i n an ener gy conve rs ion t h a t r a i se s t he t em pera tu re i n t he r up t u r ezone The f a i l e d sec t io n can expose bare jagged metal which ox id i ze s rap-i d l y and hence i n i t i a t e s and suppor ts combusti on . F igures 6a and 6b i l l u s t -r a t e a t h i n w a l l c o n di ti on .

S o l u t i o n :

An ext rem e ly va l uab l e t echn ique f o r l oc a t i n g such s tr essed ar eas i s t omachine a c l ea r p la s t i c model o f t he hous ing . Th i s model perm i t s v iew inginner and outer sur faces s imul taneously. Whi l e exac t wa l l t h i cknessescannot be measured d i r e c t l y th e t h i n areas do become obvious. Such ani n d i ca t i o n shou ld p romp t more de t a i l ed l ayou t ana l ys i s and t o l e r ance s t udyf o l l owed by s t r ess ana l ys i s o f t he l o ca l a r ea t o de t er m ine whe ther a pr ob-l em ac t u a l l y ex i s t s . To le rances t hen ca l l e d ou t on the m anu f ac t ur ingdrawing shou ld be t i g h t enough t o p rec lude s t re ss concen t ra t i ons .

The t h i n w a l l i n t he f i g u r e i s p r i m a r i l y th e r e s u l t o f an o v e r d r i l l duet o l ack o f a t t e n t i o n du r i ng des ign o r t o an ove r to l e rance . The d im en-s i on s o f a d r i l l e d i n t e r s e c t i o n s h ou ld be p la nn ed more c a r e f u l l y o r t h et o le r a n c e s s e t more t i g h t l y . t may even be poss i b l e t o e l i m i na t e t he i n -

t e r s e c t i o n a l t o g e t h e r as shown i n f i g u r e 6c. A l l i n t e r sec t i ons shou ld beexamined by X- ray o r borescope t o ensure t h a t t h e d r i l l i n g was accompl ishedi n an ac cepta ble manner.

hln wall

ntersect ing dri l l

Shallow anglerill

W e l d p l u g J

F ig ur e 6.- Component ho usi ngs - Th i n wa l l s .



B l i n d Passages o r Dead End Cav i t i es ORiGfNAL PAGE SSOF POOR Q?IAL.I IY

P o b 1em:

A s t ag n a n t a r e a a t t h e end of a d r i l l e d passage te n ds t o c o l l e c t d e b r i se i th e r f ro m manufac ture o r f rom norma l use. D u r i n g r a p i d p r e s s u r i z a t i o no f gaseous oxygen and i t s a t ten dan t compression heat ing, the d eb r is be-c o m e s f u e l f o r i g n i t i o n . When an underexpanded j e t impinges on o r f l o w sacros s) a s tagn ant ca v i ty , a pe r i od ic pressure wave may be formed th a t os-c i l l a t e s i n t h e ca v it y , h e a ti n g t he gas w i t h i n i t I f ) a r t i c l e s a r e p r e s -ent , ho t gaseous oxygen could i g n i t e them. Blind passages and dead endc a v i t i e s a l s o p r es en t i nc re as ed d i f f i c u l t y d u r in g c le a ni ng . They requ i ret h a t t h e p a r t be t u rn e d d u r i n g so ak in g t o e l i m i n a t e a i r p o ck e ts . And spe-c i a l n o zz le s o r e x t en s io n s most be used t o f l u s h s uch d i f f i c u l t - t o - r e a c ha re as . F i g u r e 7a d e p i c t s a b l i n d passage c r e a t e d b y p l u g g i n g a d r i l l e dpassage. F igure 7b dep ic ts a d e a d e n d c a v i t y c r e a t e d b y o v e r d r i l l i n g a ni n t e r s e c t i n g p a ss ag e.

S o l u t i o n :

Gaseous oxygen components shou ld be designed so t h a t a j e t w i l l not im-p i n g e on o r f l o w a c ro s s a s ta g n a nt c a v i t y . Je ts shou ld be g radua l l yexpanded and s tagnan t c a v i t i e s shou ld be e l im in a te d o r ke p t as sha l low asp o s s i b l e . I n f i g u r e 7 a t h e b l i n d passage ca n b e e l i m i n a t e d by m ak in g t h ec o u nt e rb o r e f o r t h e p l u g much de ep er a nd i n s t a l l i n g t h e p l u g c l o s e r t o t h ereg u la to r s tem. The ca v i t y may no t be comp le te l y e l im ina ted , bu t thet o t a l dead volum e i s s i g n i f i c a n t l y re du ce d. The c a v i t y shown i n f i g u r e 7bc a n b e e l i m i n a t e d b y p a y i n g c a r e f u l a t t e n t i o n t o d im e ns io ns and t o l e r a n c e so r , p r e f er a b l y, b y r e d e s ig n i n g t o e l i m i n a t e th e i n t e r s e c t i n g h ol es . I n -spe c t io n w i th a borescope can be done t o v e r i f y t h a t passageway len g ths

a r e w i t h i n t o le r a nc e .

llnd passage

Dead end cavityb)

Fig ur e 7.- Component hous ings B l i n d passages o r dead end c a v i t ie s .

4 4



Sharp Feathered Edges ORlbfNAC PbQS ISO POOR QU LITY

Problem:

Sha rp f ea t he r ed edges a re su rf aces w i t h l a r ge ar eas bu t l i t t l e mass. I n

an envi ronment where compress ion heat i ng shock heat i ng o r f l o w f r i c t i o ni s p resent t he re may be i n su f f i c i e n t mass o f meta l t o conduc t heat away.Thus hea t can co nc en trate i n such an edge and t can become an igni t ionp o i n t . Any two i n t e r s e c t i n g pa ssa ge s t h a t a r e d r i l l e d o f f c e n te r o r a t anangle other than 90 degrees w i l l produc e an edge fea th er ed t o some degree.Other machin ing s i tuat ions may a lso cause a feathered edge. F i gu r e 8 de-p i c t s a f e a th e r e d edge caused b y an o f f c e n t e r d r i l l i n t e r s e c t i o n w i t h t h esm a l l e r d r i l l s t opp i ng a t t he c av i t y edge and a l l ow i ng t he 120 -deg ree coneang l e o f t he ho l es t o p r oduce a pronounced feathered edge.

S o l u t i o n :

The prob lem shown can be a l l e v ia te d e i t h e r y d r i l l i n g th ro ug h o r b ys to p pi ng s h o r t o f t h e o r i g i n a l p o s i t i o n as i l l u s t r a t e d b y f i g u r e s 8band 8c. Dur ing design t i s a s im p le t as k t o f i n d p o t e n t i a l fe a t he r e dedges. A l l i n t e r s e c t i n g d r i l l s s h ou ld b e exam ined f o r feathered edges.

eliminatedy drillingthrough

avoidedy stoppingshort

F i g u r e 8. Component housings - Sharp feathered edges.



B u r r Remov a1

Pro bl em:

Smal l a t tached sp l in te rs of metal c reated dur ing machin ing are ca l ledb u r r s f i g . 9). These burrs are usual y removed during manufacturing;however, i f t he b ur r I s i n an inacces s ib le passage , t may not be detected.The problem i s th a t the bu r r much 1 ke the fea thered edge ju s t d iscussed)I s a t h i n p i ec e o f m eta l w i t h l i t t l e mass and l a r ge a rea which can byl oca l i zed hea t genera t ion eas i l y become an ign i t i on po in t o r a source o ffue l . The bu rr a ls o has impact po te nt ia l because i t could be dis lodgeddur ing opera t ion . t i s a f ixed contaminant which cannot be f l ushedaway o r even de t ec t ed w i t h c e r t a i n t y .

S o l u t i on :

De tec t ion and cor re ct io n must come e ar ly i n the des ign cyc le . When a pos-

s i b l e b u r r l o c a t i on i s i den t i f i ed , t he a rea shoul d be redesigned. f ti s n o t p o s s ib l e t o e l i m i n a t e t h e c o n d it io n , t he n s p e c ia l i n s p e c ti o n t o o l ssuch as borescopes should be spec i f ed and de bu rr i ng procedures developed.

Bu rrs and sharp edges are so c r i t i c a l i n h igh pressure oxygen systems t h a ttheir removal should be emphasized dur ing the design phase by speci f icdrawing ca l l ou ts t o every edge and corner t h a t w i l l be exposed t o t he f lo wstream. I n addi t io n, spec i f c inspect o n procedures should be def ined byprocedura l document a lso c a l le d out on in d i v i du al drawings. Such emphasisi s necessary s ince bu rr removal on most o ther hardware i s usu al l y ca l le df o r by genera l note, po or ly cons idered i n design, o f t en neglected i n manu-fac tu r in g , and ignored i n inspec t ion . This has been found y spot inspec-t i o n t o be the case even i n cr uc ia l h ig h pressure oxygen systems when such

emphasis was n o t made.

Bur r removal i n sma ll d iamete r i n t e r na l passageways a t the in t e rs ec t io n o fc ross d r i l l s has been one o f the most d i f f i c u l t techniques to develop .Bes t r es u l t s have been ob ta ined w i th sma l l moto r ized g r ind ing too ls andw i t h e l e c t r i c a l d is c ha r ge m ach in ing EM).

F igure 9.- fimpone nt housing s B u rr Removal.

4 6



Flow Impingement on Aluminum Housings

P rob1em:

S i nce aluminum cons t i t u t e s a f u e l i n an oxygen f i r e and s i nc e t he oxygen

f l o w m ig ht c o n t a in p a r t i c u l a t e m a t te r t h a t c o u l d i g n i t e t h i s f u e l o ni m

pac t , t he f l o w shoul d no t be a l l owed t o i mp inge d i r e c t l y on an a luminumhous ing wa l l ( f i g u r e 10a).

S o l u t i o n :

The housings o f newly manufactured hardware shou ld be made o f f i r e -re s i s ta n t m ate r i a l such as Monel o r some o th er h ig h-n i cke l a l l oy . To cor-r e c t f o r im pin ge men t i n e x i s t i n g hardw are, c r i t i c a l a re as o f h i g h p r e ss u r eand h i g h f l o w c an be s h i e ld e d w i t h f i r e - r e s i s t a n t m e t a ls . Rerout ing andd i f f u s i n g f lo w ca n a l s o sl ow o r b l o ck i m p a c t in g p a r t i c l e s ( f i g u r e l o b ) .

Flow impinging LMonel rhleld rotated 4Son elumlnum hourlng to reroute and dlffure flow

neleld

F ig u re 10.- Component hou sing s - Flow impingement on aluminum housings.

4-7



VALVES

Conven ti onal v a l ve p a r t s a r e des igned t o p r ec l ude ga l l i n g and t ow i t hs t and t he h i gh s t r esses o f e l eva t ed p r essu r e and sp r i ng f o r ces . M one la l l o ys a r e f i r e - r e s i s t a n t and the r ange o f hardnesses i n which t hey a reproduced can be used t o m in im ize g a l l i n g p rob lems. The harder, st r on ge r

a l l oys such as K-Monel can be used f o r h i g h ly s t ressed, smal l d iameter ,moving p a r t s such as va lv e stems. 400-ser ies Monel can then be used f o rthe va l ve body . Sp r ing s can be wound f rom Monel wi re . Mi n ia tur e spr in gscan be made o f E l g i l o y o r be r y l l i um coppe r i f small d iameter Monel w i re i sno t ava i l ab le . Tungs ten car b id e and s tee l poppet b a l l s shou ld be rep lacedw i t h s a p p h ir e b a l l s s i n c e s a p p hi re has a lo w er l e v e l o f r e a c t i v i t y (a ndt h e r e f o r e i s l e s s c o m bu s ti b le ) t h a n e i t h e r t u n g s te n c a r b id e o r s t e e l . t

i s a l so m ore r e s i s t a n t t ha n t ungs t en ca r b i de t o b r eakup under a m echani ca limpact i n oxy en. Lock r i ng s and re t a i ne r nu ts th a t a re no t exposed t o ox-ygen can s t i l be made o f l i gh tw e i gh t a luminum s in ce they are no t sub jec tt o t h e o x yg en i g n i t i o n h az ar d ( a1 h ou gh g a l v a n i c c o r r o s i o n o f d i s s i m i l a rm e ta ls m us t s t i l l be c o n si de re d ).

The work ing par ts , i f made o f combust ib le mate r i a l s , can co nt r i b u t es i g n i f i c a n t mass t o f u e l a f i r e . F r i c t i o n between m oving p a r t s can i n i t i -a t e com bust ion w i t h i n t he va l ve . S t a t i c o r i m pac t loads on subm i ni a tu r e ,h i gh l y s t r essed pa r t s can cause f r ac t u r e o r hea t i ng o f t hese pa r t s , wh ichc an t h e n i n i t i a t e c om bu stio n. F lo w-in du ce d o s c i l l a t i o n o r c h a t t e r i n g ofa po pp et w i t h i n a v a l v e ca n r e s u l t i n f r e t t i n g and h i g h l y l o c a l i z e d he a tg e n er at io n , w h ic h ca n le a d t o i g n i t i o n .

Volumes upst ream o f a va lve may be a f fe ct ed y h i g h v al v e a c t u a t i o nr a t es . The f a s t c l os i n g o f t he va l ve cou l d p roduce a wa te r hamner e f f e c t ,sending a press ure pu ls e upstream, which cou ld then cause a temperaturer i s e by ad iabat i c compress ion . uch a p u l s e c o u l d a l s o c aus e s t r u c t u r a lf a i l u r e i n an upst ream com ponen t o r con t a i ne r .

Volumes downst ream o f a v alv e may a lso be af f ec te d by h ig h va lveac t ua t i on r a t es . The f a s t open ing o f the valve could subject passagewayso r com ponents t o ad i aba t i c compress ion, wh ich cou l d r e su l t i n ho t spo t sand p o s s i b l e i g n l o n o f n on me ta l 1 c s o r p a r t i c u l a t e c on ta m in an ts .

These prob lems and suggested s o lu t i o ns are p resented i n the f o l l o w i ngv a l v e d e s i g n a r t i c l e s .



O?:Cj?: .L p p;cz [SStat ic and Impact Loads on Subminiature Parts

~ P ok

Problem:

Valves f o r h ig h pressure oxygen systems may be designed w i t h s ubmin iaturepa r t s to reduce p ressu re fo rces so tha t regu la t i ng sp r ings can be kep t areasonab le s ize . I f t hese pa r t s ge t t oo sma l l , t hen they may be h i gh l ys t ressed by the o rd ina ry s ta t i c and impac t l oads . f h e h i g h s t r e s s e sa re a p p l i e d q u i c k l y , t h e l o c a l e ne rg y t r a n s f e r r a t e s c an be h i g h enough t of r a c t u r e a m i n i a t u r e p a r t o r h e a t i t e n o u g h t o i g n i t e i t or any contami-nan t p resen t f i g . 11) .

So l u t i o n :

High pressu re oxygen systems should be designed so th a t wo rk ing loads onv a l v e s w i t h s u b m i n i a t u r e p a r t s a r e low. Fa s t a c t u a t i o n whic h c o u l d a p p l yimpact loads t o such submin ia ture p ar ts shou ld be avo ided, and the p ar ts

should be made o f ma te r ia l s t h a t a re no t impac t sen s i t i ve . Furthermore,each sys tem shou ld be des igned f o r c lean l i nes s and I s o la t i o n o f con tami -nants.

l -mm ball

F igu r e 11. Va lves S t a t i c and impac t l oads on s u b m i n ia t u re p a r t s .

4-9



Check Valve Chatter ORlGlNAL PAC? 3

O POOR QUktfSY

Problem:

Under some f l o w r a t e cond it i on s, check valves i n oxygen ser vic e maychat te r as a re su l t o f a resonant coup l ing o f the dynamical ly induced

f l ow fo r ces (w hic h are dependent on check v al ve geometry, system geometry,f l ow rate , and oxygen pres sure and temperature) w it h th e check valv e seat-i ng sp r i ng fo r ces . C h a tt e ri n g r e s u l t s i n t h e p op pe t' s h i t t i n g t h e se at a ta high f requency and can cause an ig n i t i o n at t he seat due t o the h ig hloc a l i zed hea t genera t ion . Furthermore , the cha t t e r in g can genera te par -

c u l ate matter which can inhib i t the funct ion of downstream componentso r ac t as a fue l f o r i g n i t i o n fa r th e r downstream.

So lu t ion :

Check va lves a r e av a i l ab le i n a broad va r i e t y o f con f i gu r a t i ons . F igure12 shows the c ross-sect io n o f a ty p i ca l check va lve.

Successful checkva l ve des ign i nc ludes se lec t i o n o f app r op r ia te ma t e r i a l s; se le c t i on o fto ler ances t o avo id ga l l i n g o f moving pa r t s; and con t r o l o f t o le r ancest o a vo id l a t e r a l i n s t a b i l i t y ( c h a t te r ) o f t h e poppet i n i t s gu ide . Toc o n t r o l a x i a l c h a t t e r , a v a r i e t y o f t ec hn iq ue s a re a v a i l a b l e . The useo f a so f t - sea t ing spr in g can min imlze c rack ing p ressure so th a t on ly aminimal f low holds the valve open. O r the valve may be designed so thatthe poppet must move s u b s t a n t ia l l y o f f i t s s ea t be fo re t he f l o w p o r t sare uncovered,

Close at t e n t i o n should be g iv en t o dynamic ana lys is o f the check v a lve de-s ign ac ross i t s e n t i r e f l ow r ange and fo r t he e n t i r e spec tr um of expec tedoxygen temperatures and pressures t o show i t s dynamic st a b i 1 y Becauseo f th e d i f f i c u l t y o f such ana lyses, the va lve must be a lso tes ted as a com-

ponent and i n a complete sys tem co n f i gu ra t ion (see sec t io n 7).Seat ,Sof t spring

Orif ice 4 places) Poppet substant ial t ravto open f low orif ices)

Fi gu re 12.- Valves Check va lve ch at te r .



Poppet OSC ll t i o n ( As y mn e t r i c a l F l o w)ORIW?:F L PAGE i

OF POOR QUALITY

Problem:

A s y m t r i c f l o w a c r os s a v a l v e po pp et c re a t e s a dynam ic i mba la nc e o f f l o w

for ce s on the poppet, caus ing t t o o s c i l l a t e t ra n s v er s el y a ga in s t i t sbore. T h is t ra n sv e rs e o s c i l l a t i o n r e s u l t s i n t he p op pe t s h i t t i n g th eb o re a t a h i g h f r eq u e n cy and ca n c au se a n i g n i t i o n due t o t h e h i g h l o c a l -i z e d h e a t g e n e r a ti o n . Fu r t h e r mr e , t h e t r a n s v e rs e os c a t o n c an g e ne ra tep a r t i c u l a t e m a t t e r wh ic h c an i n h i b i t t h e f u n c t i o n o f d owns tre am componentso r a c t as a f u e l f o r i g n i t i o n f a r t h e r d ownstream , f i g u r e 13a.

S o l u t i o n :

Where poss ib le , t he i n te rn a l f l o w geometry w i t h i n va l ves shou ld p rov id es y m t r i c a l f l ow a cros s t he poppet. An e f f e c t i v e a l t e r n a t e a pproach i s t omount the poppet i n the bore by means o f f l ex ur e assembl ies , wh ich are

v er y f l e x i b l e i n t he l o n g i t u d i n a l d i r e c t i o n (and t hu s do n o t i n h i b i t t h ev a l v e s o pe n/ cl os e a c t i o n ) b u t wh ic h r e s t r i c t t h e tr a n s v e r s e mo t io n o f t h ep op pe t. The f l e x u r e a ss e mb li es a c t t o c e n t e r t h e p op pe t i n t h e b o re a ta11 t imes and thus prevent any t ransverse contac t . Bore and poppet mate-r i a l s s ho uld be s e le c te d t o m inim iz e th e p o s s i b i l i t y o f i g n i t i o n . Bo ths u r f a c e s may be me t a l l u r g i c a l l y h ar de ne d t o m i n im i z e d e t e r i o r a t i o n due t o

r e t t 1ng. igure 3b. Sonic orif ice

f l o w

. 0

or fice Unbalanced press ure load

Flow contro l orlflcas

f l o w

PoppetF i g u r e 13.- Va lv e s Pop pe t Os c i l l a t i o n ,

4-11



A c tu a t i o n R a te s

Problem:

A c t u a t io n o f a f as t -o p en in g s h u t o f f v a l v e s u b je c t s t h e f i r s t s t ag e r eg u la -t o r and passageways immed ia te l y upst ream o f the re gu la t o r t o a sudden i n -c rea s e i n p re s s u re as shown s c h e ma t i c a l l y i n f i g u r e 1 4 a. T h i s s udden p re s -s u re r i s e ca n c au se a d i a b a t i c c omp re ss io n r e s u l t i g i n l o c a l i z e d t empe ra -t u r e s h i g h enough t o i g n i t e n o n m e t a l l ic s e a ls o r p a r t i c u l a t e c o nt am in a-t i o n .

F a s t c l o s i n g a l lo w s b o t t l e p r es s ur e s t o p u t h i g h im p ac t l o ad s o n t h e v a l v es ea t. E ne rg y t r a n s f e r r e d i n t h e i mp ac t c an i g n i t e c o n ta m i n a t io n o n t h eseat .

S o l u t i o n :

The s y stem re q u ir e me n ts s h o u l d be e v a l u a te d w i t h t h e g o a l o f e s ta b l i s h i n gas sl ow an ac t ua t i on r a te as fe as ib l e . Once the min imum ac tua t i on ra te re -q u ir em e nt i s e s t a b li s h e d , t h e a c t u a t i n g v a l v e ca n be de sig n ed s p e c i f i c a l l yt o a c hie ve t h i s r a t e . O r i f i c e s o r r e s t r i c t i o n s may be r e q u ir e d t o l i m i t

p r e s s u r i z a t i o n r a te s . For components a l re ad y e x i s t in g , thermodynamic ana l -y s i s t e ch n iq u e s s h ou ld b e u se d t o i d e n t i f y a re as o f concern. The r a t e canth e n be d e crea se d b y c o n v e r t i n g a f a s t -w o rk i n g p u s h b u t t o n a c tu a to r t o as l o w e r t h re a d e d - t y p e a c tu a to r .

A n o th e r method, shown s c h e ma t i c a l l y i n f i g u r e 1 4b, i s t o i n c o rp o ra te t h es h u t o f f f u n c t i o n i n t o a r e g u l a t o r s ta ge u s i n g th e r e g u l a t o r v a l v e as t h es h u t o f f s e a l . No s e p a ra te s h u t o f f v a l v e i s t h e n re q u i r e d . B e fo re t h e r e g-u l a t o r i s a ctu ate d, t h e f i r s t s ta ge i s cl o se d w i t h h i g h pr e ss u re up stre am

o f th e va lv e seat and medium pres sure downstream. The second s tage i sa l s o c l o s e d w i t h medium p re s s u re u p s tr e am o f i t s v a l v e s e a t a nd no p re s -sure downstream. A f t e r t h e r e g u l a to r i s a ctu ate d, d ow nstrea m p re s s u re i n -c re as es o ve r a r e l a t i v e l y s m a ll d i f f e r e n t i a l . No sudden increases occur,so no heat-prod uc ing compress ion take s p lace . Th is method o f decreas ingt h e a c t u a t i o n r a t e i s u s e f u l e ven when l o n g t e rm s t o ra g e i s a f a c t o r . ft h e f i r s t s t ag e s lo w l y l ea ks , t may i n t im e i n c r e a s ~ h e i n t e r s a ge p re s -

u re t o t he l e v e l o f the s u p p l y p re s s u re (7400 I b / i n o r 51 MN/m i n thei l l u s t r a t i o n ) . When t h e seco nd s t ag e r e g u l a t o r ( f u n c t i o n i n g a l s o as ashu to f f va l ve ) i s opened, th e r e w i l l be a s u rg e o f f l o w . B u t t h e r e g u l a -t o r w i l l q u i c k l y c l o s e a g ai n s i n c e i t s d e s i r e d d ow nstrea m p r e s su r e w i l l bei m d i a t e l y reached. f t h e - i n t e r s ta g e volu me i s s ma ll - and t should bes ma l l b y d e s i g n t h e n t h e re w i l l no t be much oxygen t o suppor t a sus-

ta i ned su rge .

The d e f i n i t i o n s o f f a s t and ' ts lo w depend o n t h e s i t u a t i o n . F a c to r s t h a ts ho ul d be co ns id er ed i n e s t a b l i s h i n g a c t u a t i o n r a t e s i n c lu d e t h e i g n i t i o nte mpe ratu re s o f t h e n o n me ta l l ic s and me t a t l i c s d ow ns tre am o f t h e v a l v e , t h et o t a l vo lume imne d ia te l y downst ream o f the va l' ve , the o pera t i ng temperatu re ,t h e o p e ra t i n g p re s s u re , t h e p re s s u re r i s e r a t e s i n vo lumes d ow ns tre am o ft h e v a l ve , and t h e h e a t t r a n s fe r c h a r a c te r i s t i c s o f t h e ox yg en and t h e p as -sageway walls. S in ce a l l t h es e f a c t o r s w i l l var y f rom system to system,



it i s d i f f i c u l t t o e s t a b l i sh v a l v i n g r a te s o r p re ss ur e r i s e r a t e s t h a twou ld be accep tab le f o r each case . Bu t ex tens i ve pneumati c impac t te s t i n gw i t h o xyg en has i n d i c a t e d t h a t an a c t u a t i o n r a t e o f 50 m i l l i s e c o n d s o rl e s s t o b r i n g do wn stre am p re s s u re t o 95 percen t o f upst ream p ressure doesr o u t i n e l y cause i g n i t i o n . T h is r a t e and any f a s t e r r a t e s ho uld d e f i n m ybe c o ns id e re d f a s t. B a l l v a lv e s a r e v e r y f a s t ; t h e i r a c t u a t i o n r a t e has

been measured a t le ss than 2 mi l l i s e c o n d s . A t the o the r ex t reme, a r a t eo f 0.5 second t o ach ieve the same downstream-to-upstream pres sure r a t i ohas b en found o ca use no i g n i t i o n s i n e x t e n s i ve t e s t i n g up t o 2000b / i n (14 MN/m . Thi s r a t e and any s lower should be acceptab ly s low

f r o m t h e s t a n d p o i n t o f a d i a b a t i c c o m p r e s s i o n i g n i t i o n .

There may be a l i m i t however, t o the ns lowness t h a t should be des ignedi n t o a p a r t i c u l a r s y s t e m . f a va lve opens too s lowly , i t p r e s en t s i n ef -f e c t a s l o w l y ex pa nd in g o r i f i c e t o t h e f l o w s tre am . f the upstream anddo wn stre am p re s s u re s and o r i f i c e c h a r a c t e r i s t i c s a re su ch t h a t t h e f l o wbecomes superson ic , then pa r t i c u l a te con tamina t o n may be acce le r a ted t oa h ig h ve lo c i ty . Such a ve lo c i ty can be much h ig he r tha n would be exp er i -enced i n a fa s t t1 opening (and s l ower f l ow in g ) va l ve. Wf th the i nc reased

k i n e t i c en er gy , p a r t i c l e im p ac ts a r e more ca pa ble o f c a u s in g i g n i t i o n .Ev idence o f t h i s phenomenon e x i s t s i n oxygen te s t p rog ram exper ience . Tod e te rm in e t h e b e s t t r a d e -o f f , a t h oro ug h a n a l y s i s o f t h e a c tu a t i o n , c on -s i d e r i n g a l l t h e f a c t o r s l i s t e d above, s ho uld be pe rf or m ed f o r eac h i n d i -v i d u a l s h u t o f f v a l v e .

With fast opening With shutoff function

a )shutoff valve

b)in regulator

(- psi

opsFpsi 4 psi

Before valve After valve Before valve After valveopening opening opening opening

F i g u r e 14.- Valves - A c tu a t i o n r a te s .

7 psi 7 psi

2 psi 2 psi

psi 4 psi

t



S i ng l e B a r r i e r F a i l u r e-.e. ;.JfiA; pG: 5

c:h .s t

OF P R Q ~ J A L ~Problem:

A l eak i n wh ich on l y the p r ima r y con ta inmen t s t r uc tu r e i s b reached i sde fined as a s in g le ba r r ie r fa i lu re . Such a leak in troduces oxygen in t oa reg ion which i s n ot norma l ly exposed t o oxygen. I n t h i s reg ion the ma-t e r i a l s o r c o nf ig u ra t io n o f p a r t s m y not be compat ib le wi th h igh pressureoxygen. I n the p ressure t ransducer shown i n f ig ur e 15 rup tu re o f thebourdon tube wou ld cons t i tu te a s ing le bar r ie r fa i lu re s ince oxygen wo l~ ldleak i n to the sur round ing cav i t y .

So lu t ion :

Any s i tu a t i o n i n which the r e i s a s ing le b a r r i e r th a t may f a i l should beana lyzed dur ing the design phase. Such s in g le ba r r ie r fa i l u re ana lys iscan cons i s t o f an enginee r ing ev a lua t i on o f the con f igu r a t i on i nc lud ing

ana lys i s o f ma te r ia l s or a co nf ig ur at io n t e s t may be performed. I n thecase o f the pressure trans duc er shown below a co nf ig ur at io n t e s t wasperfo rmed by d r i l l i n g a ho le i n the bourdon tube then p r essu r i z ing i t

with oxygen. A spark f rom the res is tanc e wiper arm caused i g n i t i o n andthe re su l t in g explos ion destroyed the transducer . The co nf ig ur at io n wassubsequently changed y adding an oxygen-compat ib le o i l t o the c av i ty t oprevent spark ng

Resistance wiper arm

Pressure sensing

Hole d rilled forconfigura tion test lL ~ o u r d o nube

F igu r e 15. V alv es S i n g l e b a r r i e r f a i l u r e .

4 14



Rotat ing Stem Valves

Prob 1em:

manual, screw-type va lv e w i t h a r o t a t i n g stem, f ig u r e 16a, migh t seem de

s i r a b le i n a h igh p ressu re oxygen sys tem because such a va lve can p rov idea s low ac tua t io n ra te . However, a r o ta t i n g s tem va lve presents contamina-t i o n prob lems es pe c i a l ly when combined w i t h a non me ta l l ic seat . Such asea t can e as i l y be damaged by excess ive c l os ing to rque o r by sh redd ing o rgas eros ion dur ing bot h opening and c lo s in g. Fur thermore, so l d contami-nants can become embedded i n such s o f t sea t ma te r i a l . If he seat i s madeof meta l , t must be hardened t o p reven t g a l l in g by the r o t a t in g s tem. Suchhardened mater ia ls can f rac ture or even f ragment as a r e s u l t o f e x c e s s i v ec l o s i n g to r qu e o r c l o s u r e o n t o h a rd co nt am in an ts ( l i k e s i l i c o n d i o x i d e ) .A ls o, s e at g a l l i n g i s s t i l l p o s s i b l e when th e v a l ve stem r o t a t e s ag a in s ta m e t a l l i c s e a t .

S o l u t i o n :

A manual va lv e w i t h a no nro ta t ing stem, f i g u r e 16b, and a m e t a l l i c s ea tcan be chosen to ach ieve the des i red s low ac tua t ion ra te . I n t h i s case,the meta l seat can be made o f a much so f t e r ma te r i a l and the seat can beformed b y c o in i n g ( p re s su re mo ld in g b y t h e stem i t s e l f t o c re a te a p e r -fe c t match). Contaminants w i l l not cause f ragme ntat ion o f such a seat .Ga l l in g cannot occu r un less t he non ro ta t ing fe a tu re i s cornpromtsed. Thesea t and body o f such a va lv e can be fabr ica ted f rom such meta ls asInc one l or Monel, wh ich have been shown t o be com parat iv e ly u nr ea ct i vew i t h oxygen.

Rotating

ody seat / operator thread

L ~ o n m e t e l l l cseat b)

Fig ure 16.- Va lves Ro ta t i on s tem va lves.

4 15



SE LS

S e a ls us ed i n v a lv e s and f i t t i n g s a r e made o f r e l a t i v e l y s o f t non-m e t a l l i c m a t e r i a l s . l l such mater ia ls wi th adequate mechan ica l p roper -t i e s are i g n i t a b l e a t r e l a t i v e l y l o w t emp er at ur es c ompared t o t h e i g n i t i o ntemperatu res o f t he su r round ing me ta l pa r t s . Se a l l o c a t i o n s a r e t h e r e f o r eamong the most l i k e l y combust ion s i te s . To decrease the r i s k c rea ted bythese lo ca t io ns th e number o f seals used shou ld be minimized. Where the yar e used they sho uld be sh ie l de d o r removed f rom the f l o w stream.

The f o l l o w i n g a r t i c l e s d is c u s s n o t o n l y some t e ch n iq u e s o f s h i e l d i n gsea ls f r om f lo w impingement bu t a l so some methods o f a vo id i ng such seal-e rod ing con d i t i on s as a l t e rn a t i n g p ressu re sea l ex t rus ion sea l squeezesea l ro t a t i o n and the e f f e c ts of poo r sea t shape. A l so p resen ted a resome co ns ide rat ons on us ing dynamic sea ls and metal - to-m etal rubb ingsea ls .



Flow Impingement

Problem:

I f t he oxygen f l o w s t ream impinges d i r e c t l y on an exposed nonme ta l l i c o fl ow i g n i t i o n t e mp er a tu r e s uc h as O- r i n g ma t e r i a l , t h e r e i s a r i s k o f i g n i -t i o n due t o i mp ac t b y c o nt am i na n ts c a r r i e d a lo n g i n t h e f l o w s tr ea m

f i g u r e 1 7a ).

S o l u t i o n :

Th is p rob lem can be so lved y s h i e l d i n g t h e O- r i n g f r o m t h e f l o w s t r e a mwi t h a b a c k u p r i n g o f a m a t e r i a l w i t h a h i g h e r i g n i t i o n t em p er at ur e o r bydes ign ing the hous ing bore and sea led component so t h a t m eta l i s bo t tomedon m e ta l, c r e a t i n g a f l o w b a r r i e r t o p r o t e c t t h e O - ri ng f i g u r e s 1 7b and17c).

Bottomed outFlow impinging onO-ring-

a) Flow

Backup ring shieldsO-ring-

metal-to-metalbarrier p rotects

O-ring-

Fi gu re 17.- Sea ls - Flow impingement.

4-17



-.c- 'J

Al te rna t ing Pressure (Redundant Sea l1c;f j@ :;;li:... . 'O POOF: ~;j&Li;':'

Problem:

When two s e ts o f sea ls a re used a t th e same lo c a t i o n i n a long te rm pres-

s u r i z e d s t o ra g e a p p li c a t i o n , e v e nt u al p e r mea t io n o f t h e f i r s t s e a l p r o -duces a pres sur ized volume between the sea ls . The pressure i n t h i s zonewould be grea ter than th a t on the low press ure s i de o f the component bu tles s than opera t i ng pressure . When th e va lv e i s opened and the low pres-s u r e s i d e i s r a i s e d t o o p e r a t i n g p re s su re , t h e s ec ond s e a l i s e xpo se d t op ressu re on i t s downs tream s ide wh ich i s now g rea t e r t han tha t i n t heint erm ed iat e zone. As the component goes thro ugh sev eral use cyc les , thed i r e c t i o n o f t h e p r es s ur e f o r c e a l t e r n a t e s f r om one s i d e t o t h e o t h e r .Th i s a1 e rn a t g press ure can cause seal work g and er os io n o r b lowbacko f co n ta m in a nt s ( f i g u r e 18a)

So l u t i o n :

The s o l u t i o n I s t o e l i m i n a t e t h e sec ond r ed un d an t s e t o f s e a ls ande ns ure t h a t t h e f i r s t s e t o f s e a ls i s adequate i n ox yge n c o m p a t i b i l i t y ,Shore hardness , and proper use o f backup r i ng s t o per fo rm the se a l in gt a s k a l o n e ( f i g u r e 18b .

r ow pressure

2nd seal

lntermedzone

1st seal

a)High pressure

iate

L ~ i g hressure

F i g u r e 18.- Se al s A l t e r n a t i n g p r e s s u re ( re d u nd a n t s e a l ) .

4-18



Q R V ~ J ~ ~ ~ E 7 P n . - 7,~?&*<=', :\; .

Sea l Ex t ru s io n Backup R ings r OF POOR Q:JAL: i i

Prob 1em:

I n h ig h pre ssur e oxygen systems, t i s c r i t i c a l t o m in im ize both s e a l e ro -

s i o n and contaminant generat on. Wi thout backup r in gs , 0 - r i ngs can be pa r-t i a l l y e x t r u d e d i n t o t h e r a d i a l gap b etw ee n p a r t s . Even t ho u gh t h e O - r in gmay s t i 11 sea l , such ex tr us io n over a number o f cy cle s may wear o f f mate-r i a l , thus degrad ing the sea l and con tamina t i ng the sys tem w i th nonmeta l -1 c p a r t i c u l a t e s . I n s ys te ms w l t h v e r y h i g h pres s ure s, o rd i n a r y ba ckupr in g s may a lso be p a r t i a l l y ex t ruded , caus ing the same p roblems f i gu re s19a and 19c).

S o l u t i o n :

Fo r safe ty i n h ig h pressure oxygen systems, one should use backup r ln gs onthe l ow p ressure s i de o f O-r ings even at pres sures where s tandard O -r ing

p r a c t i c e does not d i c t a t e such u e f o r gases i n g e ne r a l. . A t pressuresr e a t e r t h a n 1 1b / i n2 7 MN m , more sop his t i c a t ed backup r i n g shapess uc h as d e l t a r i n g s s h o u ld be used f i gu re s 19b and 19d) .

Low pressure Low pressure

O ring and o

backup ringpartially

extrude

Non

delta

extruding

Very high pressure Very high pressure

LOW pressure Low pressure

0 rlng

extrud

Hiah pressure

Controlled rrdir

~ e t r ~verlap

d) 11gh pressure

Fig ur e 19.- Seals - S e a l e x t r u s i o n b ac ku p r i n g s ) .

4-19



Seal Squeeze

Problem:

ORlQwAL p; ,.:.;.,:

OF POOR QilALiTY

B u i ld u p o f t o le r a nc e s o n v a l v e p a r t s o r an u n fa v o ra b le c o n f i g u r a t i o n i n

w h ic h t o ma ch ine a g l a n d may r e s u l t i n a g la n d t o o s m a ll f o r i t s O - r i n gsea l. S i nce a ce r t a i n amount o f com pr essi on o r squeeze i n t he a x i a l d i -r e c t i o n i s necessa ry t o ach ieve t he p r ope r sea l i ng l oad t he r e must bespace f o r t he O - r i ng t o expand r a d i a l l y . I f t h i s r ad i a l space canno t beprov ided the O- r i ng w l l b e p a r t i a l l y e x tr u de d fr o m t h e g la n d and t h i se x t r u s i o n w l l r e s u l t i n p a r t i c u a l t e p ie c e s b e in g s haved o f f .

S o l u t i o n :

C a r e f u l a t t e n t i o n s ho u ld b e gi v e n t o d i me ns io ns and t o le r a n c e s o f a l lp a r t s i n t he va l ve assembly . I d ea l l y adequate g land s i ze shou ld be pro -v ided i n th e i n i t i a l des ign . When adequate g land s i z e cannot be ach ieved

a sp ec ia l sea l w i t h an ova l c ross sec t on may be used. Th i s sea l re ta in st he r eq u i r ed d im ensi on a x i a l l y bu t has a r educed c r oss - se c t i ona l w i d t h .Thus th e seal w l l occupy le ss space si de t o s id e even when compressed

f ig . 20).

land too small SpecialO ring oval ring

Standard0 rlng

Special Compressed

oval ring oval ring

Fi gu re 20.- Seals - Seal squeeze.

4-20



R o t a t i on o f S eal s

Problem:

Sealed par ts t h a t req u i re r o ta t i o n a t assembly (such as O- rings on

threaded shaf ts) can generate p a r t i c le s which may mig rate i n t o the f lo ws tr ea m as shown i n t h e f i r s t i l l u s t r a t i o n . P a r t i c u l a t e g en e r at i on a l s oocc ur s i n b a l l v a l ves w here ope r a t i on o f t he v a l v e r o t a t e s a b a l l on anonme ta l l i c sea t.

A re la t e d phenomenon which may be de scr ibe d as fe at he ri ng occurs whenvalve stems are rotated against some nonmetal l ic seats such as KEL-F. Be-

cause of the mechanica l proper t ies o f some nonme ta l l ics , a th in , fea the r-l i k e p r o j e c t i o n o f m a t e r i a l i s e x tr ud ed f r o m t h e s e at . The f ea thered fea-t u r e i s m r e i g n i t a b l e t h an t h e s e at i t s e l f w ould have been ( f i g u r e 21a).

S o l u t i on :

Ins tead o f a ro ta t i ng sea led par t , the sea led pa r t cou ld be designed asa push - in p l ug l oc k ed i n p l ac e y a second p a r t wh ich i s th readed b u t n o tsealed as shown i n f ig ure 21 b. A l te rn at e l y the sealed threads could ber ep lac ed w i t h a f langed and bo l t ed connect ion. K e l F seals should not beused i n r o t a t i n g c on f i gu r a t i ons a t a l l and b a l l v a lv es a r e no t recommended f o rf o r oxygen systems not on ly because of p a r t i c l e generat ion b ut a lso becauseo f f a s t a c t u a t i o n ra t es .

Threads requirerotation of sealat assemblyl

Threads removedseal ot rotatedat assembly

eal

F i gu r e 21.- Sea ls Ro ta t i on of sea ls.

4 21



Seat Shape

P rob1em:

Designs which seal an O-r ing on an unusual seat shape may set the stage

f o r i nc reased wear problems o r undu ly acce le ra ted e x t r us ion o f t h e non-m e t a l l i c . Such e f f e c t s c a n g e ne ra te p a r t i c u l a t e c o n t a m i n a ti o n wh ic h w i l li n c r e a s e t h e r i s k o f c o mbu st io n. An examp le o f such a des ign i s seen i nf i g u r e 22a wherein a face - t ype O- r i ng sea l i s sea ted on the edge o f t h esea 1 g su r f ace.

S o l u t i o n :

Nonmetal 1 c sea l i ng i n t e r fa ce s are a necessary compromise; however th edes igns can be opt imized. The example i s ob jec t io na b le because t u t i -l i z e s an O- r i n g i mp r op e r ly . The m s t r e l i a b l e v a l v e and r e g u l a t o r c on -f i g u r a t i o n s h ave been fo un d t o b e a m e t a l l i c o r s a p p hi re b a l l i n a

washer-shaped Vespel seat as shown i n f i g u r e 22b.

O ring seatedimproperly

Washer shapedseat

a)

Corner on seat

F i g u r e 22.- Se als Sea t shape.

4 22



Dynamic Sealso ~~.Qf;;,pi~C:,7 :. l .>

OF PGOR QLfALITY

Problem:

When a p o r t i o n o f a v a l v e o r f i t t i n g moves i n r e l a t i o n t o a s e a l in g s u r -

face, f r i c t i o n can genera te p a r t i c l e s a t t he i n te r face . The amount o fp a r t i c u l a t e ma t t e r depends o n t h e l o a d and c o e f f i c i e n t o f f r i c t i o n b etwee nthe m e t a l l i c pa r t and the nonm eta l l i c sea l and on the s t reng th o f t henonmeta l1 c se a l m ate r ia l . Unfo r tunate ly , even th e bes t nonmeta l 1 c mate-r i a l s f o r O - r in g s i n h i g h p re s su re ox ygen s e r v i c e h ave a f a i r l y s ub sta n-t i a l f r i c t i o n c o e f f i c i e n t and a r e l a t i v e l y low s t re n gt h ( f i g u r e 23a).

So l u t i o n :

For app l i ca t i ons up to abou t 1200 lb / in 2 (8.3 MN/ ), th e O-r ing may berep laced by a spr ing- loaded T ef lo n sea l. The Te f lo n has bo th a lower coef-f i c i e n t o f f r i c t i o n and a h i g h e r s t r e n gt h . Such s e a ls may r e q u i r e mo d i f i -

c a t j o n o f t h e s e a l g ro ov e i n r a d i a l s e a l a p p l i c a t i o n s s i n c e t h e y ca nn ot best ret ch ed as much as e las tom er ic O-r ings f o r assembly. Spr ing- loadedTe f lon sea ls may no t be adequa te f o r use as r o t a t i n g sh a f t sea ls o r o the rcon t inuous -mo t ion app l i ca t i ons s ince f r i c t i ona l hea t bu i l dup becomes aproblem. I n suc h a p p l i c a t i o n s , s p e c i a l c o n f i g u r a t i o n s may be r e q u i r e d t op r o v id e h e a t r e j e c t o n .

F o r v a lv e s and f i t t i n g s us ed a t p re s su re s above 1200 1b / in 2 ( 8.3 M N / ~ ~ ) ,seals made of pure Tef lon PTFE) may be acceptable i f t he reduced sea l i ngc a p a b i l i t y due t o c o l d f l o w can b e t o l e r a t e d . A ls o, b a t c h - c e r t i f i e d V i t o no r KEL F 81 may be used, a l thoug h V i to n may harden and pe rm it leakage a ttemp eratur es o f -40° F (23 K ) and lower ( f i gu re 23b .

Moving stern- \Ordinary O-ring \

a)

Spring-loadedTeflon seal

0

F i g u r e 23.- Seals - Dynamic seals.



Met a l - to-M eta l Rubbing Seals

Problem:

D e si gn r e qu ir e m en ts f o r v a l v es t h a t c o n t r o l t h e f l o w o f h o t oxygen a t h i g hp r e ss u r e r u l e o u t s o f t s e a ls . I n t h i s s i t u a t i o n , s o f t s e a ls a r e re pla ce dby meta l - to -meta l rubb ing sea l s. H igh p ressure and h ig h f l o w ra te s canproduce s i de l oads and o s c i l l a t i o n s on the poppe t seal ; these s i de l oadsand o s c i l l a t i o n s can cause f r e t t i n g o r g a l l i n g . F r e t t i n g , i n t h i s case,means m e ta l d e t e r i o r a t i o n c aused b y r e p e t i t i v e h i g h f r eq ue nc y v i b r a t i o n a tt h e i n t e r f a c e b etw ee n two s u r f a c e s. G a l l i n g i s a more se ve re c o n d i t i o ni n v o l v i n g s mea ri ng and t r a n s fe r o f ma te r i a l f r o m one s u r f a c e t o t h e o th e r .Both occurrences are problems i n oxygen systems. The valv e poppet co ulds eiz e, r e s u l t i n g i n l o ss o f f un ct io n; t he f r i c t i o n a l h ea t o f t h e f r e t t i n go r g a l l i n g c ou l d le a d t o i g n i t i o n o f t h e v alv e; o r t h e p a r t i c l e s ge ne ra te dy t h e f r e t t i n g o r g a l l i n g c o u ld cause m a l fu n c t io n o r i g n i t i o n o f a n ot he r

component downstream ig u r e 24a.

S o l u t i o n :

Where pos s ib le , th e va lv e poppet should be d e si gn e d f o r s y mn e t r i ca l f l o wso t h a t no o s c i l l a t o r y s i d e l oa d s a re c re a te d . The symnet r i ca l f l ow w l lcen te r t he poppe t i n the bo re and ma in ta in des ign c l ea rances between thepoppet and bore surfaces.

For gaseous systems i t may b e p o s s i b l e t o r e du ce t h e v o l u me t r i c f l o w r a t ea nd t hu s t h e m a gn it ud e o f o s c i l l a t i o n s and s i d e l oa d s ) b y i n s t a l l i n g a n

o r i f c e d ow nstream of t h e p o p pe t t o m i ni m iz e t h e p r e ss u re d i f f e r e n t i a 1occur r i ng ac ross the poppe t .

ti s a l s o p o s s i b l e t o f l e x u r e m ount t h e p op pe t i n t h e b o re and t o i n -c rease the c l ea rance be tween the poppet and the bo re by i nco rpo ra t i n g l aby -

r i n t h s e a l g r oo ve s i n t h e p o pp et s u r fa c e .

Poppe t and bo re mat e r i a l s shou ld be se lec te d t o min lm ize the chance o f i g -n i t i o n . B o th may be h arde ne d b y a p roc e ss l i k e n i t r i d i n g t o m i n im i z e mate-r i a l l o ss due t o f r e t t i n g o r g a l l i n g , f i g u r e 24b



... e .ORleliv;..L ;

O POOR QilkLlTY

Rubbing surface

___

Return sprlngSolenoid actuatornot shown

flexure

flexure

o 2 out

assembly

assern bly

Figure 24. Seals Metal to metal rubbing seals.

4 25



F TERS

Contaminat i on can never be comple te l y e l im ina ted f rom a fluid systems i n c e i t i s a lways being gene rated t o some degree by moving pa r ts . t i st h e r e f o r e u s u a l l y n e ce ss ar y t o c o n t r o l and r emove p a r t i c u l a t e s f ro m t h ef l o w s tre am c o n ti n u ou s ly . F i l t e r s a re t h e de v ic e s most c o m n l y used t o

co nt ro l pa r t i c u l a t es . Whi l e they do t ra p most con taminants above a spe-c i f i c s i z e t h e r e a re c on ce rn s a s s oc ia te d w i t h t h e i r use. One i s t h a ta f t e r some use t he f i l t e r becomes a po t e n t i a l com bus ti on s i t e j u s t becauseo f t h e h i gh c o m b u s t ib i l i t y o f i t s c o l l e c t i o n o f f i n e p a r t i c le s Anotherc o nc e rn i s t h a t f i l t e r s a r e made o f v e ry s m al l d ia m e te r m e t a l l i c w ir e sos m a ll t h a t a v e r y s l i g h t a d d i t i o n o f h e a t c an cause h o t s p o ts i n t h e w ir e .

P ro pe r d es ig n o f f i l t e r s must i n c l u d e a c a r e f u l t r a d e - o f f s tu d y t oen sure t h a t i g n i t i o n p o t e n t i a l i s reduced ra th er t han inc reased. Use o ff i r e - r e s i s t a n t m a t e r i a l s such as pu r e n i c ke l o r Monel can ease some o f t hec on ce rn . A m a in te na nc e p l a n t h a t c a l l s f o r f r e q u e n t c l e a n in g o r r e p l a c e -ment o f f i l t e r s c an a ls o h e lp .

O t he r t ec h n iq u e s a r e d i sc u s se d i n t h e f o l l o w i n g a r t i c l e s on t h e u seo f f i l t e r s a t t h e i n l e t s and o u t l e t s o f modules u ps tre am o f v a lv e s ea tsand around d i f f i c u l t - t o - c le an passageways.



F i l t e r s a t I n l e t s and Ou t l e t s o f ModulesORIMN L PA@: [ S

O P R QUALITY

Problem:

Modular pre ss ure system components, such as re g ul a to r assemb lies, which

are manufactured, teste d, shipped, and handled as independent un it s , ares u b je c t t o t h e i n t r o d u c t i o n o f c on ta m in an ts th r ou g h t h e i r i n l e t and o u t l e tpor ts . These po r ts a re sea led o f f y f i t t i ngs and tubes du r ing no rma loperat ion, but these openings m y be unpro tec ted b e fore the modu le i si n s t a l l e d i n t h e s ystem.

So lu t i on :

I n s t a l 7 a t i n l e t and o u t l e t p o r t s f i l t e r s t h a t r em ain i n p l ac e whetherc on ne ctin g f i t t i n g s a r e i n o r ou t. The t y p i c a l i n s t a l l a t i o n i s showni n f ig u re 25.

Figu re 25.- F i l t e r s F i l t e r s a t i n l e t s and o u t l e t s o f modules.

4 27



F i l t e r s U p str ea m o f V al ve S ea ts

OF POOR QUkLIVI.Problem:

V a lv e s ea t s I n h i gh p r ess u r e oxy gen sy stems a r e c r i t i c a l s ea l i ng po i n t s

which must be c are fu 1 y designed and manufactured t o pro v ide leakpr oof ,r e l i a b l e p r e s s u r e c o n t r o l . P r ope r m a t e r i a l s e l e c t on and s ea t - f o rm i ngt echn i ques a r e c r uc i a l i an adequate seal i s t o be a ch ie ve d f o r l o n gte rm s to rage a t h igh p ressure and f o r thousands o f cyc les o f use. Theper fo rmance o f such a sea l i s degraded by the t rap p in g o f con taminan tp a r t i c l e s a t i t s s e al in g i n t e r f a c e f i g u r e 26a).

S o l u t i o n :

I n s t a l l v e r y f i n e mesh e.g., 10 -m i cr on) f i l t e r s i m ned i a t e l y ups tr eam o fv a l v e s ea ts f i gu r e 26b ).

r V a l ~ e Va Iveseat seat

lter

F i g u r e 26.- F i l t e r s F i l t e r s upstream o f va lve sea ts .

4-28



F i t e r s I s 01a t ng Unavo idab ly D i r ty PassagewaysORIG(:\ A i P Gf [SOF POOR QUALITY

Problem:

Some po r t io ns o f the f lo w s t ream i n an oxygen sys tem may be ex t reme ly d i f -

f i c u l t t o c l e a n d u r i ng m a nu fa ct ur in g. The pr e s su r e b o t t l e shown i n f i g u r e27a has t u b i n g br az ed t o t h e i n s i d e o f t h e w a l l w hic h i s d i f f i c u l t t oc le an adequa tel y . The long passageway with a smal l diameter , shown i nf i g u r e 27b, c o u l d n o t be s a t i s f a c t o r i l y c l e an e d o nc e t h e p l u g was weld edi n p la ce . Welds and solde red and brazed jo in ts , i f l e f t i n t h e as-form edcond i t i on , m y leave s lag , roughness, po r os i t y , o r c racks wh ich can gene r-a t e o r t r a p c o n t a m i n a n t s .

S o l u t i o n :

F ine mesh f i l t e r s shou ld be added i rmted ia te l y ou t s id e the unavo idab lyd i r t y i t passageways t o co n ta in and co n t r o l c on tamina t ion th a t canno t be

e l im i n a te d . Welds s ho ul d be s p e c i f i e d as f u l l p e n e t r a t i o n so t h a t a l lc o n t a c t i n g s u r f a c e a r e a i s j o i n e d t o g e t h e r t o p r e v e n t e nt ra pme nt o f p a r -t cu la te s and e l i m ina te unc leanab le b l i n d su r faces . Exposed we ld su r -faces shou ld then be g round t o a smoo th f i n i s h t o enhance c lean ing .

Tubing brazed I Welded plug

passageway

difficult to clean

b)

F i g u r e 27.- F i l t e r s F i l t e r s i s o l a t i n g u n a v o i d a b ly D i r t y t t passageways.

4 29



NC1LLARY EQUIPMENT

I n a d d i t i o n t o h ou sin gs v a lv e s s e al s and f i l t e r s h i g h p r e s s u r eoxygen system s t y p i c a l l y c o n t a i n a v a r i e d c o l l e c t i o n o f an ci 11ary compo-ne nts such as tan ks pumps he at er s and senso rs. These components

sho uld be designed j u s t as c a r e f u l l y as th e oth er components we haved iscussed. They have t h e i r own un lque set o f des ign cons idera t ions .

Tanks f o r h i g h pre ssu re oxygen systems f o r instan ce may no t be madeh s t re n g th - t o -we i g h t r a t i o s

T i t a n i u m and i t s a l l o y s a r e im -pa c t se ns i t i ve - i n oxygen a tmospheres.

Pumps compressors fans and blow ers i n oxygen se rv ic e must be care -f u l l y d es ig ne d t o a vo i d r o t a t i o n a l f r i c t i o n o r r u bb in g w hic h can q u i c k l yl e ad t o an i g n i t i o n . Boo ts t rap pumps i n wh ich a fu e l - r i c h gas d r i ves atu rb ine on a comnon sha f t w i th t he oxygen pump pre sen t th e sp ec ia l prob-l em o f avo id i ng f l u i d con ta c t a l ong the comnon sha f t .

Heaters and sensors i n oxygen systems presen t a spe ci a1 se t o f prob-lems because they i n t rod uce e le c t r i c a l cu r re n t i n t o an envi ronmen t wherea sh o rt c i r c u i t o r an arc wou ld cause an ign i t ion .

The fo l lo w in g pages d iscus s some o f th e des ign prob lems and so l u t io nsr e1ated to anc 1ary components.



Bootstrap Oxygen Turbopump

O R i ~ l ~ , '

O POOR QOli~1 j y

Problem:

Bo ots trap oxygen turbopumps, such as are employed i n boo st pro pu ls io n

systems, u t i l i z e ho t f u e l - r i c h c om bus tion gases t o d r i v e a t u r b i n e w hic halso dr ives the oxygen turbopump on the comnon shaft . M i x l ng a l ong t hec o m n s h a f t o f t he f u e l - r i c h c om bu stio n gases w i t h t h e h i g h p re s su reoxygen being pumped w i 11 produce h igh temperature combust ion that w i 11destroy the turbopump.

S o l u t i on :

Use o f an add i t i ona l , i n te rmed ia te se t o f sea ls a long the sha f t c rea tesa s epa r a ti on a rea wh ic h i s t hen c on t i nuous l y pu rged w i t h an i n e r t gas t oavo id the development o f a hazardous gas mix tu re ( f i g . 28).

-Inert gas

Liquid oxidizer and Inert gas Fu el rlch gas and inert g

Hot fuel rlch gas

Liquid seals

F i gu r e 28.- A n c i l la ry equipment Bo ots trap oxygen turbopump.

4 31



Heaters ORIGIN L P GE \SOF P R QU LIV

Problem:

I n ce r ta in cases hea te rs a r e r equ i r ed t o fun c t i on w i th in the h igh p ressu re

oxygen environment. A m a lf un ct io n i n t he h ea te r o r i t s c o n t ro l c i r c u i t r ycou ld r e su l t i n ove rhea ting, a sho r t c i r cu i t , o r a r cing, which would i g -n i t e sys tem ma te r ia ls .

So lu t i on :

Heater tempera tures shou ld be co n t ro l le d t o va lues s ub s t an t ia l l y below thetemper atur e a t which i g n i t i o n o f t h e hea te r su rface ma te r ia l o r a iiy ad ja -cen t m at er ia l could occur. This margin should be a t le a st 200° F 111 K .

I n e s t ab l is h i ng it the des igner should cons ider the poss ib le temperaturedi f ference between the thermal sensor and the hot test heater sur face loca-t i o n , t h e u n c e r t a i n t y i n sen sor re ad in g , and th e u n c e r t a i n t y i n i g n i t i o n

temp erature. Redundant the rma l sensors should be used i i nd ica ted by afa i lu re modes and e f fec ts ana lys is .

Ig n i t i o n due t o e l e c t r i ca l ma l func t i on o f t he hea te r may be pr even ted byus ing doub le - insu la t ed heater w i re . An ad d i t ion a l sa fe t y fea tu re t h a t canbe used i s the d i f f e r e n t i a l cur ren t sensor, which mon i to rs heater cu r ren ti n bo t h t h e i n l e t and t h e o u t l e t w i r e and t u rn s t h e h e a t er power o f f i apredetermined imbalance develops (such as from a short r an arc from thehe a t e r to ano the r e lemen t i n the sys tem). Ma te r ia l s , bo th m e t a l l i c andnonmeta l l i c , should be chosen t o min imize the chance o f i g n i t i o n shou ld ashor t o r a rc occur .

/ifferential current sensor

Signal conditioner

Double Insulated heater wiresS sheath

lnsulatlon conductor

F i g u r e 29.- Anci 1 a r y equipment - Heaters.



Sensors

Problem:

Sensors ar e r e qu ir ed i n oxygen systems t o measure such parameters as tern-pe ra tu re p ressure dens i ty 1 q u id l eve 1 and f l o w ra te . m a l f u n c t i o ni n t h e sensor o r i t s s i g n a l c o n d i t i o n e r c ou ld r e s u l t i n h i g h c u r r e n t f l o wo v e rh e a ti n g a s h o r t c i r c u i t o r a r c in g w hic h s h ou ld i g n i t e s ys te mm a t e r i a l s .

S o l u t i o n :

S en so r and s i g n a l c o n d i t i o n e r c i r c u i t r y s h ou ld be de sig ne d t o m i n im i z e t h ec u r r e n t f l o w a nd th u s t h e o v e rh e a t in g and a r c i n g t h a t m i g h t r e s u l t f r o m as h o r t i n t h e se ns or system. Ma te r i a l s b o th m e t a l l i c and n o n me ta l l i cshould be chosen t o min im ize the chance o f i g n i t i o n shou ld a sh or t occu r.I n s i t u a t i o n s w here a r c i n g c an o cc ur t e s t i n g s ho ul d v e r i f y t h a t t h emax imum p o s s i b l e s pa rk e n er gy i s i n s u f f i c i e n t t o c ause i g n i t i o n o f a d j a-c e n t m a t e r i a l s .

No f i g u r e i s used t o i l l u s t r a t e t h i s ite m.



5. SYSTEMS DESIGN

t i s o u r p urp os e i n t h i s s e c t i o n o f t h e handbook t o b u i l d on t h eg u i d e l i n e s f o r m a te r i a l s e l e c t i o n a nd component d es ig n g i v e n i n s e c t i o n s3 and 4 and t o extend these gu ide l ine s t o the systems des ign le ve l . These

added gu ide l i nes a re no t exhaus t i ve bu t focus on those spec ia l cons ide ra -t i on s req u i re d i n the des ign o f an oxygen system.

t i s assumed th a t th e des igner w i l l adequate ly handle those s tandarda n aly s es r e l a te d t o sy stem f lo w c a p a c it y , dynam ic and s t a t i c s t r u c t u r a ll oads , the rm a l l y induced l oads, hea t t ra ns fe r , e t c . These ro u t i n e ana l -yses are n ot un ique t o h ig h pressu re oxygen systems, bu t inadequate a t t en -t i o n t o t hem ca n re s u l t i n s ys te m fa i l u r e s whose r e s u l t s a re ma g n i f i e d be -ca use o f t h e e x tr eme r e a c t i v i t y o f o xygen.

Many o f t he spe c ia l ana lyses re qu i re d i n the des ign o f oxygen sys -tems, as w el l as many o f th e po te n t i a l des ign prob lems and the des ign prac-t i c e s f o r overcoming them th a t were p resen ted i n sec t i on 4 a t th e component

le v e l a ls o app ly a t the system le ve l . These areas have a l rea dy been ade-q u a t e l y d i sc us s ed i n s e c t i o n 4 and the i n fo rmat i on w i l l not be repeatedhere.

Two areas o f impor tance i n the des ign o f h i gh pressu re oxygen systemst h a t shou ld be no ted a re as fo l l o ws :

1 I n t h e p e rforman c e o f t h e f r a c t u r e me ch an ics and f l a w g row th a n a l -yses, which should be a p a r t o f any system des ign, th e des igner sh ould beaware tha t the p resence o f oxygen i nc reases the fa t i gue c rack g row th ra tei n meta l s as compared t o the r a t e i n an i n e r t atmosphere . A lso, i n gas -eous oxygen systems, th e presence o f water vapor can f u r t h e r acc e le ra t ef a t i gue crack growth.

2. The se l ec ted a rc h i te c t ur e o f h igh pressu re oxygen systems imposesc e r t a i n co ns t ra in t s on system opera t i ons such as th e sequence and t im in gof commanded component fu n c ti o n s . As an example, d u ri n g shutdown o f ac ryogen i c boos t p rop u l s i on sys tem, the eng ine s 1 q u id oxygen p reva l vesm s t be c lo se d and the LO i n l e t l i n e t o t h e o xy ge n tu rb opu mp p re s s u r i z e dw l t h i n e r t g as w i t h i n a cf o s e l y s p e c i f i e d t i m e t o a v o i d c a v i t a t i o n a n da dangerous overspeed co nd i t i o n i n th e l i q u id oxygen tu rbopump. As p a r to f the s tandard f a i l u r e modes and e f fe c t s ana lyses FMEA) a comprehensivesystem opera t i ng an a l y s i s shou ld be pe rfo rmed t o unders tand th e con-s t r a i n t s im posed by a p a r t i c u l a r a r c h i t e c t u r e on b o t h n orm al a nd f a i l u r e -mode operat ons.

I n t h i s s ec tio n, we p re s e nt d e s ig n c o n s i d e ra t io n s f o r t h e u se of h i g h

p re s s u re o xy ge n w hic h r e q u i r e s p e c i a l a t t e n t i o n a t t h e s ys te m l e v e l . Wehave grouped these des ign g u i de1 es and spec i a1 con s id era t ons i n t o t hef o l l o w i n g c a t e g o r i e s f o r d i s cu s si on :

S y s te m a rc h i t e c tu reSystem f low dynamicsSystem therm al de si gnSystem c lean 1 ess



We w i l l d i s t i n g u i s h b etw ee n c r y o g e n ic l i q u id s u p e rc r i t i c a l and gaseou so xy ge n sys te ms w hen t h e d i s t i n c t i o n i s imp o r ta n t.

SYSTEM RCHITECTURE

S yste m a r c h i t e c tu re c o n s id e ra t o n s i n c l u d e i d e n t i f y i n g t h e c omponen tsreq u i re d t o pe r fo r m th e func t ion de f i n i ng redundancy requi remen ts andlo c a t i n g c omponents w i t h i n t h e v e h i c l e and i n r e l a t i o n t o one a n o th e r.Fa i l u r e modes and e f fe c t s ana ly s is FMEA) i s an e f f e c t i v e t o o l i n th e i n i -t i a l p ro ce s s o f d e s ig n in g sy ste m a r c h i t e c tu re and s h o uld be u se d i n s e le c t -in g components es ta b l i s h i ng redundancy leve ls and eva lua t ing sp ec i f i cs ys te m g eo met ri es r a t h e r t h a n as an a f t e r - t h e - f a c t j u s t i f i c a t i o n of a sys-tem a r ch i te c t u re t h a t was de r ived by les s d i sc ip l i ne d means. There a resystem geometry co ns i der at io ns r e1a t e d t o 1ow dynamics the rm al d e sl gnand cle an 1 ness which w i 11 be discussed subsequently under those headings.The fo l low in g two i tems a re impor tan t sys tem a r ch i te c tu re cons ide ra t ion sfor oxygen systems.

P ro te c t i o n of System Redundancy

Problem:

A component o r s ys te m -l ev e l f a i l u r e ca n i n i t i a t e a f i r e w i t h i n t h e system .Oxygen f i r e s once s t ar ted spread rap d l y us i ng any exposed nonmetal 1 c sand even some meta ls as fu e l . The f i r e may no t on ly eng u l f the a f fe c t edcomponents bu t a l so spread t o adj ace nt components and de st ro y systemredundancy.

S o l u t i o n :

C on ta in men t o f a f i r e t o as s ma l l a n area as p o s s ib l e i s d e s ir e d . f h ef i r e can be l i m i t e d t o a s i ng le component o r t o a sma l l a rea redundan tcomponents shou ld be ab le t o ca r ry on the system func t i on . No t on lys h o ul d a l l s yste m m a t e r i a l s be s e l e c t ed w i t h an e ye t o t h e i r c o m b u s t i b il -i t y b u t w he re ve r p ra c t i c a b le t h e y s h ou ld b e s e le c te d t o p ro v id e f i r e -brea ks between system components. N ic k el and Monel ar e candida te r e -re s is ta n t ma ter ia ls . Fur thermore redundant system components shou ld no tb e l o c a te d i n a c o m n ass embly o r a d ja c e n t t o one a n o the r becau se t h ef a i l u r e o f one o f t h e components c o u ld t h e n l ea d t o f a i l u r e o f t h e o th e r s .The redundant components shou ld be separated geometr ica l ly and a lso byf i reb reaks whereve r posstb le . F i g u re 30 il u s t r a t e s t h e use o f f i r e b r e a kppl i c a t i o n i n sys tems a rch i tec tu re .



ORIG NAL' P GE s

OF P R QUALITY

/onel inlet fitting

Figu re 30.- System ar ch i te ctu re Pr ote ct i on o f system redundancy.

Loc at ion of Oxygen System R e l i e f Po r ts

Problem:

A l l h igh p ressure oxygen sys tems a re p rov ided w i th p ressure r e l i e f po r tst o p r ev en t s t r uc t u r a l f a i l u r e due t o ove rp res su re . Improper l y loca tedoxygen vents can damage adjacent components or cause an ignit ion.

S o l u t i o n :

The des igne r must eva l uat e a l l s ys tem r e l i e f po r t l o c a t i ons t o ens ur e t h a toxygen w i l l not be ven ted overboard near a fu e l o r i n te rn a l l y i n to an a reac on t a f n i ng a f u e l and an i g n i t i o n sour ce . f xygen i s ve nte d i n t o i n t e r -

n a l v e h i c l e c a v i t i e s a c a v i t y ana l y s i s s hou ld be done t o v e r i f y t h a t nohazardous s i tua t ion w i l l develop as a r e s u l t o f t h e v en t. As p a r t o f t h esystem-1 eve1 FMEA a s lm i l ar compartment hazard a na lys is should be donet o de termine th e e f f e c t s o f any system leaks . Where cryo gen ic oxygen i svented the po te nt ia l t o f reeze adjacent components of o th er systemsshould be evaluated

No f i g u r e i s used t o i l l u s t r a t e t h i s ite m .



SYSTEM FLOW DYNAMICS

Cons idera t ions o f sys tem f low dynamics inc lude f low ve loc i ty e f fec ts ,p a r t i c le impact, e ros ion, cav i ta t ion , induced v i b r a t io n , geysering , waterhamner, and pr es su re spik es. P a r t ic l e impact effe cts, water hammer, and

adi aba t ic compression ef fe c ts have been discussed i n se ct io n 4. The fo l -lowing fo u r i tems deal w i th aspects of f lo w dynamics as they a f f e c t oxygensystems.

Because o f the complex ity and the v a r ia b i l i t y o f sys tem des ign, no a t -tempt was made t o i l l u s t r a t e the i tems discussed i n the re s t o f t h is sec-t io n. We be l ie ve the problem statement and so lut ion s are adequate f o rc le ar unders tand ing.

System Erosion

Problem:

Ero sio n o f system components due t o flow phenomena such as p a r t i c l eimpacts , impacts o f d rop le ts ent ra ined i n a gas f low , and ca v i ta t i on canexpose f resh, rea ct iv e surfaces to oxygen and pro vide the lo ca l iz ed heatgenera t ion necessary to cause i gn i t io n .

S o lu t i on :

Good des ign prac t i ce t o prevent erosion, as i n the case o f p a r t i c le impact, inc lude s ve lo c i ty con tro l , a f lo w geometry th a t minimizes impactang le , adequate f i l t r a t i o n , se lec t on o f i g n i i on - re s i s tan t m a te r i a l s , andco nt r o l o f loc a l i z ed sys tem pressure drop and heat in pu t t o m in im ize cav i -

t a t i o n p o t e n t i a l.

C a v i t a t i o n i n R o ta t i ng E quipm ent

Problem:

C a v i t a t i o n c r e a t i o n o f l o c a l i z e d area s i n th e f l u i d h a vi ng p re ss ur es b e-low the vapor pressure) i n l iq u id oxygen feed systems upstream o f oxygenturbopumps can re su l t i n a v a ri e ty o f turbopump hazards. These hazards in -c l ude e ros ion o f t he im pe l l e r and l o ca l i z ed bu rn ing o f t he im pe l l e r due tobubble col lapse. Exten sive c a v it a t i o n may cause turbopump overspeed le ad-Ing t o c r i t i c a l r o to r dynam ics prob lems, i nc l ud ing rubb ing o f t he im pe l l e ron t h e h ou sin g w i t h r e s u l t a n t f r i c t i o n a l i g n i t i o n .

S o lu t i on :

The system design must provide adequate net posi t ive suct ion pressureNPSP) t o oxygen turbopumps by es ta bl is hi ng adequate supp ly tank pres sure



and c a r e f u l l y c a l c u l a t i n g and c o n t r o l l i n g f l o w s ys te m t he rm a l i n p u t s o r b yus in g a bo ost pump upstream o f the turbopump.

o w -I nd uc ed V i b r a t i o n i n B el lo w s and F l e x i b l e J o i n t s

Problem:

Oxygen f l ow th rough be l lows and f l ex ib le jo in ts can induce h igh - leve l p res -su re f l uc tu a t io ns i n these componen ts wh ich can lead t o r ap id fa i l u r e duet o s t r u c t u r a l f a t i g u e.

S o l u t i o n :

Flow v e lo c i t y through thes e components should be minimized. Where pos si-ble be l low s should be l in ed . Where l i n e d bel lo ws cannot be used thesy ste m s h o ul d be a n aly ze d f o r s u s c e p t i b i l i t y t o f lo w -i nd u ce d v i b r a t i o n .

Geyser ing i n Cryogenic L iq u id Oxygen Propu lsion Feed Systems

Problem:

Geysering occurs i n v e r t i c a l sys tems w i th a tank and a long feed l ine fromt f i l l e d w i t h cr y o g e n ic oxygen. H ea t t r a n s f e r i n t o t h e l i n e causes gas

bubbles t o form and b e g i n r i s i n g i n t h e l i n e . As t h e b ub ble s r i s e t h e yc oa le sc e t o f o rm l a r g e r bu bb le s. I n a l i n e t h a t i s l o ng w i t h r e s p ec t t oi t s d ia m e te r t h e r e s u l t i s an e xp an din g v ap or b u bb le o f s u f f i c i e n t s i z et o e x p el t h e l i q u i d a bove i t i n t o t h e t an k w i t h a f o r c e l a r g e enough a tt imes t o ru pt ur e the tank o r t o damage i n te rn a l tank components such asbaf f les screens o r le v e l sensors . When the q u id subsequently ree nter st h e l i n e t can cause la r g e water hamner fo rc es w it h accompanying systemdamage.

S o l u t i o n :

Geysering can be -c on t r o l l e d by co n t ro l l i n g tank p ressure choos ing appro-p r i a t e f e e d l i n e g eom etry i n s u l a t i n g t h e f e e d l i n e and r e c i r c u l a t i n g t h ef l u i d f ro m t h e l ow p o i n t i n t h e l i n e back t o t h e ta nk . C o n tr o l c o n s i s t so f k ee pi ng t h e oxygen i n t h e l i n e from reach ing i t s vapo r i za t io n tempera -tu re and p ro v id fn g adequate l i n e d iamete r t o hand le the vapor bubb le perco-l a t i o n t h a t s t i l l o ccurs.



SYSTEM THERMAL DES I N

Sys tem therma l des ign cons idera t ions inc lude s ta r tup the rma l con-d i t i o n i n g , i n s u l a t i n g t o p r e v e n t e x t e r n a l s ys te m c o nd e n sa ti o n, and a v o id -

g the locku p o f c ryogen ic oxygen i n a system segment.

St ar tu p M al fu nc t io ns i n R ot at in g Equ ipment and Dynamic System Components

Problem:

I n cry og en ic oxygen turbopump systems, t i s necessary t o b r in g compo-n en ts t o t h e rm a l e q u i l i b r i u m b e f o r e s t a r t i n g up t h e s ys te m t o a v o idhazardous componen t the rma l t ra ns ie n t s which may a f fe c t f i t s and c le a r -ances, cause ro to r dynamic i n s ta b i l i t i e s , o r l ead t o h igh speed rubb ingf r i c t i o n . Any o f these prob lems may re s u l t i n an ig n i t i o n .

S o l u t i o n :

Prov ide thermal co nd i t io n i ng o f t he cryog enic system and components bygra du a l l y b leed ing th rough c ryogen ic gas, then 1 qu id . Once approximatet he r m al e q u i l i b r i u m i s ac hie ve d, m a i n t a i n t b y u s i n g p u m p s t o c i r c u l a t ep r o p e r l y c o n d i t io n e d f l u i d t hr o ug h t h e s ystem b e f o r e s t a r t u p .

Condensation on E xt er na l System S ur f aces

Problem:

Exposed cryo gen ic surfa ces i n oxygen systems can for m l a r g e amounts o fI ce . The f a l l i n g i c e can damage the veh i c le o r i t s components dur in gground opera t ions o r l aunch .

S o l u t i o n :

Exposed cryogen ic surfaces should be ins u la ted . Any of th e var io us i ns u l a-t i o n schemes spraye d-on foam, wrap-around c lo s e d -c e ll segments, vacuumjacke ts ) used t o c on t r o l h ea t i np u t t o c ryogen ic oxygen systems can beuse d t o p r e cl u d e th e f o rm a t io n o f i c e o r l i q u i d a i r on s u rf a ce s . The de-s i g n e r s h o u l d e n s u r e t h a t t h e r e re no uninsu la ted system areas or exposedgaps between insu l a te d a reas wh ich perm i t the bu i ld up o f i ce .



Lockup o f Cryoqenic Oxygen i n System Segments

Problem:

Cryogenic oxygen hydrau l ica l ly locked up between two va lves or f low con-t r o l components can absorb heat and through t he in.crease of press ure causes t r u c t u r a l f a i l u r e .

S o l u t i o n :

The system and components shou ld be designed t o pr ov id e ap pr op ria te pr es-su re re1 e f and the reby p rec lu de unaccep tab le p ressu re bu i ldup . E i th e r as e pa ra te r e l i e f s y stem may be i n c o rp o ra te d i n to t h e s ys te m o r b a c k - re l i e fva lves may be b u i l t in t o th e components . System r e l i e f dev ices shou ld bep ro te c te d b y i n s u la t i o n and pe rh ap s b y p u rg in g w i t h n i t r o g e n r h e l i u m t op re ve nt i c e b lo ck ag e o f t h e r e l i e f p o r t .

Condensat o n o f Contaminants W it hi n Cryogenic Systems D uri ng Loa din g

rob em:

Load ing c ryogen ic oxygen can re s u l t i n condensat ion wa ter o r any o th e rcondensable vapor i n s i d e the system. I n la rg e systems even contamin ant

l e v e l s m easured i n p a r t s p e r m i l on can produce a s izab le f rozen masstha t cou ld impede f low o r sys tem func t ion .

S o l u t i o n :

Befor e a cryog enic sys tem i s loaded a l l a i r water and condensable vaporsshould be purged o r evacuated from th e system. Exp eri me nta t ion may bere q u i r e d t o d e f i n e t h e d eg re e o f p u rg e o r t h e number o f e v a c u a t io n c y c le srequ red .



SYSTEM CLEANLINESS

S ys te m c le a n l i n e s s i s e x t r e me ly imp o r ta n t i n oxygen. M e t a l l i c andnonmetal1 c con taminan ts and no nv o l a t i le res idues may be l e f t i n compo-nents and systems af t e r fa b r ic a t i o n and assembly. The component des ignp r ac t ic e s i d e n t i f i e d i n s e ct io n 4 concern ing contaminant generat ion andco n t ro l a re a ls o a pp l i cab le t o system des ign as a re the c lean assemblyte c hn iq ue s d i s cu s s ed i n s e c t i o n 6 and the c lean ing techn iques d iscussedi n s ec t i on 8.

The design er sh ould recog nize, however, t h a t component f e r s a l o n emay not be adequate t o hand le contaminants b u i l t in t o the system or gen-e ra te d a t t h e sy s te m/ le v e l. S e pa ra te s y s te m- le v e l f i l t e r s may b e r e q u i r e dt o c o n t r o l p a r t i c u l a t e c on ta m in a t io n , and a p p ro p r i a te sy stem f l u s h andpurge p o r ts should be designed i n t o th e sys tem.

Sys tem Leve l F i 1 e r s

Problem:

The mos t r igo r ous a t te n t io n t o des ign ing a sys tem fo r c lean assemb ly andc le a n o p e ra t o n a nd t o m in im iz i n g c o n ta m in a nt c o l e c t o n a re as c a nn o t t o -t a l l y e l i m i n a t e c o n ta m i na t io n b u i l t i n t o t h e s y st em and g en er at ed b y t h esys tem dur ing opera t ion . I f s y s te m- le v e l c o n ta m in a tl o n c o n t r o l and re -moval fe atu res are no t prov ided, per formance and saf e t y may be se ve re lydegraded.

S o l u t i o n :

A de qu ate s y s tem- lev e l f i l t e r s s h o u ld be p ro v id e d f t r a t i o n r a t i n g,d i r t - h o ld i ng c a p a c i t y t o h an d le b u i l t - i n c o n ta m in an ts and sy stem-genera ted con taminan ts . The sys tem f i l t e r s shou ld be loca te d so as t oprotect component f ers f rom con tamina t ion ove r load .

Sys tem F lush and Purqe F i t t i n q s

o b1em:

The mos t r igo r ous a t te n t io n t o d es ign ing a sys tem fo r c lea n assembly andc l e a n o p er a t io n and t o m i n i m i t i ng contaminant c o l l e c t i o n a reas canno t to -t a l l y e l i m i n a t e c o n ta m i n at io n b u i l t i n t o t h e system, g en er at ed b y t h e s y s-

tem dur ing opera t ion , o r in t rodu ced i n t o the system dur ing ma in tenanceopera t ions . I f sys tem- leve l con tamina t ion co n t ro l and remova l fea tu r esar e no t provided, performance and saf et y may be se ve re ly degraded.

S o l u t i o n :

S ys te m f l u s h a nd p u rg e f i t t i n g s s h o u ld be l o c a te d a t a p p ro p r l a te h i g h a ndlow p o i n t s t o a l l o w e f f e c t i v e f l u s h o r p ur ge o f t h e s ystem i n a l l e xp ec te da t t i t u d e s .

5 8



6. CLEAN ASSEMBLY AND INSPECTION

CLEAN ASSEMBLY TECHNIQUES

An area of foremost concern i n h ig h pressure oxygen systems i s contam-

i n a t i o n c o n t r o l . C on ta mln an ts a r e t h e m ost l i k e l y s ou rc e o f r e a d i l y i g n i t -ab l e m a t e r i a l . f h e y a re n o n m e t a ll ic t h en t h e y h ave r e l a t i v e l y l ow i g -n i t i o n t em per at ur es . f the y are m e ta l l i c they have been abraded o f f metalsu r faces . Such a p r oduc t o f m e t a l l i c ab r as i on w i l l have bare uno xid ize dmetal as a po r t i on i f no t a l l o f i t s exposed su r f ace a rea. Th i s su rf ace i sre a d i l y i g n i ta b l e when hea t f r om impact shock o r compression ra i se s thel o c a l t em pe ra tu re t o a c r i t i c a l v a lu e. E l i m i n a t i o n o f a l l c on ta min an ts i sh i gh l y des i r ab l e bu t no t t o t a l l y ach i evab le i n complex assem b li es whi chinc l ude nonme ta l l i c sea ls th reads screw lock p lugs press f i t s we ldssoldered and brazed jo ints and lu br ic an ts . Fo r tun ate ly th ere are somebe ne f i c i a l t echn iques th a t can be used to m in im ize the bad s ide e f fe c t s ofthese somet imes necessary features.

Assernbl inq Seals

Des igns t h a t a l l ow o r cause ha r m f u l cu t s o r ab r as ions t o t he i n - p l aceseals dur ing assembly can create contaminants and can set up future contam-in an t genera t ion as the se a l w i l l c o nt in u e t o s hed p a r t i c l e s d u r i n g i t sf u n c t i o n a l l i f e . A t y p i c a l e x a m p l e f i g u r e 31 i s t h e asse mb ly o f a s h a f ti n t o a bore co nta in in g an O- r i ng . The sh af t cou ld cu t t he O- r i ng becauseof a nbnex istent o r inadequate chamfer on the end o f the s ha f t . Perhapseven more comnon i s t he fo rc in g o f an O- r i ng over sc rew th reads t o p os i -t i o n t he sea l on a t h readed sh a f t o r bo l t . The c r e s t o f t he t h r eads w i l l

cu t and ch i p t he sea l and i f the assembled components are not recleanedt h e n t h e c on ta m in at ed i t e m i s l e f t i n t h e system .

Sea ls shou ld no t be fo rce d i n t o bores or over sh a f t s w i thou t generouschamfers. These pa r t s most be inspecte d f o r bur r s and sharp edges be fo rethey are assembled. t i s i m p o r ta n t t o n o t e t h a t a ch am fe r w i l l have asharp edge unless i t i s s p e c i f i c a l l y removed. Hardened st ee l may have avery p ronounced sharp edge a t t h e i n te rs ec t i o n o f t he chamfer cu t and theou t e r d i am e t e r o f t he sha f t .

I n s ta l l a t i o n o f an O- r i ng over th reads whose major d iameter exceedst he i ns i de d i am et er o f the O-r ing should be avoided i f poss i b l e . f t h i sdanger o f cu t t i n g i n t o the O- r i ng cannot be avo lded then th e assemblys p e c i f i c a t i o n s s ho u ld a l l o w f o r a d d i t i o n a l c l e a n in g a f t e r t h e O -r in g andthe threa ded p a r t have been assembled and before th e components are i n -s t a l l e d i n t he n e xt l e v e l o f assembly. A l i g h t c oa t in g o f s e a l l u b r i c a n tshould be used t o ease th e assembly.



p r e s s e nd

wel e plu

Figure 31 . ontamination generation during assembly.NOTE: Care must be exercised in the installation ofO rings into bore.



Threaded Assembly

Threaded connec t i ons oc cur r i ng i n f l u i d sys tems can genera te con tami-nan ts as the th reads a re engaged and t i gh tened , as shown i n the f i r s t ill u s t r a t i o n o f f i g u re 32. One way t o a v o id t h i s p rob le m i s t o r e d e s i g n t h e

thre ade d members as shown i n t h e second i u s t r a t on , where in the smoothp o r t i o n o f t h e p l u g i n te r f a c e s w i t h t h e s e a l b e fo re t h e t h rea d s engage.T h i s s o l u t i o n , however, does i n v o l v e r o t a t i n g a p a r t a g a i n s t i t s s e alc a u si ng r e a l damage. A l t e rn a te l y , t h e i n - l i n e t h rea d ed f e a tu re c o u l d berep laced w i t h a f l anged and bo l te d connect i on , wh ich p laces the th readedp o r t i o n s o u t s i d e t h e f l u i d s tre am , as shown i n the th i r d f i gu re . Us ing an-o th e r method, the fu nc t i on o f the th readed member can be ca r r i e d ou t by as e pa rate n u t d e v i c e t h a t i s n o t i n s e r t e d u n t i l t h e s e a l i n g h as b ee n accom-p l i s h e d w i t h a p u s h - in p l u g , as s hown i n t h e f o u r t h f i g u re , A n d f i n a l l y ,a no th er o p t io n i s t o i n s t a l l a b a r r i e r r i n g t o b l oc k t h e m i gr a t io n o fp a r t i c u l a t e ma t te r , as shown i n f i g u re 32e.

Deformable Par tsPar ts such as sc rew l oc k in g dev ices , us ua l l y non met a l l i c i ns e r ts ,

w hic h f u n c t i o n b y a l l o w i n g o th e r p a r t s t o d e form th em a re c o n tam i na n t g en-e ra to r s . T h e i r us e s h o u ld be l i m i t e d as much as p o s s i b l e and t h e i r i n s t a l -l a t i o n shou ld be sequenced so th a t they a re d r i v en i n one t ime on l y . Suc -cess ive assembly and d isassembly o n ly compounds th e amount o f p a r t i c u la t ec rea ted .

P r e s s F i t s

P re ss f i t s g e ne ra te p a r t i c l e s d u r i n g t h e i r assem bly f ro m t h e r e l a t i v emo t i o n o f t h e two h i g h l y l oa d e d su r fa c es . T h e s e p a r t i c l e s c a n b e p a r -t i a l l y rem oved b y c l e a n in g t h e j o in e d p a r t s i m m e d ia t el y a f t e r p r e s s i n gthem toge the r, and th i s s tep shou ld be ca l l ed f o r on the subassembly d raw-i ng . D i r e c t i o n s h ou ld be g i v en i n the assemb ly p rocedure document th a tt h e i n s t a l l a t i o n o f p re ss f i t push f i t a n d t h r e a d e d v a l v e p a r t s i n t ohous ing bo res shou ld be pe r fo rmed w i t h the hous ing i nv e r te d bo re op ningpo in t i ng down) so t h a t assemb ly -genera ted con taminan ts f a l l away f rom th ecomponent r a t h e r t h a n i n t o c r i t i c a l f l o w p at hs .

Welded, S oldered, and Brazed J o in ts

Welded, soldered, and brazed jo in ts , i f l e f t i n t h e a s-fo rm ed c o n d i-t i o n , may l eave s l ag , roughness , po ros i ty , o r c racks wh ich can generate o r

t r a p c on tam i na n ts . The us e o f s uch j o i n t s s h ou ld be m i n im i z e d i n h i g hpre ssu re oxygen components. When th e use o f welds cannot be avoided, th eys ho ul d a t l e a s t be s p e c i f i e d as f u l l p e n e t r a t i o n so t h a t a l l c o n t a c t in gs ur fa ce a re a i s j o i n e d t o p r e v e n t e nt ra pm e nt o f p a r t i c u l a t e s and e l i m i n a t eunc leanab le b l i n d sur faces. Exposed weld sur f aces should then be groundt o a smooth f n i s h t o e nh an ce c l e a n i n g .



hreading generatescontaminants

Flow stream

Smooth shaft sealsbefore threads engage

Separate locking nut Barrler seal ringprotects flow streamfrom thread-generatedcontaminant

F ig u re 32. Threaded ssembly generates contaml nant

6 -4



Bur r s

emoval of bu r r s and sharp edges i s c r i t i c a l i n h i g h p r essu re oxygensys tems. Accompl ish ing t h i s i n smal l - d iameter i n te rn a l passageways a t t hei n t e r s e c t i o n o f c ro s s d r i l l s i s a comnon p ro ble m. The b e s t r e s u l t s ha v6been o b t a in e d w i t h s ma ll m o t o ri z e d g r i n d i n g t o o l s and w i t h e l e c t r i c a l d i s -ch ar ge machi nS ng EDM)

L u b r i c a n t s

Lu br ic an ts should be used wherever necessary t o reduce ab rasio n anddamage t o sea l s du r ing assembly and t o enhance the se a l i ng o r s l i d i n g o fpa r t s op era t i on a l l y . Care shou ld be taken however t o app ly l ub r i c an tsl i g h t l y and t o r emove excess t o p r even t f u t u r e m i g r a t i on . On ly approvedba t ch / l o t t es t ed l ub r i c an t s shou ld be used such as ba t ch - ce r t i f i e d K r y t ox240 C o r B r ayco t e 3L-38RP. t should be noted th a t a l tho ugh such ap-p r oved l ub r i ca n t s a r e i de n t i f i e d as oxygen com pa ti b le t hey can r eac t w i t hoxygen when system design 1 m i s on temperature p ressure o r p ressure

r i se ra tes a re exceeded.



INSPECT ION R QUIR M NTS

Th is design guide po in ts out design, assembly, and cont am inatio n prob-lems that should be avoided i n hi gh pressure oxygen systems. The problems,t h e i r causes, and the means of avo idin g them are tr ea te d i n cons iderd bled e t a i l i n the sectio ns on design requirements. The design guide1 nes re -comnended i n t h i s document should be reviewed and app lic ab le fe at ur esin co rpo ra te d whenever po ssi ble . However, even in co rp or at io n o f as many asposs ib le i s no guarantee against er ro rs . Therefore, spec ia l inspe ct ionprocedures should be used to i d en t i f y ce r ta in prob lems tha t a re po te n t i a l l ydangerous t o oxygen systems.

The problems t ha t tend t o increase the i g n i t i o n hazard i n h igh pres-sure oxygen systems and, a t the same time, le nd themselves t o i ns pe ct io nare 1 s t e d below, along w it h t he recomnended in sp ec tio n methods. These add i t i on a l i nspec ti on r equi remen ts w i 11 inc rease the ove ra l l re1 a b i 1 t y o fth e system and should be imposed whenever fe as ib le . These a dd it io n al i n -spec t ion procedures should be used i n conju nct io n wi th , not i n p lace of ,inspect on procedures norma l ly used t o v e r i f y component in te g r i ty , c lean1

ness, and conformance t o s p e c if ic a t ons.

Thin Walls

Radiography X-ray) i s a most ef fe ct iv e ins pec tion method f o r imagtngand measu ring t h in wa ll s . P r epa r a ti on o f a c lea r p la s t i c b lock f i gu r econ ta in ing a the passageways i s a use fu l inspec t ion a id f o r v is ua l z in gdistances and to1erances be tween passageways. An example o f a machinedp l a s t i c b l o c k i s shown i n f i g u r e 33. Such a b lock would a lso a i d i n v isuai z in g the X-ray v iew required.

Blind Passages or Dead End CavitiesOf ten a dead end ca v i ty i s the unintended res u l t o f an ove rd r i l l .

X-ray i s an e xc e ll e nt ins pe ct ion method f o r imaging and measuring dead endc a v i t i e s . There i s a lso some po t en t ia l f o r imaging m eta l l i c debr is i n theca v i ty us ing the X- ray method. Visual examination i s another exc el le ntmethod fo r f i nd in g dead end c a v it ie s where holes are la rge enough f o r aborescope to be in serted .

Feathered Edges and Machine Burrs

Visual inspe c t ion i s the most e f fe c t iv e means o f de tec t ing fea therededges and machine b u r r s when a borescope can be in se rt ed . X-ray has some

po t en t i a l f o r de tec t i ng these condi t ions , bu t t i s 1 m f te d by o r i e n t a t i o ncons iderat ions and the genera l ly large overa l l th ickness of the par t com-pared to tha t o f fea thered edges o r bur rs .



ORIQtN L P GZ SOF POOR QU LITY

Figure 33. Machined plastic block



Seal and F i l t e r P lacement

Improper p lacement o f sea l s such as reve r s ing the po s i t i on o f sea l sand backup r in g s can r e s u l t i n e x t r u s i o n o f t h e s e a l o r p a r t i c u l a t e m at-t e r i n t o t h e o xygen f lo w . X-ray i s q u i t e e f f e c t i v e i n im aging m e t a l l i cs e al s b ac ku p r i n g s and f i l t e r s w h i l e n e u t ro n r a d i o gra p h y i s e x c e l l e n t

f o r imaging hydro gen-beari ng nonmetal 1 c sea ls and backup r gs.

Debr i s

D e b r i s i s p a r t i c u l a t e ma t te r t h a t c an ca us e i mpa ct h e a t i n g whenc a r r i e d b y a h i g h v e l o c i t y gas s tr ea m o r f r i c t i o n h e a t i n g when e nt ra p pe db e tw e e n s l i d i n g s u r f aces. Where a borescope can be inse rted vi su a l in -s p e ct io n i s t h e ost e f f e c t i v e means o f d e te c t i n g d e b r i s . X-ray has somep o t e n t i a l f o r d e t e c t i n g l a r g e r m e t a l 1 c p a r t i c l e s a lt ho u gh o v e r a l l p a r tt h i ck n e s s i s a l i m i t i n g f a c t o r . N e ut ro n r a d io g r ap h y c an be used t o d e t e c thyd rogen-beari ng nonmeta l 1 c debri s bu t aga fn ov e r a l l p a r t th i ckness i sa l i m i t i n g f a c to r a l th o u gh n o t as p ro no un ce d as f o r X- ra y d e te c t i o n o f

m et a l l i c debr i s . Neu t ron rays a re no t absorbed by the meta l hous ing asr e a d i l y as X - rays . A t h i r d means o f d e t e c t i n g de b r is o r l oo s e p a r t i c l e si s t o v i b r a t e the p a r t w i t h a c o u s t i c s en so rs a t t a c h e d t o t h e h o u s in g . I n -spec t i ons fo r deb r i s shou ld be pe rfo rmed a f t e r c l ea n ing and cou ld even bec o n si de re d a f t e r assembly as a f i n a l v e r i f i c a t i o n o f s y ste m c l e a n 1 n e ss .



RE INSPECTION RECOMMEND T ONS

Oxygen components and systems should be pe r i o d ic a l l y re ins pec ted t oensure t h a t sa f e t y and com ponent i n t e g r i t y a r e m a in t a ined du r ing t he l i f eo f the system. Determina t ion o f system and component re ins pe ct on t e r i

va ls has proved t o be a complex task . De ta i le d knowledge of c on st r uc t io nma ter ia ls , pressure lev els , the use environment, and the se rv ic e the sys-tem i s per formin g must be app l ied. For example, a system th at sup pl ieshigh pressure oxygen t o f l i g h t h ard wa re i s r e in s p e c te d w i t h g r e a t e r f r e -quency and i n g r ea t e r d e t a i l t han i s a low p ressu re oxygen system i n af a c i l i t y w e ld in g shop.

I n e s t a b l i s h i n g th e re i n s p e c t i o n i n t e r v a l s , t h e f o l l o w i n g i te m sshould be considered.

a) Rout i ne d isassembly and reassembly o f p ip lng sys tems in va r ia b l y i n -c reases the l eve l o f sys tem contaminat i on because par t i cu la tes a regenerated.

b Sam pling o f an assembled system o r component f o r gasborne contami-n an ts y i e l d s o n l y l i m i t e d d at a on th e i n t e r n a l c l e a n li n e s s o f t h e o v e r a l ls ys te m because t h e a b i l i t y o f f lo w i ng gases t o e n t r a i n p a r t i c u l a t e s i s af un c t i o n o f pa r t i c u l a t e mass and i den t i t y , gas fl ow ve l oc i t y , gas v iscos -i t y , sys tem con f i gura t i o n , and o the r f ac to rs . We must emphasize th a t t h i sm ethod of sys tem sam pl ing cannot be d i r e c t l y co r r e l a t e d w i t h t he c l e a n l i -ness o r con taminat i on o f i n te rn a l component o r system s ur f aces.

C The re in spe c t i o n p lan ,must address the des ign se rv i ce l i f e o f com-ponents. t must id e n t i f y problems a sso ciate d w i t h anomalous component be-hav i o r such as cha t t e r i n check o r r e l i e f val ves , va l ve i n t e r n a l leakage,and r e g u l a t o r p re s su r e c o n t r o l i n s t a b i 1 t i e s ) and a dd re ss t h e d i s p o s i t i o nof these problems.

d Add i t i ona l i n s i gh t r ega r d i ng syst em con tam ina t on l ev e l s can begained through sy stemat ic Insp ect o n o f components e g., t ransducers,f l e x hoses, r e l i e f v al ve s, f i l t e r s ) removed f o r c a l i b r a t i o n , p ro o f-t es t i ng , o r pe r i o d i c m a in tenance.

R e v e r i f c a t i o n o f c le a n 1 n e ss l e v e l s I n c om ponents and systems thathave been i n s er vic e i s the subject o f S e c ti on 8, Cleaning Requirements.



7 COMPONENT AND SYSTEM-LEVEL TEST REQUIREMENTS

OBJECTIVES

The main ob jec t i ve s o f i n d i v i du a l component and sys tem- leve l t e s t i n ga re t o i n v e s t i g a t e t h e p e rfo rm an ce and o p e r a ti n g c h a r a c t e r i s t i c s o f t h ei n d i v i d u a l com ponents and t o th e n in v e s t i g a t e t h e e f f e c t s o f t h e i rin te r a c t o n when assembled and ope rated as a system. Component t e s t i n ge v a lu a t es and v e r i f i e s t h a t t h e s p e c i f i e d f u n c t i o n a l p e rf orm a nc e 1 f er e l i a b i l i t y and s a f e t y a re s a t i s f i e d ; w h i l e s ys te m -l ev el t e s t i n g s a t i s f i e sth e same purpose a t th e h ighe r assembly le ve l . Some system componentssuch as l i nes connec to r s f langes and senso rs a r e t es t ed f o r t he f i r s tt i m e a t t he sys t em l eve l . A f u r t h e r o b j e c t i v e o f s y ste m- le ve l t e s t i n g i st o d ef i ne the range o f co nd i t ion s encountered by each component as th esystem i s o pe ra te d o ve r i t s f u l l sp ec i f i ed ope r a t i ng range and t o ve r -i f y t ha t t he i n d i v i d ua l com ponent sp ec i f i c a t i on s m eet t hese cond i t i on ss a t i s f a c t o r i l y .

TYPES OF TESTING

Three t ypes of component and sys tem- leve l t e s t i n g are o f i n te re s teng i nee r i ng developm en t t es t s qu a l i f i c a t i o n t es t s and acceptance tests.

Engineer ing Development Tests

The comple te range o f f u nc t i o na l requ irements the en t i r e spect rum o fimposed e n v ir o nm e n ta l c o n d i t io n s and t h e f u l l l i f e c a p a b i l i t y of t h e com-ponents and system should be demonst rated i n engin eer in g developmentt e s t s . H ardw are o f t h e h i g h e s t f i d e l i t y p o s s i b l e sh o u ld be us ed and t h e

te s ts shou ld be done w i t h oxygen. The purpose o f t hese te s t s i s t o comet o a f u l l un ders tand ing o f t h e perfo rmance o f t h e component and systemo ve r t h e f u l l s p e c i f i c a t i o n ran ge w h i l e i t i s s t i l l p o ss ib le t o change t h ehardware . Eng ineer ing development tes ts a re no t burdened w i t h the r i g o r -ous d i s c i p l i n e o f f u l l q u a l i t y c o n t r o l coverage. S a t i s f a c t o r y e n g i n e e r i n gdeve lopment te s t s o f adequate scope can he lp t o guarantee a success fu lformal qua1i c a t o n program.

C o n s id e r a ti o n s h o ul d be gi v e n t o r u n ni n g s e l e c t e d o f f - l i m i t s t e s t s t odetermine t he re a l 1 m i t s o f the components and system. Such test ing maybe pa r t i c u la r l y va lu ab le where hardware per fo rmance marg ins a re no t knownwhere s i n g l e p o i n t f a i l u r e s may e x i s t o r where u n c e r t a i n t y e x i s t s i n t h espec i c a t o n s.

Q u a l i f i c a t i o n T es ts

These components and systems must demonstrate under f u l l q u a l i t y con-t r o l d i s c i p l i n e t h e i r f u n c t i o n a l p erfo rm an ce e n a b l in g them t o w i th s t an dt he p os s i b l e s t r esses and t o m eet t he env i ronm en t a l cond i t i ons o f t h e i r ap-p l i c a t i o n t h e i r l i f e expectancy and t h e i r s a f e t y and r e l i a b i l i t y . Q u a l i -f i c a t i o n t e s t s a re p e rfo rm ed on ha rd wa re of t h e h i g h e s t p o s s i b l e f i d e l i t y



wi th the t e s t system arranged as c lose to the actua l con f ig ur at io n as pos-si b le . These te s ts must be run w it h oxygen. The component or system i sa lw ays sub jected t o a f o rm a l accep tance te s t as t he i n i t i a l po r t i o n o f t hequa1 f i c a t i o n t e s t . e

H ig he r l e v e l q u a l i f i c a t i o n t e s t in g o f t e n c a l l e d v e r i f i c a t i o n t e s t -ing i s f requ en t ly done on an oxygen system to v e r i f y th a t t i n t eg ra tessa t i s fac to r i l y w i t h o the r veh i c l e sys tem s . An example i s an inte gr at edveh i c l e t e s t i n wh ich t he sys tem so f tw are i s ve r i f i e d t o ope ra te t he sys -tem sa t i s f a c to r i ly . Other examples are large-sca le v ibro -aco ust ic andthermal tests.

Acceptance Tests

I n acceptance te st in g th e component or th e as -b u il t system must dem-o n s t r a t e t h a t i t meets func t iona l requi rements i s safe and i s compat ib lew i th oxygen as i t s work ing f lu id .

GENER L SYST M T ST REQUIREMENTS

Several con side rat io ns are common to a l l th ree types o f component andsys tem- leve l tes t ing .

The f i d e l i t y of both th e hardware and the t e s t system geometry shouldb e a t t h e h i g h e s t l e v e l p o s s i b l e f o r l l t es t s .

Clean1 ess i s c r uc ia l i n oxygen components and systems. Extremecare must be tak en t o ensure t h a t a71 corn onents have been cleaned byapproved procedures t h a t th e system has L Zen assembled f o l 1owing approvedprocedures and th a t i t s c le an l ine ss has subsequent ly been ve r i f f ed as

meeting the standards f o r gaseous and 1 q u i d oxygen usage. See se cti on s6 and 8 o f t h i s handbook fo r recomnended in spe ct ion and c leanin g standardsand procedures.

A l l f l u id s t o be pu t in to th e te s t sys tem must f i r s t be sampled f romthe ground serv ic e equipment and analyzed t o v e r i f y acceptable qua l i t y .A l l f l u id s in t roduced in to the te s t sys tem fo r sys tem- leve l te s ts must bef ered to an approp r la te lev e l a t the sys tem-load ing in ter fa ce. Theground system f i l t e r s must be as f ine as or f in e r than the f i ne s t onboardf i l t e r t o keep fr om l oad ing i n to t he system pa r t i c u l a te s t ha t would reducet h e c a p a c it y and l i f e o f t h e f l i g h t system f i l t e r s . A f t e r t h e t e s t sam-ple s of f l u i d s should be removed f rom th e te s t system f o r a naly s is and f i l

t ra t io n . These tes t s should detec t any change i n f l u i d prop er t ie s or deg-r a d a t i o n i n f l u i d q u a l i t y . They s ho uld al s o d e te c t any p a r t i c l e s p ic k edup by t he f l u i d w hich may i nd i c a te f a i l u re i nc j p i e n t f a i l u re o r designproblems within the system.

As a c ry og en ic l i q u i d i s lo ad ed i n t o a t e s t system care must betaken t o avoid excessive thermal shock and t o prevent pressure vessel i m

p lo s io n due t o pressure co llapse.



Care must a l s o be ta ke n t o v e r i f y t h a t i n s u l a t i o n i s p r o p e rl y i n -s t a l l e d on cr yogen i c a reas t o p reven t excessi ve i c e bu i l dup on t he t e s tsystem.

l l ground serv ic e equipment shou ld be ca re fu l l y assessed to v e r i f yi t s adequacy t o suppor t th e t e s t requ irements under both normal and con t in -

gency ope rat ions .

Tes t des igne rs m ust v e r i f y t h a t any n on f l i gh t hardw are o r i nst rum en-t a t i o n used i n component or systems te s t i n g does no t compromise the t e s to b j e c t i v e s o r syste m s a f e ty . I n p a r t i c u l a r , i f any inst rumentat ion suchas a pressure t ransducer i s connected i n t o the system by a tube stub, th et e s t d i r e c t o r s h o ul d e ns ure t h a t t h e o r i e n t a t i o n o f t h e t u be does n o tcause i t t o ac t as a con tam inant co l l e c t i o n po in t , t h a t t he t ube s tub doesnot become an acoust i c hea t ing ca v i ty source, th a t the po te nt ia l fo r cav-t y compression hea t ing i s minimized, and th a t th e inst rume nt i s supported

t o a vo id v i b r a t i o n f a i l u r e .

TEST PROGRAM CONTENT

Much o f th e recommended t e s t program con tent f o r enginee r ing de velop-ment t es t s , q ua l i f i ca t i o n t es t s , and acceptance tes t s i s t he same f o r bo thin d i v i du a l components and f o r sys tem- leve l tes ts .

Enq ineer inq deve lopment tes ts shou ld inc lu de the f o l lo w i ng as aminimum.

1 P r e t e s t f lo w and f u n c t i o n a l v a l i d a t i o n t e s t s , i n c l u d i n g t e s t s ofi n s t ru m e n t a t i o n o p e r at io n . These t e s t s t o v e r i f y t h a t t h e t e s t s ys te m andcomponents are opera t ing cor rec t l y shou ld be per formed w i th a c lean iner tf l u i d .

2. S t ress t es t i n g . These tes t s exe rc i se t he sys tem ove r t he e n t i r ecombined range o f t e s t parameters (pressure , temperature, f lo w), concen-t rat ing on those combinat ions of parameters which produce the worst systemst res s . S t res s tes t in g can be accomplished by ope ra t ing the component a ttes t p ressures tha t exceed the h ighes t p ressure and temperature expectedi n o p e r a t io n b y a t l e a s t 10 pe r ce n t. F a c i l i t y and g round suppor t equ ip -ment should be chosen so t h a t i t s maximum al lo wa ble working p ressureMAWP) i s s u f f i c i e n t l y above p la nn ed use l e v e l s t o a l l o w a 25 -p er ce nt t e s t

p ressu re m arg in and s t i l l be be low the MAWP I n a d di ti on , f l i g h t e qu ip -ment sho uld be exposed t o a pneumatic surge (gaseous impact) a t le a stt w i c e t h e r a t e t i s expected t o expe ri ence i n use. P ressu re r i s r a te sfrom 20,000 t o 100,000 l b pe r in 2 pe r second (140 t o 690 MH per pe r

second) are commonly used. ra p id pres sure surge can, by th e process o fad iab at i c compression o f th e oxygen, heat in te rn a l s o f t goods o r assembly -genera ted contam inan ts t o t h e i r i g n i t i o n tem pera tu res. I f a componentpasses t h i s t e s t phase, user conf idence shou ld be s ig n i f i c a n t l y enhanced.

r s t s t s m ust be ~ e r f o r f w d s i n g oxyqen. These tests demonstrate thea b i l i t y of th e component o r system t o opera te over the requ i red range ofparameters s a t i s fa c t o r i l y , and w i th some safe t y margin.



3. Environmental te st in g. These tes ts expose th e component o r sys-tem, bo th op era tin g and nonoperating, t o the ap pl ica tio n s ex ected rangeo f environmental con dit ion s ( temperature, pressure (o r vacuum , humidi ty ,sand and dust, ra in , acoustics, v ib ra ti o n) . Env ironmenta l tes ts must be

per fo rme d wi th oxyqen i n the system. These tes ts demons t ra te the ab i l i t yof the component or system t o operate sa t is f a c t o r i ly i n the expected env i-ronment.

4. L i f e cyc le tes ts . These te s ts t o assure tha t the sys tem w i l ll a s t the p lanned l i fe t im e may inc lu de mechanical cyc les, thermal cyc les,pres sure cycles, and load cycle s. hpcp t qts rwd. be mr fo rugd w i th oxv -qen. The number o f cyc les t o be performed i s determined from theant ic ip a te d use. For f l i g h t equipment , the number o f te s t cyc les i s t y p i -c a l l y s p e c i fi e d t o b e 4 t imes th e expected l i f e cyc les fo r each opera-tional mode. For f a c i l i t y and ground support equipment, which i s us ua l lydesigned and cons t ruc ted f o r longer l i f e and a g rea te r fa c to r o f sa fe tythan f l i g h t equipment, t he number o f c ycles i s t yp i c a l l y l im i te d t o tha trequ i red to demons t ra te func t iona l i t y and oxygen compatibil i ty; however,a s t a t i s t i c a l l y s i gn i f i c an t number o f cyc les shou ld be performed i n each

op era t io na l mode. Exper ience ind ica tes th at 50 cyc les i n each mode shou ldiden t i fy inheren t opera t iona l p rob lems.

5. Pos t tes t f l ow and fun c t i o na l va l i da t i on tes ts . These tes ts t oi d e n t i f y any changes i n component or system per formance re su l t in g f rom th et e s t program o r from exposure t o oxygen should fo l l ow the same proceduresused f o r t h e p r e t e s t f l o w and func t iona l va l ida t ion .

6. Disassembly and in sp ec tio n. Af te r th e eng inee ring developmentte s ts have been completed, system components should be examined i n d e t a i lt o ide n t i f y ev idence o f damage, wear, fa i l u r e , o r in c i p i en t fa i l u r e . Spe-c i a l a t te n t i o n shou ld be d i r ec t ed t o the cond i t i on o f so f t goods and thepresence of con tam inati on. Sources o f any observed contaminat io n should

be thorough ly inve st iga ted. I n t h i s manner, anomalies such as f r e t t in g ,ove rs t ress ing , and o the r func t i o na l l y i nt roduced fa i l u r e s can be i d en t i -f i e d and cor rec ted before th e component i s put i n t o use.

Qua1i c a t io n te st s should a lways begin wi t h the approved acceptancetes t . Therea f ter , the au a l i f i c a t io n te s t p rogram shou ld be as describedfo r the eng ineer ing development tes ts . Q u a l i f i c a t io n tes ts , o f course,are co nd ucte d un de r th e d i s c i p l i n e o f f u l l c o n f f g u r a t io n co n t ro l , d e t a i l e dte s t p rocedu res, and spec i f i ed pa ss / fa i l c r i t e r i a . l l a u a l i f i c a t i o n

es ts (eXCPDt t h e Dre tes t f low and func t i ona l v a l i da t i on ) nntst be ~ e r -formed usina oxvQen,

Acceptance t es ts should inc lud e the fo l l ow in g as a minimum.

1 Pr e tes t f low and func t iona l eva lua t ion t o ver i fy tha t the compo-nent or sys tem i s opera t ing co r rec t ly , meets spec i f i ca t ions , and h s t hesame performance c h a ra c t e ri s ti c s as th e qua1i f cat ion can onent or system.

ness standards.h is eva lua t lon shou ld be conducted wi th an i n e r t f l u i t a t meets c1ea n l iL



2. F lo w and f u n c t i o n a l t e s t s i n c l u d i n g l i m i t e d c y c l e t e s t i n g u s i n goxygen t o v e r i f y system c o m p a t i b i l i t y . Cyc le t e s t i n g shou ld be an abbre-v i a t e d v e r s i o n o f t h e q u a l i f i c a t i o n t e s t p r oc ed ur e. To e ns ur e s a f e t y andfu nc t i on a l i t y pres sure and temperature lev e l s shou ld exceed th e maximuma n t i c i p a t e d u s e l e v e l s . The number o f cyc les shou ld be on ly that needed

t o demonstra te oxygen compat i b i ty Du r i ng cyc le te s t i ng each components h o u ld b e e v a lu a te d f o r f u n c t i o n a l a n oma li es .

3. P o s t t e s t f l o w and f u n c t i o n a l e v a lu a t i o n u s in g o xyge n.

TEST PROGRAM EVALUATION

I n a l l t e s t s s p e c i a l a t t e n t i o n sh ou ld be p a i d t o t h e d e t e c t i o n o f po -t e n t i a l l y d an ge ro us c h a ra c te r i s t i c s - - p re s s u re s u rg es s u s ta i n e d p re s s u reo s c i l l a t i o n s s ta n d in g a c o u s t i c waves i n c a v i t i e s o r b l i n d pa ssages v a l v eo r r e g u l a t o r c h a t t e r f r i c t i o n a l c o n t a c t of component p a r t s e t c .

Any t ime an anomaly i s detected th e system o r component should be

d is as se mbled and i n s p e c te d t o d e te rm in e t h e c o r re c t i v e a c t i o n t h a t must b etaken.

Any di sc re pa nt o r anomalous hardware must be sub jec ted t o an estab-l i s h e d s ys te m o f c o n t ro l l e d re view rew ork and re i n s p e c t i o n be fore t i sc o n s id e re d f o r r e u s e .



8 CLE N ING REQUIREMENTS

Clean1i ess c o nt am i n a t i o n c o n t r o l ) i s c r i t i c a l i n oxyg en componentsand systems. There are two obvious reasons. F i r s t , contam inat ion le ve lsmay be su f f i c i e n t t o cause fu nc t i on al anomal ies such as lea k in g va lves or

regu la to r s . Second, the p resence o f con tamina t i o n can cause ig n i t i o n o fcomponents o r systems by a v a r ie t y o f mechanisms such as p a r t i c l e impact,mechanical o r pneumatic impact, o r spontaneous i g n i t i o n . These mechanismsare d iscussed more tho rough ly i n o ther pa r ts o f t h i s handbook.

The c lean ing o f an oxygen system should begin w i t h d isassembly t o thee l e m e n t a l o r p i e c e p a r t l e v e l . f c lean ing i s a ttempted by f l ow ing so lu -t i o n s th roug h a component, vul ne rab le in te rn a l elements may be damaged bythe so lu t i ons requ i red t o c lean the ma jo r elements o f the component. A lsocontam inants and cle an in g s o lu ti on s may become entrapp ed i n componentrecesses and may u l t i m a t e l y re ac t wi th oxygen. When th e component hasbeen disassembled, th e p a rt s should be grouped accor ding t o the method o fc lea ning . Spe cial c le an in g procedures must be developed t o remove en-

t rapped contaminants . D isassembly a lso a l lo ws assessment o f the ser v ice -a b i l t y of the component elements. f eal ing surfaces are damaged orc racks a re observed i n the m et a l l i c pa r ts , the component mus t be repa i re dor rep laced. Spec ia l a t te n t io n shou ld be d i r ec t ed t o the component so f tgoods. Damaged o r worn s o f t goods sh ou ld e rep laced w i th so f t goods f romthe same batch if oss ib le . f s o f t goods of the same batch are not a va i l -ab le , re qu a l i f i c a t io n o f each component w i t h th e new ba tch o f so f t goodsi s recommended un less oxygen compat ib i 1 t y can be e sta b l is he d by oth ermeans.

Each system and component element must be subj ec ted t o cl ea ni ngprocesses which employ the fo l lowing genera l techniques.

P r e c l e a n i ng of in di v i d u a l p ar ts must be performed t o remove contami-n a n ts fro m r e a d i l y a c c e s s ib l e su r fa c es . The f i r s t s t e p sh o u ld be adegreas ing o f the surfaces. Nonm eta l l ics and used m e ta l l ic pa r ts can beadequa te ly degreased b y r i ns in g w i t h t r i c h l o r o t r i f uoroethane Freon PCA,MIL-C-813026, amendment 1 t y p e 11) newly machined p a rt s and un us ua l lyd i r t y p a r t s s ho ul d be va po r-d eg re as ed u s i n g t r i c h l o r o e t h y l e n e o r 1 1 1-t r i ch lo roe t han e . Cau t ion must be exerc i sed i n the use o f vapor degreas ingsin ce some metals, such as magnesium, co uld r ea ct w i th t h e degreasing so l-ven t. Var ious c lean in g so lu t i ons can then be emp loyed i n con junc t ion w i thu l t ras on i cs . Comnonly used c lean ing so lu t ion s inc lude the fo l l ow ing .

A l k a l i n e c l e a n i n g s o l u t i o n , t y p i c a l l y co n t a in s s odiu m h yd ro xi de , so-dium carbonate, sodium metasi ca te, sodium phosphates, and su rf ace -act ive

we tt in g) agents. Such so lu t i on s may be used a t temperatures up t o 1800 F

355 K . An example i s O ak it e HD126.

A c i d c l e a n i n g s o l u t i o n , w hic h t y p i c a l l y c o n t a i n s ph os p ho ri c a c id ,e thy lene g ly co l monobu ty l e ther , and we t t i n g agen ts . These solutions maybe used a t tem peratures up t o 1500 F 338 K . Oak i te 33 i s an example.

M i l d a l k a l i n e l i q u i d d e te rg en t, w hic h t y p i c a l l y c o n t ai n s a ni o n ic andnon ion ic sur fa ce-a ct ive agents , ch e l a t in g agents , and sodium me tas i l ic a te .



Such a det er ge nt may be used a t temp eratures up t o 1800 F (355 K . Exam-p le : O a k i t e L i q u i - D e t 2.

R u st a nd s c a le r emov er, w h ic h t y p i c a l l y c o n ta in s s od iu m h y d ro x id e ( a tmuch h ig h e r l e v e l s t h a n i n an a l k a l i n e c l e a n in g s o lu t i o n ) , s od iu m carbon:

a te , su r fac e -a c t i v e agen ts , and ch e la t in g agen ts. Such so lu t ions are usedfrom 1600 F (344 K t o b o i l in g . Oak i te Rus t r ippe r i s an examp le .

The sequence o f c le an ing s o lu t io ns t o be used depends on the m at e r ia lt o be c leaned. S t a i n l es s s t ee ls (300 ser ies ) , Monel, and In c o n e l n o rma l l yare c leaned i n a l k a l i n e s o l u t i o n and t h en i n a c i d s o l u t i o n . Carbon s t e e li s c leaned by r u s t and sc a le remover, i r e q u ir e d , f o l l o w e d b y a l k a l i n e s o-l u t i o n . Copper and b ra s s a re cl ea ne d i n a l k a l i n e s o l u t i o n and b r i e f l y i nac id . A lu minu m i s c le a ne d i n l i q u i d d e te rg e n t . S o f t goods a re c l ea n ed i nl i q u i d d e te rg e n t e x c e p t f o r T e f lo n , w hic h may be c le an ed i n a l k a l i n e s o l u-t i o n f o l l o w e d by a ci d. O th er s p e c i a l i z e d m a t e r i a l s may r e q u i r e d i f f e r e n tsequences, and con s id e ra t ion must be g iven t o me t a ls re a c t i v i t y . O the rs p e c i a l i z e d s o l u t i o n s s uch as p i c k l i n g o r m e t a l - br i g h t e n in g ( ch ro m ic a c i d )solut ions may also be employed. A tho rough wa te r r inse be tween c lean ings o l u t i o n s i s man da to ry . F o l l o w in g t h e l a s t w a te r r i n s e , t h e p a r t s s h o u ldbe f l u s h e d w i t h i s o p ro p y l a l c o h o l , t h e n F reo n PCA. D u r i n g t h e e n t i r ec l e a n in g p ro ce ss , t h e p a r t s s h o u ld be v i s u a l l y i n s p e c te d and me c h a n i c a l l yc l e an e d when ne ce ss ary. V i s u a l i n s p e c t i o n sh o u ld b e r e q u i r e d b e fo r e f i n a lc l ean i ng s in ce g ross chemica l contami na t ion canno t be removed i n f i n a lc lean ing .

The prec leaned pa r t s shou ld then be moved t o a c le an room. We havefound t h a t a C lass 100 lam inar f low envi ronment , as d e f i n e d i n Fe d e ra lStandard 209B, i s adequate . F in a l c lean ing, sampl ing, and an a l ys is i sp er fo rmed b y r i n s i n g ea ch p a r t w i t h F reo n PCA, then samp l ing t h e r i n s ef l u i d . S oa kin g i n an u l t r a s o n i c F re on PCA ba th may be nec essary t o removep a r t i c u l a t e s . The volum e o f r i n s e f l u i d r e t a i n e d f o r s a mp li ng and a n a l-

y s i s i s d i r e c t l y r e l a t e d t o t h e r i n s e d p a r t s u r fa c e area; e.g., 100 m l / f t 2(1080 m llm 2). The r i n s e f l u i d i s f i l t e r e d t o a s ce r t a in t h e p a r t i c u l a t ec on ta rn in an t l ev e7 s; t h e n t h e f l u i d i s s u b je c te d t o c h em ica l a n a l y s i s f o rd e te rm in a t i o n o f t o ta l h y d ro c a rb o n c o n te n t .

A d d i t i o n a l i n f o r m a t i o n may be o b ta i n ed f r om a p p l i c a b l e s e c t i o n s o fJSCM-5322B 1982, JSC Contamination Control Requirements Manual .

A t y p i c a l p a r t i c u l a t e s p e c i f i c a t i o n t h a t has been f ou nd t o be adequatef o r o xy ge n syste ms i s shown i n t h e f o l l o w i n g t a b l e .



MAXIMUM LLOW BLE PARTICULATES PER SQUARE FOOTPER SQUARE METER OF CRITICAL SURFACE

P a r t i c l e s iz e range Max imum Per Sq.

P ~ P guant ~ meter

No s i l t i n g Noneperm i t t ed

F ibe r l eng th um l

I n a d d i t i o n , a t o t a l hydrocarbon con ten t THC) assessment should beperform ed i n 1 eu o f t he no rm a l l y spe c i f i e d n on vo la t i l e r es i due NVR) as -sessment. Determ inat ion o f THC perm i ts a q u a l i ta t i v e as we l l as a quan t i -t a t i v e measure o f t he e f f e c t i v ness o f t he c l ean ing p rocess . S ince t heHC 1 m i t of 3 p g / f t 2 32 ug/m ) o f c leaned sur face area based on a 100-

m l sample o f f lush ing f l i d ) i s f a r more s t r i n g e n t t h a n t h e n o rm al NVRp e c i f i c a t i o n o f m g /f t 11mg/m2), use rs o f t h i s THC proce ss can be

b e t t e r a ssu re d t h a t t h e i r hardware i s e s s e n t i a l l y f r e e o f n on pa rt c u l a t econtaminants

Exper ience has shown th a t approx imate ly one-ha l f o f a l l p ar ts c leanedw i l l f a i l t o m eet e i t h e r t h e p a r t i c u l a t e o r t h e THC s p e c i f i c a t i o n on th ei n i t i a l sa mp lin g; c on se qu en tl y, r e c le a n i n g i s r e q u i r e d u n t i 1 a1 p a r t spass both spec i f c a t o n s.

A f te r a p a r t has been c leaned to t hese spec i f i ca t i on s , t should bebagged b y i t s e l f i n FEP Te f lo n f i lm . The Tef lon used f o r bagg ing oxygensystem p a r t s should be as c le an as the i te m being packaged. Te f lo n hasbeen chosen f o r t he i n i t i a l packag ing o f oxygen sys tem pa r t s ove r such a l -t e r n a t i v e m a t e r i a l s a s p o ly e t h y le n e and n y l o n because i t s s u r f a c e i s r e l a -t i ve ly nonshedd ing, i t i s more e a s i l y c leaned, and i t i s more oxygen com-p a t i b l e . Some drawbacks o f Tef lon are i t s h igh cost , i t s tendency t o de-

v e lo p a n e l e c t r o s t a t i c c ha rg e w hic h a t t r a c t s p a r t i c l e s , and i t s p er me a bi l-i t y t o w a te r. To re du ce p a r t i c u l a t e co nt am in at io n, t h e p a r t i s s e al ed i nt h e T e f l o n bag w h il e i n t h e f i n a l c l e a n i n g a re a l a m i n ar f l o w c l e a n room)us ing a spec ia l hea t sea le r. The Te f l on bag i s t hen cove red w i t h a po l y -e thy lene ou te r bag w hich i s hea t sealed . Th i s ou te r bag p ro tec t s t heT e f l o n and t h e p a r t f r om a br as io n, s t a t i c a l l y a t t r a c t e d p a r t i c l e s , andmois ture . A lab e l shou ld be a f f i x e d to each bagged pa r t t o document thec lean1 ness le ve l achieved.

* pm i s micrometer. pg i s m ic rogram. mg i s m f l l g ram.



Af te r system and component disass em bly and cle an ing , reassembly ofcomponents and sys tems must be s t r i ngent l y con t ro l l ed to assure tha t t heachieved c l ea n l nes s l e v e ls are no t compromised. A1 1 components re q u i r in greassembly (such as valves, re gu la to rs , and f i l t e r s ) should be reassembledi n a f i l t e r e d - a i r e nv ir on m en t s uch as a Class 100 c l ean r oom o r f l owbench. Personnel shou ld be pro pe r l y a t t i r e d i n c lean room garments andg l oves . A l l t o o l s t h a t con t ac t component i n t e r n a l must be c leaned t o t hes p e c i f i e d l e v e l s . On ly approved l ub r i c an ts such as ba tch-c er t i f e d K r y t o x240 C o r Brayc ote 3L-38RP should be used, and then spa r ing ly . Bear i nmind th a t l ub r i ca n ts , a1 hough i d e n t i f i e d as oxygen compat ib le , can rea c tw i th oxygen when system design temperature, pressure, o r pressure r i s er a t e l i m i t s a r e exceeded . A l so , a l ub r i c an t can m i g r a t e i n t o an a rea t ha tshou ld no t be l ub r i ca ted , t hereby caus ing fu nc t i o na l anomalies ( such asr egu l a t o r co n t r o l m echanism s t h a t f a i l t o respond p r o pe r l y because o f con-t am i na t i on by excess l u b r i ca n t ) .

Reassembly o f systems sh ould be accompl ished i n a manner which m in i -mizes co nta mi na tio n o f th e system. Some tech niqu es commonly employed in -c lud e bu i ldu p o f the system as subassemblies us in g the same techniques as

f o r com ponents ( f i t e r e d - a i r envi ronm en t, e t c .) When the s ize or loca-t i o n o f a system p r ec ludes t h i s p r a c t i ce , a low p r essu re purge of t he sys -tem by a c l ean i n e r t gas du r i n g r eassem bl y o r a po r t ab l e c l ean t e n t can beused t o reduce contami nat io n.

A f te r t h e system has been reassembled, a p ressure i n t e g r i t y and l eakt e s t s h ou ld be pe rfo rm ed , u s i n g an a p p r o p r i a t e l y f i l t e r e d i n e r t gas t h a thas been analyzed f o r contaminants. Then the system shou ld be purged w i t ha h i gh p r essu re , h i gh volume c l ean i n e r t gas i n an a t tem p t t o m ob i l i ze andrem ove any p a r t i c l e s gene r at ed du r i n g reassemb ly . A f t e r t h i s pur ge o rHblowdown, th e system may be vented, th en pr es su riz ed w it h oxygen. I t i sa good p r a c t i c e t o p e r fo r m t h e f i r s t ox yg en p r e s s u r i z a t i o n o f a sy ste m b yremote con t ro 1 s ince i g n i t i o n o f assembly -genera ted contaminants can occur .

System c l e a n l ne s s v e r i f i c a t i o n and r e v e r i f c a t i o n pro ce du re s s h o ul dbe performed whenever signi f icant disassembly and reassembly has occurredo r con t am i na t i on i s suspect ed . Also, i f the oxygen system contains com-p on en ts w i t h a h i s t o r y o f i n - s e r v i c e f a i l u r e , a p p r o p ri a te t r a p s ( e g .f t e r s ) o r o t h e r e a s i l y an alyz ed components should be removed, insp ecte d,and rep1a c e d p e r i o d i c a l l y

Oxygen systems can be sampled f o r gasborne p a r t ic u la te s by at ta ch in ga f i l t e r t o each o u t l e t o f t h e t e s t s ys te m and t he n f l o w i n g a c le a n i n e r tgas o r oxy ge n t h ro u g h t h e f i l t e r as f a s t as i s p o s s i b l e w it h o u t e xc ee din gt h e maximum a l l o w a b l e w o rk in g p r e s s u re f o r e i t h e r t h e f i l t e r o r t h e s y s-.tem. b e t t e r measure o f t h e s y ste mis a b i l i t y t o d e l i v e r o xyg en o f a de -s i r ed c l ean l i ness can be t aken i f the sample f low rate exceeds the sys-tem end-use f l o w ra te . The q u a n t i ty and s i ze as we1 1 as th e type of par -t i c u l a t e can be de te r m ined by pe r f o r m i ng a chem ica l/ m e ta l l u r g i c a l a na l -y s i s o f t h e tr ap p ed p a r t i c l e s .

Gasborne p a r t i c u l a t e a n a l y s i s i s c o m n l y used on a gas s am plin g v o l -ume of 35 s t anda rd cu b i c f e e t 1 cu bic meter ) . Using a standard volume

8 4



perm i t s d i re c t compar ison w i t h o th e r gasborne pa r t i c u l a t e samples; how-e ve r, t h i s method o f s y ste m s am plin g i s n o t d i r e c t l y c o r r e l a t i v e t o t h esampl ing of in te r n a l component o r system surf aces.

Oxygen systems can be sampled f o r sur face-borne p a r t i c u la t e s and

hydrocarbons, halocarbons, and ot he r non vo la t i e res idue by removing sys-tem l i n e s o r components th a t len d themselves t o contamjnant entrapment,e i t h e r b y p o s i t i o n o r d e s ig n e.g., a s ys tem lo w p o i n t o r a f i l t e r i n gdev ice ) and sub jec t in g the l i n e s or components t o sampling and ana ly s is .Sp ec i f ic so lv ents may be used t o separa te se le c te d ma ter ia ls ; e.g., carbont e t r a c h l o r i d e may be used t o d i s s o l v e h al oc a rb on o i l w i t h o u t a l s o m b -i l i z i n g K r y to x o r B r ay c ot e l u b r i c a n t s . A f t e r a l i n e o r component hasb ee n f lu s h ed o r v i s u a l l y i n sp e c te d , t shou ld be rec leaned before t i sr e i n s t a l l e d i n t h e o x yg en s ystem.

I n summary, wh i le c le an l in es s w l l not make a poor ly designed fab-r i c a t e d system safe, con tam inat i on can cause the be st systems and compo-nents t o be hazardous.



9 SUMM RY

Much ana ly t i c a l and exper imenta l work has been done i n recen t years

t broaden the unders tand ing o f t h e i g n i t i on - t r i gg e r in g mechanisms andphy s ic a l combust ion processes o f meta l1 c and nonmetal 1 c ma te r ia l s i n

pure oxygen environments. However, because o f the imnense com plex i ty o ft h i s m any-faceted problem, 1 t t l e headway has been made i n deve lop ingan a l y t ic a l mode ls fo r the des ign o f such sys tems. On the o the r hand, majorp rog ress i n advanc ing the a b i l i t y o f oxygen sys tems t o cope w i th the de-mands f o r hi gh er performance, press ures, temp eratures , etc,, has been madet hr ou gh t h e a p p l i c a t i o n o f e m p i r i c a l t e s t i n g o f m a t e r i a l s i n c o n f i g u r a -t i on s rep resen t ing th e i r i n tended uses and th rough the use o f des ign tech -n i q u e s wh i c h p r o t e c t o r s h i e l d t h e ma r e s u s c e p t i b l e n o n me t a l l i c s f r o m d i -re c t impingement o r i n te r fa ce w i th th e oxygen . Th is handbook, th er e f or ei s an a t temp t t o document the p ra c t i c a l ' s ta te - o f - the -a r t wh ich has beendeveloped by a s ig n i f i c an t e lemen t o f t he Aerospace commun ity i n recen tyea rs fo r t he des ign o f h igh p ressu re oxygen sys tems .

Th is handbook presents a un ique and usefu l synops is o f a g rea t bu lko f d a t a on t h e i g n i t a b i l i t y o f b o t h m e t a l l i c s and n o n m e t al l ic s i n oxygena t v a r i o u s p r e s s u re c o n d i t i o n s . The s y n t h e s i s o f t h i s d at a i s in de ed atremendous t ime saver s ince t a l l ows the des igner t o deduce a t a g lancethe be t t e r pe r fo rming ma te r ia l s f o r oxygen usage. Fu rthe rmore , t hehandbook a1so presen ts many examples o f proven component d esign fe at ur esa l o n g w i t h i l l u s t r a t i o n s o f u n d e s i r a b l e f e a t u r e s wh i c h s h o u l d b e a v o i d e d .A dd i t i on a l ly , the handbook t r e a t s the impor ta n t aspec ts o f component andsys tems te s t i n g and c lean ing and hand1 ng, in fo rm at io n der iv ed f rom manythousands o f manhours o f e f f o r t d i re c te d toward the improvement and per fec -t i o n of manned space veh ic l es . y c a r e f u l a t t e n t i o n and u t i l i z a t i o n o fthe recomnended d e ta i l e d component and systems design f ea tu re s p res cr ibe dh e r e in , a l on g w i t h t h e a dh eren ce t o t h e l i m i t e d b u t a de qu ate l i s t of

recomnended ma ter ia ls , the des igner shou ld be i n a good pos ture t o a vo idth e many p i t f a l l s and prob lem areas t h a t have been exper ienced by o thersI n the pas t. When requ i remen ts d i c ta te the use o f m a te r ia l s no t con ta inedon the recomnended l i s t , t he des lgne r shou ld p roceed w i t h c au t ion and ve r -i f y design adequacy by appropr iate component and systems conf igurat ion ando v e r s t r e s s t e s t s .



10. REFERENCES

1 Aerospace Safety Research and Data Inst i tute ASRDI) Oxygen TechnologySurvey Volume I 972 T h e m p h y s ic a l Pro per t ie s NASA SP-3071 ed i t edby Hans M. Roder and Ll oy d A. Weber Cry oge nics Div. I n s t . Bas ic

Stand. Nat. Bur . Stand. Bou lder Colo.

Volume 11 1972 Cleaning Requirements Procedures and V e r i f i c a t i o nTechniques NASA SP-3072 b y H. Ba nk ai t is and Car l F Schuel lerAerospace S af et y Research and Data I n s t i t u t e Lewl s Research Center.

Volume 111 1972 Heat Tr an sf er and F l u i d Dynamics--Abstracts o fSele cted Tec hnic al Reports and Pu bl ic at io ns NASA SP-3076 ed i t ed byA. F. Schmidt Cryoge nics Div. I n s t . Bas ic Stand. Nat. Bur. Stand.Boulder Colo.

Volume I V 1974 Low Tem peratur e Measurement NASA SP-3073 by L a r r yL. Sparks Cryo gen ics Div. In s t . Ba sic Stand. Nat. Bur . Stand.

Boulder Colo.

Volume V 1974 De nsi ty and L i q u i d Leve l Measurement Instr um en tat ionf o r th e Cryoge nic F lu id s Oxygen Hydrogen and Ni tr og en NASA SP-3083by Hans M. Roder Cryo genics Div. In s t . Bas ic Stand. Nat. Bur.Stand. B ould er Colo.

Volume V I 1974 Flo w Measurement In st ru m en ta t on NASA SP-3084 b yDouglas B. Mann Cry og en ics Div. Inst. Basic Stand. Nat. Bur.Stand. Bou lder Colo.

Volume V I I 1974 Ch ara c te r i s t i cs o f Meta l That In f l ue nce SystemS afe ty NASA SP-3077 by James J. Pelouch Jr. Aerospace S af et yResearch and Data In s t i t u te Lewis Research Center.

Volume V I I I 1975 Pre ss ur e Measurement NASA SP-3092 b y John M.Arv ids on and James A. Brennan Cry oge nics Div. I n s t. B as ic Stand.Nat. Bur. Stand. Bou lder Colo.

Volume I X 1975 Oxygen Systems Eng in eeri ng Review NASA SP-3090 byHaro ld W Schmidt and Donald E. Forney Cryogenics Div. In st . Ba sicStand. Nat. Bur. Stand. Bo uld er Colo.

2. Cl ar k A la n F. and Jerome 6 Hust 1974 A Review o f th e Compati-b i l i t y o f S t r u c t u r a l M a t e r i a l s w i t h O xygen I Journal 12:441-454.

Documents

NASA Design Guide for High Pressure Oxygen Systems