Vent Silencer Application Guide Confidential Report 189

THIS DOCUMENT CONTAINS CONFIDENTIAL AND PROPRIETARY INFORMATION OF UNIVERSAL SILENCER AND IS NOT TO BE TRANSMITTED TO ANYONE WITHOUT THE EXPRESS WRITTEN CONSENT OF UNIVERSAL SILENCER’S DIRECTOR OF ENGINEERING. PRINTED COPIES OF THIS DOCUMENT ARE UNCONTROLLED.

UNIVERSAL SILENCER ENGINEERING REPORT Report No. 189 Rev. 1 Page: 1 of 44Vent Silencer Application Guide Date: 10/14/03

UNIVERSAL SILENCER

VENT SILENCER

APPLICATION GUIDE

(Filename: EngReport189.doc) REVISIONS: Rev. 0 06/24/93 Original Issue Rev. 1 10/14/02 Converted to MS Word PREPARED BY: Lee Moritz DATE: 10/14/02



VENT SILENCER APPLICATION GUIDE

TABLE OF CONTENTS

INTRODUCTION .............................................................................................................................5 SCOPE .......................................................................................................................................5 TYPICAL APPLICATIONS.........................................................................................................5 TYPICAL CUSTOMERS ............................................................................................................5

SELECTING THE VENT SILENCER SIZE......................................................................................5 GETTING ACCURATE DESIGN DATA .....................................................................................5 ESTIMATING THE FLOW WHEN IT IS UNAVAILABLE...........................................................5 ESTIMATING THE FLOW FROM THE VALVE COEFFICIENT, Cv..........................................6 CALCULATING THE FLOW RATE IN ACFM ...........................................................................7 AVAILABLE SIZES AND GRADES...........................................................................................8 HVSD VENT SILENCERS..........................................................................................................8 MAXIMUM VELOCITY FOR TYPE OF VENT SILENCER SERVICE........................................8 FLOW GENERATED NOISE .....................................................................................................9 MAXIMUM VELOCITY FOR STRUCTURAL INTEGRITY .......................................................10 CALCULATING THE PRESSURE IN THE SILENCER INLET PIPE ......................................10 VENT SILENCERS WITH SMALL HIGH PRESSURE INLETS...............................................12 VENT SILENCERS WITH LARGE INLETS .............................................................................12 CALCULATING THE PRESSURE DROP THROUGH THE SILENCER .................................12

SELECTING THE VENT SILENCER ACOUSTICAL GRADE ......................................................12 VENT NOISE CALCULATION PROCEDURE .........................................................................12 DEFINITION OF VARIABLES..................................................................................................12 SONIC VELOCITY ...................................................................................................................13 MECHANICAL POWER CALCULATION ................................................................................14 ACOUSTICAL EFFICIENCY FACTOR ....................................................................................14 ACOUSTIC POWER CALCULATION .....................................................................................15 OVERALL SOUND POWER LEVEL CALCULATION.............................................................15 PEAK FREQUENCY....................................................................................................156 ESTIMATED ORIFICE DIAMETER FOR GIVEN FLOW .........................................................16 FREQUENCY WEIGHTINGS ...................................................................................................17 SOUND POWER LEVEL IN OCTAVE BANDS .......................................................................17 DIVERGENCE ..........................................................................................................................17 AIR ATTENUATION.................................................................................................................18 DIRECTIVITY ...........................................................................................................................18 UNSILENCED SOUND PRESSURE LEVELS.........................................................................18 UNSILENCED A-WEIGHTED SOUND PRESSURE LEVELS.................................................18 OVERALL UNSILENCED LEVELS .........................................................................................19 SILENCER ATTENUATION CALCULATION ..........................................................................19

PACK SECTION ATTENUATION ......................................................................................19 DIFFUSER AND PLENUM EFFECT ..................................................................................20



PACK SECTION VELOCITY CORRECTION .....................................................................20 TEMPERATURE CORRECTION ........................................................................................21

SILENCED SOUND PRESSURE LEVELS ..............................................................................22 SILENCED A-WEIGHTED SOUND PRESSURE LEVELS......................................................22 OVERALL SILENCED LEVELS ..............................................................................................22 GUARANTEED NOISE LEVELS .............................................................................................22 CUSTOMER SUPPLIED UNSILENCED NOISE LEVELS.......................................................23

SPECIAL APPLICATIONS............................................................................................................23 COMPRESSOR BLOWOFF APPLICATIONS .........................................................................23 ABSORPTIVE SILENCERS ON HIGH PRESSURE APPLICATIONS ....................................23 HIGH PRESSURE APPLICATIONS ........................................................................................23 LOW PRESSURE APPLICATIONS .........................................................................................23 MATERIALS FOR HIGH TEMPERATURE APPLICATIONS ..................................................24 MATERIALS FOR LOW TEMPERATURE APPLICATIONS...................................................24 BLOWDOWN SILENCER APPLICATIONS ............................................................................24 RESTRICTIVE DIFFUSERS TO CONTROL BACK PRESSURE............................................26 EJECTOR APPLICATIONS .....................................................................................................26 OXYGEN APPLICATIONS.......................................................................................................26 SWITCH VALVE APPLICATIONS...........................................................................................27 STEAM TURBINE EXHAUST APPLICATIONS ......................................................................27 NATURAL GAS STARTER MOTOR APPLICATIONS............................................................27 PRESSURE REGULATOR VALVE INLINE SILENCER APPLICATIONS..............................27

FABRICATION REQUIREMENTS ................................................................................................27 STANDARD CONSTRUCTION................................................................................................27 ASME CODE CONSTRUCTION ..............................................................................................28 STANDARD CARBON STEEL MATERIAL SPECIFICATIONS..............................................28 CERTIFIED MATERIALS.........................................................................................................28 STANDARD WELDERS AND PROCEDURES........................................................................28 ASME CODE QUALIFIED WELDERS AND PROCEDURES..................................................28 SPECIAL INTERNAL CLEANING AND PAINTING ................................................................28 STANDARD EXTERNAL CLEANING AND PAINTING...........................................................29 SPECIAL EXTERNAL CLEANING AND PAINTING ...............................................................29 CORROSION ALLOWANCE ...................................................................................................29

DOCUMENTATION .......................................................................................................................29 DESIGN CALCULATIONS.......................................................................................................29 WELDING INFORMATION ......................................................................................................29 INSPECTION AND TEST REPORTS ......................................................................................29 INSTALLATION INSTRUCTIONS ...........................................................................................29 PARTS LISTS ..........................................................................................................................29

APPENDIX A - EJECTOR SILENCER APPLICATIONS ..............................................................30 INTRODUCTION ......................................................................................................................30 DESIGN DATA REQUIRED .....................................................................................................30 THE TYPE OF SILENCER TO RECOMMEND ........................................................................31



SIZING PROCEDURE..............................................................................................................31 ACOUSTICAL NOISE PREDICTION .......................................................................................32

APPENDIX B - PRESSURE REGULATOR VALVE INLINE SILENCER APPLICATIONS ..........33 INTRODUCTION ......................................................................................................................33 DESIGN DATA REQUIRED .....................................................................................................33 THE TYPE OF SILENCER TO RECOMMEND ........................................................................33 PRESSURE VESSEL DESIGN ................................................................................................33 SIZING PROCEDURE..............................................................................................................33 ACOUSTICAL NOISE PREDICTION .......................................................................................34

APPENDIX C - VENT SILENCER INSTALLATION, OPERATION AND MAINTENANCE ..........36 APPENDIX D - STEAM TURBINE EXHAUST APPLICATIONS...................................................37

INTRODUCTION ......................................................................................................................37 DESIGN DATA REQUIRED .....................................................................................................37 THE TYPE OF SILENCER TO RECOMMEND ........................................................................37 ACOUSTICAL NOISE PREDICTION .......................................................................................37 SIZING PROCEDURE..............................................................................................................37 SIZING EXAMPLE ...................................................................................................................38

APPENDIX E - ANSI/ASME B31.1 and B31.3 APPLICATIONS ..................................................39 INTRODUCTION ......................................................................................................................39 SPECIFICATION REQUIREMENTS ........................................................................................39 UNIVERSAL'S RESPONSE.....................................................................................................39

APPENDIX F - NATURAL GAS COMPRESSIBILITY CHARTS ..................................................41 INTRODUCTION ......................................................................................................................41

APPENDIX G - ASME/ANSI B16.5 FLANGE PRESSURE-TEMPERATURE RATINGS .............42 INTRODUCTION ......................................................................................................................42 FLANGE DESIGN PRESSURE AND TEMPERATURE ..........................................................42

APPENDIX H – PRESSURE SWING ADSORPTION (PSA) APPLICATIONS.............................43 APPENDIX I – DRIP ELBOWS .....................................................................................................45



INTRODUCTION SCOPE: This guide is written to answer frequently asked questions regarding vent silencers, establish consistent application guidelines, and provide detailed information regarding the computer programs used for vent silencer applications. This guide contains proprietary information and is for internal use only. TYPICAL APPLICATIONS: Steam boiler relief valves, superheater header relief valves, boiler start-up and purge, high pressure air vents, natural gas blowdowns, switch valves, compressor blow-offs, autoclaves. Some of these applications are described in detail in the Appendix or "SPECIAL APPLICATIONS." TYPICAL CUSTOMERS: Engineering firms, oil and gas companies, refineries, utilities, chemical processing plants and food processing plants. SELECTING THE VENT SILENCER SIZE GETTING ACCURATE DESIGN DATA: Use Vent Silencer Sizing Sheet 88-0063 to get as much technical data as possible. The need for accurate design data cannot be overemphasized. Incorrect or estimated design data will result in a less than optimum silencer selection. ESTIMATING THE FLOW WHEN IT IS UNAVAILABLE: The vent silencer sizing program calculates an estimated maximum mass flow for a given pressure, temperature, molecular weight, ratio of specific heats and valve size. The mass flow calculated is usually conservative and will result in an oversized and also more expensive silencer. The customer should try to get the actual flow rate from the valve manufacturer whenever possible, enabling us to select the most economical silencer for the application. The equations below are from API-RP-520, Part 1, December 1976, page 3:

( ) ( ) ( ) ( )( ) ( )TZMWPAKDCW =

W = mass flow, lb/hr

11

12

15452.323600

−+

+=

KGKG

KGKGC

C = a constant based on KG KG = ratio of specific heats KD = 0.85, Discharge coefficient for a typical valve



4

2DA π=

A = valve flow area, sq in D = valve size, in P = absolute upstream pressure, psia MW = molecular weight of gas Z = compressibility factor T = absolute upstream temperature, degrees Rankine

The mass flow, W can be converted to SCFM by the following equation:

( )( )( )( ) ( ) ( ) ( )MWWQ

1447.14605301545

=

Q = flow rate, scfm W = mass flow, lb/hr MW = molecular weight of gas

ESTIMATING THE FLOW FROM THE VALVE COEFFICIENT, Cv: Occasionally a customer may provide a Cv value for a valve instead of the flow rate. The customer obtains this number from the valve manufacturer. Cv is defined as the flow of water in GPM at 60°F with a pressure drop of 1 PSI across the valve. The equations below come from a paper titled "Estimating Capacity of Valves Under Sonic Gas Flow", printed in Plant Engineering, August 19, 1976. The equation that expresses flow capacity for saturated steam is:

( )( ) ( )( )211.2 PPPCvW +∆=

W = saturated steam flow, lb/hr Cv = valve flow coefficient, provided by the valve manufacturer ∆P = P1 - P2 P1 = absolute upstream pressure, psia P2 = absolute downstream pressure, psia

For gases or superheated steam the general equation is:

( ) ( )( )( )( )T

PPPSGCvW 212.72 +∆=

W = gas or superheated steam mass flow, lb/hr Cv = valve flow coefficient, provided by the valve manufacturer



SG = specific gravity (air = 1.00) ∆P = P1 - P2 P1 = absolute upstream pressure, psia P2 = absolute downstream pressure, psia T = absolute upstream temperature, °R

CALCULATING THE FLOW RATE IN ACFM: The Actual Cubic Feet per Minute (ACFM) flow rate for gases is calculated using ideal gas equations. When the flow of a gas is given in pounds per hour, the ACFM flow rate is calculated by:

( )( )( )( ) ( ) ( ) ( )MWPA

TOOMHQ14460

1545=

Q = gas flow rate, ACFM MH = gas mass flow, lb/hr TOO = absolute upstream temperature, °R PA = absolute downstream pressure, psia MW = molecular weight of gas

When the flow of a gas is given in SCFM, where standard conditions are 14.7 psia and 70°F, the ACFM flow rate is calculated by:

=

5307.14 TOO

PASCFMQ

Q = gas flow rate, ACFM SCFM = gas flow at standard conditions of 14.7 psia and 70°F, SCFM PA = absolute downstream pressure, psia TOO = absolute upstream temperature, °R

When the flow of a gas is given in ACFM, the ACFM flow rate is used directly. Steam flow is normally given in pounds per hour. The ACFM flow rate for steam is calculated using the steam tables. Since a valve does no work, the enthalpy of the steam upstream of the valve equals the downstream enthalpy. This relationship allows a three step calculation of the ACFM at the downstream pressure. 1) Look up the enthalpy for the given upstream pressure and temperature. 2) Look up the specific volume at the downstream pressure and enthalpy found in step 1. 3) Calculate the ACFM using the equation:

( )SVAMHQ

=

60



Q = steam flow rate, ACFM MH = steam mass flow, lb/hr SVA = specific volume at the downstream pressure, cu ft/lb

AVAILABLE SIZES AND GRADES: HV vent silencers are available in standard sizes ranging from 2 inch to 112 inch. The sizes represent the internal flow area through the silencer pack section. For example, a 36 inch size would have an internal flow area equal to the area of a 36 inch diameter pipe, approximately 7.1 square feet. HV vent silencers are available in standard grades ranging from HV05 to HV30. The two digit grade number represents the L/D ratio of the pack silencer pack section. L/D ratio is the ratio of the pack section length divided by the width of the flow gaps through the pack section. For example, an HV20-36 vent silencer would have an L/D ratio equal to 20. HV sizes 2 to 10 inch are available in either HV20 or HV30 grades. HV sizes 12 and larger are available in HV05, HV10, HV15, HV20, HV25 and HV30 grades. HVSD VENT SILENCERS: HVSD vent silencers are similar to SD blower silencers with some modifications. The modifications include an inlet diffuser, hi-heat aluminum paint and fiberglass pack material with glass cloth and 316SS wire mesh wraps. The standard outlet flange sizes range from 2 inch through 30 inch. This type of silencer is useful for vent applications requiring good low frequency performance, such as low upstream pressure applications with large valves. This type of application may have peak frequencies in the 250 or 500 Hz octave bands. The HV series of vent silencers do not have comparable low frequency performance until the HV25 or HV30 grades. MAXIMUM VELOCITY FOR TYPE OF VENT SILENCER SERVICE: The three types of vent silencer service are CONTINUOUS, INTERMITTENT and OCCASIONAL. These terms are defined below. The type of service determines the maximum operating velocity through the pack section and outlet of the silencer. The vent silencer sizing program issues a warning if the maximum velocity is exceeded. CONTINUOUS: Normal silencer operating time exceeds one hour duration, regardless of how often (or seldom) the silencer operates. These silencers will be sized for 12000 ft/min maximum outlet velocity. INTERMITTENT: Normal silencer operating time is less than one hour duration. The silencer operates at least once a week, or on a periodic schedule. These silencers will be sized for 15000 ft/min maximum outlet velocity. OCCASIONAL: Normal silencer operating time is less than one hour duration. The silencer operates only during emergencies, at intervals greater than once a week or on a non-periodic schedule. This service includes blowdowns to atmosphere, such as gas pipeline, gas turbine startup/shutdown, compressor bleed and safety valves. These silencers will be sized for 18000 ft/min maximum outlet velocity.



TYPE OF SERVICE

MAXIMUM SINGLE USE DURATION

FREQUENCY OF OPERATION

MAXIMUM OUTLET VELOCITY (FT/MIN)

CONTINUOUS

=> 1 HOUR

ANY

12000

INTERMITTENT

< 1 HOUR

> ONCE A WEEK OR PERIODIC

15000

OCCASIONAL

< 1 HOUR

< ONCE A WEEK

18000

FLOW GENERATED NOISE: Flow generated noise increases as the silencer internal and exit velocity increase. A flow noise calculation has been integrated into the vent silencer sizing program. The overall flow generated power level is calculated from an equation, which accounts for any atmospheric pressure:

( )( )( )( ) dBVRHOAREAPwl 2410 26 −×= .log

Pwl = overall flow generated power level, dB

576

2DAREA π=

AREA = silencer flow area, sq ft D = silencer nominal size or outlet diameter, in

( )( )( )

( ) ( ) ( )2.324601545144+

=T

MWPARHO

RHO = density, lb/ft3 PA = atmospheric pressure, normally 14.7 psia MW = molecular weight of gas T = temperature of gas, °F V = exit velocity, ft/sec

By setting PA = 14.7 psia and substituting T (in °R) for (T+460), we can derive the flow noise equation given in Universal’s Silencer Application Handbook.

( )( )( )( ) ( ) ( )( )

==

TMW

TMWRHO 0425

2321545144714 .

..

Substituting for RHO into the PWL equation at the top of the page:



( ) ( )( ) dBVTMW

AREAPwl 24042510 26 −

×= ..log

( ) ( ) ( )dBVTMW

AREAPwl 2404251010 26 −×+

×= .loglog .

( ) ( ) ( ) dBdBVTMW

AREAPwl 2471310 26 −−+

×= .log .

( ) ( ) dBVTMW

AREAPwl 3810 26 −

×= .log

Next, weightings are subtracted from the Pwl to get an acoustical spectrum. Octave band center frequency, Hz: 31 63 125 250 500 1k 2k 4k 8k Pwl spectrum weighting, dB: -3 -5 -9 -17 -19 -18 -17 -16 -19 The vent silencer sizing program issues a warning if the flow noise is within 6 dBA of the silenced overall A-weighted noise level. Flow noise can be significant in high-grade installations, even at velocities less than 15000 feet per minute. The velocity may need to be reduced if flow generated noise is within 6 dBA of the specified overall silenced level. MAXIMUM VELOCITY FOR STRUCTURAL INTEGRITY: Maximum velocity for structural design should not exceed 25000 feet per minute and should only be used when noise is not a consideration, such as an emergency shutdown. CALCULATING THE PRESSURE IN THE SILENCER INLET PIPE: The vent silencer sizing program requires input of the silencer inlet size. It then calculates the pressure assuming sonic flow at the inlet pipe outlet. The equations below are based on API-RP-520, Part 1, dated December 1976, page 3:

( ) ( ) ( )( ) ( )TZMWAKDC

WP =

P = absolute pressure in the silencer inlet pipe, psia W = mass flow, lb/hr



11

12

15452.323600

−+

+=

KGKG

KGKGC

C = a constant based on KG KG = ratio of specific heats KD = 0.85, discharge coefficient for a pipe

4

2DA π=

A = inlet pipe flow area, sq in D = inlet pipe inside diameter, in MW = molecular weight of gas Z = 1, compressibility factor assumed 1 for all gases T = absolute temperature, °R

For sonic flow, the pressure drop due to the gas expanding out of the inlet pipe into the silencer is equal to the pressure in the inlet pipe. If the pressure is less than 1.75 times the ambient pressure, the computer uses a subsonic equation to calculate the pressure drop from the inlet pipe as follows:

AQV =

V = inlet pipe velocity, ft/min Q = gas flow rate at ambient pressure and upstream temperature, ACFM A = inlet pipe flow area, sq ft

SGT

VcP

+

=∆

460530

4005

2

∆P = pressure drop, in H2O c = 1, inlet pipe pressure drop constant V = inlet pipe velocity, ft/min T = temperature, °F SG = specific gravity



VENT SILENCERS WITH SMALL HIGH PRESSURE INLETS: When using small inlet pipes, the flow is usually choked (sonic velocity) at the pipe exit into the silencer diffuser. These applications require that the inlet nozzle and flange are capable of withstanding the pressure and temperature within the inlet pipe. The proper inlet flange rating is selected from tables in ANSI B16.5. The inlet nozzle thickness is selected in accordance with the ASME Code. The selections are based on the pressure calculated in the inlet pipe and the upstream temperature of the gas. Plate flanges are acceptable for 15 PSIG maximum pressure at -20 to 650°F. VENT SILENCERS WITH LARGE INLETS: Consider using an absorptive silencer if the velocity through the inlet of a vent silencer is less than 20000 feet per minute. For example, an SU5-20 with an 18 inch inlet could be used as a vent silencer. See the Special Applications section for more information on using absorptive silencers on high pressure applications. CALCULATING THE PRESSURE DROP THROUGH THE SILENCER: The pressure drop calculated by the vent silencer sizing program uses silencer pressure drop coefficients ranging from 10.75 for HV05 to 12 for HV30 silencers. The pressure drop coefficient for the HVSD series is 7.5. This pressure drop is after the flow has expanded into the silencer standard diffuser. It is calculated using the standard equation for pressure drop:

SGT

PAVcP

+

=∆

460530

7.144005

2

∆P = pressure drop, in H2O c = silencer pressure drop coefficient V = silencer internal velocity, fpm PA = absolute downstream pressure, psia T = temperature, °F SG = specific gravity

Additional pressure drop occurs when the flow expands from the inlet nozzle into the diffuser. This pressure drop is dependent upon inlet nozzle velocity which increases as inlet size decreases. SELECTING THE VENT SILENCER ACOUSTICAL GRADE VENT NOISE CALCULATION PROCEDURE: A description of the acoustical portion of the vent silencer sizing program is included below. DEFINITION OF VARIABLES: Octave band variables used in the noise prediction are: AA(I) = Air attenuation, dB B(I) = Octave band center frequencies, Hz C(I) = A-weightings, dB D(I) = Attenuation, dB E(I) = Directivity, dB



FW(I) = Frequency weightings, dB G(I) = Linear unsilenced levels, dB H(I) = A-weighted unsilenced levels, dBA L(I) = Linear silenced levels, dB M(I) = A-weighted silenced levels, dBA S(I) = Power levels, dB Vent noise input data: D = Valve diameter, inches m = Mass flow, lb/sec U = Distance to desired measurement location, feet PO = Stagnation pressure, psia PA = Ambient pressure, psia TOO = Stagnation absolute temperature, °R TA = Ambient absolute temperature, °R RHOO = Stagnation density, lb/cu ft RHOS = Static density in the throat of the valve, lb/cu ft RHOA = Ambient density, lb/cu ft KG = Venting gas ratio of specific heats KA = Ambient gas ratio of specific heats MW = Venting gas molecular weight MWA = Ambient gas molecular weight Computer calculated vent noise data: RHOS = Static density in the throat of the valve, lb/cu ft v = Valve sonic velocity, ft/sec CA = Ambient sonic velocity, ft/sec Wm = Mechanical power, watts E = Acoustical efficiency factor Wac = Acoustical power, watts Pwl = Overall power level, dB pf = Assigned peak frequency, Hz ORIFAREA = Estimated orifice area for the given flow, sq in ORIFDIA = Estimated orifice diameter for the given flow, in DIFFHOLE = Estimated diffuser hole size, in DIVERGENCE = Hemispherical divergence, dB VALVE SONIC VELOCITY: Velocity through the valve is considered sonic velocity regardless of upstream pressure. This is conservative for non-critical pressure ratios, where the velocity through the valve would be subsonic. Experience has shown that using subsonic velocities resulted in extremely low unsilenced noise levels.



( ) ( )( )

+

=

1215452.32

KGTOO

MWKGv

v = Velocity through valve, ft/sec KG = Venting gas ratio of specific heats MW = Venting gas molecular weight TOO = Stagnation absolute temperature, °R

MECHANICAL POWER CALCULATION: The mechanical power of the flow stream is derived from the classical equation for kinetic energy:

( )( )gcvmWm

2

21

=

Wm = Mechanical power, ft-lbf/sec m = Mass flow, lbm/sec v = Velocity through valve, ft/sec gc = 32.174 lbm-ft/sec²-lbf

Converting the mechanical power from units of ft-lbf/sec to units of watts:

( ) ( )

×

−×

−

=sec/

8.10540012854.sec174.322

1 2

BTUwatts

lbfftBTUlbfftvmWm

( )( ) wattsvmWm

46.47

2

=

ACOUSTICAL EFFICIENCY FACTOR: An acoustical efficiency factor determines how much of the mechanical power of the flow stream is converted into acoustical power per Beranek's Noise and Vibration Control Fig. 16.3:

11

12 −

+=

KG

KGRHOORHOS

RHOS = Static density in the throat of the valve per Fundamentals of Classical

Thermodynamics, page 533, equation 14.42, lb/cu ft RHOO = Stagnation density, lb/cu ft KG = Venting gas ratio of specific heats



( ) ( )( )TAMWA

KACA

=

15452.32

CA = Ambient sonic velocity, fps KA = Ambient gas ratio of specific heats MWA = Ambient gas molecular weight TA = Ambient absolute temperature, °R

25

5106

×= −

RHOARHOS

CAvE

E = Acoustical efficiency factor. Note that the maximum acoustical efficiency factor allowed

is 0.0015 to prevent unrealistically high acoustic power levels at high upstream pressures.

v = Velocity through valve, ft/sec CA = Ambient sonic velocity, fps RHOS = Static density in the throat of the valve, lb/cu ft RHOA = Ambient density, lb/cu ft

ACOUSTIC POWER CALCULATION: Wac = (Wm)(E) Wac = Acoustical power, watts Wm = Mechanical power, watts E = Acoustical efficiency factor OVERALL SOUND POWER LEVEL CALCULATION: Pwl = 10 log(Wac) + 120 dB (Note 120 dB is the conversion from 10-12 watts) Pwl = Overall Power level, dB ESTIMATED ORIFICE DIAMETER FOR GIVEN FLOW: The estimated orifice diameter is calculated based on the specified flow rate, PO stagnation pressure and TOO stagnation temperature. Rearranging terms of the equation given in API-RP-520, Part 1, dated December 1976, page 3, derives the equation:

( ) ( )( ) ( ) ( )( ) ( ) ( )

( )121

12

15452.32 −

+

+

=KGKG

KGTOOZKGMWKDPO

mORIFAREA

ORIFAREA = Estimated orifice area for the given flow, sq in m = Mass flow, lb/sec



PO = Stagnation pressure, psia KD = Orifice flow coefficient, 0.85 MW = Molecular weight of gas KG = Venting gas ratio of specific heats

Z = Gas compressibility factor TOO = Stagnation absolute temperature, °R

( )( )

π4ORIFAREAORIFDIA =

ORIFDIA = Estimated orifice diameter for the given flow, in

PEAK FREQUENCY: The peak frequency orifice diameter is used in our noise prediction calculation. It is calculated with the same equations above, except KD = 0.60 instead of 0.85, so it is slightly larger. Rather than recalculating another orifice area, the equation below relates PFORIFDIA directly to ORIFDIA. The coefficient 0.60 was required by Jim Cummins 03/27/96.

( )600850

.

.ORIFDIAPFORIFDIA =

PFORIFDIA = Peak frequency orifice diameter, in

Peak frequency is based on the estimated orifice diameter calculated above using a Strouhal number of 0.2.

( )( )( )PFORIFDIA

vpf 1220.=

pf = Assigned Peak frequency, Hz v = Velocity through valve, ft/sec PFORIFDIA = Peak frequency orifice diameter, in

If a restrictive diffuser is used, the peak frequency is based on the diffuser hole size, which is estimated assuming 32 holes are drilled. This is a good approximation because restrictive diffusers are usually drilled with 16 to 48 holes.

( )32

2ORIFDIADIFFHOLE =

DIFFHOLE = Estimated diffuser hole size, in

( )( )( )DIFFHOLE

vpf 122.0=



FREQUENCY WEIGHTINGS: The nearest octave band center frequency is selected as the peak frequency. Next frequency weightings (dB) are added to the overall Pwl to get an acoustical Pwl spectrum. The frequency weightings are based on the peak frequency Pwl being 4 dB below the overall Pwl and are as follows:

pf/128 pf/64 pf/32 pf/16 pf/8 pf/4 pf/2 pf 2pf 4pf 8pf 16pf 32pf 64pf

-46 -42 -38 -30 -22 -14 -7 -4 -6 -10 -14 -18 -22 -26

SOUND POWER LEVEL IN OCTAVE BANDS: S(I) = Pwl + FW(I) Pwl = Overall power level, dB S(I) = Power levels in octave bands, dB FW(I) = Frequency weightings, dB DIVERGENCE: The sound pressure level generated by the valve decreases as a function of the distance from the noise source to the desired measurement location. Beranek relates Spl to Pwl by equation 7.3 from Noise and Vibration Control, page 166. This equation is for a point source hemispherically radiating sound into a loss free atmosphere above a flat rigid surface: Spl = Pwl - 20 log(r) - 8 dB r = Distance to desired measurement location, meters Converting the units to feet: r = (U)(3.28 ft/meter) U = Distance to desired measurement location, feet Spl = Pwl - 20 log[(U)(3.28)] - 8 dB Spl = Pwl - 20 log(U) + 20 log(3.28) - 8 dB Spl = Pwl - 20 log(U) + 10.3 dB - 8 dB Spl = Pwl - 20 log(U) + 2.3 dB The distance is measured from the silencer centerline to the desired measurement location. This has a significant effect on large units measured at small distances. Silencer shell radius is calculated in feet as follows: HV silencers 12 inch and larger have a shell diameter of approximately 1.33 times the nominal size, so

( )( )( ) ( )122

33.1minalSizeNosShellRadiu =

Radius of outlet nozzles on non-HV silencers, ft

( ) ( )122minalSizeNosShellRadiu =

Divergence, dB DIVERGENCE = -20 log (Shell Radius + U) + 2.3 dB (Rounded to the nearest integer.)



AIR ATTENUATION: Atmospheric attenuation was deleted from the program 11/27/95. DIRECTIVITY: Directivity corrections tabulated below can be used if the angle between the flow path and the desired measurement location is 90° or greater. Directivity, dB, is a function of silencer size. The greater the size, the greater the directivity effect. This data is from Table 2-3, page 14 of the Industrial Silencing Handbook, by Bill Golden. These values should not be used for applications that have weatherhoods or outlet elbows. Directivity cannot be accurately predicted in the near field and should not be applied at distances of 10 feet or less.

Directivity in Octave Bands Silencer Size 31 63 125 250 500 1K 2K 4K 8K <5 0 0 0 0 0 0 0 -1 -3 >=5 and <=6 0 0 0 0 0 0 -1 -3 -6 >6 and <=14 0 0 0 0 0 -1 -2 -5 -11 >14 and <=24 0 0 0 0 0 -1 -3 -7 -13 >24 and <=32 0 0 0 0 -1 -3 -5 -9 -14 >32 and <=48 0 0 0 -1 -3 -6 -7 -11 -15 >48 and <=66 0 0 -1 -2 -5 -8 -10 -13 -16 >66 0 -1 -2 -5 -7 -10 -12 -15 -17

UNSILENCED SOUND PRESSURE LEVELS: Divergence and directivity corrections are applied to the Pwl octave bands to calculate sound pressure levels at the desired measurement location. G(I) = S(I) + DIVERGENCE + AA(I) + E(I) G(I) = Unsilenced SPL in octave bands, dB S(I) = Power levels in octave bands, dB DIVERGENCE = Hemispherical divergence, dB E(I) = Directivity in octave bands, dB UNSILENCED A-WEIGHTED SOUND PRESSURE LEVELS: The A-weighted values tabulated below are added to the unsilenced SPL to calculate the A-weighted unsilenced sound levels. H(I) = G(I) + C(I) H(I) = A-weighted unsilenced levels, dBA G(I) = Linear unsilenced levels, dB C(I) = A weightings, tabulated below, dB

A-weighting Values in Octave Bands Center frequency, Hz 31 63 125 250 500 1K 2K 4K 8K A-weighting, dB -39 -26 -16 -9 -3 0 1 1 -1



OVERALL UNSILENCED LEVELS: Next the unsilenced linear and A-weighted octave bands are combined logarithmically to calculate the overall linear and A-weighted sound levels. SILENCER ATTENUATION CALCULATION: The silencer attenuation is calculated by combining four factors: pack section attenuation, diffuser and plenum effect, pack section velocity correction and temperature correction. The vent silencer sizing program acoustical prediction screen includes this information in a temporary window. If you need to study the calculation, simply press the pause key on the computer to hold the window open on the screen. Then press any other key to continue. The silencer attenuation is calculated for each octave band as follows: Attenuation = Pack + Diff + Velc + Temp Attenuation = Silencer attenuation in each octave band, dB Pack = Pack section attenuation, dB Diff = Diffuser and plenum effect, dB Velc = Pack section velocity correction, dB Temp = Temperature correction, DB PACK SECTION ATTENUATION: Pack section attenuation is calculated at zero ft/min flow velocity and 100°F temperature. The attenuation is calculated for the pack section in each octave band using the equation:

( )( )( )( )12

/ MULTLODGAPftdBPack =

Pack = Pack attenuation, dB dB/ft = dB per foot from table below GAP = Flow gap width in the pack section, in LOD = Length over diameter ratio MULT = Pack section multiplier due to cumulative attenuation in long units

Pack section LOD ratio & multiplier Silencer Model LOD MULT HV05 5 1.000 HV10 10 0.975 HV15 15 0.950 HV20 20 0.925 HV25 25 0.900 HV30 30 0.875



Pack Attenuation in dB/ft in Octave Bands at 100oF

Silencer Size

Flow Gap Width

31

63

125

250

500

1K

2K

4K

8K <12 1.30 2.1 4.3 8.7 14.1 17.9 20.1 21.2 20.6 17.9 >=12 and <=19.5 4.00 0.7 1.4 2.9 4.5 5.8 6.6 6.8 6.7 5.8 >19.5 and <=33.5 4.25 0.7 1.4 2.8 4.4 5.7 6.5 6.7 6.6 5.7 >33.5 and <=47 6.25 0.6 1.3 2.6 3.7 4.7 5.2 5.3 5.0 4.2 >47 and <=61 8.25 0.6 1.2 2.2 3.0 3.7 4.0 3.9 3.4 2.5 >61 and <=74.5 7.50 0.6 1.2 2.4 3.4 4.1 4.5 4.4 4.0 3.2 >74.5 and <=90 7.50 0.6 1.2 2.4 3.4 4.1 4.5 4.4 4.0 3.2 >90 and <=105 8.75 0.5 1.1 2.1 2.9 3.5 3.8 3.7 3.2 2.3 >105 and <=112 9.75 0.5 1.1 2.0 2.6 3.0 3.3 3.1 2.7 2.0

DIFFUSER AND PLENUM EFFECT, dB: Test data has shown that diffuser low frequency performance improves slightly as flow velocity increases, while high frequency performance decreases as velocity increases.

Diffuser and Plenum Attenuation in Octave Bands at 100oF Velocity, ft/min 31 63 125 250 500 1k 2k 4k 8k <=7500 4 5 6 9 12 15 17 17 17 >7500 and <=12500 6 6 6 8 10 13 15 15 15 >12500 and <=17500 7 7 6 7 9 12 14 14 14 >17500 8 8 7 6 8 11 13 13 13

PACK SECTION VELOCITY CORRECTION, dB: Pack section performance decreases as flow velocity increases. This occurs because the holes in the perforated metal have greater resistance and appear less open acoustically as the velocity increases.

Pack Section Velocity Correction in Octave Bands at 100oF Velocity, ft/min 31 63 125 250 500 1k 2k 4k 8k <=7500 0 -1 -2 -3 -4 -4 -4 -4 -3 >7500 and <=12500 -1 -2 -4 -5 -5 -5 -5 -5 -4 >12500 and <=17500 -1 -3 -5 -6 -6 -6 -6 -6 -5 >17500 -2 -4 -6 -7 -8 -8 -8 -8 -7



TEMPERATURE CORRECTION, dB: Pack section attenuation values are calculated at 100°F. Corrections are required for higher or lower operating temperatures.

Temperature Correction in Octave Bands if T <= 0o F Silencer Model 31 63 125 250 500 1k 2k 4k 8k HV05 0.5 0.5 0.5 0.0 0.0 0.0 0.0 -0.5 -0.5 HV10 0.5 0.5 0.5 0.5 0.0 0.0 -0.5 -0.5 -0.5 HV15 1.0 1.0 1.0 1.0 0.5 0.5 0.0 -0.5 -1.0 HV20 1.0 1.0 1.0 1.0 0.5 0.0 -0.5 -1.0 -1.5 HV25 1.0 1.0 1.0 1.0 0.5 0.0 -1.0 -1.5 -2.0 HV30 1.0 1.0 1.0 1.0 1.0 0.0 -1.5 -2.0 -2.5

NO CORRECTION IF TEMPERATURE > 0°F AND <= 175°F

Temperature Correction in Octave Bands if T > 175oF and <= 375oF Silencer Model 31 63 125 250 500 1k 2k 4k 8k HV05 -0.5 -0.5 -0.5 -0.5 -0.5 0.0 0.5 1.0 1.0 HV10 -1.0 -1.0 -1.0 -1.0 -0.5 0.0 0.5 1.0 1.0 HV15 -1.5 -1.5 -1.0 -1.0 -0.5 0.0 1.0 1.5 1.5 HV20 -2.0 -2.0 -1.5 -1.5 -1.0 0.0 1.0 1.5 1.5 HV25 -2.0 -2.0 -1.5 -1.5 -1.0 0.0 1.0 1.5 1.5 HV30 -2.5 -2.5 -2.0 -2.0 -1.5 0.0 1.5 2.0 2.0

Temperature Correction in Octave Bands if T > 375oF and <= 625oF Silencer Model 31 63 125 250 500 1k 2k 4k 8k HV05 -2.0 -2.0 -2.0 -1.5 -1.0 0.0 1.0 2.0 2.0 HV10 -3.0 -3.0 -3.0 -2.0 -1.0 0.0 1.5 3.0 3.0 HV15 -3.5 -3.5 -3.5 -3.0 -1.5 0.0 2.0 4.0 4.0 HV20 -4.5 -4.5 -4.5 -3.5 -2.0 0.0 2.5 5.0 5.0 HV25 -5.0 -5.0 -5.0 -4.0 -2.0 0.0 3.0 5.5 6.0 HV30 -5.5 -5.5 -5.5 -4.5 -2.5 0.0 3.5 6.0 7.0



Temperature Correction in Octave Bands if T > 625oF and <= 875oF

Silencer Model 31 63 125 250 500 1k 2k 4k 8k HV05 -2.5 -2.5 -2.5 -2.0 -1.0 0.0 1.5 2.5 2.5 HV10 -3.5 -3.5 -3.5 -2.5 -1.5 0.0 2.0 3.5 3.5 HV15 -4.0 -4.0 -4.0 -3.5 -2.0 0.0 3.0 4.5 4.5 HV20 -5.0 -5.0 -5.0 -4.0 -2.5 0.0 3.5 5.5 5.5 HV25 -6.0 -6.0 -6.0 -5.0 -3.0 0.0 4.0 6.0 6.5 HV30 -7.0 -7.0 -7.0 -6.0 -3.5 0.0 4.5 6.5 7.5

Temperature Correction in Octave Bands if T > 875oF Silencer Model 31 63 125 250 500 1k 2k 4k 8k HV05 -3.0 -3.0 -3.0 -2.0 -1.0 0.0 2.0 3.0 3.0 HV10 -4.0 -4.0 -4.0 -3.0 -2.0 0.0 2.5 4.0 4.0 HV15 -5.0 -5.0 -5.0 -4.0 -2.5 0.0 3.5 5.0 5.5 HV20 -6.0 -6.0 -6.0 -5.0 -3.5 0.0 4.0 6.0 6.0 HV25 -7.0 -7.0 -7.0 -6.0 -4.0 0.0 5.0 6.5 7.0 HV30 -8.0 -8.0 -8.0 -7.0 -5.0 0.0 6.0 7.0 8.0

SILENCED SOUND PRESSURE LEVELS: The silencer attenuation is subtracted from the unsilenced SPL to get the silenced SPL in octave bands. L(I) = G(I) - D(I) L(I) = Linear silenced levels, dB G(I) = Linear unsilenced levels, dB D(I) = Silencer attenuation, dB linear SILENCED A-WEIGHTED SOUND PRESSURE LEVELS: The A-weighted values tabulated previously are added to the silenced SPL to get the A-weighted silenced sound levels. M(I) = L(I) + C(I) M(I) = A-weighted silenced levels, dBA L(I) = Linear silenced levels, dB C(I) = A weightings, dB OVERALL SILENCED LEVELS: Next the silenced linear and A-weighted octave bands are combined logarithmically to get the overall linear and A-weighted sound levels. GUARANTEED NOISE LEVELS: The computer printout shows a "predicted" silenced noise level. Our quotations should include the following disclaimer: "PLEASE NOTE: Our predicted silenced noise level of



___ dB(A) is for reference only, and is not guaranteed. Our warranty for performance is based upon your specified level of ___ dB(A)." This gives us a margin of safety for complying with the customer's specified noise levels. CUSTOMER SUPPLIED UNSILENCED NOISE LEVELS: Our computer calculated valve noise prediction is simply an estimate for a typical valve. It is not as accurate as actual data supplied by a valve manufacturer. Therefore, use customer's unsilenced Pwl data when it is available. When using the customer's data, our quotation should clearly state that the silencer selection is based on the customer's unsilenced data. Remember that customer data may be in error and when questionable, verification is required. The vent silencer sizing program is capable of accepting customer's unsilenced Pwl data or calculating the unsilenced noise for comparison. SPECIAL APPLICATIONS COMPRESSOR BLOWOFF APPLICATIONS: Compressor or rotary positive blowoff silencers should not be sized solely on the machine's intake or discharge flow unless we are assured that the flow is correct. The flow could be much greater or less than the flow the compressor will pass, depending on the piping volume upstream of the valve and the valve size. If the process piping is isolated from the blowoff valve by a check valve, we can safely use the compressor intake flow to calculate the blowoff flow for silencer sizing. ABSORPTIVE SILENCERS ON HIGH PRESSURE APPLICATIONS: A vent silencer with a diffuser should normally be used for high pressure applications. However, absorptive silencers can be used provided the customer takes proper precautions with design of the piping between the valve and the silencer. Ten pipe diameters of the nominal silencer flow size are recommended between the valve and the absorptive silencer inlet. This span of piping is required to allow the flow to expand and slow down prior to entering the silencer inlet. Smaller than standard inlet sizes may be used, but the velocity through the inlet of an absorptive silencer should not exceed 20000 feet per minute. The transition from the valve size up to the required pipe diameter can be accomplished by installing pipe reducers backward to serve as expanders. HIGH PRESSURE APPLICATIONS: Vent silencers for applications with upstream pressure equal to or greater than 500 PSIG should be submitted to engineering to assure that they are properly designed to withstand the pressure in the inlet nozzle and the high velocity jet impinging on the diffuser. Engineering will check the pressure and temperature conditions in the inlet nozzle and select proper nozzle thickness, inlet flange rating and materials for the application. LOW PRESSURE APPLICATIONS: Absorptive or chamber silencers should be used for applications with upstream pressure equal to or less than 15 PSIG. The velocity through the inlet of the silencer should be less than 20000 feet per minute. Higher inlet velocities will require a vent silencer with a diffuser. Special diffusers may need to be designed for low pressure applications to keep the pressure drop low. Alternatively, an absorptive silencer can be designed with a conical inlet nozzle to reduce the velocity to less than 20000 feet per minute. The cone’s total included angle (apex angle) should not exceed 14°. The cone’s outlet to inlet area ratio should not exceed 2. Multiple cones may be needed to keep the area ratio from exceeding 2. Vent silencers may be used for applications requiring high attenuation, provided the pressure drop is acceptable for the application.



MATERIALS FOR HIGH TEMPERATURE APPLICATIONS: Standard carbon steel can be used for temperatures up to 950°F. Use 409 stainless steel for sheet thickness through 1/4 inch (409Ni or 410S for thicker plate) for a temperature range of 950 to 1100°F. Note that heads cannot be formed with 400 series stainless steel, since the material is prone to cracking. Use 304 stainless steel for heads and either 304 or CrMo materials for plate, pipe and forgings for 950 to 1100°F. Use 304 stainless steel material for a temperature range of 1100 to 1600°F. Metals for higher temperatures are selected on application. Fiberglass cloth and pack can be used for temperatures up to 1000°F. Die-cut basalt mineral is good up to 1200°F. Use 42 mesh 304L stainless steel bolting cloth next to perf followed by Carborundum Duraback 4 lb/cu ft density pack material for temperatures from 1001 to 1700°F (the limit of Duraback). Applications with skin temperature requirements should be referred to engineering. Carborundum Durablanket 8 lb/cu ft density pack should be used on the outermost ring because of its good insulating properties. Applications above 1600°F should be referred to engineering. MATERIALS FOR LOW TEMPERATURE APPLICATIONS: Both vent gas temperatures and ambient environmental temperatures must be considered when discussing low temperature vent silencer applications. Carbon steel can be used for ambient temperatures down to -20°F. At temperatures below -20°F carbon steel becomes brittle and can fracture from impact loads. This type of loading occurs in a vent silencer diffuser. While some carbon steel materials, such as normalized SA-516-70 plate, SA-333-6 pipe, SA-420-WPL6 pipe caps, or SA-350-LF2 flanges can be used in low impact applications to -50°F, we should normally use stainless steel materials for the inlet flange, nozzle, and entire diffuser for applications with temperatures below -20°F to be sure these parts can withstand the severe impact loads. Type 409 and 410S (see UHA-51(e)(3)) should not be used at temperatures below –20°F, since their coarse grain structure makes them susceptible to brittle fracture. Types 304, 304L, 316, 316L and 347 and can be used to -155°F without impact testing the weld metal per ASME Code Section VIII, Division 1, Paragraph UHA-51(e)(2)(a). The rest of the vent silencer is not normally subjected to impact loads and can be carbon steel for temperatures from -20 to -50°F. Use an appropriate stainless steel throughout for temperatures below -50°F. Fiberglass cloth and pack can be used for operating temperatures down to 0°F. At lower temperatures the fiberglass material may suffer damage from brittle fracture and freezing of absorbed condensation. Use 42 mesh 304L stainless steel bolting cloth wrap material instead of fiberglass cloth for temperatures below 0°F. Die-cut basalt mineral wool used in Acousti-tube vent silencers is good down to -100°F. Use Carborundum Duraback 4 lb/cu ft density pack material instead of fiberglass pack for temperatures from 0°F to -250°F. Polyester blanket pack material may be used at temperatures down to –320°F, but is limited to only 400°F maximum temperature. BLOWDOWN SILENCER APPLICATIONS: Venting of a pressurized, trapped volume is called a blowdown. Typical blowdown applications are found in natural gas compressor stations or autoclaves. The blowdown is initiated by opening a vent valve. The flow of gas during a blowdown is transient in nature; starting with a high flow rate at the initial (maximum) gas conditions and terminating at atmospheric pressure. The customer usually specifies a maximum duration for the blowdown. The maximum blowdown time specified is critical, and most significantly impacts the silencer size and price. The greater the blowdown time allowed, the smaller the silencer can be.



Regardless of the trapped volume, it is the gas upstream density that dictates the initial peak flow rate through the silencer and creates the "worst case" condition around which we design. A restrictive diffuser can be installed into a vent silencer to reduce the peak flow rate while meeting the required blowdown time. Reducing the flow rate allows selection of a smaller silencer for the application. Universal's blowdown time computer program calculates peak flow and blowdown time. The peak flow is calculated using the equation from API-RP-520 (see ESTIMATING THE FLOW WHEN IT IS UNAVAILABLE) except that KD = 0.6, which is the discharge coefficient for a sharp edged orifice. The restrictive diffuser is drilled with sharp edged holes. The diameter and quantity of holes is selected to equal the area of the orifice required (A) for the desired blowdown time. The blowdown time equation is based on "Calculating Pressure-Release Times" from Chemical Engineering Magazine dated 07-17-67.

=

PFPO

XVOLBDT ln

1

BDT = Blowdown time, sec VOL = Upstream trapped volume (actual physical tank volume), cu ft

( ) ( )( ) ( ) ( )( ) ( )12

1

1215452.32

1441

−+

+

=

KGKG

KGTOO

MWZKGAKDX

KD = Discharge coefficient, 0.6 For sharp edged orifice A = Actual physical valve orifice area, sq in KG = Ratio of specific heats Z = Compressibility factor MW = Molecular weight of gas TOO = Absolute upstream temperature, °R PO = Absolute initial upstream pressure, psia PF = Absolute final downstream pressure, psia

Always submit any vent silencers requiring restrictive diffusers to engineering to assure that they are properly drilled and designed to withstand the pressure. All restrictive diffusers are designed in accordance with ASME Code to assure that they will withstand the pressure. The restrictive diffuser assembly USED TO CONTROL BLOWDOWN TIME must be designed for the pressure and temperature upstream of the vent valve. This way we are assured that the diffuser will safely contain the upstream pressure and temperature if the diffuser holes become plugged or the valve malfunctions. The restrictive diffuser will be constructed by welding a pipe cap to the end of an extended inlet pipe. The assembly is then hydrotested at 1.5 times the design pressure. After a successful hydrotest and satisfying



any customer specified NDE requirements, the assembly is drilled to get the proper flow area. The restrictive diffuser assembly is inserted into the standard flow diffuser, space permitting. Various piping codes regulate installing restrictive devices downstream of safety relief valves. Typical examples are: ASME Section VIII, Division 1, Nonmandatory Appendix M, Paragraph M-8(c); ASME B31.1-1989, Paragraph 122.6.2(C); ASME B31.3-1990, Paragraph 322.6.1. When quoting any silencers with restrictive diffusers, we should state the following: 1) "We recommend that all piping leading up to the silencer be rated for the full pressure upstream of the control valve." 2) "The customer should assure himself that the control valve will not malfunction from the excessive back pressure caused by installing a silencer with a restrictive diffuser." RESTRICTIVE DIFFUSERS TO CONTROL BACK PRESSURE: Some vent applications require a specified back pressure downstream of the control valve while passing a specified flow. This is done to prevent the valve from choking and reduce valve body noise. The blowdown time program can be used to calculate the orifice diameter required to provide the necessary back pressure. The back pressure desired should be entered as the initial pressure. Atmospheric pressure is entered as final pressure. Gas temperature, molecular weight, ratio of specific heats and compressibility factor is entered as required. Blowdown time is not a concern in this case, so enter any large number, such as 9999 cu. ft. for the trapped volume. Adjust the orifice diameter so that the peak blowdown flow equals the specified flow rate. The restrictive diffuser will be drilled to provide an area equal to the area of the orifice diameter selected. Always submit any vent silencers requiring restrictive diffusers to engineering to assure that they are properly drilled and designed to withstand the pressure. The flange of a restrictive diffuser assembly USED TO CONTROL BACKPRESSURE must be rated (per ANSI/ASME B16.5) to handle 2 times the required backpressure or the upstream pressure, whichever is less. The diffuser pipe and pipe cap materials will be rated to meet or exceed the MAXIMUM pressure rating of the FLANGE. The restrictive diffuser will be hydrotested at 1.5 times the maximum pressure rating of the flange. This will provide a reasonable factor of safety, if the customer’s actual flow rate is higher than what they specify. EXAMPLE: A customer has steam at 1700 psig and 900°F upstream. They want a 150 psig backpressure. The silencer shall have a 6 inch carbon steel inlet flange and restrictive diffuser. DESIGN: The flange must be rated for 150 x 2 = 300 psig at 900°F. An SA-105 Class 600 flange is rated for 345 psig at 900°F. 6" SCH 40 SA-106-B pipe is rated (per Pressure Vessel Handbook, 8th Edition, page 140) for 1143*6500/15000 = 495 psig at 900°F. The restrictive diffuser assembly will be hydrotested at 345 x 1.5 = 518 psig prior to drilling. EJECTOR APPLICATIONS: Refer to separate directions for ejector discharge silencer applications found in Appendix A. OXYGEN APPLICATIONS: Maximum velocity through the pack section and outlet should not exceed 12000 feet per minute. All material in contact with the flow should be 304 SS unless specified otherwise by



the customer. This includes shell material that is behind pack material. Surfaces having impingement velocities exceeding 10000 feet per minute should be monel or have monel cladding. Monel is a non-sparking material, which reduces the potential for fires due to particle impingement. Internals must be cleaned for oxygen service per 88-0129. Use 40 to 60 durometer viton gasket material if gaskets are required. Glass wool pack material is required per 88-0129. SWITCH VALVE APPLICATIONS: Switch valves are a system of quick acting blowdown valves. Under normal flow conditions, the open valves discharge a continuous stream of moisture saturated nitrogen. Under these normal flow conditions, low pressure drop is a primary consideration. Every few minutes, however, the cycle changes and the valves that were open close while the valves that were closed open. Pressurized air in a vessel is suddenly released to atmosphere. Under these circumstances of blowdown, the silencing of the sudden air release and the silencer strength and durability to withstand this cyclic loading are primary considerations. The silencer must be sized to perform acoustically during the blowdown. Usually the blowdown flow is much higher than the normal flow, and the pressure drop through the silencer during normal flow is very low, easily complying with the pressure drop specified. Some manufacturers rate a skid for service flow. Do not confuse the service flow with the blowdown flow, which is much higher. STEAM TURBINE EXHAUST APPLICATIONS: Refer to separate directions for steam turbine exhaust silencer applications found in Appendix D. NATURAL GAS STARTER MOTOR APPLICATIONS: These motors are small high speed turbines powered by compressed natural gas. They are used to start the engines that power the compressors in a natural gas compressor station. Absorptive silencers are usually recommended because they offer low pressure drop and good high frequency performance. The computer program for calculating vent noise is not valid for starter motor applications because the source of the noise is the starter motor - not a valve. Try to get unsilenced motor noise whenever possible. PRESSURE REGULATOR VALVE INLINE SILENCER APPLICATIONS: Refer to separate directions for pressure regulator valve inline silencer applications found in Appendix B. FABRICATION REQUIREMENTS STANDARD CONSTRUCTION: Vent silencers are open to atmosphere. When vent silencers are correctly sized, exit velocity is subsonic and the silencer outer shell is not pressurized. Vent silencer inlet diffusers are designed to withstand the dynamic force of the entering flow and have sufficiently open flow area so that the pressure drop across them is always less than 15 psig. Therefore standard vent silencers are completely non-code construction. No material test reports, qualified welders, post weld heat treatments, hydrostatic tests, mechanical tests, radiographs, magnetic particle examinations or any other types of tests are provided for standard non-code construction. Vent silencers are all welded carbon steel construction. Diffusers are constructed with 23% open perforated carbon steel. Inlet plenums on HV series 12 inch and larger are externally lined with 1/4 inch thick Durablanket-S ceramic blanket and carbon steel shell. The diffuser open area is one half of the pack



section annular flow area. Pack sections are fabricated with 23% open perforated carbon steel, a layer of glass cloth and fiberglass pack material packed at a density of 4 pounds per cubic foot. Lifting lugs and a bottom drain are standard. Paint is high heat aluminum, which can withstand temperatures up to 1000°F. ASME CODE CONSTRUCTION: Some customers require vent silencers to be designed and fabricated in accordance with ASME Code Section VIII, Division 1. We should always question the customer if ASME Code construction is specified because: (1) Paragraph U-1(c)(8) says vessels having an internal operating pressure not exceeding 15 psi are not considered to be within the scope of ASME Code Section VIII, Division 1. (2) ASME Code units are more expensive and require longer delivery times. ASME Code construction can be provided, if required. When required, the customer must specify the vessel design pressure and temperature range. Vent silencers built per ASME Code are designated with a "C" added to the standard HV model, for example HV20C-36. Some customers require vent silencers to be designed and fabricated in accordance with ASME Code Section VIII, Division 1, but not stamped. We will offer true Code units, since the Authorized Inspection fee is a small percentage of the overall silencer cost. STANDARD CARBON STEEL MATERIAL SPECIFICATIONS: Cold rolled carbon steel sheets in 22 through 16 gauge thickness will comply to ASTM A-366. Hot rolled carbon steel sheets in 14 through 7 gauge thickness will comply to ASTM A-569. Material certification papers are not available for ASTM A-366 or ASTM A-569 carbon steel sheet. Hot rolled carbon steel plate in 3/16 inch and greater thickness will comply to ASTM A-36, but material certification papers are usually not provided because our standard fabrication procedures do not require material traceability. We cannot positively identify the material specification of our stock non-code F & D heads because our suppliers do not maintain material traceability. CERTIFIED MATERIALS: Certified material can be offered at additional charge. Material traceability will be maintained and material will be documented with material test reports or certificates of compliance. If a customer requires certified material for carbon steel sheet (A-366 or A-569), we must increase the thickness of all carbon steel sheet materials to 3/16 inch and offer ASTM A-36 plate, which is available with certification papers. Non-code F & D heads must also be ordered specially made with certified ASTM A-36 plate. Note that ASME Code allows use of A-366 or A-569 materials for non-pressure parts. STANDARD WELDERS AND PROCEDURES: We are using qualified procedures for non-code welding with the following qualifications: We do not control joint design. We do not look for 100% penetration of welds. We cannot guarantee that qualified welders are used. ASME CODE QUALIFIED WELDERS AND PROCEDURES: Welders and welding procedures qualified in accordance with ASME Code Section IX can be provided at additional charge. Welding Procedure Specifications (QW-482) and Procedure Qualification Records (QW-483) can be provided for the customer's review upon request. Any changes to these specifications which would require Procedure requalification may result in additional charges to compensate for the time and material required for requalification. Welder Qualification Records (QW-484) will be available, upon request, for inspection at time of fabrication.



SPECIAL INTERNAL CLEANING AND PAINTING: Silencer internals can be cleaned and painted, however we are unable to guarantee 100% coverage on internal coatings. While we make every effort to get 100% coverage, the heat affected zones of some welds may not be accessible for touch-up after assembly. STANDARD EXTERNAL CLEANING AND PAINTING: Standard external surface preparation consists of solvent cleaning per SSPC-SP-1 and hand tool cleaning per SSPC-SP-2. Hi-heat aluminum paint is applied at 1 to 1.5 mil DFT per 88-0103. SPECIAL EXTERNAL CLEANING AND PAINTING: Silencer externals which require blast cleaning or special paint systems will have lag shells fully seal welded. Units with standard hi-heat aluminum paint have skip welded lag shells. CORROSION ALLOWANCE: General guidelines for customer specified corrosion allowances: 1/16 inch corrosion allowance requires a minimum of 14 gauge internals and lagging and 10 gauge for shell, heads, nozzles and diffusers. 1/8 inch corrosion allowance requires a minimum of 10 gauge internals and lagging and 3/16 inch for shell, heads, nozzles and diffusers. If our standard gauges are greater than these minimums they will be neither increased nor decreased. DOCUMENTATION DESIGN CALCULATIONS: Customer specifications may require submittal of calculations such as blowdown time calculations, acoustical calculations, ASME Code vessel design calculations, maximum nozzle loads, wind, snow, seismic and operational loading calculations. This information is usually required prior to the start of fabrication. WELDING INFORMATION: Welding Procedure Specifications (QW-482), Procedure Qualification Records (QW-483) and weld maps can be provided for the customer's review upon request prior to the start of fabrication. Welder Qualification Records (QW-484) will be available, upon request, for inspection at time of fabrication. Some customers may require Quality Control Manuals for review prior to the start of fabrication. INSPECTION AND TEST REPORTS: The following are examples of documentation that can be provided upon shipment of equipment, if required. Note that this information must be requested prior to the start of fabrication to assure that the required information is recorded during fabrication: material test reports, certificates of compliance, inspection traveller copies, manufacturer's data reports, nameplate photocopies, post weld heat treatment charts, hydrostatic test records, or NDE reports. INSTALLATION INSTRUCTIONS: Normally vent silencers are shipped without instructions. Brief installation, operation and maintenance instructions are included in Appendix C for customers who insist on receiving instructions. PARTS LISTS: No spare parts manuals are required or available for vent silencers. Silencers are complete weldments installed using standard techniques for ordinary piping components or vessels having no wearing or replaceable parts.



APPENDIX A - EJECTOR SILENCER APPLICATIONS INTRODUCTION: All ejectors (sometimes called venturi eductors, jet pumps, hogging jets or injectors) operate on the principle of a fluid entraining a second fluid. Although design and construction may vary, this applies to all ejectors. All ejectors have three common features: inlet, suction, and discharge. These function as follows: Inlet - The operating medium (liquid, gas or steam) under pressure enters the inlet and travels through the nozzle into the suction chamber. The nozzle converts the pressure of the operating medium into a high velocity stream, which passes from the discharge side of the inlet nozzle. Suction - Pumping action begins when vapor, gases or liquid in the suction chamber are entrained by the high velocity stream emerging from the inlet nozzle, lowering the pressure in the suction chamber. The resulting action causes the liquid, gas or vapor to flow toward the discharge. Discharge - The entrained material from the suction system mixes with the operating medium and acquires part of its energy in the parallel section. In the expanding section part of the velocity of the mixture is converted to a pressure greater than the suction pressure, but lower than the operating medium pressure. DESIGN DATA REQUIRED: The noise generated from the high inlet velocity and suction pass through the ejector discharge. The silencer is located downstream of the ejector discharge. The following information is required to properly select the correct silencer: Either At the Inlet Connection: At the Suction Connection: Type of gas Type of gas Upstream Pressure, psia Pressure is assumed atmospheric, 14.7 psia Upstream Temperature, °F Temperature, °F Mass flow, lb/hr Mass flow, lb/hr Or At the Discharge Connection: Molecular weight of gas mixture Pressure is assumed atmospheric, 14.7 psia Temperature of gas mixture, °F Mass flow, lb/hr Other data which are helpful, but not mandatory: Silencer inlet size and flange pressure rating Maximum allowable pressure drop, if any, psi Unsilenced noise level, if available, dB Silenced noise level required at a specified distance, dBA overall at feet



THE TYPE OF SILENCER TO RECOMMEND: Fiberglass packed absorptive silencers can be used for 8 inch or smaller ejector discharge lines. Absorptive silencers should be sized for an outlet velocity of 4000 to 15000 feet per minute. Use SD or RD silencers for ejector discharge lines over 8 inch size. SD or RD silencers should be sized for an outlet velocity of 4000 to 10000 feet per minute. Make sure that the blower silencer paint and pack material are correct for the temperature of the application. Usually pressure drop will limit velocity to less than the maximum allowed above. The line size into the silencer must be large enough so the inlet velocity is less than 20000 feet per minute If the inlet velocity is too great or the silencers listed above do not provide enough attenuation, a vent silencer may be necessary. Use HVSD vent silencers if the velocity into the silencer is greater than 20000 feet per minute. If the pressure drop is a concern, either enlarge the diffuser to provide lower restriction or recommend an absorptive silencer and a larger line size leading up to the silencer to lower the pressure drop to an acceptable level. Consider using a water separator silencer if a steam ejector has a high liquid water carryover that an absorptive or blower silencer could not separate. Size the separator silencer using velocity of 4000 to 5500 ft per min. to assure proper separation. Make sure that the separator silencer paint and pack material are correct for the temperature of the application. SIZING PROCEDURE: For cases when the ejector inlet and suction flows are given separately, we will assume that the mixture will act as an ideal gas, even if steam is part of the mixture. Ideal gas equations will be accurate enough. Calculate the physical properties based on the mass flow (M) ratios of the mixture: Molecular weight of mixture,

( ) ( )2211 MWMtotalMMW

MtotalMMWmix

+

=

M1 = Ejector inlet mass flow, lb/hr M2 = Ejector suction mass flow, lb/hr Mtotal = M1 + M2, lb/hr MW1 = Molecular weight of ejector inlet gas MW2 = Molecular weight of ejector suction gas



Temperature of mixture (°F),

( ) ( )2211 TMtotalMT

MtotalMTmix

+

=

T1 = Temperature of ejector inlet gas, °F T2 = Temperature of ejector suction gas, °F

Ratio of specific heats of mix,

( ) ( )2211 KMtotalMK

MtotalMKmix

+

=

K1 = Ratio of specific heats of inlet gas K2 = Ratio of specific heats of suction gas

ACOUSTICAL NOISE PREDICTION: Use customer's unsilenced noise levels, if available. If unsilenced noise levels are not available, use the vent silencer sizing program to predict the noise levels. Use the total flow rate of the mixture discharged from the ejector to predict the unsilenced noise. Estimate valve size using the approximate size necessary to get the total flow rate of the mixture discharged from the ejector, based on the inlet pressure and the mixture temperature.



APPENDIX B - PRESSURE REGULATOR VALVE INLINE SILENCER APPLICATIONS INTRODUCTION: Pressure regulator valve inline silencers are installed downstream of a pressure regulator valve in a pressurized line in a closed piping system. The purpose of these silencers is to reduce the noise level inside the pipe and thereby reduce noise transmitted through the downstream piping to plant personnel. DESIGN DATA REQUIRED: The following information is required to properly select the correct silencer: Type of gas Molecular weight of gas Ratio of specific heats of gas Flow rate, pounds per hour Pressure upstream of regulator valve, psia Temperature upstream of regulator valve, °F Pressure downstream of regulator valve, psia Silencer inlet size and flange pressure rating Silencer outlet size and flange pressure rating Other data which are helpful, but not mandatory: Maximum allowable pressure drop, if any, psi Unsilenced noise level, if available, dB Silenced noise level required at a specified distance, dBA overall at feet THE TYPE OF SILENCER TO RECOMMEND: The type of silencer used depends upon line size, flow rate, maximum allowable pressure drop and required attenuation. ASME Code absorptive silencers such as U5C or CCD are used if the velocity into the inlet of the silencer is less than or equal to 20000 feet per minute. PR (pressure regulator) series silencers are used if the inlet velocity is greater than 20000 feet per minute, or if the additional performance of an inlet diffuser is required. PR silencers consist of vent silencer internals installed into an ASME Code pressure vessel. PR silencers are not designed with restrictive diffusers and have minimal reduction of pressure in the line. PR silencers have flanged inlet and outlet nozzles so they can be hydrotested per Code. PRESSURE VESSEL DESIGN: All types of pressure regulator valve inline silencers are designed and fabricated in accordance with ASME Code Section VIII, Division 1. The vessel must be designed to be capable of withstanding the pressure and temperature upstream of the regulator valve. This way we are assured that the vessel will safely contain the upstream pressure and temperature if the pressure regulator valve malfunctioned and no safety relief valve was installed downstream. We will design the vessel for the lower downstream pressure only if we receive written confirmation that the end user of the vessel will install a properly designed pressure relief device. SIZING PROCEDURE: The silencer is sized for the downstream pressure and temperature as ambient conditions. The vent silencer sizing program can be used to size silencers for pressure regulator valve



applications. The key to using the program is changing the default ambient conditions to the actual conditions downstream of the regulator valve. A step-by-step sizing procedure follows: 1) Load the vent silencer sizing program and enter the required customer data. 2) Type 0 to edit the Ambient Conditions Worksheet conditions of pressure, temperature, molecular weight

and ratio of specific heats. Revise the four default ambient conditions to the actual conditions downstream of the regulator valve. The pressure should be the pressure downstream of the regulator valve, which is the pressure the silencer will see in service. The temperature should be the temperature upstream of the regulator valve, since we assume the upstream temperature is approximately equal to the downstream temperature. The molecular weight and ratio of specific heats should be for the gas in the pipe rather than the defaults for air. This step is critical to assure the sizing is done correctly. Type 1 upon successful editing, or 0 to edit them again.

3) Enter the information on the Silencer Sizing Worksheet. Normally the application would be for

continuous service and a restrictive diffuser would not be used. 4) Enter the information on the Acoustical Prediction Worksheet as normally done for vent silencer

applications. The PR silencer series has the same available sizes and performance grades as the HV series of vent silencers. Pressure drop coefficients and attenuation curves are calculated identically to the HV series. The maximum velocity through the silencer will be 15000 feet per minute for inline applications.

Sometimes the customer specifies an outlet size that is too small for a velocity of 15000 feet per minute. In this case we must check the flow generated noise. Excessive flow generated noise may require the customer to change their downstream piping to a larger size. The silencer nominal size must be selected so the silencer internal velocity does not exceed 15000 feet per minute, regardless of what outlet size is required by the customer. ACOUSTICAL NOISE PREDICTION: Use customer's unsilenced Pwl levels, if available. If not available, use the vent silencer sizing program to predict the Pwl levels. The vent silencer prediction will be conservative (the prediction will be high) for subsonic pressure ratios, since the program assumes sonic flow. Note that the vent silencer program Pwl levels are within the pipe. The customer typically specifies noise levels outside the pipe. Therefore, sending the acoustical prediction computer print to the customer could result in confusion. The noise levels outside the pipe, will be lower due to the pipe wall transmission loss. The method used to calculate the pipe transmission loss is outlined in Noise and Vibration Control by Beranek, section 16.7, page 529. Typical pipe transmission loss is 20 to 25 dB, but it can be much greater at high frequencies when using thick wall pipe. The method to calculate the silenced noise level, in octave bands, is: Pwl inside the pipe upstream of the silencer (from customer or computer)



- Silencer attenuation (from computer) - Pipe transmission loss (calculated manually) Power level outside the pipe - Divergence to desired measurement location (from computer) Silenced SPL at specified location Directivity is not normally used in these applications, since a pipe of significant length radiates noise as a line source, not a point source.



APPENDIX C - VENT SILENCER INSTALLATION, OPERATION AND MAINTENANCE GENERAL INFORMATION: Customer _____________________________ Customer Reference _____________________________ Universal Silencer Reference _____________________________ Universal Silencer Model ______________________________ Universal Silencer Drawing No. ______________________________ FLOW CONDITIONS: Gas ______________________________ Upstream Pressure (PSIG) _____________________________ Upstream Temperature (°F) ______________________________ Mass Flow (LB/HR) _____________________________ Valve Size (IN) ______________________________ INSTALLATION: Inspect the piping leading up to the silencer. The piping should be clear of any debris internally. Low points in the piping should have drains. These drains are required to remove any water which may accumulate in the piping. Slugs of water could impact the silencer internals causing serious damage to the silencer. Piping should be properly supported to withstand the dynamic forces of the venting flow. The piping should also accommodate any thermal expansion. Please review the Universal Silencer drawing listed above for proper silencer orientation and for any special installation instructions. Install the silencer using standard techniques for ordinary piping components. The silencer drain should be connected to an appropriate drain pipe. OPERATION: Low points in the piping leading up to the silencer should be drained prior to each blow down. Personnel should stand clear of the silencer outlet during operation. Do not touch the silencer wall on high temperature installations. Contact Universal Silencer prior to using the silencer for conditions exceeding the flow conditions listed above. MAINTENANCE: Spare parts are not required for silencer products. Silencers are complete weldments having no wearing or replaceable parts. Inspect the silencer internals every six months to check for excessive corrosion. Keep the drain open to prevent the silencer internals from filling with water.



APPENDIX D - STEAM TURBINE EXHAUST APPLICATIONS INTRODUCTION: Steam turbines are used to convert steam energy into work. They normally exhaust to atmosphere and require some type of exhaust silencer. Turbine exhaust noise is broadband, resulting from the steam expanding as it passes through the turbine to atmosphere. The exhaust spectrum also contains discrete frequency mechanical noise corresponding to the blade passing frequencies of the turbine. DESIGN DATA REQUIRED: The following information is required to properly select the correct silencer size: Type of gas is assumed to be steam. Flow rate, pounds per hour Pressure upstream of steam turbine, psia Temperature upstream of steam turbine, °F Other data which is helpful, but not mandatory: Maximum allowable pressure drop, if any, psia Unsilenced noise level, if available, dB Silenced noise level required at a specified distance, dBA overall at feet THE TYPE OF SILENCER TO RECOMMEND: Steam turbine exhaust applications are similar to gas turbine applications. Excessive silencer pressure drop could affect turbine performance so vent silencers should be used with care. Absorptive silencers are usually recommended because they offer low pressure drop and good high frequency performance. ACOUSTICAL NOISE PREDICTION: The source of noise is the steam turbine. Therefore, the computer program for calculating vent noise is not valid for steam turbine applications. We are unable to guarantee silenced noise levels, unless unsilenced noise levels are provided. Try to get unsilenced turbine noise whenever possible. SIZING PROCEDURE: The sizing procedure assumes that the steam expansion through the turbine is reversible and adiabatic (no heat transfer) with negligible changes in kinetic and potential energy. Since the process is steady state, steady flow, reversible and adiabatic we are able to write the following thermodynamic equation: From the second law of thermodynamics: s1= s2 s1= entropy into turbine, BTU/lbm s2= entropy out of turbine, BTU/lbm If we are given the upstream conditions listed above, and s1= s2 , we are able to look up the specific volume of the gas at the downstream atmospheric pressure and determine the flow rate through the silencer.



SIZING EXAMPLE: Assume 9500 lb/hr of steam at 20 psia and 230°F enters a steam turbine. The turbine exhausts to atmosphere. Determine the silencer size required. Look up the entropy for steam at 20 psia and 230°F. s1= 1.7320 Btu/lbm °R s1= s2, so the downstream conditions in the turbine exhaust are: P2= 14.7 psia s2= 1.7320 Btu/lbm °R Find the quality of the downstream conditions, x: s2= sg - (1 - x) sfg s2= 1.7320 Btu/lbm °R sg (From steam tables at 14.7 psia) = 1.7568 Btu/lbm °R sfg (From steam tables at 14.7 psia) = 1.4447 Btu/lbm °R 1.7320 = 1.7568 - (1 - x) 1.4447 x = .9828 Find the specific volume at the downstream conditions, v2: v2= vg - (1 - x) vfg vg (From steam tables at 14.7 psia) = 26.799 cu ft/lbm vfg (From steam tables at 14.7 psia) = 26.782 cu ft/lbm v2= 26.799 - (1 -.9828) (26.782) v2= 26.338 cu ft/lbm Calculate the turbine exhaust flow, Q: Q = (m / 60 min/hr) (v2) Q = (9500 lbm/hr / 60 min/hr) (26.338 cu ft/lbm) Q = 4170 ACFM For an SU5-12 silencer: Silencer flow area, A = (3.1416)(6)2 / 144 = .7854 sq ft Silencer internal velocity, V = Q / A = 4170 ACFM / .7854 sq ft = 5309 ft/min Silencer pressure drop, ∆P = (.75) (5309/4005)2 (530 / 690) (18 / 29) = .63 in. water



APPENDIX E - ANSI/ASME B31.1 and B31.3 APPLICATIONS INTRODUCTION: Some customers require vent silencers fabricated in accordance with either ANSI/ASME B31.1 or B31.3. ANSI/ASME B31.1 is a Power Piping Code used for power boiler applications. ANSI/ASME B31.3 is a Chemical Plant and Petroleum Piping Code. Both of these specifications were discussed with our Authorized Inspector in February 1990. He said we can fabricate piping per ANSI/ASME B31.1 or B31.3 but cannot stamp them. He said that B31.1 requires a "PP" stamp and B31.3 requires an "S" stamp. We are currently unable to find anything in these specifications requiring application of code stamps or symbols. SPECIFICATION REQUIREMENTS: B31.1 paragraph 100.1.3(C) states that it does not apply to steam piping designed for 15 psig or less. B31.3 paragraph 300.1.3(a) states that it does not apply to piping designed for 15 psig or less provided the fluid handled is nonflammable, nontoxic and not damaging to human tissue and its design temperatures is from -20 to 366°F. B31.1 paragraph 127.1.1 and B31.3 paragraph 328.2.1(a) require welders and welding procedures qualified per ASME Code Section IX. B31.1 paragraph 137 and B31.3 paragraph 345 require pressure leak tests. UNIVERSAL'S RESPONSE: Vent silencers are open to atmosphere, so the impact of the specifications on vent silencer design is unclear. Since both of the specifications apply to pressurized piping, it is possible that only the pressure bearing components (inlet nozzle and flange or a restrictive diffuser) of a vent silencer may have to comply. Whenever a customer requires compliance to ANSI/ASME B31.1 or B31.3 we must, before quoting, discuss each application with the customer. We must ask the customer two questions: 1) Will ASME qualified welders and welding procedures be required for the entire silencer or just the pressure bearing components? 2) Will a hydrotest be required for pressure bearing components or not? Depending upon the answers we receive, our response will be: 1) We can state that restrictive diffusers will comply with B31.1 or B31.3. We will use certified material.

Welders and welding procedures will be qualified per ASME Code Section IX. The restrictive diffuser assemblies will be hydrotested prior to drilling, but will not be stamped.

2a) Units with a standard inlet diffuser (not the restrictive type) will have the inlet nozzle and ANSI B16.5

pressure rated inlet flange fabricated with certified material. Inlet nozzles will be fabricated with certified material thick enough for the design pressure. Welders and welding procedures for the inlet nozzle and flange only will be qualified per ASME Code Section IX. Unless specifically requested, pressure testing will not be provided.

2b) If required, we can hydrotest the inlet nozzle and flange, for an additional charge. The additional

charge will cover attaching a weld cap to the inlet nozzle and flange assembly, hydrotesting and removal of the weld cap. Code stamp will not be provided.

3a) The balance of the silencer is non-code. Vent silencers are open to atmosphere. When vent

silencers are correctly sized, exit velocity is subsonic and the silencer outer shell is not pressurized. Standard vent silencer inlet diffusers (not to be confused with restrictive diffusers) have sufficiently open flow area so that the pressure drop across them is always less than 15 psig. Therefore, except



for the inlet nozzle and flange, vent silencers are completely non-code construction. Unless specifically requested, the balance of the silencer will not be welded with ASME Section IX qualified welders.

3b) If required, we can use ASME Section IX qualified welders and procedures throughout, for an

additional charge. 3c) If required, the entire silencer can be fabricated and stamped per ASME Code Section VIII, Division

1, for an additional charge.



APPENDIX F - NATURAL GAS COMPRESSIBILITY CHARTS INTRODUCTION: Compressibility is the property of a gas or mixture that causes it to differ in volume from that of a perfect gas when each is under the same pressure and temperature conditions. The compressibility factor (Z) is the ratio of the actual volume of the gas to the volume determined according to the perfect gas law. It is a multiplier of perfect gas volume. Charts are available for compressibility factors for natural gas mixtures of various molecular weights. The factors should be used when running calculations for natural gas blowdown applications. For blowdown applications other than natural gas, the compressibility factor can be assumed to be one. The charts are available from the Gas Processors Suppliers Association (GPSA), Engineering Data Book, Volume II, Tenth Edition dated 1987.



APPENDIX G - ASME/ANSI B16.5 FLANGE PRESSURE-TEMPERATURE RATINGS INTRODUCTION: Tables are available from ASME B16.5-1996 Edition, 1998 Addenda. The ratings are the maximum working gauge pressures listed for various materials at different operating temperatures. Universal Silencer purchases SA-105 flanges for carbon steel applications. SA-105 falls under Material Group No. 1.1. Cr-Mo low alloy steels are listed by chemical composition. Austenitic stainless steels and other high alloys are listed by their generic trade names for convenience. FLANGE DESIGN PRESSURE AND TEMPERATURE: The inlet nozzle and flange on a vent silencer must be capable of withstanding the pressure and temperature in the silencer inlet nozzle. The design pressure for a vent silencer inlet flange is the inlet nozzle pressure drop printed on the first page of the vent silencer computer printout. Non-code plate flanges can be used if the inlet nozzle pressure drop does not exceed 15 PSI. The design temperature is the temperature upstream of the valve. At temperatures approaching 900°F, carbon steel flanges have little strength and 304 or 316 stainless steel flanges may be required. When a restrictive diffuser is provided to put back pressure on a valve, it shall be designed for 2 times the back pressure at the upstream temperature, or the upstream pressure, whichever is less.



APPENDIX H – PRESSURE SWING ADSORPTION (PSA) APPLICATIONS The most economical form of oxygen supply is an on-site oxygen gas generation plant. These plants are highly reliable and have been built to supply oxygen economically and safely. Two basic types of oxygen generator designs are employed. The Pressure-Swing Adsorption (PSA) System is generally used for most small to medium size plants, and the traditional cryogenic air separation process is employed for larger size plants. The main components of the PSA System are shown schematically below and include:

1) Feed air compressor 2) PSA skid, consisting of adsorber vessels manifolded to control valves 3) Automatic cycle control system 4) Air dryer to provide clean, dry instrument air 5) Liquid oxygen storage tank and vaporizer for backup and peak demand requirements

The PSA System uses multiple adsorber vessels, which are cycled sequentially to provide a steady, continuous flow of oxygen gas. The feed air is compressed to about 40 psig by a non-lubricated compressor and flows to the adsorber vessel that is on the adsorption cycle. A special grade LINDE Molecular Sieve adsorbent selectively attracts and traps (adsorbs) carbon dioxide, water vapor, and most of the nitrogen gas, producing a high-purity (90-95%) oxygen gas product. The adsorption step continues until the adsorbent bed is loaded with impurities. At a predetermined time in the cycle, the feed air flow is switched to a regenerated bed and the loaded bed goes on the regeneration (desorption) cycle to remove the adsorbed carbon dioxide, water, nitrogen and other trace Impurities in preparation for the next adsorption cycle. The regeneration cycle proceeds as follows:

1) The adsorber bed is depressurized to atmospheric pressure, which by the nature of the Molecular Sieve, causes release of trapped impurities from the adsorbent.

2) The adsorbent bed is purged with some of the product oxygen gas to displace the impurities, which remain in the adsorbent vessel.

3) The adsorbent vessel is repressurized to adsorption cycle pressure and is ready to go back into the next adsorption cycle.



APPENDIX I – DRIP ELBOWS Some piping designers will design high temperature steam vent piping leading up to a vent silencer with a “drip elbow”. A drip elbow is a break in the piping and a 90° elbow discharging vertically into a larger diameter stack. The stack attaches to the vent silencer inlet. This arrangement provides for thermal expansion of the piping and allows condensate from the silencer to fall onto a drip pan installed below the elbow. The drip pan is piped to a drain. The drip elbow creates a break in the inlet piping to the silencer, which can result in two types of field problems. The first problem is the break in the line will allow noise to escape. This increases the noise level of an installation, because the break is before the silencer allowing unsilenced noise to escape. Anytime a customer has a vent silencer related noise problem we should always check if they have a break in their piping for thermal expansion, or a drip elbow. The second problem is blow-back of steam, which can be a safety hazard; if people contact the hot steam, they could be burned. The piping downstream of the elbow and the vent silencer have some back-pressure. We can only guarantee no blow-back for a drip elbow if the customer provides the following:

1) Silencer inlet size required. 2) Pressure drop required at the end of the silencer inlet pipe. 3) The mass flow rate passing through the pipe. 4) The pressure and temperature of the steam.

The use of vent drip elbows should be discouraged because of the problems described above. We should recommend flexible expansion joints to accommodate piping thermal growth, because an expansion joint prevents steam and noise from escaping to atmosphere.

Documents

Vent Silencer Application Guide Confidential Report 189