Braided Packing An Old technology With a Modern Twistc.ymcdn.com/sites/ on diameters, bolt stress, ... effort 8 mm effort 10 mm effort 12 mm 3mm 12mm ... 250 0 20 40 60 80 100 120

March 10, 2016 - VMA Technical SeminarMarch 10, 2016 - VMA Technical Seminar

Braided Packing

An Old technology With a Modern Twist

March 10, 2016


What is Compression Packing?

• A material made from soft, pliable ingredients that is cut or formed into rings and compressed in an annular cavity to seal around a moving shaft.

• Compression packings are contained and compressed within a cavity called a stuffing box by a packing gland.

• Applications include pumps, valves, mixers and other unique types of equipment.


An Old Technology Perception


Motion Packing Seals

Reciprocating Motion

Helical Motion


Types of Packing Constructions

• Braided

• Twisted

• Wrapped, Rolled and Folded

• Extruded

• Laminated

• Bulk

• Die Formed


Braided Mechanical Packing

• Braided Mechanical Packing is a “system” made of – Fibers– Braid Style– Lubricants

• Break-in• Blocking• Corrosion Inhibitors

• Some general requirements for packing– Resilience– Chemical Resistance– Strength– Temperature Resistance


Types of Braided Packing

• Square braided (plaited) • Usually soft

• Uses fewer, larger diameter diameter yarns

• Large percentage of of lubricants

• Used in high-speed rotary rotary service at low low pressures

• Used in old and worn worn equipment

• Used for small cross cross sections

2 -Track Structure


Types of Braided Packing

• Inter-braided

• Even distribution of yarn density yarn density throughoutthroughout

• Uses more strands of smaller smaller diameter than square braid

3-Track Structure

4-Track Structure

March 10, 2016 - VMA Technical Seminar

Braid Design

• Different Braiding Machines and Styles

• Square Braid• 1/8” – 1/2” cross sections• Highest coating pick-up percentage

Interbraid

Square Braid


Bulk Material

• Flexible graphite can be molded to make solid rings

• Other material are used in extrusion, die forming, or molding

• PTFE

• Elastomers• Buna-N

• Ethylene-Propylene

• Neoprene

• FKM

• Silicone


Carbon or Graphite Fiber

Price

Cleanliness

Disadvantages

Temperature

Heat Transfer

Chemical Resistance

Low Friction

Advantages

Carbon and graphite fibers are inert to most

chemicals and have low frictional coefficients.

pH range 0- 14 except for strong oxidizers


ePTFE/Graphite Fiber

ePTFE/Graphite fiber is a fiber that combines the

properties of PTFE and graphite. It is limited only by the

temperature range of the PTFE - pH range 0 -14

Temperature RangeDisadvantages

Heat Transfer

Chemical Resistance

Low Friction

Good tensile strength

Advantages


The Main Properties of Flexible Graphite Material

• Density: Is light in weight and has compressibility &

recovery

• Purity: 98% to 99% purity

• High & Low temperature: From -245°C to 850°C

• Corrosion resistant: Chemically inert except strong

oxidizers

• Excellent thermal conductivity

• Low thermal expansion

• Impermeability

• Self lubricating

• Flexible

• High compressibility

• Resilient


Exfoliated Natural Graphite Flake (Enlarged View)


Braided Flexible Graphite

• Flexible Graphite by

itself does not have

enough tensile

strength to braid.

• To create a

braidable yarn,

manufacturers use

a carrier or

support to give the

material the

mechanical

strength that by

itself it lacks.

• Typically


Outer Jacket

• Graphite Tape Yarn Encapsulated in an Inconnel Wire Mesh

• 4532°F (2500°C) max temperature

• 0 to 14 pH range

• Low Friction

Core

Outer Jacket

Corners (x4)


Metals

• Some metal wires are used for fiber reinforcement– Stainless steel– Inconel– Copper– Brass– Monel

• Some metals are used in foils– Lead– Aluminum– Copper


Lubricants

Packing Lubricants

- Compression packings generally contain lubricants

- Lubricants provide resiliency that allows the packing to

deform and recover under slight mechanical deficiencies such as shaft movement or flexing. Some lubricants can also be called ‘blocking agents’.

- Many packing manufacturers offer blends of materials. As a result, limitations and properties vary.


Lubricants

Materials- Colloidal Polytetrafluoroethylene

- Animal & Vegetable Lubricants

- Petroleum (Mineral) Lubricants, (petrolatum)

- Solid Lubricants: - Graphite powder or flake

- molybdenum disulfide

- Boron Nitride

- Silicone oil

- Bio-lubricants (environmental implications)


Coating Formulation

• Individual strands must be coated prior to braiding• Greatest challenge:

• Flexibility• Adhesion• Permeability

Sample Formulations

Flexibility Testing


Coating Application

• Wet-Braiding

• Coat the packing while it’s being braided

• Higher coating content between the strands

Wet-Braiding on

Inverted Braider

Machine


Valve Packing Characteristics

• Square-Braid Design • Small cross-sections• High coating content

• Outer Jacket• Anti-extrusion capabilities

• Core• Internal spring characteristics

• Wet-Braiding• High coating content

• Low permeability Coating• Emission capability

Coatings act as a

fluid barrier to

enhance sealing

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&docid=87u92uHrmKo2IM&tbnid=C4QEZmi9DxNpTM:&ved=0CAUQjRw&url=http://www.indiamart.com/company/8951525/pump-compression-packing.html&ei=jaXKU4azKoypyATHuICQDA&bvm=bv.71198958,d.aWw&psig=AFQjCNEWIgYmbKCGjZCZ4txtTCkgZEBY3g&ust=1405875914602586

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Testing & Validation

API-622 Test


Testing and Validation

• Testing of packing in a fixture such as that specified by API 622 is not a guarantee that the same emission level will be achieved in a given valve.

• Factors such as surface finishes, concentricity, tolerances on diameters, bolt stress, and deformation under load all affect emission results

• Tests must be done first to qualify the packing and then to qualify the valve with the packing


Testing & ValidationNo Longer an Old Technology

ISO 15848 and API-624 Testing


Packing Behavior Study

Typical case and assumptions

Packing Rings

Packing Ring Size

Bolt Lubricant

Packing Gland Bolt Torque Applied

Gland Stress Applied

5 Cut Rings

1.0”(ID) x 1.5”

(OD) x 0.25”(CS)

Sliding Paste

(0.18 nut factor)

40 ft.-lbs

8,575 psi



• CONTEXT Increasing demand from the end-users

Reduction of fugitive emissions

Reduction of opening/closing forces

Need for the differentiation from different packing types

No standardized method for packing calculation nor packing full characterization (mechanical, friction, sealing performance vs. packing load,..)

Existing standards for bolted flange joints with gasket with EN1591 and EN13555

=> FSA and ESA joined with CETIM and its industrial partners to work on the creation of a packing design tool, based on the system developed for bolted flanges


Page 28

2015/03


• SEALING TEST CELL

Study Test Equipment

Stem movement

(translation or

rotation) generation

Stem movement

transmission equipped

with load sensor or torque

meter

Sealing test cell

(room temperature)

Compression press gland

load application

He

To spectrometer


Page 29

2015/03


Vacuum chamber -

(Stuffing box/gland sealing)

Pressurized chamber

(Stuffing box/stem sealing)

• SEALING TEST CELL


Page 31

2015/03


• Mechanical test cell

Stuffing

box

Gland

Strain

gauges


Test Equipment Design Verification


Page 33

2015/03


-2.00E-06

0.00E+00

2.00E-06

4.00E-06

6.00E-06

8.00E-06

1.00E-05

1.20E-05

0 20 40 60 80 100 120 140 160défo

rmat

ion

circ

onfé

rent

ielle

position suivant la hauteur (mm)

cas n°2

Stuffing box design:

Stuffing box thickness : 10 mm

Materials: 1.0481 – P295 GH (EN10028-2)

Load case2 (min stress)

P=10 MPa, Length= 3 mm, T=20°C

3mm

P=10 MPa

ResultsDeformation peak 1 E-05=> OK for

gauges => stuffing box thin enough



Page 34

2015/03


• Contact pressure on internal diameter vs. Circumferential deformation

– variable packing/stufing-box contact length (3 to 12 mm)

– Constant contact pressure of 1 MPa

Contact length [mm]

3mm

12mm

y = 3.074E-07x + 1.329E-07R² = 9.989E-01

0.00E+00

5.00E-07

1.00E-06

1.50E-06

2.00E-06

2.50E-06

3.00E-06

3.50E-06

4.00E-06

0 1 2 3 4 5 6 7 8 9 10 11 12 13

max def (1 MPa)

max def

Linéaire (max def)

-5.00E-07

0.00E+00

5.00E-07

1.00E-06

1.50E-06

2.00E-06

2.50E-06

3.00E-06

3.50E-06

4.00E-06

0 20 40 60 80 100 120 140 160

déf

orm

atio

n c

irco

nfé

ren

tiel

le


effort 3 mm

effort 5 mm

effort 8 mm

effort 10 mm

effort 12 mm

3mm

12mm

def

orm

atio

n

Proportionnal to contact length on internal diameter for a

given contact pressure level



Page 35

2015/03


• Check of distance between gages

– strain gage chain (10 gages at 1mm distance each)

– Load case2: P=10MPa over 3mm => signal « flat » enough for a 1mm grid

-2.0E-06

0.0E+00

2.0E-06

4.0E-06

6.0E-06

8.0E-06

1.0E-05

1.2E-05

55 60 65 70 75 80 85 90 95

défo

rmat

ion

circ

onfé

rent

ielle


maillage



Page 36

2015/03


• Experimental calibration using elastomeric rings

– Hypothesis: K=1

– Test on a dedicated compression press using the mechanical cell



Page 37

2015/03



1 2

3 4

5 …

..10

A,B,C Gauges (position angle 120°), same axial position => good alignement

-50

0

50

100

150

200

250

0 20 40 60 80 100 120 140 160 180

µm ChA Jauge 01

µm ChB Jauge 01

µm ChC Jauge 01



Page 38

2015/03



0

50

100

150

200

250

300

0 10000 20000 30000 40000 50000

max

de

form

atio

n[µe

]

Force de fond [N]

max deformation mesuré (µ€)

max deformation calculée (µe)pour H =9mm




=> Good order of magnitude for measurmement and calculation (initial

uncompressed packing height 12.7 = 2*6.35mm

Test



Page 39

2015/03


• SEALING TEST PROCEDURE

– 1 Apply initial axial stress of 1 MPa (reference)

– 2 Apply (and maintain) an axial stress of QA

– 3 Apply M stem movements (translation or rotation) handling an axial stress of QA (M=30)

– 4 Connect He spectrometer (check of vacuum and leakage level without He)

– 5 Pressurize (and maintain) with Helium at pressure level P

– 6 Leakage measurement over 2 hours

– 7 Unload to stress level Q1

– 8 6 Leakage measurement over 2 hours

– 7 Unload to stress level Q2

– ….



Page 40

2015/03


• SEALING TEST CURVE EXAMPLE

1.0E-08

1.0E-07

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

0

10

20

30

40

50

60

70

80

90

0 1 2 3 4 5 6 7 8 9 10 11 12 13

Axi

al

stre

ss [

MP

a]

-He

Pre

ssu

re [

ba

r]

Time [hr]

Sealing test curve example

(QA=80MPa, 4 graphite rings, 10 bar He, translation)

Stress [MPa]

Pressure [bar]

Leakage [atm.cm3/s]

He spectrometer

connection

Pressurization

Leakage

measurement @80MPa

Leakage

measurement @60MPa

Leakage

measurement @40MPa

Leakage

measurement @30MPa

Leakage

measurement @20MPa

Test Results


Page 41

2015/03


1.00E-07

1.00E-06

1.00E-05

1.00E-04

1.00E-03

1.00E-02

1.00E-01

1.00E+00

0 10 20 30 40 50 60 70 80 90 100

Leak

age

[m

g/s

/m o

f st

em

pe

rim

ete

r]

Packing axial stress [MPa]

Leakage diagram (4 graphite rings, 10 bar He, translation)

40MPa_10b_1

40MPa_10b_2

60MPa_10b_1

60MPa_10b_2

80MPa_10b_2

A

B

C

Initial packing stress QA [MPa]

TIGHTNESS CLASS

LEAKAGE [mg/s/m] 40 60 80

C 1.00E-02 20/- 27/31 26

B 1.00E-04 - - 36

A 1.00E-06 - - 53

Test Results


On-Going Work

• Testing continues

• Different packing formulations must be tested to determine their behavior

• Algorithms will need to be developed

• Standardization will be essential


Conclusions

• The performance demands are higher than ever• The products have higher performance than ever• Compression Packing formulation, design, and

testing use some old technology but also state of the art engineering tools

• Parameters such as compressive loads and friction will no longer just be based on experience and occasional verification

• Compression packing emission sealing is a modern technology

Documents

Braided Packing An Old technology With a Modern Twistc.ymcdn.com/sites/ on diameters, bolt stress, ... effort 8 mm effort 10 mm effort 12 mm 3mm 12mm ... 250 0 20 40 60 80 100 120