external bending movement tightness

7/29/2019 External Bending Movement Tightness

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Tightness Testingand ResearchLaboratory

ROOM TEMPERATURE EXTERNAL BENDING MOMENT TIGHTNESS TEST (ROBT)ON THE SELCO SEAL 4" cl150 Ib 316SS/GORE-TEX GASKET STYLEReport

prepared forMr Mel Lowry

SEALING CORPORATIONMr Nitin R. ParekhOLINCHEMICALS

andMr David Mills

W.L. GORE & ASSOCIATES, INC.by

Hakim Bouzid and Michel Derenne


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2temperature ( bolt-up ), pressurization with Helium (operation), and application of externalbending moments.ESTABLISHMENT OF TEST CONDITIONS

For some gasket products, ROSTtest conditions can be chosen on the basis of the workthat is being done for the PVRC on the effect of external loads on the leakage behaviourof some typical gaskets and from manufacturer and user field experience data available todate.

The conditions for the ROST test performed on the SELCO Seal 4" cI 150 Ib 316SS/GORE-TEX gasket product were specified by OLINCHEMICALS and SEALING CORPORATION.These test conditions are 25,000 psi and 50,000 psi bolt-up stress and 400 and 800 psigHe pressure with a maximum bending moment of 800 ft.lb.GASKET SPECIMEN

The SELCO Seal 4" cl 150 Ib SS/GORE-TEX gasket samples were provided by SEALINGCORPORATION, to the dimensions as defined in the proposed ASTM Draft No.9 for ROTTtesting of non-sheet gasketing materials: 4.5 in. 10 x 6.88 in. 00. Our laboratory test codefor this material is SS01.TEST RIG FEATURESDescription of the ROBT rig

A specially designed external bending load tightness test rig, the ROST rig facility existsat TTRL. It consists of a NPS 4 schedule 40 pipe with a pair of class 150 Ib weld-neckflanges mounted on two V-shape supports which are part of a rigid frame base. Theexternal bending moment is applied through two single acting hydraulic jacks located atsome distance between the supports. Two strain gages located on the top of the external


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3Monitored parameters

Bolt load, flange rotation, external bending moment, fluid pressure, leak rate and theelapsed time are measured throughout the test using a microcomputer based dataacquisition system and a test software.Leakage measurementsWith the ROBTrig, leakage measurements are performed using the pressure decay method.The rig is equipped with a measuring system that can detect leakage values as low as0.0002 mglsec of Helium with reliability. A 0.0002 mglsec leak corresponds to a Tp ofaround 2000 for an internal gas pressure of 400 psig.Test specificsTest temperature:Pipe joint:Initial bolt stress:Helium nominal pressure:Bending Moment:

75F :i:5FNPS 4 schedule 40 pipe with class 150 Ib weld-neck flanges25,000 and 50,000 psi400 and 800 psi.Applied in step up to maximum specified value ( 800 ft.lb ).

ROBTTEST PROCEDURE

The ROBTtest can be described as being a three step procedure. The first step consistsof seating the gasket by conducting a R.T. loading. The second step is to subject thegasket to the required pressure. The third and final step is to apply in steps the specifiedexternal bending load.The details of the ROBTtest procedure are as follows:Step 1 - Gasket seating (see Fig. 1):


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4TEST OUTPUT PARAMETERS

Bolt load, flange rotation and tightness results are presented graphically, for each test, inthe following format:~ Bolt load scatter is plotted for each external bending moment applied on a linear scale.~ Top and bottom flange rotation as a function of the external bending moment on alinear scale.~ Tightness as a function of the external bending moment on a semi-logarithmic scale.

RESULTS AND ANALYSIS50,000 psi Bolt Stress

Based on an area of 8.44 in2, the gasket stress of the SELCO seal is 7300 psi at 400psi He and 6070 psi at 800 psi He. The bolt load scatter shown in Figs. 1a and 1b whichrefers to the 400 and 800 psi gas pressure does not seem to be very much affected as thebending moment is increase gradually to 800 lb. ft. Initially, before releasing heliumpressure, the bolt-up was evenly applied for the purpose of achieving gasket stressuniformity. As a result, the bolt load variation at zero bending moment is quite constant.

The small difference between the zero bending curve and the other curves of Fig 1a,which appears to be a shift in the curve, is due to the creep-relaxation that has taken placebefore applying the first bending moment to the pipe. Consequently, a maximum of around200 Ib per bolt seem to have been lost. However, as the gas pressure is increased to 800psi, all bolts experienced the same drop in their loads as is seen in Fig. 2b. It is to be notedthat, as the 800 lb.ft bending moment was applied, the load in the bolts has slightly beenaffected with a maximum change of around 300 Ib corresponding to 3.3 %.

The rotation of the flange is also of importance in terms of leakage. Figs. 2a and 2bshow the change in flange rotation as the bending load is increased. Obviously, the topof the flange experience an increase in rotation while the bottom part shows a decrease


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~

5A maximum of around 0.009 deg. of change in flange rotation is observed in this case.

The general trend obtained is very similar to the previous case of 50,000 psi bolt-up. Thisindicates that the bolt-up does not have a significant effect on the change in flangerotation.

With 25000 psi bolt-up, the tightness of the SELCO seal gasket is shown not beaffected by the application of the range of bending moment that has been considered. In,fact at both Helium pressures tightness is shown to be relatively constant. The tightnessrepresented in Fig. 6 are rather low because of the low gasket stress that is applied as aresult of the 25000 psi initial bolt-up.


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6Appendix 1 -Tightness Parameter, Tp: Definition

Any specific measure of mass leak rate is strongly correlated to the applied fluid pressure.To permit the comparison of the leakage behaviour of gaskets tested at different fluidpressures, the effect of pressure must be taken into account. This has led to the definitionof a non-dimensional Tightness Parameter, Tp, which relates a given measured value ofleak rate to the pressure at which this leak rate was actually obtained:

Tp = ~ ( Lrm' )0.5

P' Lrm

where: PP'LrmLrm'

= Fluid pressure (MPa or psig)= Reference pressure (0.101 MPa or 14.7 psig)= Mass Leak Rate (mg/s)= Unit Mass Leak Rate (1 mg/s for a 150 mm 00

gasket in a joint).In other words, Tp was developed so that at a given state of condition of a gasket, thesame tightness value be obtained whether leakage is measured with fluid pressurized at200, 400, 800 psig or any other pressure.Tp is proportional to pressure and inversely proportional to the square root of leak rate.More precisely, Tpcan be thought of as the number of atmospheres required to cause ahelium leak of 1 mg/sec for a 150 mm gasket 00 in a joint. Since this is about the sameas the 00 an NPS 4 in. joint, the pressure to cause a leak of 1 mg/sec of helium for thatjoint is its tightness. A higher value of Tpmeans a tighter joint. Because of the squareroot, a joint that is 10 times tighter leaks 100 times less.


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10000950090008500-

::9 8000-Cn:J0 7500..J...-0 7000aJ6500600055005000

0

ROST ON SELCO SEAL 4" cl150 Ib 55 316/GORETEX, . ..u... .!Initial bolt stress: 50000 psi:!He@400 psi

-------- - -- --- -- ---

1800,,

i900 i\ i( ) : ( )'-- .' -+- " - \

)" () \

, (.: )::) 2700)-'--;-~ ( -) /( )' () ,,

.-- ...- - - Bending=O lb. ft ,- -6- Bending=300b.ft:- 0- - Bending=600b.ft,

0 Bending=800 lb.ft :00 L~~~_!~rv13 i

45 90 135 180 225 270 315 360Angular Position of Bolt on Flange

Figure1a


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10000950090008500

-:E 8000-Cca0 7500...J....-0 7000aJ6500

600055005000 a

ROST ON SELCO SEAL 4" cl150 Ib SS 316/GORETEX

: Initial bolt stress: 50000 psiHe @ 800 psi

-15-- --~-&-- . -- --55

1800II

(): ( )

i- - - Bending=O lb.ft: - -/:s- Bending=300 Ib.ft:- {}- . Bending=600 Ib.ft, 0 Bending=800 Ib.ft

I, (I

( ) - 2700( )(...) : I )900 ,

00 l~~~_~~-~~~J

45 90 180 270 3601535 225Angular Position of Bolt on Flange

Figure1b


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0.0100.008 .-

g> 0.006C-cO.0040;C'O'0 0.002a::(1) .C') 0.000cC'Oii: -0.002c.-~-0.004cC'O


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ROST ON SELCO SEAL 4" cl150 IbSS 316/GORETEX

8"'""'"

"'""'"

..0-'"'""'""'""'"

-0-""'''''' .....-------------

0.0100.008 ! Initial bolt stress: 50000 psi;He @800 psi- -C) 0.006Q)C-c 0.0040.;:;

CtS15 0.002rx:~ 0.000cCtSu: -0.002 -c.-~-0.004cCtSc3 -0.006 -

I- -- -- -I- {J - Top Flange,L___~ BottomFlall!!e;1800

1--

( )' ( )- f--

i ) ( i

900 ( ) 2700( I ' )--TO

-0.008-0.010

0 20000 300 400 500 600 700Bending Moment (ft.lb)

Figure2b

( ), ( I---~---

00

@~~?_I~-~6~]800 900 1000


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ROST ON SELCO SEAL 4" cl150 Ib SS 316/GORETEX1000

[Initial bolt stress: 50000 psi i900800 II [JI \'I \'I \'I \',I \ 'I \ '

1 \ 'I \ 9I \ II \'I \ II \ I1\ \ I uI b~ nloadingpointI II II CI~I Resolution l imitIII Isso~01 10 100 1000 10000 100000

Tightness Parameter

Figure3.'

- 700.c-..... 600C(1)E

500 1. 400 psi-H;]0:E I- {J - OOpsi -J

C')c 400-"'CC(1)CD 300

200

100


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6000

5500

5000-c-'Cca0 4500..J~0m40003500

3000 r0

ROST ON SELCO SEAL 4" cl150 Ib 55 316/GORETEX

--- ---------. -,-""".- . .

'

j- - - Bending=OIb.ft- -l:J- Bending=300b.ftI-

. .

0- - Bending=600 lb.ftl_- 0 _u~ending=800Ib.ft

45

Initial bolt stress: 25000 psiHe @ 400 psi

~~:::::",:-

90 135 180

1800I

-- . ;--- "- "(--') : (-.).. ,""'---

)'

() , ( )900 v - ( - I . ) - --- - -2700() ._,' ()( ) I ('.) /I

I---.--[~~01BMO~J0

225 270 315 360Angular Position of Bolt on Flange

Figure4a


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6000

5500

5000-c-"Cca0 4500..J..--0m 40003500

30000


- - - Bending=OIb.ft ;- -li - Bending=300 Ib.ft

I

i

- 0-' Bending=600b.ftL 0 Bending=800 Ib.~J

45

:Initial bolt stress: 25000 psi iiHe @ 800 psi

1800I

90

( ): (").

(-- " '

)(- ) /~ ,(-)

., "',~ .. C

,

> ' )-~'~ ,-

,

'

,

-2700( ) " I ; ( J'.." --r'- "'..,-" (_J: (J "

0 ~01 BM03190 135 180 225 270

Angular Position of Bolt on Flange315 360

Figure 4b


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0.0100.0080.006 '.-) 0.004Q)C-c: 0.0020:t:iS 0.0000a::

Q) -00020)'c:~u: -0.004 '-0.006-0.008-0.010

0

ROBT ON SELCO SEAL 4" cl150 Ib SS 316/GORETEX

fin-i'ti-c:iI bolt stress:-iSOOO'psidl~~-@? -~~-~ psi " J

_-D CI-------...0-----'""'""'"

"'""'""'"

"'"900

1800'--~// ,--, I :.~---(~ - (~): () )(~) /--;-~ (-- )- -- '~- ( : ) 2700( ( )\ ' !

( I, ( )

00

~;-~;~~::;~:n~er~-~01BM031

100 200 300 400 60000 700 800 900 1000Bending Moment (ft.lb)

Figure5a


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ROBTON SELCO SEAL 4" cl150 Ib SS 316/GORETEX0.0120.010

. h___' ' ,.---..Initialbolt stress: 25000 psi.He @ 800 psi

1'--" -- , _.. ,I

-.

Q -.

TOPFlangeI. - A .. BottomFlan~e- -_-


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!Initial bolt stress: 25000 psi I, . J

~1\1\1\1\I \0\I \I \I \1 \I \I 0IIa\ \ \\ \ \ \ \

\ \

Unloading points

10 100 1000Tightness Parameter

Figure6

IIIIIIIIIIIIIIIIIIII~ Resolution limitIIIII

r~. ;_.~:;~~;;:.~~

10000 100000

1000

900800- 700.0-:::600.c(1)E0 500:!:

C)C 400-"CC(1)m 300200

100 .IrSS01 BM031I0 -

1

external bending movement tightness

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