ML20198E474

Valve Manufacturers Assoc Seminar Flexible Graphite Non- Asbestos Gasketing Matl

ML20198E474
Person / Time
Site:	San Onofre
Issue date:	08/08/1986
From:	Petrunich P UNION CARBIDE CORP.
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ML20198E466	List: ML20198E459 ML20198E474
References
NUDOCS 9801090106
Download: ML20198E474 (9)

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i i

Valve Manufacturing Association of America l

i GRAFO E Brand Flexible Graphite L

Flexible Graphite Non-Asbestos l

Gasketing Material l

Presented by P.S. Petrunich Union Carbide Corporation i

at the ASBESTOS SUBSTITUTE GASKET

& PACKING MATERIALS SEMINAR 4

t 1

inter Continental Hotel Houston, Texas l

August 6 7. 1966 4801090106 900105 DR ADOCK 050003 1 1

m.

. VALVE MANUFACTURERS ASSOCIATION SEMINAR FLEXIBLE GRAPHITE NON-ASBESTOS GASKETING MATERIAL By P.S. Petrunich Union Carbide Corporation A8STAACT the API-601 Stancard. To derrve maximum cost-effective The basis of Gasket Technology for valves and flanges benefits f rom the use of flexible graphite for gasketing, the has been elastomenc bonced, fiber filled matenal3 with f abncator, valve manufacturer, and end user must possess asbestos libers in the compressed process histoncally knowiedgeof ttscharactensticsandbehavior.Utilizingthese perceived as affording the optimum pr co performance engineenng parameters at the design stage will enable in.

benehtsforflatnon metallir gasketing.:nclusionof ametal novative approaches to solving gasketing problems The 1

support structure. pnmanly that proviosd by Ihe higher pric.

potential sayings through added safety, higher reliability, fluid ed spiral wouna gasket, was promoted by the need to and energy savings. reduced maintenance, and simplified enhance reliability at high pressures and temperatures.

design outweigh the initial pnce disadvantage generally Binder free, non asbestos, flexible graphite has associetea with use of flexible grapnite gaskets.

temperature pressure sealabikty capabiJties I,upenor to The non metallic matenals that comprise the bulk of thoseof asbestos basedproductsanciscompatiblewithone past gasket technology have been based on vanous com.

of thewidestrangesof fluidsof anysinglegasketmatenal, binations of fiber and particulate hilers or, more recently, a There are no known health hazards associated with use of more limrted use of sohd or reinforced PTFE for temperatures flerable graphite. Essential charactenstics of flexible graphite under 600*F(260*C). The fdiers are usually chemically bond-gasketing, including metal inserted composites and spiral ed with some type of elastomer compatible with the fluids be.

wound designs are overviewed and compared with those of ing sealed, either through the compressed sheeterof beater compressed asbestos and non asbestos matenals. Ex.

process. The beaier process is more extensively used in the posure to specific in service fluids such as steam, hydrocar-U S. for the fillers in spiral wound gaskets, while the com.

?ns, and other chernicals is discussed.

pressed sheeter process is used in flat gasketing. European design spiral wound gsskets have used comptested sheet THE PURPOSE of this paper is to overview flexible as a f dier. Histoncally, the dominant fiber has been asbestos, graphite, a distinctive gasket material which contains no but more recently other organic and inorganic fibers and asbestos and is changing the basic culture of gasketing combinations of fibers and fillers, again elastomerically matenais. Current emphasis on ohmination of asbestos bonced, have been introduced, pnmanly for insurabihty, gasketing, safety reliability, and the need to reauce.emis.

legal, reputatory, health, and environmental reasons. The sions lie a kagepar environmental, e nergy, and mate nal sav-premium compressed asbestos gasket matenals generally ing reasons has focusec the need for improvea nori asbestos have been applied where maximum scryice pressures co not gaskets Examplesotthessneeaswereaiscussedinarecent exceed 2000 psi (13.8M Pa) or temperature s 1000*F (540*C).

user survey conducteo y the Pressare Vessel Researen Service temperature and pressure are interoependent. Max.

Committee s (PVRC) Subcommitten Task Group on gasket smum allowable service pressure aecreases sa temperature testing. (1)* In this survey respondents from the Power in.

increases and. consecuently, as service pressure incre asos dustry iridicated valve bonnets were the most troublesome the maximum allowable temperature decreases.

joints and Petrocnemical/ Refining respondents listed them Compressed asbestos sheet has been the performance as second most tioublesome. Flexible graphite, sometimes standard for non-metallic gasketing materials used in valves referred to as " graphite toil,'"'expandea graphite" or "recom.

and flanges for industnal applications. it has been recogniz-pressed expanced graphite," has received increased ed that the compressed non-asbestos " replacements" havt, recognition as a cost effective packing and, more recently, been generally higher in pnce than their asbestos counter.

gasket matorial. This recognition is typified by the introduc.

parts, yet do not havte their breadth of performance capabihty.

tion of the materialwithin Amencan Society forTesting and This has been attnbuted to the use of higher levels of binder Matenals (ASTM), Amencan Petroleum Institute (API), as and reduced fiber reinforcement with attendant increased well as nuclear / fossil power and many other specifications particulate filler content. While most of the compositions are ano standaros. For example, flexible graphite is classified a s held as propnetaryit is well known that aramids are used as Type 6 matenal within ASTM Stancaro F104 "Stancara the fiber reinforcement in most commercial non-asbestos Classification System for Non metalkc Gasket Matenals" compressed prooucts. Glass fiber ais,,ns used, but to a lesser and is hstod as an approvea filler for spiral wouno gaskets in extent.

While flexible graphite is a relatively new gasket wmws.n m.,rmi o...,s.i.%,,,.nm.un..no os ino.w matenal. compared with asbestos-oased products it has 1

been apphed extenstvely, wonowice. not only as a tiller for TABLE 1 - TYPICAL PROPERTIES OF FLEX 18LE spiral wound gas Aets but as a flat gasket. more generally with GR APHITE SHEET a s uitable metalinsert reinforcement. Sweaen has one of,if not the most, advanced National Pokey on the ban of Puutuu

' csbestos products with total eniusion currently scheouled for January 1,1987. Based on extensive testing and ex.

MattRIAt.

P IT S sios ponence the Swooish Electncal Power Board has standar.

Densiiv-dized on spiral wound gaskets with flexible graphite filler to

'Mt' N 0'm's M

m) 120 it e) replace the ascestos based procuct. Metal inserted flexible graphite ga skets are rspidly replacing premium compress.

7n,,,,, con,,c,,,,,

ed asbestos in high performance services and their standar.

BTU *inittaboar rem.m>

Aiong Longin a W.oin 960 t140)

<4 t < osi dization is espected shortly. Revisions to the APl Refining Th'ougn Thicanent 36 (S)

N/A N/A Division valve standards are neanno completion These revi.

sions address the charge of specifying one non asbestos

,Naom,,,ne e, pac king and gas ketir'g materialin every standard where an Througn Thicknelt 4810-6 (2:10 N/A N/A csbestos product is listed. Drafts of these revisions show

.4cm is) a metal inserted flexible graphite as the hsted non asbestos bonnet gasket materialin gate valve standaras API 603 and

$*[,$'g sN API-604, where compressed asbestos was hated. A flexible soo 16) 6.000 (411 graphite filled spiral wound bonnel gasket is being introduc.

Leachabio ed to steel gate valve Standarcs API.000 and API 602.

Chlorice pom

< 100

< 200 MATERIAL CHARAC' ERISTICS (SpecsalGracel Graphite is one uf the most thermally stable and helium. Charactenstics oi the llexible graphite can be tallored enemically resistant matehals known to man. In a neutral.

for specific gasket apphcations simply by changing the star.

teducing, or vacuum environment, it does not melt but tingdensityof thesheet.increaseddensitydecreasesCom-subbmes, changing from sohd to gas at temperatures over 5400*F(3000*C), wellabove the melting point of metals. A pressibihty, permeabihty, and increases recovery, finsile strength, and abrasion resistance. Typical continuous su ess-common asbe stos fiber (chrysotile) begins to decompose at strain diagrams for flexible graphite show how compressibili-900*F (480*C) and the orgaruc elastomene binder in a typica!

ty is changed by precensifscatson. (3) Where a relath'ely large gasket material begms to decompose at a much lower temporature. In ihe presenee of oxygen, inciplent burning degree of Conformability is needed and sealing loads a (oxidation) of graphite can occur above 850*F (450*C). But either retatively low, or the high compression caused by higli the degres of oxidation and consequent usef ullife ls a com-load do not cause mechanical problems, then s lower den-plex phenomenon depending on many vanables such as the sity, l.c. 50 tbJft.8 (0.B MgIm8),is used.Whers high recovery, extent of exposure, gas velocity, and oxygen concentration, low compressibility, and minimum permeability is needed, to name a few. Therefore, the 850*F (450*C) temperature has such as in conf mea space wit h high tntemal gas press ure, a and should not be considered a maximum use temperature

gher density, i e., 90 Ibitt.8 (1.4Mg/m8) is preterred. The ultimate density of flexible graphite is 140 lbitt.8(2.2 Mg/m 8) in cir FurtfOmore,oxidationinhibitors ate available which which would occur at 50% compression of the 70lbitt.8(t 1 significantly reduce graphite oxidation rates. (2)

Mg/m8) matenal. The eage surfaces of the flexible oraphite Flexible graphite ts a cistinctive material with essential ch ractensticsof graptuteandcomptementarypropertiosot sheet are more permeable than the flat surfaces. Since this flexibihty.compactabthey,conformabihtyandresthence Flex.

eoge permeabikty is inversely telatec to sheet eensity, gasket ible graphite is manufactured employing a process that in-designs sometimes employ densification of edges near troduces no organte or inorganic binders, filters, or other bores to the ultimate censity to prevent any fluid penetration, The resilient behavior of flexible graphite is typified in potentially fugitive ingredients. The process has been Figure 1 which shows the continuous appheation and release pr:viously described. (3) Since the forming of flexible of load on a flexible graphite sample with attendant graphite involves only mechanicalinterlocking of worm like denstitcation.

c xpanded flakes, the resulting sheet product is essentially When load is released, the flexible graphite will recover purp graphite, typically wett over 95% elemental carbon by or sonng back to a thickness between the no-load and uncer.

weight, with a highly akgned structure. Typical proporties of the flexible graphite sheet are hsted in Table 1.

load thickness with proportional reduction in densrty from the Adensityof 70tbitt,8(t1 Mg/m3)isoftentypicalOf the under load condition. The behavior will be that described by processea matenal since it is the most usef ut ior 1he majori-the figure so long as the load is greater than the highest ty cf industrial gasket apphcations While this density is ap-previouslyapphed. Asthecensityof the flexiblegraphitein-proximately 50% of the theoretical density of graphne, the creases with increased load, a flattening of the stress strain througn thickness sheet permeaoshty to fluids, as measured behavior is effected, This charactenstic restoration or by the hehum admittance test. as extremelylow This anomaly resihence has been attributeo to the frnsshgnment of ttm results from comoresse ind consecuent seating of the sur-graphite bashi planes relative to the sheet plane (4). Since tacmayers of graonito by the oressurizing gas. in this case this spring hke benavior is inherent in the flexible graphic structure tt is stable so long as the structural integrity is mai, 2

FIGURE 1 - FLEXlBLE GRAPHITE COMPRESSite AND SPRING BACK FIGURE 2 - GASKET MATERIAL LOAD 8 EARING A81LITY

!WI,13 AL OCNsifY es Ls/Ft I (1.3 NG/N ag wea Pli a too.

waa Psl I 1003 110

- it <

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,g 03 P.4 310 427 0#

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rtMetRatVAt N ft tach cupyt af ppt $tytt twt man! Hun YtuotRAtung.

100 90 80 to s0 pat $ssnt pc!wt son THE Galktf mattRIAL sf4AIN s CF DAlalNAL THICKNts:

tamed. This stabi.,ty extends from temperatures as low as gasket material's rel ability under combined high fluid cryogenic to those well over the melting point of common f sr.

temperature and pressure conditions is compromised.11is tous and non-ferrous metals, in non oxidizing atmospheres.

apparent from this data that, unlike compressed asbestos (or stihence, thersiore, also is stable over this range. For this even more so, non asbestos), flexible graphite service

, vason, many " fire safe" valve designs are based on the use temperature and pressure are essentially independent. Flex-of flexible graphite gaskets leading to the general accep.

ible graphite, therefore, is a much more reliable gasket lance of flexible graphite as a " fire safe" matenal Numerous material under combined high temperature and pressure valve manufacturers have qualified their valves to various service conditions.

Fire Test Standards such as API 607, API 6FA, BS 5146, and The ASTM creep relaxation characteristics at temp.

Exxon BP1V4 4 through the use of " fire safe" flexible orature are partico arly noteworthy since they elso relate to graphite gaskets.

This temperat ure insensitivity was shown by one a uthor clampmg load stabihty and. consequently, to reliable soahng under comDinud high fluid temperatures and pressures. A who plotted gasket load bearing ability at temperatureets comparison with compressed asbestos and non asoostos shown in Figure 2. (5)The curves of maximum load bearing materials at two temperatures employing ASTM Stancard coihty at temperature are plotted for three typical gasket Method F 381s foundin Table 2.

materials and compared with that of unreinforced flexible graphite. Each curve is developea from the points wnere TABLE 2 ~ CREEP RELAXATION-GASKET temperature-pressure combinations produce an irreversible MATERIALS-ASTM F.38 METHOD 8 distortion /decompositionof thecashot.Thetiexiblegraphite

% metAxavioN was able to withstand the 145N ps:(100 MPa) apparatus rir r soo F pressure, without f ailuto.ovo tne entire temperature range oco c) race c) to the 850*F(450*C) maximum that was employed. A max.

Fieniois orsorvie

ft.8 Since flexible grophite is resistant to attack by virtually (1,1 Mg/m3) density, 0.015 inch (0.38 mm) thick flexible all common organic and inorganic fluids except concen.

graphite will lose 1% of its weight in 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. The at.

tr;ted, highly oxidi:mg mmeral acids, it is an extremely mosphere used is air flowing totally around the sample, The chemically resistant matenal For example,it is compatible use of this type of oxidation data should be rustncted to deter-with the entire pH range trom o to 14. Graphite ts beingused mirung the relative oxidation resistance between the vancus successfully as a matenalof construction for corrosion resis-types of flexible graphite. This is an academic worst case t:nt e nemical process equipment such as he at exchangers scenano which would not be expected in actual use, in a ano pumps and has been for many years. Sieam at all com-asketing application, between ftanges with a pipe es strymg mercial pressures and temperatures is compatible with fiex.

<a oxidizing atmosphere, the contact are a with tne gasket is ibb graphite and ts the ftuid historicatty most widely sealed very small. Also, the high thermalconductivity of the flexible with flexible graphite gaskets. In addition to being compati-graphite can reduce the bulk temperature of the gasket an

ble with the more commor chemicals, 'lexiole graphite is reouce the oxidation rate to an acceptable level, or elimina 4

I l

oxidation entirely. Likewise, the velocity of the oxicizing at-matenal. somsi additional cnteria saould be constoered mosonere also is important. High fluid velocities break up the when applying flexible graphite gasitets to these service s. it

'undary layer and increase the oxidation rate. Therefore.

a choice is possible. Spiral wound gaskets should be used, 0 B$0*F (450*C)1emperature should not be considered a since their design exposes the lower permeability flexible maximumbse tem' etature in air. Flexible grapnite gaskets graphite surf ace to trie bore. Care should be taken to assure p

1 have ethstood years of extenor edge plane air exposure proper bniting procedures as wetl as maximum flatness and successfully in reducmg fluid temperatures as high as parallelism between surfaces. (Proper bolting procedures 1500*F (815'C).

Ambient air oxidation of a flexible graphite gasket is have become so important that the Botting Technology r: lated to the motecutar wsght of the reducing media. Suc-Council has been organized to address botting problems.)

If spiral wound gaskets are not used, the thinnest gasket con-cessf ullong term expenence for spiral v.ound gaskets with sistantwiththeflatnessandparallelismof theserviceShould a conventional flexible graphite filler was reported in both be chosen to minimize through body lea kage. in either case.

stearn and hydrogen rich hyorocarbons at service temp-sealing stress well above the minimum load required to main-eratures of 1200'F (650*C). (7) These fluids are neutral or tain the sealshould be used.

reducing to flexible graphite, at this temperature. Protection The ASTM tests for chemicai resistance, such as F 146 by the metal windings. coupled with a protective ponneation

" Standard Test Method for Fluid Resistance of Gasket f rom fluids with molecutar weights lower than air. resulted in Materials." are primarily directed to determining the extent long lif e, even tnough fluid temperature wa s well above the of solvent attack on the gasket material's binder. The same oxidabon threshold for flexible graphite.

is true for the ASTM Ignition Loss Standard, F-495, which Recently introduced oxidation inhibited grades pnneipally was cesigned to measure thermal decomposrtion significantty teduc e oxidation rate s. (8)T he initiation temo-(volatilization)of thegasketmatenal'selastomencbinder.Ex-erature for these grades is approximately 975'F(525'C), a posure of flexible graphite to this test procedure produces 125'F (52*C) increase over the uninhibited materials. These weight loss througn oxidation. since the test ts conducted in grades snould be considered where oxidation could pose a air since this test does not measure the thermal stability of prot 8cm. Further improvements in oxication resistance of flexible graphite, but the oegree of oxidation, results could itxible graphites are expected.

lead to erroneously low service temperature limits.

From a safety and re!iability standpoint, the most pru.

Commonprocessfluidssuchassteam hydrocarbons, dent course when considering application of flexible gr aphite caustics, and gases can permeate the edges of the flexible naskets for service conditions where bulk temperatVres can graphite especiallyif the samples are unconstrained, such coed 650*F(450*C)in either an oxidizing media or with a as in the F 146 le sts. As mentioned previously, this physical Jucing media in ambient air is to consult the manufac-penetration is controlled by compression dens Ceation. Table turer's Technical Servics Organization for design and ap.

4 compares ASTM F 146 test results for flexible graphite wrth plication recommendations.

those of a premium compressed abestos.

Premiurn compressed asbestos is resistant to chemical attack by a wide range of fluid media. However, compress.

TABLE 4-ASTM F 145 FLUID RESISTAW ed asbestos is subject to chemical attack of both the filler and the r'.Jber binder. The binder phase can be attacked by MAximuMINCREAsE organic solvents of oils, and the proper choice of bind 0r for AFTEsisuuEMiioN Specific service is essential to reliable operation. The type Qi TEMPER-ATURE THMX-asbectos tiller also influtinces chemicai resistance. espacial-i u ATERI AL _

Fluio

'FPC)

WsS % WEloHT %

ly to inorganic fluids. For example. one ptemium compre ss-I Prerruum J

ed asbestos with a styrene butadiene syntt' etic rubber Comomsed FusiB bander.issubiecttoattackbynitrit chromic.andhydrofluonc ASD'558 7'Jgt,;*

m20 0

9 acid in addition to those solvents which attack the binder.

Agairt. Chemical resistance vanes widely depeno ng upon

,,,v,,,

p a, g Gro n o e.e a m2n 3

12 the rubber binder used and the Quality of the compressed

$' w'a' sheet ett. elf. Generally then, while a specific grade of com-3emium pressed asbestos sheet is available for a range of fluids. no Comoresseo smgie grade has chemical resistance to as wide a range of

^$0**'o*

No 3 0

330501

'O mooia as flexible graphite.

FleoDie Hydrogen gas and hydrogen beanng hydrocarbons G'*""

N' 3 0

300 1

• 5 represent a difficult gt.itketing problem, especially At high NcTE F~eisiMusammerien temperatures and prelisures, primarily because of hydrogen's low molecuiar weight. However hydrogen is a IRRADIATION RESISTANCE reducing gas, and it increases flexible graphite's upper temo-Flexible graphite is the most irradiation resistant non.

cc:ture range. Flexible graphite attoros supenor sealing metallic gasketing matenal.This characteristic coupled witn charactenstics at the interface Detween the gasket body ano t he tlange. However, because it doe s poss ess permeability the inherent low levels of potentially corrosion accelerating impunrics makes flexible graphite a supenor gasketing tally througn the bocy or eoge plane of the flat gasket material for nuc: ear service. This ts especially true of nuciear 5

Quality grades where adhesive and mechamcally bonded i

metal anserted laminates are Demg pove6oped which meet metat inserted lammates, but offer superior blow out a

. the most sinngent current chemistry requirements, even resistance m hign pressure applications. Other insert those of Gengral Electnc D50YP12. These improvements materials such as very thin, i e., 0.0005 in. (0.013 mr

' andthedeve6opmentofimprovedcorroseninhibitednucasar polyester are bemg proouced to enhance handleabil..,

flexible graphite bnng more safety and reliability to this wnere metal reinforcement is not practical. While this type of service.

insert material may oetenorate in service it does not adverse-Table 6 shows changes in select mechanical and func.

ly affect the functonal charactenstics of the gasket.

Cuttingof thelammatematenalintogasketscanbeac.

i tonal gasket properties of flexible graphile after being expos.

complished with cons entionat steel rule die cutting techn!-

i ed to tadiaton levels eaulvalent to the expected 30-40 year Ques using standard tool steels for att but the tang matenal, lifetime in a commercial power reactor. Note: no signif6 cant which usually requires compound dies. A relative index of i

change occurred afterirradiaten, which shows the stabiltty cuttmg ease is shown m Table 6 and compares flexible of theflexiblegraphite.

graphite laminsites with premium compressed asbestos.

TABLE 6-MECHAM6 CAL PROPERTIES OF RADIATED' FLEXIBLE ORAPHlTE AFTER 170 MEGA RADS EXPOSURE SEALASILITY -

Astu The ultimate purpose of a gasket is to seal, and vanous isst isst muuangs test procedures are bemg used to measure sealing effec-vitimate tensne comroi 73016 3)

Pos2 tiveness. While there is a large body of data on sealing strenginosituPat tiraciatea 830(s 7) stausucatty charactenstics of gasket materials, all these have limitatens

% chanoe

• i4 in sio"" *

• E6onganonni conitos is Fasr and generally are allindicators of results under specific, hmited conditions. When addressmg the "real world"

- N$.* o, Ye I,InItc n, scalabihtyof gasket matenals, allof the operatingparameters t

Cr w Cm AW for a specific service impose their influence, to some extenti j

Re:auuon % ti) irraaieseo 3

d

!&fatesucally on the overall performance of the gasket, These include, but

% channe "+ 20 inesonisirani are not hmited ia: the physical natute of the fluid, i.e., gas, li-comorn contros s2 F.3e guld, moleculai weight, aggressiveness of the fluid on the sio inty (%)

Irreo.aws si staustaity

% chanoe 1

insionit " "'

gasket matonal, flaid temperature and pressure, ambient A*covery(N Corurot 23 F36 temperature as well as interactons between these vanable Physical size of the gasket and Ppecifica of the joint dos.

itself also interplay with the above factors and influence the I3 o

effectiveness of the gasket to seal, Gasket matenals' handie.

O,'"a,*.7n'Emm'eNcoo'.*[ v',cNe","r U'[Es';",g' abikty and shelf life also can ultimately contribute to the con a.on.eenooaciorsouv,,

gasket's effoctiveness. in some cases, as can the installation GASKET CONSTRUCTION Effective sealabihty is mherent m the flexiole graphite its;lf by virtue of its low creep relaxation and stabildy unoer The sealabihty cata presented in i a section must be a wice range of compressive loao temperature concitions-coupled with the informaton presented earlier to make an of-tective assessment of how flexible graphite gaskets compare G:sket tabncation and design are basically simple. Since the with asbestos baseo traterials. As in the case for all tenstie strength of flexible grapnite is significantlylower than generalitations, the comparison presented may vary to a th:t of:he binder contaming como essed products, a center lesser or greater ocgros depending on the quahty of the insert metalis commonly employed to fortify the flexible graphite for most apphcations. Other constructions such as asbestos baseo proouct and the flexible graphite, achesive backed taps on metal gaskets or, alone, as well as Table 6 shows ASTM functional test aata for the metalin-fi:xible graph 9e filled enveloped gaskets have been sorted flexible graphite gasket laminates and compares results with those for premium compressed asbestos. Note employed for specific services. Either conventional sealability ot all the flexible graphite gasket lammatos tested mecnanical cimchmg (tangingl or chemicat achesive con-eing to flat metal or wire screen can be used to produce the unoer the low clamping loads,1000 psi (6.8 MPa), was superior to that of the premium comprosed asbestos, The Icminate or comoosite gasket matenal, Stamtess steels.

only exception to this conclusion was the laminate that con.

suen as AISI Grada 316, as well as alummum. carbon steel, tams a 24 mesn stamtess steel screen insert. While this and allovs required for specific valve service, suoh as relatively course mesn screen effectively enaancea blow out '

Monel*and inconel* have been used depencing upon the resistanceof thislaminate,itprocucesleakpathsant' arrow corrosion resistance needed While the tang or periorated width gaskets, particularly at low loads. This style screen m.

core has been used most extensively, more recent ettorts senectammatesnoutabeuseoonlyathightoaos particular.

hrve oeen oirected to chemical bonomg to effect maximum ly when the gasket has a narrow width, Note when the stalabihty and gasket cutting ease. Generally the tang ano wira screen versions require htoner compressive loaos to et.

sealabikty test is performed at a high clamping load this

'cet the same level of sealabihty as the unre nforcea or flat material snows resu tts similar to other laminates (See Tat A.

6 s;

. - -... ~ -.

TABLE 6 - FUNCTIONAL TESTS - FLEX 18LE GRAPHITE GASKET LAl.11N ATES

'l F.s 7 F.se/ sos (21 NoteledAL

$EALASILITT(11 ContPREssio6LITY F.S$(slCMaaP THICKNESS N,

Ful'L A A*fo MECoVEMY MELAXAfl0N MELATIVE (4)

(4ESCfbPflON iNCHf s tmme m4/hr et 54 CUTTINo EAsi Fien06e Greatete 144 10 4)

Il

<02 60 25

<6 V32 (08) 35

<05 40 20

<6 1

1/1s (16) 40

< 05 46 15

<s ile (3 PI B0

<06 46 15 6

Adheswely Boncea 1/32 (0 8) 16

<0$

46 16

<5 to Flat S S 1716 f16) 35

<06 35 P0

<6 d

Aaneswety Bonoed l

To Aivmmum it18 #1 61 i

80

<0$

40 P0 P

Mechensauy 1/32 (O SI 40

< 0.6 20 60

<6 10 BonoeoftenmtoSS-171 6 f t 6) 60

<05 30 30 e6 Acheswely Bonood V32 (08) 12000 71 40 15 6

To 8 3 tt16 0.6) 7000

$s 40 16

<6 Wire Sc'oen (6) ist f 3 2) 4000 40 40 15 e6 Adheewe 0 005(0.131 3 < 0.1 55 50 7

~

Beeeed Tope 0 016(0 39) 20 <01 46 25 7

Adhetwely lionoeg 1/32 (Q s) 35

<02 40 16 7

1 ToFWresset 1tto it el 66

<02 40 16 7

tremeum Com.

peesseo Asbeesos it16 #16) 9600 90 15 60 35 8

4 revyisym.

C:mprested Nonasbeseos 1/18 il 66 800 60 90 4%

30 N0t t Ailletta weie run por Astu F.to4 Procoowe owomes a m woie enense.ron Astu ras to Astu rme.noe meai ensenes taminaies mivaies ei m cre.o roie onicemoriormeeerity(ioo ci opone ooe.ea. ion invenom allr4 edoen a wide range of flange surface roughness also is apparent TABLE 7 - F.378 SEALABILITY OF WlRE SCREEN from these studies, LAMINATE WITH NITROGEN GAS AT VARIOUS One valvo manufacturer reports sionificantly lmproved CLAMPlNG FORCES-LEAK RATEIN ML/HR test results when a metalinserted flexible graph 6te bonnet gasket replaced a spiral wound asbestos filled gasket in a CLAMMNG FoMCE, poi (Mpe) gate valve. (11) The field indicative screening procedure

'Y

"'" O'"

CKNE&s 2.e00 3M0 4 000 6.000 leakage base line checks at room temperature and after a INCHEsimmi ns.si ne ri nysi ne s' four hour soak at 750*F(400*C), with no acjustments. While 1/32(0 el 12.000 6 2500 l 250 5

l leakage of the asDestos filled splial wound gasket normally ine n 6 7.000 SA00 460 25 meresses to 60 90 ml/ minute after heat soak, reroleakage was exponencea with the metal inserted flexible graphite IQ32 4 000 l 1600 600 85 l

gasket, This valve manu'acturer ahi observed that wioe vanations are expenenced in leak performance from gasket manufacturertomanufacturerduringtestsof asbestos-filled Comprehensivecomparisonsof thesealabilityof flexe.

spiral wound gaskets. However, consistent " leak-free" ble graphite lilled spiralwoun3 gaskets with that of one type results are oDtained when the filler is flexible graphite, of low bindei beater aodition asDestos have been mace regardless of the manufacturer, The use of thinner metal-previously as part of the PVRC sponsored exploratory test inserted flexible graphite gaskets to replace asbestos and program. (9) Spiral wound gaskets werr' tested at vanous elastomencally bound non asbestos fuled spiral wound thnge finishes, two levels of nitrogen pressure, and two gaskets may reouire design changes m some cases, but levels of gasket sealing stress. Results showed significant.

would afford b0th improved performance and reduceo cost, ly tower leak rates with the llexible graphitu filled gasket. Leak Removal of a flexible graphite gasket from service rates for the asbestos filled gasket were from 1000 to 10.000 sometimes tesuits in transfer of graphite particles to cne or times greater than those with the flerbie graphite. This and both surfaces t'ecause of flexible graphite's " micro sealing" other PVRC sponsored tests have shown flexiole graphite tith Qualities. Any aonereo pamcles are easily removed with gen.

cd spiral wouna gaskets have tower seating stress (Y) and tie brushing or scraping, After.servtce removal and flange inac to maintain a seal (M) than.ssoestos tilica gaskets. (10) reconoitioning for compressed asbestos requires much tible grapnite's ability to conform to and etfectively seat more aggressive mecnanical anc/or chemical methoos.

7

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ASME CODE MAINTENANCE (M) AND SEATING (Y)

REFERENCES l

FACTORS

1. J.R. Payne. "PVRC Flanged Joint User Survey" An entensive test program under the auspices of the Welding Research Council Bulletin 306. July 1985.

(

- PVRC is oo@ing relative to establishing updated seating

2. R.W. Wallouch and E.A. Heintz, " Oxidation 9, stre s s (Y)ano load required to maintain a seal (M)Ior a wide Graphite: Zone 11 Omission" Carbon, Volume 12,1974.

range of gasket matenals, including flexible graphite. An 1 P.S. Petrunich " Gasket Designs and Appications us-asse ssment which would enable a direct compenson bet.

ing Flexible Graphite" SAE 830214, International Congress ween flexible gmphite and compressed asbestos and non-and Exposition, Detroit, Michigan, February 28-Maren 4, aabestos. of a range of Qualities. es forthcoming. Histoncal.

1983.

ly, the values of M and Y for flexible graphite have been

4. M.B. Dowell and R. A. Howard, " Tensile and Com-significantly lower than those for compressed asbestos. The pressive Pruperties of Graphite Foils", CARBON, Volume 24, ASTM sealability and other test data correlate with these ear.

1986 ly finoinga. Until the new code values are approved, a prac-

5. E.M. Sauter, " Current and Future Gasket Materials -

tical, conservative approach to substitution of compressed Methods of Evaluating Some of Their Functional Properties",

asbe stos with metalinserted flexible graphite ol 70 lb/ft.8(1.1 Transenpt of Oral Presentation Maos at the Fluid Sealing Mg/m 8) den saty would be to use 75% of the loaos normally us.

Association Meeting, October 1981.

ed for compressed asbestos. These would be higher than re-

6. Union Carbide Corporat6on " Industrial Chemicals Quiredformostof thestyles,butwouldinsuregoodsentability Handled Dependably, Economically by GRAFOlL' Flexible for the more compressible flexible graphite even for low Graphite", Catalog Section G 8805, Revision 5, October molecular weight gases. Since sealability can be affected by 1985.

the type of insert and the consity of the flexible graphite, the

7. S.F. Thomas and G.R. McKillop, " Asbestos Substitu-manufacturer / supplier should be consulted to assure op-tion in Packing and Gaskets for Refining Service", APl 51st timum performance for a specific material ano service.

Midyear Refin'ng Meeting, Session on Environmental And Technological Piping Challenges. May 1986. San Diego,

SUMMARY

AND CONCLUSIONS Califomia.

Flexible graphite gaskets, pnmanty metai reinforced to

8. Union Carbide Corporation, " Protection From improve handleability and load beanng aoility have already Stainless Steel Corrosion and Oxidation". Product Bulletin been a proven suponor " replacement" for compressed Number G 201, April 1988.

asbestos under h69h temperatures / pressure service in a

9. J.R. Pe.yne, "The PVRC's Gasket Test Program il-A '

wide range of fluic.. As a consequence.they has been wide.

Status Report", API 45th Midyear Refining Meeting, Sess' ty accepted by standards settmg bodies such as the API.

on APITankUpdate May1980, Houston, Texas.

Flexible graphite is more tolerant to variations in flange sur.

10. A.Bazc gueandL.Marchand,"ATestProcedurefor r

face finish, requirea lower sealing stress and load to maintain Determining Room Temperature Properties of Gashets," Pro-a seal and is more compressible than asbestos based coeding of 1985 ASME Pressure Vossel Piping Conference, gasketing. Better quantifiestion of these advantages is for.

Volume 98 2, thcoming through improved test procedures developed for

11. Telephone discussion and latemal Report. G.A. Jolly, the PVRC Gasket Testing Program. Ease of removal from Henry Vogt Machine Company.

flanges arter service is supenor to that of the asbestos bas-eo procuct. Limitations remain exposure to oxidizing meo e ACKNOWLEDGEMENTS such as air, above the temperature / pressure limit of com.

The author wishes to thank the Specialties and Services presseo asbestos, and several strong oxidizing mineral Group of Union Carbide Corporation for permission to acios.Fabncationandhandlingof themetal-insertedgaskets publish this paper. He also would like to acknowledge Ron cre generally comparable with that of premium comptessed Howard, Development Associate, Parma Technical Center, csoestos. Unlike elastomenc asbestos, shelf life is essential-for his contnbuting data, ano Ms. Kathie Forbes for her ly infimte and standard storage requirements are less diligence with oroouction of the manusenpt, sinngent. Improvements in flexible graphite gasketing in-t ciude more corrosion and oxidation resistant compositions.

" nuclear" ouality gasket laminates whose enemistry meets the most exacting requirements of nuclear reactor manufac-turers and improved constructions. Contmued irr-provements are expected, which will further broaden the ap-plication range for flexible prachite gasketing. While initial purenase once of flexible graphite gasketing is oetreasing it remains an issue since it is generally higher than that of compressed asbestos or non asbestos. However, flexible

< graonite remains a better value gasket baseo on improved S;tely, reilability. reduced fluid ano energy losses, and reduc-co maintenance, 8

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