Paper No.

407

Alain !XatillonTankccn FRP Inc.

4250 Marcel I=casseBoisbriarxis, Quebec

.J~~ ~~~

ABSTRACT

pe ~eman~ for fluoropolymer 1ine?d highway ~a:go tanks ‘as

risen drmatic~.li~ = the ~n~ustr:~ p’ush.esfor c’nemlcals with

higher cm.centrations and higher purity. Recognizing thedifficulties associated with flUCrOpG~~Xi=~S and present daytechnology to manldfactU~e fluoropciymer lined highway ~arg~

tanks, we successfully develcped a f’usion weldir.g nacb.inetJ1.3weld

the fluoropolym.er ~qd tom,-~ined this with the prover. performance~eirlforced plasti~of fiberglass

~,n;(~~P} ‘highway CargC ta~lk. ..LLS

new fl’uoropolymer lined FRP cargo tar,k does away with numerous’

problems associated wit~h other constructlc.ns specifically lirier

inte~.rity, liner bonding, and secondary welding. This :LLsi3?.

we]ding ~~~~~nolOg”y a~lows the welding af coils of flluoropoiymer,

effectively reducing the n’umber of welds, and testing the l~rii~gintegrity prior to appli~~.ti~~~ of a~y structural material, such

Upon completion of the l~n~ng, IEP was applied to -theas FPbF.~laSS backing embedded into the thermoplastic, ensuring apermanerlt. arid corj~lete b~nd $~ trAe load ‘L:earin.gstructure of the

ba~~e~ . T~lis -f~~~ar:.,polyiner lined FRP

Copyright

01996 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole must be made in writing to NACEInternational, Conferences Division, P.O. Box 218340, Houston, Texas 77218-8340. The material presented and the views expressed in thispaper are solely those of the author(s) and are not necessarily endorsed by the Association. Printed in the U.S.A.

~~rre~ W=JS bolted down Onta a S%ee~ cradle with a ty-pical runninggear cf highway cargo tank. We have now effectively intr~d~~ed ~new generation of cargo tar.ks t’nat meets specific transpcrtaticmindustry needs.

This paper deals with

INTRODUCTION

fluoropoly-mer lined FiberglassReinforced Plastic (FRP) highway ~argo tank.

- ——The use of

fluoropolymer as an effective barrier of chemical resistancedates back to the early 70’s and the use of FRP as a structuralmaterial to construct highway cargo tanks dates back to the mid60’s.

In fact, since the early 60’s, FRP has been used toconstruct ~ig~way cargo tanks in c~ada, as can be seen cm Fig-ureI., WRP cargo t~k built in 1965, which toa recent picture of a,n ..this day cop.tinues to see service. ‘TO d2t.e, such tanks havealready covered nearly 25 millicns road miles and hiave proventlhat.they are as safe as cop.ver.ticn~~ metal highway cargo tar.’ks.As the transportation industry grows, the range and type ofchemicals transported increases dramatically and new containmentmaterials are in growing demand. ~:qer~J~p~as~iCS S’UClh as

fl’uoropolymers became a focal point, specifically given theirsignificant corrosion resistance characteristics and, this, inspite of the fact that it has been necessary to develop newexpertise to weld such materials.

Among the pioneers in this field. was Chapman Ind’ustrles Inc.who lir.ed the first metal highway cargo tank in 1972 ~~ith an FEPloose liner (see Figure 2) . But after two years, this conceptwas abandoned because of excessive iiowntiy,e. They attributed thispremature failure to “road abuse from flexing, vibration andsloshing” . Regardless, the demand for f~u~~~p~~~er lined cargo

tanks increased throughout the 7’0]s srnd metal cargo tanks linedwith fluoro~olyrners were used with varying degrees cf success.In 1994, -after decades of experience with Fi?P cargo tanks,Tankcon FRP Inc. identified a breakthrough opportur.i.ty usir.g theproven chemical resistance of fluoropclymers and successfullymanufactured the first FIX’ ~irled \yith fluoropoiyrner lhighway carga~ank in North America as shown in FiEure 3.+

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EVALUATION

The fluoropolymer selected was glass backed 0.060” ETF’ETef~el (1) . These linings normally are supplied in sheets of 4’x 8’ or coils of 4’ x 100’. Consequently, joining of the sheetsor coils was required.

Given two variables i.e. the type as well as the thicknessof the material selected, two potentiai welding methods wereinvestigated: hot air welding and fusion welding. The firstmethod, hot air welding, is usually used in the industry,typically using hand held heat guns and a variety of tips. Thesecond method is a specially designed machine to melt thethermoplastic, it has been used on a limited basis as the entrycost is much higher tharn hot air welding.

When using hot air welding, an operator melts rods and capstrips of thermoplastic onto both sides of the sheet in order tojoin them. To achieve a consistent quality, free from defect,the labour force has to be higkil~ skilled, land even then,consistency is directly proportional to be the operators skill.We came to the conclusion after much research, that the fusicnwelding teckmique is far more reliable and consistent because amachine is used to melt and join sheets, effectively eliminatingmany human and processing variables.

The concept of FRP to construct a highway cargo tanks hasalready been proven over the past 30 years. In fact, FiberglassReinforced Plastic {FRP) cargo tariks have been recognized by theUnited States Department of Transport as an acceptableconstruction material for the 300 Series and the new 400 seriesspecifications for cargo tanks. This recognition came via.exemptiorls and special permits issued since 1973 f~r the 200Serie s and more recently in 19S4 for the 40CI Seriesspecifications.

The techr.ologies to weld fluoroPo~ymer ar.d to build an FRPcargo tank both existed individually, but the compatibility ofboth materials when combined together needed to be investigated.

(i) Ilupont Polymers

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EXPERIMENT

We had to experimentally determine the dynamic effects ofroad shock transmitted to the inside barrel of the cargo tank.We bonded strain gauges inside and outside an existing FRP cargotarnk at predictable high strain areas. A total of nine straingauges of 45–0–90 and two accelerometers transmitted the

information into a ccilector as the loaded cargo tank was pulleddown the highway. Figure 4 shows a typical strain location. we

purposely put the cargo tank through a dramatic torture test onone of the worst roads available. Dynamic strain andacceleration were measured. The experimental data was used to setparameters fop laboratory testing.

FLUOROPOLYMER LINER.

Recognizing that liner integrity was of critical importanceand that weld areas typically are pctential problem areas, weconcentrated on the welding methodology. The hot air weldingmethod requires filling the bevel at the joint of each sheet fromboth sides with weld rod and cap strip. This type of weldcreated concern with its potential integrity when subjected tohigh strains during normal road transportation. Accordingly, wetested such welds to determine their physical properties. ??ecould achieve 90% to 95X tensile stren~th but always ended upwith limited strain capability. This limited strain was due tothe multiple layer of filler r-od and cap strips req~ired to joinboth sheets together, creating stress concentrations at the weldarea (see Figure 5). Considering the abuse the liner wassubjected to, and the dynamic strain previously measured, we hadnc alternative biut to leek for a better welding method. Fusionwelding was seen to offer the best solution.

The main benefit to this method was the possibility of ahigh degree of control over all relevant variables in the processof joining of the fluoropolymer sheets. A specially designedmachine permitted us to align both sheets perfectly, melt thethermoplastic at a specific temperature, apply a specificpress’ure, and cool down at a controlled rate. Our testing showedthat we were achieving a high degree of reliability and physicalproperties when compared to hot air welding-. The ultimate straincapaci t,y of fusion welded samples was nuch his’her than that

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measured for hot air welded samples, In fact, it nearly double.This was made possible by tighter controi over the variables and~l~~o by virtue of the fact that this rnet’noddid not inherentlyCreete stress concentrations (see Figure 6).

We also discovered that the tear area was of significantimportance. Indeed, the samples welded with hot air broke nearthe weld area as opposed to the fusion welded samples, whichbroke outside the welded area (see Figure 7). Further

investigation confirmed the maximum elongation of thefluoropolymerj which was fusion welded, exceeded the maximumelongation of the glass backing embedded into the material. Asseen in Figure 8, when the glass fabric embedded into thethermoplastic is strained, the glass rips away in a 100P style

fashion creating holes in the thermoplastic and forming shearareas. When testing the fluoropolymer withcut backing, itstarted necking outside the welded area but did not break (seeFigure 9). This confirmed that the glass backing embedded intothe thermoplastic was causing the material to tear at high levelsof strain. Our new welding method was now proven to be highlyefficient. We only had one more problem to solve: no suitablefusion machine was available; this forced us to design and buildone.

Recognizing that the welding of the thermoplastic is apotentially high problem area, the fusion machine wasspecifically designed to minimize the number of linear feet. of

welds for a given cargo tank.

To meet this objective., we purchased coils cut <O the

cylinder length of the barrel; this meant the- fusion machine hadto be capable of accepting coils of thermoplastic of UP tC ~’ x

44’. This permitted us to reduce the nurxber of linear feet ofwelds by nearly 50% when covering the same surface of a steellined cargo tank, which riormally wc*uId have been welded by hotair weldir.g g’uns.

MAWFACTURI??G

Production started by fusion welding 5 ceils Of

thermoplastic material of 4’ wide x 33’lGng; forming a Si?X21esheet of 20’ x 38’ . Each weld was tested with a spark testerprior to removal from the fusion machine and a layer of carbonveil was embedded OP. the “+ bcr.ding and futurefabric side to pe~~l.

spark testing. The 760 sq.ft. tb.ermoplastic sheet was cut to the

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circumference of t~4e barrel and fus ior. welded, JV.-.GA.

the cylindrical pcrtion of the barrel.h:-h CGW7 fom~d

The fluoropolymer cylinder was temporarily ~uPParted, ~hi~eall inlets,’outl ets were flared outwards and mating nozzles werehot air welded inside and outside with proper cap strips. Ther,old was then inserted into the cylinder, opened and transferredto the FRP area (see Fig*ure 10). An FIiP secondary corrosionbarrier was laid onto the glass backing of the fluoropclymercylinder as weli as on inlets/outlets. Trapped air within thelaminate was removed prior to gelling. Afterwards, alterr.stinglayers of mat and woven roving were laid down on the~luoropol:mer cylinder, and on all inlets and outlets to therequired structural thickness. Between each combination oflayers, air was removed prior to set. Once the inner FRP barrelwas completed, we applied balsa wood and then more FRP wasapplied over the balsa to complete the cylinder portion. Themold was collapsed and removed.

To complete the barrel, both heads had to be installed. Theheads were hot air welded from bath sides Gf the thernop~as~,i~and spark tested prior to any FRP lay-up. FRP laminate was laidonto the heads, completing the WE’ barrel. Again trapped air wasremoved prier to gelling.

ASSEMBLY

The ETFE/FRP barrel was set in the sub–frame within abearing pad of rubber sponge and torqued down with stainlesssteel straps, as seen in Figure 11. We found the rubber spongeto be essential in compensating for the different properties ofFRP and the steel subframe. The subframe was welded onto asuspension frame. The suspensions, axles, jack legs, upper plateand various components were attached to complete the cargo tank.Several attachments were also specified such as an integralcatwalk. This cargo tank was built in accordance with the US DOT412 specifications, as previously seen in Fig’ure 3.

CONCLUSION

Fusion welding, manufacturing process, and assembly methodof this new generation cargo tank gave us the opportunity toaddress areas of concern with present day technologies.

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The fusion welding technology developed permitted ‘us ta useceils instead of sheets reducing the nur,ber of welds; thereliability when using a fusion welding machine produced 100%weld strength at every weld. It also offered very high strain

capability when compared to hot air welding technology.

The manufacturing process permitted us to build the linerwith. b.igh integrity, since this is the first part of the cargo

tank to be constructed. If a defect is noticed, it can berectified without any negative impact on the load bearingstructure, as in this case, the FRF is not yet applied. Once the

fluoropolymer liner is perfect, the FRP is laid down over theglass fabric backing. Again, using this load bearing materialensures 100% bond to the liner as the FI?P can be worked to

contour any shape prior to gelling.

After careful review of the results frcm the road test, t’heconstruction of the barrel wa= modified tO addres= the damagingresults of hi~h strain areas due to dyna~.ic conditions by molding

radii at all inlet/outlet – cylinder interface prior ~0 ~Rp. ‘The

concept of using balsa wood over the entire surface of the barrelto increase stiffness as opposed to using stiffening rings,

eliminates stress concentrations. Further more, it leads to

uniform stress distribution t-nroughout the length. of barrel.TP~is design inherently Creates a secondary containment because

the balsa wood core is sandwiched between two Iar.inates Gf FRP;this is a significant feature in the event of accidents such asroll over or collision.

The use of rubber sponge between the barrel and the subframeduring assembly compensates for the difference in thermalexpansion between F13P and steel. It aiso ensures that all

dynamic forces are transmitted to the barrel uniformly, thereb:~

effectively reducing high strain areas.

If properly used, there is no doubt, that this newgeneration of cargo tank will be recognized for it’s efficiency’and reliability for years to come.

REFERENCES

F M Chapman, ~A~E Managing corrosion with p~=st~c, ‘?O~ 17,. .P120 to 127, 1983.

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Figure 1 FRP highway cargo ~L~nk — built in 1965 — still inservice

Figure 2 First FEP liner ever installed in a cargo tank

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Figure 3 First FRp,/~TFE lined high;vay cargo tank – 6800 Imperial

gallons

Figure 4 Strain gauge bonded inside the cargo tank

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Figure 7 Samples after tensile test – hot air welding (bcttom)- fusion welding (top)

Figure 8 Reference samples of ETFE prior to tensile failure

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Figure 11 Sub–frsme and rubber sponge

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