Welding of Dissimilar Welds of ThickWall HP Urea Vessels

This article discusses the use of dissimilar welding (austenitic stainless steel) to closevessels, which were essential components in a new urea unit. The processing

difficulties encountered in executing these welds, description of how these problemswere solved and precautions that must be taken to guarantee successful dissimilar

welds of great thickness are discussed.

Pan OrphanidesOrphanides Consultants, Athens, Greece

Etienne SoutifBSL Industries, Soissons, France

INTRODUCTION

In June 1990, UHDE awarded BSL INDUSTRIES a contractfor three vessels - one STRIPPER, one CONDENSER andone SCRUBBER - essential components in a neu urea unitfor SASKFERCO.

The very short turnaround time demanded that BSLINDUSTRIES review the assembly process that had beenused up until then for this type of equipment, themajor original feature being the use of dissimilarwelding (austenitic stainless steel) to close thevessels.

The purpose of this document is to relate the proces-sing difficulties encountered in executing thesewelds, to describe how these problems were solved, andto conclude with the precautions that have to be takenin order to guarantee successful dissimilar welds ofgreat thickness.

Ï. DESOUPTIQN OF EQUIPANT

Purpose in Urea production cycle

In Figure 1 a typical flow sheet of a Stamicarbon UreaC02 stripping process is shown.

The synthesis of urea is taking place at a pressure ofabout 140 bar and a temperature of 185°C in a emptycylindrical reactor, where urea and carbamate solutionis produced. The solution is flowing out from thereactor by means of a central downcomer pipe and iscountercurrently stripped from unreacted excessammonia and from decomposed carbamate in the CO2Stripper (decomposition heat supplied by mediumpressure steam and decomposition completed at about90% in the upper part of the Stripper tubes).

As stripping agent.compressed C02 gas is used. TheStripping agent, the stripped-off ammonia in excess,the water vapours and the carbamate decompositionproducts (C02 and ammonia) are flowing in theCarfaamate Condenser, where make up liquid ammoniapumped from battery limit, mixed in an ejector withcondensed reactor overhead vapours and recycledcarbamate solution, enters too.

C02.ammonia and water vapours are partly condensed tocarbamate solution in the Carbamate Condenser.The heatof the exothermic carbamate formation reaction is usedto produce low pressure steam at about 5 bar pressure,which is mainly utilized downstream to concentrate theurea solution.Carbamate solution and non condensedAmmonia and C02 are flowing by gravity to the lowerpart of reactor, where the rest of the carbamateformation is completed and urea solution is produced,according to the following chemical reactions:

NH3 + C02

NH2COONH4

NH2COONH4 (Ammonium Carbamate)

H20 + NH2-CO-NH2 (Urea)

Carbamate and urea solutions are highly corrosive.To keep corrosion rates under economically acceptablelimits 316L quality steel at minimum has to be used inparts comming in contact with hot urea carbamate solu-tion. Due to high erosive-corrosive conditions in thestripper tubes they are made from further morecontinuous passivation of all stainless steel parts isrequi red.

For passivation atmospheric air is usually applied,mixed with the C02 at the suction of the C02 compres-sor.The nitrogen and the non consumed oxygen, as wellas other non condensable gases (CH4 and H2) containedusually in the incoming ammonia and C02 have to bepurged constantly from the synthesis loop. This isdone from the top of the reactor.

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Anroonia, 002 and Mater vapours which are unavoidablypurged with, are recovered in a special HP Scrubberand all non condensable are safely separated anddischarged of.

Service and Design Conditions

Both vessels - stripper and condenser - generally looklike large heat exchangers.Their main dimensionalcharacteristics are given in figures 2 and 3,where twoparts can be discerned.

- A high pressure part (HP) consisting of thetubes and the two end charnels, each consistingof one shell with a hemispherical head carryinga massive flange (PAD). These components aremade of forged SA 765 Gr11. The device iscladded entirely with stainless steel (byrefilling and lining), to stand up to the verycorrosive fluids and gases that pass through itduring the process. The presence of these inter-nal parts in stainless steel, as we will seelater, has a considerable influence on theapparatus assembly procedure, and especiallytheheat treatment sequences.

- A low pressure part (LP), or calender, consis-ting of a assembly procedure, and especially theheat treatment sequences.

- A low pressure part (LP), or calander, consis-consisting of a shell (in SA 516Gr70) and anexpansion bellows (in TP 316). This paper willmainly describe the joint weld between thechannel shell and the tube sheet. It is thisweld that constitutes the limit of applicabilityof ASME VIII div.2, whereas the low pressureportion falls under ASME VIII div.1 .

The various design and service conditions areshown in figures 2 and 3.

ADVANTAGES AND DISADVANTAGES

Advantages Disadvantages

Effective annealingof channel/tube sheetwelds (the areasubjected to themaximum stress).

. The heat treatmentsensitizes those partsthat are refilled withstainless

. Major heat treatmentsystems necessary.

Major heat treatment

Tube holes need cleaningafter heat treatment.

Difficulties welding tubeto tube-sheet and machi-ning the ends (especiallyfor the outer tubes).

Lengthy dead times in thefabrication schedule.

New assembly procedure with dissimilar seal welds

To remedy the above disadvantages, a new procedure wasestablished (see figure 5) using dissimilar welds forthe channel/tube sheet joints. This made it possible,among other things,to:

- Suppress the PWHT of these welds and avoid sensi-tizing the stainless steel parts.

- Improve the tube welding and machining proceduralconditions considerably.

. Reduce the dead time in the shop to a great extent,by the possibility of working simultaneously onthree subassemblies : the calender, the upperchannel and the lower channel.

2. ASSEMBLY METHOD

BSL INDUSTRIES Experienceprocess

the previous assembly3. DISSIMILAR SEAL UELD METHOD

As was emphasized in the introduction, BSL INDUSTRIEShas lengthy experience in the manufacture of Ureaapparatus, but again,the very short time before deli-very demanded that BSL Industries consider a review ofassembly methods that had been used until that time.

The figure 4 briefly describes the manufacturingprocess used previously.

Note concerning PUHT :

The global heat treatment is also applied to theparts filled with stainless steel. The temperaturewas voluntarily limited to 510°C (950°F) which, byapplying the ASME code (section UCS 56) for a 180 mm(7") thickness, corresponded to a hold time of35 hours. It should be noted that, due to modifica-tion of section UCS 56 (addenda 88), the hold timebecomes 64 hours for 180 rim (7").

Figure 6 defines the geometry characteristics of thedissimilar welds and of their immediate environment onthe device.

The welding preparation is initially an asymmetrical(1/3, 2/3) »X» which, after filling of the faces, isre-machined to an asymmetrical dual "U".

Buttering method

It was the FCAW process (Flux Cored Arc Welding) thatwas retained with a 1.2 mm type E 309L T-1 electrode.

Buttering is carried out in two layers (+ 3 additionallayers in line with the weld root face), which corres-ponds to an 8 mm thick deposit, reduced to a minimum6 mm after remachining of the final welding prepara-tion.

The weld parameters are detailed in figure 7.

Post-weld heat treatment

After buttering, each of the two tube sheet/channelshell assemblies was subjected to an annealing heattreatment at 540°C : four hours for the tube sheet andeighteen hours for the channel shell.

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Joint execution 4. EXECUTION OF PRÖDUCTIQU KLOS Ät® TESTS

The two annealed parts Mere then assembled and »eldedby conventional SAW (Submerged Arc Welding) process(3.2 am and 4.0 mm dia. type ER 316 electrode).

Total filling Mas begun on the outside (2/3) and thencompleted in withdrawal mode on the inside of theapparatus.

Welding process qualification

The integrity of the welding method was verified onthree different specimens:

. A qualification procedure in accordance with ASIEsect.IX 40 mm thickness- (see Fig. 8 and 8a).

The Melding and heat treatment conditions (four hoursfor one side, eighteen hours for the other) werestrictly identical to those planned for manufacture,and described previously.

Tests :

- NOT, PT, X-ray- Destructive : 4 side bends

2 prismatic tensions2 sets of 3 KCV in 2AT.

All of the tests conducted were successful and noparticular observations Mere made (in particular, noobservations for the bending tests).

. a qualification In accordance with UFA 89.010(see Fig. 8 and 8b)„

At the same time as the UHDE contract, BSL INDUSTRIEShad a Urea stripper of very similar design to build,following CODAP and French legal requirements, forGRANDE PAROISSE. Another 140 mn qualification was madefor this.

Tests :

- NOT, PT, X-ray- Destructive : 4 side bend tests

4 prismatic tensions1 lengthwise tensile test in thedeposited metal

4 sets of 3 KCV in HÄZ2 sets of 3 KCV in deposited metalHardness f i l i at i on(maximum HAZ HV = 229).

All of the tests were carried out in the presence ofan outside organization and were satisfactory,prompting no objections.

. A speefaen for ultrasonic test calibration.(see Fig. 9 and 9a)

In addition to the radiographie test required by theASME, it had been decided to perform a 100 % ultra-sonic test of the dissimilar welds, before and afterthe hydraulic test.

Having had experience in this type of test, which is adelicate one because of the metallurgical structuresencountered, ESSEN TUV established a procedure thatdefines the calibration block needed to check thesensitivity of the method.

A specimen Mas thus made, which was an exact replicaof the 196 mm thick Melded joint.

Tests :

- X-ray (linear accelerator)- Ultrasonic

Neither examination revealed any unacceptable defectswith regards to the acceptance criteria established bythe code.

Buttering of Joint edges and tests of the buttering

The buttering of the joint edges Has carried out flaton a turntable with fixed torch. Welding posed noparticular problems and the final appearance of thedeposits uas very satisfactory.

After buttering, an ultrasonic test Has conducted onthe "rau Held". The subassemblies Mere then subjectedto their heat treatment and remachined to the finalMelding edge profile.

At this stage, a new ultrasonic examination Mascarried out.

None of the ultrasonic tests carried out in the jointbuttering stage revealed any defects.

Execution of closing neIds and radiography tests

The austenitic Melds Here carried out according toSAW process, with 3.2 and 4.0 mm Mires, and gave nomajor cause for concern.

The radiography of the first circular Held (Condenser,UC) Has executed using a source of Co60-15Q Ci in apanoramic shot - dual film technique, Kodak H films -and it showed many aligned indications present.

Since the radiographie test, by its principle ofprojection on a plane, cannot determine the depth ofthe defects in the material, and since there Has noreason to doubt the quality of the buttering at thisstage in the manufacturing process, these indicationscould be interpreted as slag inclusions (tunnels)trapped during the SAW welding (see figure 10).

The first grindings and the ultrasonic tests Here toreveal something quite different.

Search for a defect by grinding. Ultrasonic tests

After the report of a "typical indication" on theapparatus that Has thought to be very close to thesurface, a gouging Mas undertaken while attempting todig doun only through the melted austenitic metal.

It was not possible to identify the defect clearlynith this investigation. However, after a few tests bydye pénétrant and grinding, a linear indication remai-ned, seeming to originate from the carbon steel.

At the same time, the ultrasonic test of the stripperUC/TS joint Has carried out and the result Mas highlyinstructive (see fig.11).

- More than 70 % of the developed length of theweld exhibited indications.

- The defects were of the "planar" type, cracks.

- Most of the defects were located at depths of100 to 150 ran (from the outside of the device)"in the buttering area" (first or second pass),though the ultrasonic test Mas not fine enoughto alloy any greater accuracy.

Decision - repair procedure

Subsequent to these various observations, a solutionyas looked for to return the apparatus to conformityMithin client's delivery schedule.

a) Considering the number and location of the defects,the fact that carbon steel had to be rewelded (withthe need for heat treatment, or a special procedurefor example "half bead technique"), it seemed thatthere Mas no May to undertake local repairs. So itMas decided to reopen the Melds.

292

b) The various investigations needed to determine theorigin of the defects, added to the time needed todevelop other alternatives based on the welding ofdissimilar alloys, and considering the timeconstraint, we were led to reconsider the closingof the apparatus by similar welding followed by alocal annealing heat treatment.

It should also be pointed out that, if another dissi-milar weld were attempted, the filling of the tubesheet joint edges, once the tube bundle was assembled,would be carried out in a horizontal position, whichis all the more delicate to weld.

5. SIMILAR ALLOYS UELDS - LOCAL HEAT TREATIENT

Recutting and welding

The reçutting of the totally finished welds wascarried out by two methods :

- Cutting by water jet under pressure, which made itpossible to take a sample for later examination.

- Machining.

These operations required two weeks.

Once the cuts were made, each joint edge of the twoelements - channel and tube sheet - were remachined tototally eliminate any stainless steel and HAZ.

During the machining, we were astonished to discoverthat certain fragments of the buttering could beremoved manually and effortlessly (see figure 12).

Each fragment removed this way corresponded to one ofthe buttering passes and gave the distinct impressionthat the metal had melted with no adherence to itssubstrate.

After machining, the following tests were applied toeach joint edge :

- Copper sulfate test (to check that no stainlesssteel was present).

- Hardness measurements on the four axes (to checkthat the HAZ had been totally eliminated).

- Baumam test (to check that the defects did notresult from the presence of sulfurous segrega-tions.

- Metallographie replica.

- Magnetic particule test

- Dye penetrant test

Each channel was then reassembled with its tube sheetby a batten (see Fig. 13) to ensure that the dimen-sions of the apparatus would be the same after themachining of the joint edges. The welding was done bySAW process, which was also used for the filling fromthe completed exterior, with the battens ground offand the welding completed from the inside.

NOT Checks :

Same as for those applied previously, i.e. Cobalt 60,radiograph and ultrasonic test. A few indications werepicked up (slag inclusions), but these fell within theacceptance criteria limits of the code.

The welding this time was then found to be verysatisfactory as concerns the 850 kg of melted metaland the 200 welding passes executed for each of thefour welds.

Local heat treatment

The time needed for the reçutting and reassemblyoperations made it possible to optimize the heattreatment conditions.

The main data to be considered for the local heattreatment, using electrical resistors applied directlyto the equipment, was the following :

- Heat treatment temperature 510°C + 10°C/-0°C, toavoid sensitizing the corrosi on-resistant parts instainless steel.

- Hold time. The requested application of addenda 90of ASME Div.2 makes it possible to reduce the holdtime from 64 to 12 hours (for a 200 mm thickness).

- Heated area. 400 mm to either side of the weld.

Considering :

- That this heat treatment was to be carried out ona weld located in line with a large discontinuity(the joint between the channel and the tubesheet).

- The very different masses of the pieces to eitherside of the joint, leading to an inevitablethermal gradient between the two pieces that candevelop unacceptable stresses.

- The maximum temperatures to be sustained on thefront and rear faces of the sheets to satisfy theprocess conditions (corrosion resistance of theweld overlay and tubes s risks of sensitizing ofthe high alloy parts during PWHT).

a/ Several flnite-eleaent simulations were run, withthe computer generating temperature and theassociated stress mappings, to define :

- The positions of the resistors and the heatingpower to be developed.

- The temperature rise and fall rates

and to check that :

- Acceptable stress levels were achieved in linewith this discontinuity.

- The maximum allowable temperatures were compliedwith for the parts subject to corrosion.

b/ Corrosion tests have been carried out on testpieces where weld metal deposit and high alloytubes have been sensitized by heating up to 510°C(12 hours holding time).

During the PWHT.thirty thermocouples were used todefine the parameters initially developed by calcula-tions.

Figure 14 defines the positions of the resistorsheating power values and thermocouples.Figures 15 to 18 show temperatures repartition andstresses distribution obtained at the beginning of theholding time and at the end of it,for a rise and fallof 15°C/h.

It should be pointed out that,for a rise and fall rateof 35°C/h the developped stresses would have been toohigh.

After the local heat treatments, the finishing andhydraulic tests were executed and the apparatus wasshipped at the end of September 1991.

The study and re-execution of the main welds for bothsystems had taken two additional months of work.

293

6. ORIGIN OF THE DEFECTS

Subsequent to the ultrasonic examination, it wasestablished that the defects were in the butteringwelding. Several hypotheses were then generated :

. Defects caused directly by the cored-wire butteringweld process (lack of fusion, inclusions).

. Cold-cracking problems in the execution of the firstfiller weld pass subsequent to poor preheatingconditions.

These first two possibilities were nonethelesshighly unlikely since, as ue have seen above, theintermediate ultrasonic testing on the filler weldhad revealed no defects. So the only logical conclu-sion we could reach was ;

. Cracking subsequent to a very high stress stategenerated by welding in some zones possessing a veryfragile metallurgical structure.

The following tests were carried out on a fragment ofweld metal cut by high-pressure water jet.

Metallurgical examinations - Structures present

Many cracks were observed in a macrographic examina-tion of a cross-section of the weld metal.

These cracks were localized in the area joining theHAZ carbon steel substrate metal with the firstfilling pass (Fig. 19), and in the filler weld(Fig.20.1). They stop on the ER 316 passes (Fig.20.2).

Under micrographie examination, the structures are thefollowing :

. substrate metal : ferrite-perlite

. substrate metal-HAZ : bainite, decarburizationalong the melting line (ferritic structure).

. melting line : martensitic line, presence ofaustemte.

. melted metalfiller weld (E 309 LT-1) : austenitic matrixwith martensitic areas, absence of deltaferrite

filling weld (ER 316) : austenite and deltaferrite.

Cause of defects

Once the metallurgical structures are known, thedefects can be explained, or rather the phenomenaoriginating them can be described.

It was observed that the deposited metal was totallyin austenitic phase in the vicinity of the meltingline, which raises the possibility of high-temperaturecracking. These defects were created immediatelyduring the first filler weld pass, and so should havebeen detected in the filler weld ultrasonic test.

The fact that they were not can be explained by thefact that the ultrasonic test is never very reliablefor shallow depths because ot the "Fresnel zone" exis-ting in the vicinity of the ultrasonic transceivers.

Moreover, the orientation of the cracks, most of whichlie perpendicular to the melting line,is the leastfavorable configuration for detection when using astraight transceiver and longitudinal waves (seefig. 23).

Finally, the presence of broad martensitic areas inthe two filler metal passes validates the hypothesispreviously advanced of a "cold type cracking" due to afragile structure subjected to a very high stresslevel (shrinkage from the 150 welding passes on atotally clamped assembly).

Observing the orientation and number of cracks, itseems that the two phenomena took place successively.

The major reason for these two problems stems from toogreat a dilution of the substrate steel, which had thedirect consequence of very greatly enriching the firstfiller passes in carbon, and creating the structuresdescribed above.

It should also be noted that the filler weld heattreatment, though it did not directly cause thesituation, did nothing toimprove it either, but ratheramplified the carbon migration phenomenon.

Ue will now explain why all this happened in themanufacturing process while all of the prior testingand qualification had been satisfactory, and we willemphasize what the essential points are that need tobe verified when applying dissimilar welding.

Chemical Analysis

A series of microanalyses was carried out, to confirmthe metallurgical structures observed above. The 55measurements of nine different areas (shown in figure21) were averaged over each of the areas and thenplotted on a Schaeffler diagram (see figure 22).

It was then observed that the structure of the E 309LT-1 metal deposited is totally austenitic in thevicinity of the melting lines, and that the proportionof martensite increases through the two layers offiller weld (points 4, 5, 6) before returning to the"ideal" austemte + ferrite structure as soon as thefirst ER 316 L layer is reached (point 7, 8, 9).

Hardness Measurements

If hardness measurements are taken (HV 5 kg) on a linerunning transverse to the melting line, the same asthe chemical analysis measurements, we have clearconfirmation of the structures with very high valuesin a martensitic area (E 309LT1 filler weld).

- Substrate metal : 192- HAZ : 210.244.257.321- Filler metal E 309L T-1 : 386.386.401.412.386.407- Weld metal ER 316 s 271.257.232.257.257

7. RECOMMENDATIONS FOR THE PERFORMANCE OF DISSIMILARALLOY WELDING

Esential Parameters

On the basis of the above observations, an investiga-tion was undertaken to define :

- the reasons why the substrate metal was so greatlydiluted

- the conditions under which dissimilar welds couldbe executed with optimum quality level.

A series of tests were undertaken with differentcombinations of welding processes (SAU, SHAW, FCAW)and weld metals.

After these tests, for all of the welding processesused, it was clearly evident that one of the mostimportant parameters is the amount of overlap from onepass to the other in the first filler weld layer,(see Fig.24)

294

That is, it is observed that a very small variation ofthe order of 0.5 mm can lead to very different dilu-tion levels.so that for a given adjustment, the dis-tances at which the electrode wire is positioned, dueto the curvature of the free end of the wire (stick-out), are large enough to be the cause of unaccepta-ble results (Fig. 25).

This observation therefore leads us to :

Tests

Considering the problems that might arise withdissimilar welds, the highest level of precautions andan elaborate plan of rather sophisticated tests shouldbe adopted.

For this purpose, ultrasonic examination is anindispensable completary test. These examinations areto be applied at two points in the process :

- recommend an automatic process that ensures aconstant position, which is difficult to do with amanual process (SMAU).

- make sure the wire stick-out is straight, bystraightening it beforehand to eliminate thecurvature remaining as it comes off the reel.

- determine very precisely for the selected weldingconfiguration (process, wire diameter, stick-out,and so on) how much tolerance can be allowed thedimension "d", knowing that a reduction (andtherefore a great overlap on the previous pass)will reduce the dilution level but that too largean overlap can lead to welding defects. (SeeFig. 26).

Considering this essential point, a certain number of"secondary parameters" also affects the dilution :

- The welding Heat-input should be as low as possi-ble. Use a low welding intensity and a highspeed.

- For filler welding by SAW process, the choice ofthe flux of course has a preponderant importance.

The dilution may also be reduced by reversingpolarity of the current.

- Though the amount of preheating does not directlymodify the dilution level, it does influence themechanical properties in the HAZ and in the firstfiller weld layer (quantifiable by hardness test).

Procedures

We realized that the filler welding method used shouldbe chosen on the basis of comparative tests. Once thisis done, independently or in combination with the qua-lification test required by the applicable standard,the mechanical properties of the complete assembly(filler weld + weld metal) have to be verified in fullscale.

This means mainly that a test specimen of the samethickness as used in the manufacture have to be usedfor testing, and the assembly clamping conditions haveto reproduced as best as possible (i.e. the same levelof stress applied to the filler weld during filling).

In conclusion, we believe that a presumably satisfac-tory buttering method did not achieve results inconformity, when applied to a very thick specimen(200 mm).

The figure 27 shows an "ideal" macrography of abuttering sample. We can observe the very regularprofile of the boundary between Carbon Steel andButtering as well as the very poor dilution of CarbonSteel.

Micrographies on figures 27a and b of this areaconfirm that the martensitic line is yery fine andregular,and that structures of both sides are normal.

- Verification of the buttering. A dual examination(with straight and elbow transceivers) should beexecuted to check that the filler welding adhereswell to its substrate, while also checking thatthere are no cracks present (see section 7.4).

- Check of the final assembly as a complement to RT.

CONCLUSIONS

The example that we have just cited proves only toowell that,even when all normal weld procedurequalifications are performed in strict accordance withthe code,major problems can still arise duringmanufacture.

Netherless.difficult as they may be,dissimilar metalwelds should not be considered only as an exoticmanufacturing method,but rather as an excellent designsolution which can be very valid for vessels withinternals which should be not heated,such as thosemade from duplex stainless steels.

Moreover,it must be pointed out that post weld heattreatment on such heavy pieces,cannot be undertakenon a rule of thumb basis, but requires preciseknowledge of the temperature and stress ditributionsinduced by the exact PWHT cycle.

Thanks to BSL's hard-won experience,we hope that wehave been able to make you aware through this paper,ofthe advantages and pitfulls inherent in the use ofdissimilar metal welding and so help you specify anduse them to your benefit in future projects.

295

DISCUSSION

Dean Damin, DuPont: Even using the procedurewhich produced the weld that is on the screen rightnow, you have a thin, fine area of dilution. That's amartensitic area, and that is going to besignificantly harder than either the base metal orthe filler metal. That thin zone goes completelyfrom the inside to the outside, and that's going tobe an area that will not be detrimental from amechanical property point of view. However, ifyou have an environment that is conducive tohydrogen embrittlement, you now have a

susceptible area.Mr. Prescott mentioned yesterday that if you are

using this joint design, you need to make sure thatyou are using periodic inspection to ensure itsintegrity.Orphanides: You are right, however, in thisparticular case in the urea process we do not havethe conditions to initiate hydrogen embrittlementbecause of the low temperatures and the very lowhydrogen partial pressure. Furthermore, the weld iscovered inside by the 316L or 25/27/2 lining.

296

NU, _from BL

185"138 bar

N/C = 2.9

Reactor

HH,/CO,/H,0

L

1n

tJ

CarbamateCondenser 1

|STM~*j

[stripped]

^CO,-

Air

URÈA FOR TREATED

PRILLING OR PROCESSGRANULATION . CONDENSATES

FlG.1 STAHICARBOH (STAM) CO, STRIPPING UHEA PROCESS

FIGURE: 2Dimensions in mm

DISSIMILAR CLOSING WELD

DISSIMILAR CLOSING WELD

TUBE SOE MATERIAU SA 765 M GR II

SHELL SIDE MATERIAL; SA 516 M GR 70

HP HEAT EXCHANGER 22E001

297

FIGURE: 3Dimensions in tm

DISSIMILAR CLOSING WELD

DISSIMILAR CLOSING WELD

TUBE SEE HATERIAL: SA 765 M GR «

SHELL SIDE HATERIAL; SA 516 M GR 70

TUBE SIDE

PRESSURE

TEMP.

DESIGN

16.45 MPQ

220 "C

SERVICE

14.2 MPo

187 'C

HP CONDENSER 22E002

F I G U R E ; 4 OLD ASSEMBLY PROCESS

Clllllillllll QlHlIlIIII.l

298

FIGURE:5: ASSEMBLING METHOD WITH USING OF DISSIMILAR CLOSING WELD.

f—\—1

Omnium.!

diisimilordoling weid

n t L

—nrr vTU

diiii milorclosing weld

\

lowerporf

— ,ri n n

1 11?

FIGURE HP HEAT EXCHANGER 22E001CLOSING SEAM DETAIL

299

FIGURE:.?

WELDIHG PARAMETERS

PWHT: 540 Cduring IStlOO.

PBHT: 540 'Cduring 4hOO.

Pre heating : so to 100'C for pass X only.

3

Layers

process

Filler Metal

Diameter ma

position

Current

Aaperage A

Voltage V

Speed

1 - 2

FCAW

E 309L T-l

1.2

Flat

DC +

180 V-20

26 +/-3

50 +/-10

3-4

SAW

ER 316

3.2 - 4.0

Flat

DC +

450 - 500 +/-50

32 V-5

50 V-10

FIGURE: 8

TESTS

NOT :- PT. X-RAY

DT :- i, side bends- 2 prismatic tentions- 2*3 KCV in HAZ

SA 516 GR70

ASME QUALIFICATION

A 52 CP

TESTS

NOT :- PT. X-RAY

DT :

20 MnSV

AFNOR QUALIFICATION

- i> side bends- < prismatic tentions- 1 lengthwise tensile test in weld deposit- 4«3 KCV in HAZ- 2*3 KCV in weld deposit- Hardness filliation

300

FIGURE: 8 a

Micrography oï ASHE Procedure Qualification Tast Plata(Scala 1:1)

FIGURE: 8b

Kacrography of WNOR Procedure Qualification Test Plata(Scale 1:1)

FIGURE: 9

50 mm

6°""

ïïl^^^^i

UT CALIBRATION SPECIMENS

301

FIGURE: 9 c

Hacrography of calibration Test plate(Scale 1:1)

FIG.10

DEFECTS ;

302

FIGURE:11

STRIPPER UPPER SEAM

INDICATIONS DISCOVERED BY U L. TESTING

INDICATIONS

0 2846

270 ; I ._ 90°

180" i

Dimensions in mm

FIGURE:12

MACHINING

BOTTOM PART OF THE

BUTTERING FIRST LAYER

FRAGMENTS SPONTANEOUSLY REMOVED FROM

BUTTERING FIRST LAYER DURING MACHINING

303

FIGURE: 13 HP HEAT EXCHANGER 22E001CLOSING SEAM DETAIL

- FIGURE 14 -

THERMOCOUPLES AND ELECTRICAL POWER LOCATIONS

FIGURE: 15

SEAM WELD

TEMPERATURE DISTRIBUTION ( ' C !

START OF HOLDING TIME

304

FIGURE:'6

SEAM WELD

STRESS DISTRIBUTION: VON MISES (MPa

START OF HOLDING TIME

FIGURE: I 7

SEAM WELD

TEMPERATURE DISTRIBUTION (°C)

END OF HOLDING TIME

305

FIGURE:^

SEAM WELD

en-

R £5

STRESS DISTRIBUTION: VON MISES (MPa)

END OF HOLDING TIME

T"

BELKTIOM beetneen STOZSS and PHUT CÏCUS p IS. 103

(Importanca of heating rata)

306

HOEY TESTS RESULTS on TUBE to TUBESHEET HELD SAMPLE

after sensitizing (510*C during 12 hours)

TUBE

ff 31 X 3

Saaple A

Sonplo B

Si 25 x 2.3

Simple A

Sanple B

GRADE

25.22.2

316L US

RESULTS

Average

gr/B2.h

0.084

0.092

0.193

0.173

selectiveattack>»

20

20

40

40

ACCEPTANCE• CRITERIA

Average

gr/B2.h

Haxl0.16

Maxi0.54

Selectiveattack •fSt

Kaxi70

Kaxi200

FJG. lSb

SAMPLE N° 3

CRACKS ALONG THE rL'SWS LINE ASD

THE FROST OF THE CRACKS STOP IS Tl

,KST PASS

r\L UEPOSIT

PHOTOGRAPH N* 11 X 20 FIG.

307

PHOTOGRAPH H" 2 X 20

1 - Base métal (ferrile-perlile HV-1921

2 - Base métal - MAZ (bainile-decorburlzatifin alongmetllng llnel-IIV 210.2«.257.3Zt

3i< - Fusion zone : austenilic line with presence ofmarlensileHigh hardness

5&6 - Marlçnsilic afpa. presence of austeniteVefy high hofdrïess

9 - EB 3". 'tr^ c-nHV 230 ir> /72309L 316

FIGURE:21 EXAMINED ARE A 3

>. del'a-remle

SCHAEFELER DIAGRAMM

10 20

Cr equivalenl-56Cr*%Mo«tS»%Si.0.5»%Cb

FIG.23

DEFECT

TRANSCEIVER

ULTRASONIC BEAM

CARBON STEEL

308

FIG.24WIRE

d " adjusting of the welding wirewhich implicate the amount ofpass overlap.

FIG.25WIRE

T

d' = observed adjusting instead ofthe previous adjusting d.

FIG.26

FIG. 27

WIRE

i

BUTTERING SAMPLE

DEFECT

309

BOUMDARÏ beetvigen CARBOM STEEL and BHTTERIKG

CLIClffi «• 6 X 500F|G. 27

Pan Orphanides Etienne Soutif

310