Alternative welding reconditioning solutions without post welding heat treatment of pressure vessel

Transcription

1 IOP Conference Series: Mterils Science nd Engineering PAPER OPEN ACCESS Alterntive welding reconditioning solutions without post welding het tretment of pressure vessel To cite this rticle: D T Cicic et l 2017 IOP Conf. Ser.: Mter. Sci. Eng Relted content - Effect on property of HIC-Resistnce of vessel steel of PWHT Xinyu Zho, Yng Zou, Liye Qin et l. - The effect of stress relieving tretment on mechnicl properties nd microstructure of different welding res of A517 steel Hssn Shrifi, Solymn Risi nd Mortez Tyebi - MSR in GTA girth welded pipe flnge joint Muhmmd Siddique nd Muhmmd Abid View the rticle online for updtes nd enhncements. This content ws downloded from IP ddress on 05/02/2018 t 16:41

2 Alterntive welding reconditioning solutions without post welding het tretment of pressure vessel D T Cicic 1, C Rontescu 2, A M Bogtu 3 nd M C Dijmărescu 4 1,2,3,4 University POLITEHNICA of Buchrest, Mterils Technology nd Welding Deprtment, 313 Spliul Independentei, Buchrest, Romni E-mil: dumitru.cicic@gmil.com Abstrct. In pressure vessels, working on high temperture nd high pressure my pper some defects, crcks for exmple, which my led to filure in opertion. When these nonconformities re identified, fter certin exmintion, testing nd result interprettion, the decision tken is to repir or to replce the deteriorte component. In the current legisltion it s stipulted tht ny repir, ltertion or modifiction to n item of pressurised equipment tht ws originlly post-weld het treted fter welding (PWHT) should be post-weld het treted gin fter repir, requirement tht cnnot lwys be respected. For tht reson, worldwide, there were developed vrious welding repir techniques without PWHT, mong we find the Hlf Bed Technique (HBT) nd Controlled Deposition Technique (CDT). The pper presents the experimentl results obtined by pplying the welding reconditioning techniques HBT nd CDT in order to restore s quickly s possible the pressure vessels mde of 13CrMo4-5. The effects of these techniques upon the het ffected zone re nlysed, the grphics of the hrdness vrition re drwn nd the resulted structures re compred in the two cses. 1. Introduction Continued usge, repir or replcement of pressure vessels nd structures s relted to life extension must begin with detiled nd specific knowledge of the metllurgicl / mteril condition of the pressure vessel or structure. This type of complete engineering ssessment of existing structures must be conducted before ny run, repir or replcement decisions cn be mde [1]. Components operting t high temperture or hrsh working conditions re subjected to different filure regimes which require specil considertion. In scheduled shutdowns, criticl components re inspected nd if necessry either replced or repired. Generlly, the cost effective choice is to extend the life of ged components by repir rther thn replcement [2]. Repir welding mybe crried out using rnge of welding techniques depending on the nture of the repir. Commonly, most weld repirs require post weld het tretment (PWHT) to restore the deteriorted metllurgicl nd mechnicl properties. However, criticl issues in the course of PWHT such s time, component geometry nd unsupported loding during the time the component is hot, men tht it is not lwys possible to crry out the full procedure. Durtion of hold time during the PWHT cycle cn be very long especilly for thick wlled components which result in the extension of the unit downtime [3]. At the moment, in order to repir by welding vrious components from different industries, severl methods re used mong which we mention [3]: Content from this work my be used under the terms of the Cretive Commons Attribution 3.0 licence. Any further distribution of this work must mintin ttribution to the uthor(s) nd the title of the work, journl cittion nd DOI. Published under licence by Ltd 1

3 - Hlf-bed technique, used widely by different industries for repiring different lloys such s 2.25Cre1Mo steel. At first, this technique hs been developed in the nucler industry, but it becme one of the most pplied repiring techniques in ll the industril fields tht presuppose welding procedure [4, 5]; - Temper bed, the het input of the subsequent lyer in the TBW technique is incresed in order to ble to refine the corse grin or temper the mrtensitic/ binite microstructure of the HAZ. - Cold repir is the repir process which elimintes the need of prehet or PWHT hence time sving in shutdown repir cn be significnt; - Consistent Lyer Technique. In pplying this technique there cn be used either the method of shielded metl rc welding, or the TIG procedure, with wolfrm inert gs. This technique consists in depositing smll enough lyers, so tht the next deposited lyer hs only the tempering effect on the het ffected zone HAZ which rises from depositing the previous lyer, figure 1; - Alternte Temper Bed Technique, This technique ws developed especilly for the clsses of steel C-Mn, C-Mo, used in nucler rectors for the components of products under pressure, [6]; -Controlled Deposition Technique, This technique resulted from specil cses where the intercrystlline corrosion nd the rehet crcking my mnifest during the repir. The procedure shielded metl rc welding is used nd it consists in incresing the liner energy with certin percentge, between 1.2 nd 1.7, from one lyer to nother [6, 7], figure 2; -Weld Toe Tempering Technique. This technique involves depositing lyer or pssge of het tretment on the surfce of the welding joint to ensure the tempering of the HAZ creted by depositing the previous lyer. The mode of deposition is very importnt in order to chieve this requirement [8], figure 3. Figure 1. Appliction scheme of the consistent Lyer Technique, [9]. Figure 2. Appliction scheme of controlled deposition technique. Figure 3. Appliction scheme of Weld Toe Tempering Technique 1 Lyer of root; 2 filling lyer; 3 closure lyer; 4 lyer of het tretment. The most common welding process, used in welding repiring, pplied to recipient type products is mnul metl rc welding [10, 11], becuse of its ese of pplying nd reltively low costs. There is lso number of reserches which seek to replce the mnul metl rc welding repiring with other more productive processes, such s gs metl rc welding (GMAW) nd flux cored rc welding (FCAW) [12, 13, 14, 15] 2

4 2. Experimentl Work The bse mteril, used within the experiments, is SA387 Grde 22 Clss 2 Steel, 16 mm thick, in form of sheet, minly used in the energetic, chemicl nd petrochemicl industry. The SA387 Grde 22 Clss 2 smples were tken from disposed continer which functioned for long period of yers in the energy industry. For this reson, before the experiments, the rel chemicl composition of the smples ws determined, using the sprk method. The obtined results re presented in tble 1. Tble 1. Chemicl composition of the steel used within the experiments - comprison with the verge chemicl composition mentioned in the steel stndrd. Test Test 1 Test 2 Test 3 Test 4 Test 5 Averge Averge vlue b Difference c number C [%] (Med.)* medie (Dif.) *** Si [%] Mn [%] Cr [%] Mo [%] Ni [%] Al [%] Co [%] Cu [%] Nb [%] Ti [%] V [%] Sn [%] Zr [%] The verge of the 5 tests b In ccordnce with ASTM A387/ SA387 c Clculted with the formul: Dif. =VMS Med Anlysing tble 1, it cn be seen tht fter functioning period, chnges occur, mening the incresing or decresing of the percentge vlues corresponding to the chemicl elements from the mteril. Moreover, in the conducted tests, other chemicl elements were highlighted, such s Ni, Co, Cu, Nb etc., tht could not be found initilly in the chemicl composition of the nlysed steel. In order to pply the 3 methods mentioned bove, norml deposit (N), hlf lyer deposit (HBT) nd controlled deposit (CDT), the smples were provided with cnls, hving the following dimensions: 10mm depth, 10 mm width nd 100mm length. The smples resulted fter processing re presented in figure 4. Figure 4. The cnls of the N, HBT nd CDT smples (cnl depth: 10 mm). The welding repiring process ws robotic gs metl rc welding (GMAW), using 1.2 mm GCrMo1Si wire filler mteril nd CO2+18%Ar protection gs. The welding repiring process prmeters, estblished in ccordnce with the recommendtion of the bse mteril producer, re indicted in tble 2. Becuse the thickness of the smple in the re of the cnl ws only 6mm, the first lyer ws deposited with lower prmeters vlues in order to eliminte the risk of piercing the smple. 3

5 Tble 2. The welding repiring prmeters used in the experiments. No. Smple code Technique Lyer 1 N Norml deposit 2 HBT 3 CDT Hlf lyer deposit Controlled deposit The het input ws clculted with equqtiojn 1 Is U Prmeters used for deposit [A] [V] [cm/min] [kj/cm] n n vs El Gs debit [l/min] U I s El 60 [kj/cm] (1) vs 1000 Where: ƞ- Process yield (0.9 for MAG); U Arc voltge [V]; I s Welding current [A]; v s Welding speed [cm/min]. The removl of the hlf-lyer, needed in order to successfully pply the HBT technique, ws mde with 650W stright grinder with crbide milling cutters nd vrible speed. 3. Results nd Discussion The predetermined welding repiring prmeters (see tble 2) were monitorized during the experiments by direct reding on the disply of the source. The vlues re presented in tble 3. No Smple code 1 N 2 HBT 3 CDT Tble 3. The welding repiring prmeters recorded in the experiments. Technique Norml deposit Hlf lyer deposit Controlled deposit Lyer Is [A] U [V] Vs b [cm/min] Prmeters El c [kj/cm] Debit gz Dg[l/min] Deposit height [mm] d 18 Lyer height fter removl [mm] d NA NA NA NA 5 e NA e NA NA NA NA 4 e NA determined s the verge between the minimum nd mximum vlues red on the disply during the experiments b Vlue imposed by the robotic system; c Vlue clculted with reltion 1; d Vlue determined with the verge of 3 vlues determined s the distnce from the bse mterils surfce to the height of the deposit; e closure lyer; Smple pictures tken during nd fter the repir by welding, re shown in figure 5. 4

6 ) b) c) Figure 5. Imges tken during nd fter finishing the experiments: ) Positioning of the welding gun; b) Lyer 2 fter the mechnicl processing Smple HBT; c) The resulting smples. After cooling the smples to room temperture, wide strips of 25 mm were tken from the centrl re nd processed for the mcroscopic nlysis nd the hrdness mesuring. After obtining the mcroscopic imges with the help of softwre the following chrcteristics were mesured (figure 6): - Welded sem width, B; - reinforcement, h; - penetrtion, p; - Welded sem width, mesured t the hlf of the bse mteril thickness, LB. Figure 6. Indiction of the res of interest. ) b) Figure 7. The dimensions of the re of interest Smple N: ) Mcroscopic imge; b) Imge generted by the soft. 5

7 ) b) Figure 8. The dimensions of the re of interest Smple HBT: ) Mcroscopic imge; b) Imge generted by the soft. ) b) Figure 9. The dimensions of the re of interest Smple CDT: ) Mcroscopic imge; b) Imge generted by the soft. Obtined results fter the mesurements, s it cn be seen for ech smple in figures 7, 8 nd 9, re presented in tble 4. Tble 4 Welded sems geometricl chrcteristics. Mesured chrcteristic N CDT HBT B[mm] p [mm] h [mm] LB [mm] Vlues mesured in the bse mteril t depth of 8 mm from the surfce, see figure 6 Reconditioning methods for nlysing the effects of welding pplied were determined in ccordnce with figure 10, the resulting hrdness vlues in ech 5 points distinct positioned in the bse mteril, influenced the mechnicl stitch. For nlysing the effects of the pplied methods of reconditioning by welding, there were determined the hrdness vlues, in five distinct points, in the bse mteril, the HAZ nd in the welded sem (see figure 10). 6

8 The mesurement ws crried out on the two directions, I nd II, in ccordnce with Figure 10, nd the results obtined re indicted in tble I II Figure 10. Locliztion of the mesurement points for hrdness 1- bse mteril; 2 het ffected zone; 3 - welded sem; I, II directions of mesurement for hrdness. Tble 5. Obtined hrdness vlues on the two directions for the three smples. Zone Mesurement point b Obtined vlues on the mesurement direction** Smple N Smple HBT Smple CDT I II I II I II Averge Averge ccording to figure 10 b HV 0.2 vlues Averge The grphicl representtion of the vrition of hrdness on the two directions presented in figure 6, it cn be observed in the following figures. The figures 11 nd 12 present the vrition of the hrdness verge vlues for ll smples tken in the bse mteril, the HAZ nd the welded sem. 7

9 Figure 11. The vrition of the hrdness verge vlues on the direction I, in the bse mteril, in the HAZ nd in the welded sem - for ll smples. Figure 12. The vrition of the hrdness verge vlues on the direction II, in the bse mteril, in the HAZ nd in the welded sem - for ll smples. From nlysing the figures 11 nd 12, nd lso the indicted vlues in tble 5, it cn be drwn the conclusion tht the mximum verge vlue of hrdness on the direction of mesurement I, in zones 2 nd 3, ws obtined for the smple CDT For the direction of mesurement II it cn be observed tht the mximum verge vlue of hrdness ws obtined in zone 2 for the smple N nd in zone 3 for the smple CDT. The differences between the vlues of the hrdness s cn be explined by the different quntities of het inserted in the mteril by the welding technology, the different wy of het diffusion to the surfce of the smple, s well s the different number of psses needed to fill the cnls 4. Conclusion The following conclusions cn be drown from the crried out experiments: - The longest time climed by the reconditioning by welding ws in the process of depositing the lyers for the smple HBT, explined by the need to remove hlf of the deposited lyer prior to filing the next one; - Applying the reconditioning by welding tehnique CDT, which consisted of incresing the vlue of het input used for the deposit of ech lyer hs conducted to the reduction of the number of lyers compred with the technique N nd the tehnique HBT, which will mterilize in shorter time nd lower cost for mking the repirs; - By chnging the technique pplied for the reconditioning by welding, dimensionl chnges pper in the size of the HAZ, s cn be seen from the nlysis of the figures 7,8 nd 9 ; - The pplied technique for the reconditioning by welding leds to chnges in the hrdness vlues, so, destructive testing, such s s tensile testing or trying determinre resilience,re required when certin method is chosen. - The pplied technique hs considerble effects on geometricl elements of the sem, B, p, h s cn be seen from the nlysis of tble 5. 8

10 5. Acknowledgement This work hs been funded by University Politehnic of Buchrest, through the Excellence Reserch Grnts Progrm, UPB GEX. Identifier: UPB EXCELENTA 2016 Alterntive solutions for welding reconditioning of the recipient type products used in energetic nd chemicl industry, without post repiring het tretment, Contrct number 31/ References [1] Crl D L 2012 Houdremont Lecture Mterils nd welding considertions for determintion of continued opertion, or run / repir / refurbishment for life extension [2] Kviyrsn T nd Senthil K T 2015 Int. J. Engg. Res. & Sci. & Tech 4 (3) 86 [3] Alorier A, Al-Mzrouee A, Price J.W.H. nd Sheht T 2010 Interntionl Journl of Pressure Vessels nd Piping 87 [4] Allen P J 1997 Proceedings of Welding nd Repir Technology Cold weld repir, development [5] Odnvic Z nd Nedeljkovici Lj 2003 Steel welds by the numericl model Microstructure ppliction in the het ffected zone of GMA [6] Gndy D W, Findln S J nd Viswnthn R 1998 Temper bed welding of P numbers 4 nd 5 mterils Nottinghm, Professionl Engineering Publishing, UK [7] Sun W 1996 PhD Thesis Creep of serviced ged welds, University of Nottinghm, Englnd [8] Lundin C D Welding Reserch Council Bulletin 412 [9] Cicic D T, Solomon Gh, Icobescu G nd Rontescu C 2009 U.P.B. Sci. Bull. D 71(3) [10] Doty WD 1996 Weld Res Council Bull [11] Lnt T, Robinson D L, Spfford B nd Storesund J 2001Int J Press Vessels Pip [12] Mitchell K C nd Brett S J 2003 Power Plnt: OMMI 2(1) 1-9 [13] Mitchell K C Proceedings of the st IEE/IMechE interntionl conference on power sttion mintennce e profitbility through relibility Edinburg IEE Stevenge Englnd [14] Mitchell K C 2001 Ninth Interntionl Conference of creep nd frcture of engineering mterils London Institute of Mterils [15] Mitchell K C 2003 UK power plnt 2(1) 1-7 9