REPORT OF REFORMER TUBE INSPECTION BY LONG RANGE GUIDED WAVE ULTRASONIC METHOD (GW), METAL MAGNETIC MEMORY (MMM), EDDY CURRENTS (ET), TIME-OF-FLIGHT DIFFRACTION (TOFD), MAGNETOSCOPY, HARDNESS TEST AND METALLOGRAPHY *Ebrhim Ebrhimi 1 nd Abbs Snjbi 2 1 Deprtment of Mechnicl Engineering, College of Engineering, Kermnshh Brnch, Islmic Azd University, Kermnshh, Irn 2 Deprtment of Mechnicl Engineering, College of Engineering, Kermnshh Science nd Reserch Brnch, Islmic Azd University, Kermnshh, Irn *Author for Correspondence ABSTRACT In this rticle, report of reformer tube inspection by long rnge guided wve ultrsonic method (GW), metl mgnetic memory (MMM), Eddy currents (ET), Time-Of-Flight Diffrction (TOFD), mgnetos copy, hrdness test nd metllogrphy is ssessed. tubes ctlysts re of microlloy under trde nme of Centrlly G 4852 Micro (G-X40 NiCrSiNb 35-25) nd reducers of this reformer is mde of Centrlloy G 4859 (G-X10 NiCrNb 32-20). Results show tht tubes clssifictions includes 35.1% trouble free, 15.4% in minor risk clss, 38.5% in medium risk clss nd 11.1% re locted in high risk clss. Enlrgement of ustenite grin boundry crbides nd lso those crbides between dendrites, tngible decrese in tensile strength, hrdness nd strength ginst creep rupture my be evidence of exceeding temperture rise in tubes. Furthermore, temperture increse lso will hve significnt impct on remining life of tubes within reformer system nd increse of creep rte. Keywords: Reformer Tubes, Long Rnge Ultrsonic, Metl Mgnetic Memory, Eddy Currents, Ultrsonic Diffrction INTRODUCTION Reformer re used to produce hydrogen in petrochemicl industries. Reformer tubes re most criticl elements of reformers where due to imposed work conditions on them; those re mde of specil ustenite which hs very high resistnce ginst creep nd corrosions. These tubes re usully designed to hve ge of 100000 hours t norml opertionl conditions. However, erly ruptures frequently re seen in these tubes becuse of some mechnisms such s creep, crburiztion, oxidtion, therml shock nd overheting (Alvino et l., 2010). At high tempertures, metl prts re yielded under lower thn tension lods nd re continully deformed. This under tension nd relted to time deformtion in equipments is clled creep where is one of the min leding mechnism to rupture in reformer tubes. Therefore, in recent severl decdes those lloys with high resistnce to creep re used in order to mke reformers tubes (d Silveir TL nd My, 2006). Deformtion rte of creep impct is function of mteril type, pplied lod nd temperture. Rupture rte (or Strin Rte) is sensible to both temperture nd pplied lod or tension. Overll, ech 12ºC increse in temperture or15% tension depends on lloy leds to decrese of hlf or more performnce life (API RP 571, 2011). One of the mechnism of probble rupture is overheting where leds to loclized heting. Overheting my be cused by deficiency in fluid flow within tube nd relted problems to burners. When burners re not set, there might be turbulence in flme nd flme collides directly into tubes nd leds to flme impingement sitution. This sitution cuses increse temperture of hot spot on tube s surfce nd high rtes of oxidtion, crburiztion nd rpidness in creep process nd lso end to brittle frcture (Eschbch, Copyright 2016 Centre for Info Bio Technology (CIBTech) 370
no dte). Thus, burners should be monitored regulrly to void ny impct of unsuitble het distribution which leds to overheting in some tubes reltive to others. Unsuitble heting will ffect primry clcultions of het trnsfer in tubes. For exmple, by dvnce in rection, rte of gs flow process nd temperture in lower prt of tube would be chnged (Eschbch, no dte). High level of temperture results in tube heting expnsion nd since this expnsion is confined by reducer nd collector, tube will be bended. Tube bend is lso cuses increse in tension nd finlly creep process is become more rpid nd t lst tube rupture will occur (Eschbch, no dte). It seems tht overheting is min fctor in reformers tube bility to provide service. Wll temperture of tubes is relted to severl fctors. Regulting burner is one of the fctors tht my offset during times. Ctlysts ctivity lso becomes decresed by time, where to compenste this deficit temperture my be incresed. By increse in ctlyst ge nd grdully, there would develop preferred pth for gs flow through ctlysis ground. Therefore, cooling is not occurred uniformly t tube section (due to gs flow) nd hotter (nd brighter) zones in outer surfce of tube develop girffe neck ptterns where this phenomenon is observble through furnce s window. Even when there is more severe increses in temperture, hot spots become ovl shpes. Testing het distribution long tubes indictes tht temperture of lower hlf is more nd in some instnces it is estimted to be more thn 1000 ºC (Chudhuri, 2008). Thus, these furnces should be designed nd used to minimize developing hot spots nd loclized overheting (API RP 571, 2011). Enlrgement of ustenite grin boundry crbides nd lso those crbides between dendrites, tngible decrese in tensile strength, hrdness nd strength ginst creep re evidence for tubes overheting (Chudhuri, 2008). Strt downs nd strt ups or therml cycles re pproprite to decrese or increse temperture slopes nd lso effective in tubes ge. Implictions of therml cycles, prticulrly in second hlf of tubes ge might be led to brittle frcture in tubes (Jkobi nd Gommns, 2003). When tubes due to heting cycling re repetedly become hot nd cold, tensions re incresed temporry nd results in rpid creep rupture. Once heting nd cooling is very fst, rupture would be cused by therml shock (Huber nd Jkobi, 2011). During implementtion nd before ctlyst becomes ctive by reduction; rection provided het is not djusted. Therefore, operting reformer should be ccomplished in ccurte testing nd control to void overheting of tubes. As Schmidt + Clemens compny report, rte of therml chnges must be t most 50ºC/hr (Eschbch, no dte). Wll thickness nd level of therml cycling during tube life is importnt. Most of ruptures or frctures in HK-40 lloy of risers, mnifolds, trnsferring heders nd other components re cused by therml cycling. HP-Mod lloys ber therml tensions more efficiently (Schillmoller, 1992; Kseipoor et l., 2015). Formtion of secondry crbides due to crboniztion leds to chrome level in proximl lyers to tubes surfces nd this lyer grdully will be remined without primry crbides of chrome nd become thicker. Crbide sediments which reinforce lloy nd increse creep resistnce reduce nd finlly led to decrese in sound wll thickness feture of tube. This cuses increse in tension nd consequently rpidness in creep process within substnce (Jkobi nd Gommns, 2003). As result, most relted problems to reformer tubes is relevnt to opertionl conditions of furnce. Therefore, by proper ppliction of furnce, some cses such s overheting, flme collision, oxidtion, decrese of gs liquidity nd prticulrly brittle frcture. In this study, testing of reformer tubes No. H-2101 is ssessed by long rnge guided wve ultrsonic method (GW), metl mgnetic memory (MMM), Eddy currents (ET), Time-Of-Flight Diffrction (TOFD), mgnetoscopy, hrdness test nd metllogrphy. Job Description In this project; testing of reformer tubes No. H-2101 is ssessed by long rnge guided wve ultrsonic method (GW), metl mgnetic memory (MMM), Eddy currents (ET), Time-Of-Flight Diffrction (TOFD), mgnetoscopy, hrdness test nd metllogrphy. Copyright 2016 Centre for Info Bio Technology (CIBTech) 371
Reformer of this project is Top Fire type where its tubes ctlysts re locted in 4 rows of 52 pieces nd in different cse, its burners lso re ssembled on ceiling of this cse. Tubes ctlysts re of microlloy type under trde nme of Centrlloy G 4852 Micro (G-X40 NiCrSiNb 35-25) nd its reducers re mde of Centrlloy G 4859 (G-X10 NiCrNb 32-20). These kind of lloys re the newest types of lloys tht re used in reformers nd their utiliztion llows increse of tubes dimeters nd better implementtion nd bering higher degrees of het thn previous genertions of HK40 nd modified HP. Reformer hs 208 tubl brnches where re mde of Centrlloy G 4852 Micro (G-X40 NiCrSiNb 35-25) with outer dimeter 135.8 mm., inner dimeter 110mm., thickness 12.1 mm nd length of 12.077 m. This testing ims to ssess situtions nd level of deficiencies in tubes nd providing report nd qulittive ctegorizing by using dvnced non-destructive testing methods. Testing through long rnge guided wve ultrsonic method (GW) ws conducted under ASTM, E2775 version 2011 stndrd. The ssessment device ws Wve mker G4 nd lso received grph ws fine tuned nd filtered to mke evlution better. Testing through metl mgnetic memory (MMM) ws conducted under ISO 24497 ver. 2007 stndrd nd test ws ccomplished by using SD-1-8M probe with four verticl chnnels nd four horizontl chnnels. Assessment device ws TSC-5M-32 nd received signl ws filtered to cquire better evlution nd device s level of contrst is lso incresed. Testing through Time-Of-Flight Diffrction (TOFD) ws conducted under protocol of ASME, Section V, Article 5 version 2010 nd test device ws under brnd nme of Silver wing NDT UT 400. Selected frequency ws 1 MHz nd dt evlution ws ccomplished bsed on received wve. Testing through mgnetoscopy pproch ws conducted under ASTM, A342 stndrd Ver. 2010 nd test device ws Foerster 1.069. Testing through hrdness test method ws conducted under ASTM, E-110 Ver. 2010 nd test device ws from Proceq Testing Instruments inc. Testing through metllogrphy method ws conducted under ASTM, E-1351 Ver. 2002 nd test device ws Portble Set. Testing opertions ws pplied on four rows of fifty two tubes where totl tubes numbers reched to two hundred eight pieces. Testing Opertions Guided Wve Ultrsonic Testing In this testing method, fter mounting n long rnge ultrsonic testing ring t upper loction of reducers, wves re sent nd received completely long the tube by ccessing point on sme tube nd bsed on this procedure testing grph is prepred. Considering obtined dt from this grph, deficiencies re identified nd would be enlisted in testing schem to be tested by other testing methods. Metl Mgnetic Memory Testing Opertions In this testing method, by metl mgnetic memory testing sensor movement on surfces of tubes deficit regions nd residul tension re identified. Furthermore, testing is repeted more ccurtely nd sensitively in deficit regions where were known through long rnge ultrsonic testing method. According to obtined dt from this method, ll deficits re ctegorized nd Eddy Current Testing enlisted in testing scheme to find crck nd creep in tubes. Eddy Current Testing Opertions In this testing method, eddy current testing sensitive probe moves long surfces of tubes to identify loctions of crck, creep nd structurl chnge (Conductivity). Moreover, on ll surfces of reducers nd ll resulted deficit regions where were identified by long rnge ultrsonic nd metl mgnetic memory testing methods; eddy current testing lso ws performed. According to obtined dt through this method, ll deficits re ctegorized nd enlisted in testing scheme to endorse ultrsonic nd metllogrphy testing methods. Copyright 2016 Centre for Info Bio Technology (CIBTech) 372
Ultrsonic Testing Opertions In this testing method, by moving trnsducer of ultrsonic testing method on surfces of tubes; the loctions with crck nd drop ultrsonic wves re identified. This method is used to endorse results of other methods. Mgnetoscope Testing Opertions In this testing method, by moving mgnetoscopic testing sensor on surfces of tubes; level of mgnetic permittivity is mesured. This method is used to nlysis results of other methods. Hrdness Testing Opertions In this testing method, by using hrdness testing probe on surfces of tubes; level of surfce hrdness is mesured. This method is used to nlysis results of other methods. Metllogrphy Testing Opertions Microstructure testing ws conducted on different regions of reducers nd tubes of primry reformer furnce. Tubes Specifictions Received informtion regrding mteril, design nd performnce spects of tubes re s following: Mteril: Centrlloy 4852 Micro OD: 135.8 mm ID: 110 mm Minimum Sound Tube Wll Thickness (MSW): 12.1 mm Corrosion llownce: 0 Design pressure: 36.8 brg Design temperture: 924 C Operting pressure: 34 brg Operting temperture: 750-945 C Mettlogrphy Testing Considering cquired structure from new smple of reformer pipe nd comprison of modified still HP structure s shown in Figure 1, it my be concluded tht existing pipes re sme type. Chemicl nlysis of this lloy is demonstrted in Tble 1. Figure 1: Microscopic Structure of Foundry Smple under HP still Centrifuge Technique, Dendrite Crbides re in Austenite Bckground (de Almeid et l., 2002) Tble 1: Chemicl Compound of Modified HP still (Alvino et l., 2010) C Si Mg Cr Ni Nb Ti Fe HP-Nb Modified 0.45 1.5 1.00 25.00 35.00 1.50 Vr. Bl. Copyright 2016 Centre for Info Bio Technology (CIBTech) 373
As shown in Figure 1, this still hs n completely ustenite bckground long with bundnt mount of rich in titnium nd niobium crbides where re formed t dendrites border lines, vilbility of niobium nd titnium in this type of still prevents chrome crbides formtion. Referring to mentioned issues, grdully by increse in temperture both M 7C 3 nd M (C, N) crbides in this still trnsform into chrome rich crbides of M 23C 6 nd M 6C where by considering process temperture of mentioned lloy (About 900 1000 ºC) this result is inevitble. In Tble 2, formtion nd expnsion of these crbides respected to temperture re demonstrted. Tble 2: Imge Anlysis Results of some Exmples of Modified HP still Creep Testing (Berghof- Hsselbächer, 2007) In cse tht mettlogrphic opertion to identify type of crbide being conducted in specified experimentl conditions, type of crbide might be identified by opticl microscope where exmples my be observed in Figure 2. But through testing microstructures of inner tubes of furnce nd tking operting conditions out of lbortory, identifiction of crbide type with opticl microscope is not possible. However, wht is completely explicit is observble chnge in structure due to service t high tempertures lmost in ll cses. This issue is expressed compring to referrl imges in Figure 3. These phse relted chnges nd formtion of secondry crbides, however is not ment the end of tubes lifetime nd wht is known s dmge nd risk fctor for tubes being discrded is micro-crcks which re developed by connections between resulted micro-crcks of creep process. In Figure 4, exmples of these micro-crcks re demonstrted. Copyright 2016 Centre for Info Bio Technology (CIBTech) 374
Figure 2: Different Types of Crbides nd Method of their Identifiction by Opticl Microscope (Berghof-Hsselbächer et l., 2007) Figure 3: Mettlogrphic imge of HP still : ) Originl smple, b) ged nd c-f) liquidtion for one hour t c) 1000 ºC, d) 1100 ºC, e) 1200 ºC, f) 1250ºC (Hsegw, 2001) Copyright 2016 Centre for Info Bio Technology (CIBTech) 375
Figure 4: Developed Micro-Crcks by Creep Mechnism in HP still (Vnder Voort, 2004) Overll, it my be stted tht, prt from structurl chnge in mettlogrphic mterils nd tking bove issues, ll loctions re free from micro-crcks (At lest t mettlogrphized regions). But in some scrce cses (prticulrly in tube No. 48), bnorml structures nd unusul rrngements in crbides re observed where those might be results of increse in temperture up to more thn permitted pplicble levels. However, considering opertion conditions of furnces nd existing processes; formtion of crbon prticles on inner wll of tubes nd consequent permebiliztion of crbon into structure nd elimintion of elements such s niobium nd titnium my be significnt fctor in formtion nd expnsion of chrome crbides (Alvino et l., 2010), while in order to test this fctor; level of exit ctlyst from inner side of tubes my be nlyzed nd in cse of finding crbon some opertions such s clening inner side of tubes within stops nd overhul periods might be conducted. This issue is ddressed orlly with employer nd is written in this report so s to be more ssessed. RESULTS AND DISCUSSION Results Reformer Tubes: In Tble 3, clculted life spn of tubes respected to design conditions t different tempertures re observble. Furthermore, in Figure 5; grph of tube life spn ginst temperture for different design conditions is indicted. Clcultions of Tube Life Spn: In this section, tking design conditions nd relted informtion to temperture nd time where re provided by employer, tube life spn is clculted. It should be noted tht s we pointed to in API 530 stndrd, due to pproximtion in tempertures nd ignoring other fctors such s probble pressure chnges, therml tensions, strt ups nd shut downs nd etc., these clcultions re pproximtions. If temperture is designed for 924ºC nd pressure 36.8 br. In complince to API 530; we hve [3,7]: Copyright 2016 Centre for Info Bio Technology (CIBTech) 376
By inserting relted vlues to tube design conditions into bove equtions, level of tension is obtined: S=18.81 MP Lrson Miller prmeter for design is equl to low sctter bnd 28.23 nd verge 28.55. By using derived Lrson-Miller formul for this lloy, tube life spns vlues my be clculted given constnt pressure for design nd opertion conditions of low sctter bnd nd verge. Where LMP is Lrson-Miller prmeter, T temperture in Kelvin nd t r is time intervl up to rupture in hours. Given time efficiencies for tube opertion nd clculted vlues for pssed life spn of ech period of time re shown in Tble 4. Tble 3: Tube Life Spns for Different Design Conditions t Different Temperture T( C) LMP tr(hr) 924 28.23 95720 936 28.23 55844 945 28.23 37539 960 28.23 19615 972 28.23 11802 984 28.23 7171 996 28.23 4398 1008 28.23 2722 1020 28.23 1700 Low Sctter Bnd 924 28.55 177136 936 28.55 102714 945 28.55 68735 960 28.55 35653 972 28.55 21329 984 28.55 12885 996 28.55 7859 1008 28.55 4838 1020 28.55 3005 Averge Copyright 2016 Centre for Info Bio Technology (CIBTech) 377
Figure 5: Tube Life Spn Grph ginst Temperture for Different Design Conditions Tble 4: Clculted Vlues for Tubes Pssed Life Spn Opertion Period Durtion (yer) Pressure (MP) 1 6 3.68 2 0.2 3.68 3 0.7 3.68 is the interntionl unit symbol for yer Stress (MP) 18.81 18.81 18.81 Temperture ( C) 924 957 924 Accumulted dmge= Rupture Time bsed on Minimum Strength Life Frction 10.9 0.55 2.5 0.08 10.9 0.06 0.69 Rupture Time bsed on Averge Strength Life Frction 20.2 0.30 4.6 0.04 20.2 0.03 0.37 Now, by considering obtined pssed life spn, remining frction of life spn might be clculted: Minimum rupture strength: 1-0.69=0.31 Averge rupture strength: 1-0.37=0.63 Referring to tubes pssed frction of life spn t minimum rupture strength (Vlue 0.69), pssed life spn is equl to 7.5 yers while is more thn rel pssed life spn (6.9). Therefore, this difference my be mentioned s evidence for implictions of bnorml conditions on tubes. If we ssume tht tubes pss their remining life spn under design conditions, then remining life spn cn be clculted. These vlues re shown in Tble 5. Tble 5: Clculted Remining Life Spn for Tubes Opertio n Period 4 Pressur e (MP) 3.68 Stress (MP ) 18.81 Tempertur e ( C) 924 Rupture Time (Minimu m) 10.9 Rupture Time (Averge ) Remining Time bsed on Minimum Strength Life Frctio n Remining Time bsed on Averge Strength Life Frctio n Copyright 2016 Centre for Info Bio Technology (CIBTech) 378 20.2 0.31 3. 4 0.63 12. 7
As shown in Tble 5, obtined vlues for remining life spn t low sctter bnd cse is equl to 3.4 yers nd t verge strength is equl to 12.7 yers. Given tht in rel conditions, these tubes usully re designed for bout 100000 hours (11 yers), it is better tht level of remining life spn t minimum strength condition or 3.4 yers to be selected for mesure of decision mkings. Regrding results of dvnced non-destructive tests, ll tubes were ssessed qulittively nd ctegorized by registered indictions under NDT methods s 35.1% trouble free, 15.4% in minor risk clss, 38.5% in medium risk clss nd 11.1% in high risk clss. Considering results of mettlogrphy testing on new nd used smples t doubted regions, it ws identified by other NDT methods tht min bckground of tubes is ustenite type nd conducted studies on infrstructures indicte vilbility of primry nd secondry crbides t boundry grins. It my be concluded from developing secondry crbides t boundry grins tht deformtion of structure is serving t excess tempertures thn norml ttitude nd this is not relted to termintion of tubes life spn nd risk fctor in these tubes is vilbility of micro-crcks nd their connection together to develop creep phenomenon but in experimentl smple; micro-crcks re not observed t ll but in some cses bnorml structures nd unusul rrngements of crbides were observble. Regrding dvnced NDT tests nd conducted studies on obtined results of testing methods nd mettlogrphy on doubtful regions, tempertures t higher levels thn permitted ones re min fctors in confining service efficiency of reformer tubes. Enlrgement of ustenite boundry grins crbides nd lso locted crbides between dendrites, tngible loss in tensile strength, hrdness nd strength ginst creep rupture re evidence for increse in tube temperture bove permitted levels. Therefore, by proper ppliction of furnces nd observing highest opertionl tempertures levels, some situtions such s excess heting, flme collision, oxidtion, gs flow decrese nd developing brittle frctures might be voided nd suspend occurrence of creep phenomenon nd its rupture consequence. Overheting hs significnt impct on shortening tubes life spn nd its remining working time in reformer system nd creep rtes s well. Conclusion In this pper, report of reformer tube inspection by long rnge guided wve ultrsonic method (GW), metl mgnetic memory (MMM), Eddy currents (ET), Time-Of-Flight Diffrction (TOFD), mgnetoscopy, hrdness test nd metllogrphy is ssessed. tubes ctlysts re of microlloy under trde nme of Centrlloy G 4852 Micro (G-X40 NiCrSiNb 35-25) nd reducers of this reformer is mde of Centrlloy G 4859 (G-X10 NiCrNb 32-20). Following results were obtined: 1- clssifictions includes 35.1% trouble free, 15.4% in minor risk clss, 38.5% in medium risk clss nd 11.1% re locted in high risk clss. 2- Enlrgement of ustenite boundry grins crbides nd lso locted crbides between dendrites, tngible loss in tensile strength, hrdness nd strength ginst creep rupture re evidence for increse in tube temperture bove permitted levels. 3- Overheting hs significnt impct on shortening tubes life spn nd its remining working time in reformer system nd creep rtes s well. REFERENCES Alvino A et l., (2010). Dmge chrcteriztion in two reformer heter tubes fter nerly 10 yers of service t different opertive nd mintennce conditions. Engineering Filure Anlysis 17(7 8) 1526-1541. API RP 571 (2011). Dmge Mechnisms Affecting Fixed Equipment in the Refining Industry, second edition, (Americn Petroleum Institute, Wshington D.C). Berghof-Hsselbächer E et l., (2007). Atls of Microstructure, (Mterils Technology Institute Publiction). Chudhuri S (2008). Creep nd life ssessment of engineering components in power plnts nd process industries, ISBN: 81-87053 - 73-1, Remining We Assessment of Aged Components in Therml Power Copyright 2016 Centre for Info Bio Technology (CIBTech) 379
Plnts nd Petrochemicl Industries, 2, Edition A. K. Ry, S. Chudhuri, N. G. Goswmi nd R. N. Ghosh, (NML Jmshedpur 831007, Indi) 85-114. d Silveir TL nd My IL (2006). Reformer furnces: Mterils, dmge mechnisms, nd ssessment. The Arbin Journl for Science nd Engineering 31(2C). de Almeid LH et l., (2002). Microstructurl Chrcteriztion of Modified 25Cr-35Ni Centrifuglly Cst Steel Furnce Tubes. Mterils Chrcteriztion 49 219 229. Hsegw K (2001). Repir Welding nd Metllurgy of HP-Modified Alloy After Long Term Opertion, (METAL Ostrv, Czech Republic). Huber J nd Jkobi D (2011). Centricst Mterils for High-Temperture Service, Nitrogen+Syngs 2011 Interntionl Conference, Düsseldorf. Jkobi D nd Gommns R (2003). Typicl filures in pyrolysis coils for ethylene crcking. Mterils nd Corrosion 54(11). K. Eschbch, Report No 111184-2013-78, Schmidt + Clemens Group, RDS Kseipoor A, Ghsemi B nd Aminossdti SM (2015). Convection of Cu-wter nnofluid in vented T-shped cvity in the presence of mgnetic field. Interntionl Journl of Therml Sciences 94(8) 50-60. Schillmoller CM (no dte). HP-Modified furnce tubes for stem crckers, Nickel Development Institute Technicl Series No 10058 Vnder Voort GF (2004). Metllogrphy nd Microstructures, ASM Interntionl 9. Copyright 2016 Centre for Info Bio Technology (CIBTech) 380