Ruthenium Enhanced Titanium Alloys

Transcription

1 Ruthenium Enhnced Titnium Alloys MINOR RUTHENIUM ADDITIONS PRODUCE COST EFFECTIVE CORROSION RESISTANT COMMERCIAL TITANIUM ALLOYS By R. W. Schutz RMI Titnium Compny, Niles, Ohio, U.S.A. Severl new, more highly corrosion resistnt titnium lloys contining nominl 0.1 weight per cent of ruthenium hve been developed nd evluted for industril service in corrosive environments. These improved ruthenium-enhnced, -p nd p titnium lloys re lower in cost thn the corresponding plldium-contining titnium lloys, nd offer essentillr the sme corrosion performnce in dilute reducing cids nd hot brine environments. The titnium-0.1 ruthenium binry lloys cn be cost effectively substituted for trditionl titnium-plldium lloys nd should represent more ttrctive lterntive to nickel-chromium-molybdenum lloys in hot, cidic brine pplictions. The corrosion dtbse tht hs been estblished for the higher strength ruthenium-enhnced -p nd p titnium lloys in high temperture sweet nd sour brines provides the bsis for their selection for pplictions in the chemicl process, oillgs production, offshore nd geotherml energy industries. Trditionlly, the plldium-contining titnium lloys, ASTM (Americn Society for Testing nd Mterils) Grdes 7 nd 11 titnium (titnium-0.15 weight per cent plldium, Ti-0.15Pd) hve been the most corrosion resistnt titnium lloys commercilly vilble. These titnium-plldium, Ti-Pd, lloys were selected when other common industril titnium lloys, such s the unlloyed grdes, exhibited susceptibility to crevice nd pitting corrosion in more ggressive chemicl service. Severe service environments include chlorinesturted brines, wet hlogens, cidic metl chloride solutions (such s FeCl,, ZnCl,, AlCl,) nd hydrolysble, concentrted brines (such s MgCl,, CC1,) t tempertures exceeding - 80 C. The Ti-Pd lloys re lso corrosion resistnt over much wider rnge of tempertures nd/or cid concentrtions in hot dilute inorgnic nd orgnic reducing cids (1). Despite their drmticlly enhnced corrosion performnce, the utilistion of Grdes 7 nd 1 1 titnium lloys hs been severely limited over the pst thirty yers due to their high reltive cost. As is shown in Tble I, the cost of Ti-Pd lloy is lmost twice tht of unlloyed titnium nd is similr to tht of common nickelchromium-molybdenum, Ni-Cr-Mo, lloys on dimensionl (density-normlised) bsis. The higher cost of the titnium lloy results solely from its plldium content, bsed on nominl ddition of 0.15 to 0.18 weight per cent (t price tken in November 1995 of $144/troy ounce for plldium powder). Lener Plldium-Titnium Alloys Over the pst five yers titnium lloy producers hve criticlly re-evluted the minimum plldium content required in the lloy. Following closer exmintion of the originl corrosion dt estblished by Stem nd Wissenberg in the development of the Ti-Pd lloy (2, 3), it ws recognised tht significnt svings could be chieved by reducing the nominl plldium content. Stern s profiles of corrosion rtes in boiling hydrochloric cid, see Figure 1, clerly suggest tht the beneficil effect due to plldium is optimised very quickly t Pltinum Metls Rev., 1996, 40, (2),

2 Tble I Approximte Mill Product Cost Rtio* (Corrected for Density) Alloy Unlloyed Ti Ti-0.3Mo-0.8Ni Ti-0.1 5Pd Ti-0.05 Pd Ti-0.1 Ru Ti-3AI-2.5V Ti-3AI-2.5V-0.05 Pd Ti-3AI-2.5V-0.1 Ru Ti-6AI-4V Ti-6AI-4V-0.05 Pd Ti-6AI-4V-0.1 Ru Alloy C-276 (Ni-Cr-Mo) I ASTM Grde * For 6.3 mm plte Rtios re compred to the cost of unlloyed titnium Costings re bsed on November 1995 figures cost rtio 1.oo low levels, so tht only miniml improvements in corrosion occur for lloys contining bove weight per cent plldium (2, 3). This behviour ws confirmed in more recent hydrochloric cid corrosion rte profiles developed by Kitym, Shid nd collegues (4,5), nd by the uthor, s shown in Figure 2 (6). As expected, drmtic improvements in lloy crevice corrosion resistnce in hot chloride nd other hlide-rich queous medi re lso chieved t these lower plldium levels, see Figure 3 (5, 6). Bsed on these studies, severl new lenplldium lloys, which re described in Tble 11, hve been incorported into ASTM product specifictions. These lloys re llowed to contin 0.04 to 0.08 weight per cent plldium, with the nominl mount being 0.05 per cent. The resulting reductions in cost of Ti-Pd lloy mill products re significnt, nd re shown in Tble I. For pplictions where higher strength lloys re required, similr dditions of plldium cn be mde to -j3 or j3 titnium lloys to produce the cost effective lloys outlined in Tble 11. The corrosion performnce of these higher strength plldium-enhnced lloys is documented elsewhere (6, 7). Len Ruthenium-Titnium Alloys The on-going pursuit of lower cost industril titnium lloys t the RMI Titnium Compny hs led to the development of rutheniumenhnced titnium lloys. From the stndpoint of lloy formultion cost, ruthenium represents the lowest cost pltinum group metl ddition on per weight bsis. The ruthenium powder price, in November 1995, ws pproximtely $30 per troy ounce, which is fctor of four to five times lower thn tht of plldium powder. However, profiles of the cid corrosion rtes for the titnium-ruthenium, Ti-Ru, binry lloy nd for other titnium lloys suggest tht t lest twice s much ruthenium by weight is required to imprt corrosion resistnce comprble to tht of titnium-0.05 weight per cent plldium, Ti-0.05PdY see Figure 2 (6). Despite the need to double the weight of the ruthenium ddition, the titnium lloy contining the nominl 0.1 weight per cent ruthenium still chieves cost svings of pproximtely 17 per cent compred with the Ti-O.05Pd (titnium Grde 16) lloy nd pproximtely 40 per cent compred with the clssic Ti-0.15Pd (titnium Grde 7) lloy. Comprtive % HCI 3% HCI PLATINUM OR PALLADIUM, Wt % Fig. 1 Effect of the plldium content on the titnium corrosion rte in boii hydrochloric cid solutions (2,3) Pltinum Metls Rev., 1996, 40, (2) 55

3 Tble II New, Improved nd Cost-Optimised Ruthenium-Enhnced Titnium Alloys for Corrosive Service Trditionl Alloy Alloy (UNS Number) Ti-0.15Pd (R52400) Ti-0.1 5Pd* (R52250) Ti-3AI-2.5V (R56320) Ti-6AI4V (R56400) ASTM Grde New nd Improved Alloy Alloy ASTM Grde 7 Ti-O.05Pd 16 Ti-0.1 Ru 16 Ti-0.05Pd" Ti-0.1 Ru" Ti-3AI-2.5V-0.05 Pd Ti-3AI-2.5V-0.1 Ru Ti-6AI4V-0.05Pd Ti-6AI-4V-0.1 Ru I Motivtion for New Alloy New lloy Lower cost 17 Lower cost Enhnced crevice nd 28 reducing cid resistnce 24 Enhnced crevice, 29 reducing cid, nd SCC resistnce Ti-3AI-8V-6Cr4Zr-4Mo (Ti or Ti 8et-CTM) (R58640) 19 Ti Pd 20 Enhnced crevice, Ti Ru - reducing cid, nd SCC resistnce Low interstitikoft grde UNS Unified Numbering System lloy costs outlined in Tble I for thin plte product suggest tht ruthenium-enhnced titnium lloys offer substntil cost svings over the corresponding plldium-contining lloys. Mechnism of Ruthenium Enhncement The bsic mechnism of ruthenium ddition to titnium is considered to be very similr to tht of plldium nd other pltinum group metls, nd results from lloy ennoblement. In similr wy to plldium, ruthenium exhibits miniml solubility (less thn 0.1 weight per cent) in the -titnium phse, which results in fine, uniform dispersion of noble Ti-Ru precipittes withiin the lloy (8). When exposed to reducing cids, these precipittes, nd/or ruthenium-enriched surfces produced by selective dissolution, provide 1 [:ye -4 ~ t TI Grde 2 + T1-0.05Pd -A- Tt-DlSPd -0- Ti-010Ru Fig.2 Corrosion rte profle for titnium-0.1 percent ruthenium nd titnium-plldium lloys 1 2 HYDROCHLORIC ACID, Wt in boiling hydrochloric cid solutions 1 fitinurn Meth Rev., 1996,40, (2) 56

4 cthodic sites of low hydrogen overvoltge nd ccelerted hydrogen ion (H,O+) reduction (9, 10). This depolristion of the hydrogen ion reduction rection, or cthode-modifiction phenomenon, produces substntil shift in the corrosion potentil of the titnium lloy in cid towrds the noble (positive) direction where the protective surfce oxide film,tio,, is stble (l), nd full pssivity cn be chieved. This hs been highly effective nd well-known technique for improving the corrosion performnce of titnium lloy, due to the well estblished ctivepssive behviour of titnium in reducing cids nd its exceptionlly high nodic pitting potentil in cid solutions. Ruthenium lloy dditions lso effectively inhibit titnium crevice corrosion in hot queous hlide nd sulphte environments. This enhnced crevice corrosion resistnce results from the sme cthode modifiction mechnism discussed bove for reducing cids. With time, the solution within tight metl crevice exposed to hot slt solutions often becomes more ggressive deerted reducing cid (1). This explins the dul beneficil effects from the ruthenium ddition, both in reducing cid exposure nd within crevices. Creviced surfces re ennobled nd locl pssivity is mintined TEMPERATURE. C Fig. 3 Temperture-pH limits for crevice corrosion of titnium lloys in nturllyerted sodium chloride-rich brines. (The shded res re regions where lloys re susceptible to ttck) within cidic crevices. The enhnced crevice resistnce of Ti-Ru lloys is essentilly equivlent to tht of Ti-Pd lloys, s indicted by the guidelines in Figure 3. Higher Strength Ruthenium- Enhnced Titnium Alloys Greter strength in titnium is commonly chieved by the ddition of lloying elements, such s luminium nd vndium, to form Tble Minimum Tensile Strength Vlues for New Ruthenium-Enhnced Titnium Alloys I Allov ASTM Grde ASTM Ti-O.15Pd 7 Ti-0.1 Ru I 26 Alloy type Minimum Yield Stress, ksi (MP) 40 (275) 40 (275) Minimum Ultimte Tensile Strength, ksi (MP) 50 (345) 50 (345) Ti-O.15Pd Ti-0.1 Ru (170) 25 (1 70) 35 (240) 35 (240) Ti-3AI-2.5V 9 Ti-3AI-2.5V-0.1 Ru Ti-6AI-4V ELI Ti-6AI-4V-0.1 Ru P -P -P -P 70 (483) 70 (483) 1 10 (759) 11 0 (759) 90 (620) 90 (620) 120 (827) 120 (827) Low interstitillsoft grde ksi is 1000 Ibhn ELI is Extr Low lnterstitils Pltinum Metls Rev., 1996, 40, (2) 57

5 E TI-~AI-~V T1-3Al-25V Fig. 4 Corrosion rte profiles for -P titnium lloys in boiling hydrochloric cid solutions showing the benefits of ruthenium dditions u' t 150 Q d 1.00 g 050 TI-~AI- 4V- Ru TI-~AI - 2 5V- Ru -P or P-phse lloys. With the exception of molybdenum, most common lloying elements, nd especilly luminium, diminish the reducing cid- nd hot hlide crevice-corrosion resistnce of titnium lloys, with incresing content (1 1). The titnium-3 luminium-2.5 vndium, Ti-3AI-2.5V, (titnium Grde 9) nd titnium-6 luminium-4 vndium, Ti-6AI-4V, (titnium Grde 5) lloys re two such common -p lloys which exhibit ttrctive medium-tohigh strength properties, see Tble 111, but in certin environments they possess corrosion resistnce inferior to tht of unlloyed titnium. In fct, the Grde 9 titnium lloy ws recently incorported into the ASME (Americn Society of Mechnicl Engineers) Pressure Vessel Code for use t tempertures up to 3 15"C, nd offers significntly higher design llowbles compred with other titnium lloys listed in the Code. Unfortuntely, this lloy is susceptible to crevice corrosion in chloride- or other hlide-rich service environments t tempertures bove - 80 C (depending upon ph, etc.), thus severely limiting ppliction nd design opportunities. The higher strength titnium Grde 5 lloy lso exhibits susceptibility to stress corrosion in brine nd queous hlides which similrly limits its use t incresed tempertures. The deficiencies in the corrosion performnces of these high strength titnium lloys cn lso -"" I 4350 TI Grdes TI-RU or TI-Pd 0 Ti-3AI - 2 5V- Ru TI- 6AI- 4V - Ru TI Grde 12 20% NCI. ph2 25% NCI, ph3 10% FeCI, or (Nt. erted1 (deertedl 20% NO, ph2 (CI?- st1 Fig. 5 Approximte temperture thresholds for crevice corrosion of rutheniumenhnced titnium lloys in cidic chloride brines Pltinum Meth Rev., 1996, 40, (2) 58

6 I I Alloys tested I Ti-6AI-4V-R u Ti-3AI-2.5V-RU Ti-3Al-8V-6Cr-4Zr-4Mo-R~ I Ti-6AI-4V-RU Ti-3AI-2.5V-Ru Ti-6AI-4V-Ru Tble IV Results of Stress Corrosion Crcking Tests for Ruthenium-Enhnced Titnium Alloys in High - Temperture Brines I Test medi Sour gs well brine Sour geotherml brine Hypersline geotherml brine Types of SCC tests C-ring Slow strin rte U-bend C-ring Slow strin rte 9 U-bend Slow strin rte Temperture of tests, OC SCC or loclised ttck? 260 No 232, 260, 288 No 302,330 No 330 No 302,330 No 260 No 25, 260, 274 No Sour gs well brine: Sour geotherml brine: Hypersline geotherml brine: deerted 25% NCI, 1000 psig H,S. 500 psig CO,. 1 g/l S. ph ,000 ppm CY, 800 ppm SO:-. 4 ppm F-, 12,420 ppm N ppm K*, 20 psig H,S. 100 psig CO,. ph 2.3 (deerted) 15.2% NCI. 2.45% KCI. 6.7% CCI,. 200 psig CO,. ph 4.0 (deerted) be effectively reduced by nominl dditions of 0.1 weight per cent ruthenium. Corrosion studies performed upon ruthenium-enhnced -j3 titnium lloys revel substntil improvements in their resistnce to reducing cids, hot chloride crevice corrosion nd stress corrosion crcking (6). Alloy corrosion rte profiles in boiling hydrochloric cid, presented in Figure 4, show the obvious benefit of ruthenium dditions. The mechnism of corrosion resistnce is gin the sme cthode modifiction (ennoblement) nd oxide film stbilistion phenomenon s discussed previously for the binry Ti-Ru nd Ti-Pd lloys. The drmtic elevtion of the threshold tempertures t which crevice corrosion strts in nturlly-erted cidic brines is indicted in Figure 5 for the ruthenium-enhnced -p lloys. This enhncement hs been confirmed vi worst-cse Teflon gsket-to-metl crevice tests in sweet nd highly sour concentrted brines nd in deerted hypersline Slton Se geotherml brines down to ph 2 (6). In more ggressive, severely-oxidising (chlorine sturted or FeC1,-rich) cidic brines, the crevice resistnce of these higher strength lloys my be restricted to ph vlues bove 3, when tempertures exceed - 80 C. Although the Ti-3Al-2.5V lloy is not generlly susceptible to stress corrosion crcking (SCC) in queous medi, it is known tht the Ti-6A1-4V lloy cn exhibit hlide SCC susceptibility, especilly when the luminum nd/or interstitil levels increse (1 2). This serious limittion cn be llevited during exposure to hot queous hlide (brine) by ruthenium ddition to the ELI (Extr Low Interstitils with 0.13 per cent oxygen mximum) Ti-6A1-4V lloy bse. The SCC test results outlined in Tble IV support the selection of these modified -j3 titnium lloys for use in either sweet or sour sodium chloride-rich brines t tempertures s high s 330 C. These hot brine test environments re typicl of those in Slton Se geotherml brine wells in Cliforni nd in deep sour gs wells in the Gulf of Mexico. Similr improvements in high temperture corrosion behviour cn be chieved in j3-titnium lloys by the ddition of ruthenium. Corrosion studies conducted by the uthor on the Ti (titnium Grde 19) (Ti Bet- C ) lloy suggest tht the mechnism is gin Pltinum Metls Rev., 1996, 40, (2) 59

7 P w 3M3. b 6 n Crevice corrosion in sweet brine I Crevice corrosion in sour brine Stress corrosion n Stndrd Ru- Enhnced TI TI Fig. 6 Approximte temperture thresholds for crevice nd stress corrosion of stndrd nd ruthenium-enhnced Ti lloys in sweet nd sour sodium chloride brines cthode-modifiction. Of prticulr engineering vlue re the drmtic increses in the threshold tempertures for crevice corrosion nd SCC offered by the ruthenium-enhnced Ti lloy in sweet nd sour sodium chloride-rich brines (13), see Figure 6. Sttus nd Potentil Applictions for Ruthenium-Contining Titnium Alloys Since the minor ddition of 0.1 weight per cent ruthenium to these titnium lloys hs no sign5cnt influence on their mechnicl nd physicl properties, the new ruthenium-contining lloys re specified with the sme minimum tensile properties s the corresponding bse lloys. Vlues for the minimum tensile properties required by ASTM product specifictions re listed in Tble III. The four new rutheniumcontining nd -j3 lloys, with permitted ruthenium content of 0.08 to 0.14 per cent, hve been ssigned the ASTM grde numbers indicted in Tble 11. They hve recently been incorported in pproprite ASTM specifictions for sheet, strip nd plte (B265), forgings (B381), br nd billet (B348), semless nd welded pipe (B337, B861 nd B862), fittings (B363), tubing (B338) nd wire (B863). ASTM Grdes 26,27 nd 28 titnium lloys will soon be submitted for pprovl nd eventul incorportion into the ASME Pressure Vessel Code. The ASME Code design llowbles specified for these three lloys should mimic those for titnium Grdes 7, 11 nd 9 lloys, respectively, lredy in the Code. Some other possible pplictions for the titnium-0.1 ruthenium lloys (Grdes 26 nd 27) in the chemicl nd process industries re listed in Tble V. These lloys offer cost effective, direct replcement of titnium Grde 7 nd 1 1 lloys. The lower cost of these Ti-Ru lloys should lso result in incresed use of titnium in trditionl Ni-Cr-Mo lloy pplictions which involve dilute cids nd/or hlide-rich process strems. Current cndidte pplictions for the higher strength ruthenium-enhnced titnium lloys Tble V Cndidte Applictions for Titnium-0.1 Ruthenium Alloys Chlorlkli nd chlorte cell nodes, liners nd components Hot sewtedbrine plte exchngers* Hot C. Mg slt brines Hot cidic metl hlides (FeCI,, CuCI,. AICI,. NiCI, nd ZnCI,) Hot queous CI,/Br, (wet hlogens) nd CI,-sturted brines Hot dilute orgnic nd inorgnic cids MnO, nodes FGD (Flue Gs Desulphuristion) scrubber inlets/prescrubbers Steel tubesheetlvessel explosive cldding* * Requires softer. lower interstitil grdes of these lloys Pltinum Metk Rev., 1996, 40, (2) 60

8 Appliction Applicble Alloys I Ti-3AI-2.5V-Ru I Ti-GAI-4V-Ru I Ti Ru Wet oxidtion processes I x I I Other wste tretment processes I I I Hih ternderture ornic svnthesis I I I ~ ~~ ~~ ~ ~ Hydrometllurgicl ore leching processes Tble VI Cndidte Applictions nd Components for Ruthenium-Enhnced -P nd P Titnium Alloys Deep sour gs nd geotherml well tubulrs Downhole tools nd ccessories I I I Offshore flowlines, export nd ctenry risers Coiled tubing Pressure vessels, het exchngers Vlves, pumps, shfting Fsteners Agittors Semless piping Welded piping re outlined in Tble VI. Note tht the titnium Grdes 28 nd 29 lloys re lso currently in the finl stge of pprovl for incorportion in the NACE (Ntionl Assocition of Corrosion Engineers) MR Stndrd for use in sour service; llowing these new lloys to be selected for mny deep oil/gs wells nd offshore production components. References 1 R. W. Schutz nd D. E. Thoms, Corrosion of Titnium nd Titnium Alloys, in Metls Hndbook-Ninth Edition, Vol Corrosion, ASM, Mterils Prk, OH, 1987, pp M. Stern nd H. Wissenberg,J. Elecmchem. SOC., 1959, 106, (9), M. Stern, US. Ptent 3,063,835; S. Kitym, Y. Shid, M. Ued nd T. Kudo, Effect of Smll Pd Addition on the Corrosion Resistnce of Ti nd Ti Alloys in Severe Gs nd Oil Environment, Pper No. 52, Corrosion 92 Annul Conf., NACE, Houston, Mrch S. Kitym, Y. Shid nd M. Oshiym, Sumitorno Serch, Sumitomo Metls, Jpn, 1990, (41), 23 6 R. W. Schutz, Recent Titnium Alloy nd Product Developments for Corrosive Industril Service, Pper No. 244, NACE Corrosion 95 Annul Conf., NACE, Houston, R. W. Schutz nd M. io, Optimized Len-Pd Titnium Alloys for Aggressive Reducing Acid nd Hlide service Emimmem : Roc. 1% Int Corrosion Congr., 34 Sept. 1993,NACE, Houston, p E. Vn der Lingen nd H. de Villiers Steyn, The Potentil of Ruthenium s n Alloying Element in Titnium, Pper presented t Titnium Applictions Conference, October 2-5, 1994, Titnium Development Assocition, Boulder, Colordo 9 N. D. Tomshov, R. M. Altovsky nd G. P. Chernov,J. Elecmchem. SOC., 1961,108, (2), H. H. Uhlig, The Corrosion Hndbook, J. Wiley & Sons, Nu, 1948, pp R. W. Schutz nd J. S. Grumn, Fundmentl Chrcteriztion of High-Strength Titnium Alloys, Industril Applictions of Titnium nd Zirconium, ASTM STP 917,1986, pp Stress-Corrosion Crcking-Mterils Performnce Evlution, ASM, Mterils Prk, OH, July 1992, pp R W. Schutz nd M. io, Enhncing Corrosion Resistnce of the Ti Alloy for Industril Applictions, Titnium 92 - Science nd Technology, Vol. III, TMS, Wrrendle, PA, 1993, p Pltinum Metls Rev., 1996, 40, (2) 61