The new generation of CrMo(V) steel plates base material - welding 1
Content 1. Introduction 2. Application trends and resulting requirements for CrMo(V) steels 3. Metallurgical limits for PWHT- conditions 4. Processing 5. Summary 2
1. Introduction 3
conventional A broad variety of CrMo(V) steels is commercially available 1Cr½Mo ASTM/ASME A/SA 387-12-1/2 EN 10028-2: 1992, 2003 13CrMo4-5 1¼Cr½Mo ASTM/ASME A/SA 387-11-1/2 EN 10028-2: 1992, 2003 13CrMoSi5-5 2¼Cr1Mo ASTM/ASME A/SA 387-22-1/2 A/SA 542-A/B-3/4/4a EN 10028-2: 1992 10CrMo9-10 11CrMo9-10 EN 10028-2: 2003 10CrMo9-10 12CrMo9-10 2¼Cr1Mo¼V ASTM/ASME A/SA832-22V A/SA 542-D-4/4a EN 10028-2: 2003 13CrMoV9-10 3Cr1Mo¼V ASTM/ASME A/SA832-23V A/SA 542-E-4/4a EN 10028-2: 2003 12CrMoV12-10 4
enhanced A broad variety of CrMo(V) steels is commercially available 1Cr½Mo ASTM/ASME A/SA 387-12-1/2 EN 10028-2: 1992, 2003 13CrMo4-5 1¼Cr½Mo ASTM/ASME A/SA 387-11-1/2 EN 10028-2: 1992, 2003 13CrMoSi5-5 2¼Cr1Mo ASTM/ASME A/SA 387-22-1/2 A/SA 542-A/B-3/4/4a EN 10028-2: 1992 10CrMo9-10 11CrMo9-10 EN 10028-2: 2003 10CrMo9-10 12CrMo9-10 2¼Cr1Mo¼V ASTM/ASME A/SA832-22V A/SA 542-D-4/4a EN 10028-2: 2003 13CrMoV9-10 3Cr1Mo¼V ASTM/ASME A/SA832-23V A/SA 542-E-4/4a EN 10028-2: 2003 12CrMoV12-10 5
new generation A broad variety of CrMo(V) steels is commercially available 1Cr½Mo ASTM/ASME A/SA 387-12-1/2 EN 10028-2: 1992, 2003 13CrMo4-5 1¼Cr½Mo ASTM/ASME A/SA 387-11-1/2 EN 10028-2: 1992, 2003 13CrMoSi5-5 2¼Cr1Mo ASTM/ASME A/SA 387-22-1/2 A/SA 542-A/B-3/4/4a EN 10028-2: 1992 10CrMo9-10 11CrMo9-10 EN 10028-2: 2003 10CrMo9-10 12CrMo9-10 2¼Cr1Mo¼V ASTM/ASME A/SA832-22V A/SA 542-D-4/4a EN 10028-2: 2003 13CrMoV9-10 3Cr1Mo¼V ASTM/ASME A/SA832-23V A/SA 542-E-4/4a EN 10028-2: 2003 12CrMoV12-10 6
2. Application trends and resulting requirements for CrMo(V) steels 7
Application and trends for the use of CrMo(V) steels Application: typical applications are hydrotreating reactors operating temperatures up to 480 C hydrogen partial pressures up to 180 bar or even higher Trends: ever bigger and heavier reactors (already more than 1000t per unit) higher operating temperatures and pressures resulting in higher wall thicknesses increasing demand due to expansion or new construction of plants 8
Special requirements for more sophisticated steels Increasing thickness with high demand in thickness over 100mm Larger dimensions to allow for more freedom in vessel design PWHT requirements including 3 or often even 4 cycles Chemical restrictions exceeding those of the standards Improved resistance against hydrogen Specifying J- and X-factor for ultra clean steels Specifying toughness values at low temperatures in combination with PWHT Additional requirements in regard to grain size and microstructure Hardness restrictions Specifying step cooling test Additional tensile test at elevated temperatures... Many additional requirements; often in combination 9
3. Metallurgical limits for PWHT conditions 10
General influence of a PWHT on the mechanical properties of CrMo-steels R m before A v after A v, R m, R p0,2 Before PWHT A v before R p0.2 before HP-Factor After PWHT R m after R p0.2 after 11
Tensile- and yield strength of enhanced 2¼CrMo steels (N+AC+T) 1000 900 Thickness > 200 mm R p0,2 resp. R m [N/mm 2 ] 800 700 600 500 400 300 12CrMo9-10 12CrMo9-10 12CrMo9-10 Tempering 740 C/30 R m R p0.2 PWHT-Min 690 C/8h PWHT-Max 690 C/24h 19,8 20,0 20,2 20,4 20,6 20,8 21,0 21,2 HP-Factor 12
Tensile- and yield strength of enhanced 2¼CrMo (V) steels (N+AC+T) 1000 900 Thickness > 200 mm R p0,2 resp. R m [N/mm 2 ] 800 700 600 500 400 300 + 0,25% V R m V-modified R m enhanced R p0.2 enhanced 19,8 20,0 20,2 20,4 20,6 20,8 21,0 21,2 HP-Factor 13
Tensile- and yield strength of enhanced 2¼CrMo (V) steels (N+AC+T) 1000 900 Thickness > 200 mm 800 700 R m V-modified + 0,25% V 600 Rp0,2 resp. R m [N/mm2 ] R p0.2 V-modified 500 400 R p0.2 enhanced 300 19,8 20,0 20,2 20,4 20,6 20,8 21,0 21,2 HP-Factor 14
Tensile- and yield strength of enhanced 2¼CrMo (V) steels (N+AC+T) R p0,2 resp. R m [N/mm 2 ] 1000 900 800 700 600 500 400 300 A542-D-4a A542-D-4a Thickness > 200 mm Tempering 715 C/250 A542-D-4a PWHT-Min 705 C/8h R m V-modified PWHT-Max 705 C/24h R p0.2 V-modified 19,8 20,0 20,2 20,4 20,6 20,8 21,0 21,2 HP-Factor 15
Estimated impact toughness of enhanced 2¼CrMo(V) steels (N+AC+T) 350 350 Thickness > 200 mm Thickness > 200 mm 300 300 Impact Toughness [J] 250 200 150 100 50 0-20 C -40 C 0 C 2¼CrMo 19,8 20,0 20,2 20,4 20,6 20,8 21,0 21,2 HP-Factor +20 C Impact Toughness [J] 250 200 150 100 50 0-20 C 2¼CrMoV -60 C -40 C 19,8 20,0 20,2 20,4 20,6 20,8 21,0 21,2 HP-Factor 0 C +20 C 16
SA 387-22-2: Feasibility in dependence of HP, R m, R e, Ch-V, hardness and plate thickness of 2¼CrMo steel 21,2 21,0 Average 31 J 21,2 21,0 N+AC+T 195 HB Hollomon parameter 20,8 20,6 20,4 20,2 20,0 19,8 19,6 19,4 19,2 19,0 N+T -29 C -18 C N+AC+T -40 C -18 C u. -29 C -10 C 0 20 40 60 80 100 120 140 160 180 200 Plate thickness [mm] Hollomon parameter 20,8 20,6 20,4 20,2 20,0 19,8 19,6 19,4 19,2 19,0 205 HB 210 HB 215 HB 200 HB 195 HB N+T 0 20 40 60 80 100 120 140 160 180 200 Plate thickness [mm] 190 HB 200 HB 205 HB 210 HB 215 HB 17
2¼ CrMo(V), Q + T, plate delivery dimensions of Dillinger Hütte GTS 250 225 upon agreement up to 42 t 200 Thickness [mm] 175 150 125 100 75 50 25 0 N + AC + T (Q + T) up to 37 t up to 28 t Depending on grade & thickness up to 37 t 1,50 1,75 2,00 2,25 2,50 2,75 3,00 3,25 3,50 3,75 4,00 4,25 4,50 4,75 5,00 5,25 Width [mm] Maximum thickness is often limited by requirements from specifications As rolled (plates for hot-forming) up to 37 t 18
Conclusion 1 CrMo steels with ¼V offer improved performance for petrochemical reactors compared to enhanced 2¼Cr1Mo steels. Plates are commercially available up to about 250 mm thickness. The steels tolerate very high temperatures 690-710 C for post weld heat treatment. DH-GTS is a long term supplier with plenty of know how for highly sophisticated steels A wide range of dimensions can be supplied. 19
4. Processing 20
4. Processing - Index 4.1 Reference to API 934 - Recommended Practice 4.2 Impact toughness requirements test conditions 4.3 Step cooling 4.4 Flame cutting 4.5 Forming and subsequent thermal treatment 4.6 Welding Weld design Welding procedure qualification Production testing Preheat and minimum interpass temperature HAZ-hardness Welding consumables Production tests 4.7 Post weld heat treatments Intermediate post weld heat treatments PWHT - final PWHT 21
Title and introduction of API 934 API recommended practice 934 : 2000 Materials and Fabrication Requirements for 2¼ Cr-1Mo & 3Cr-1Mo Steel Heavy Wall Pressure Vessels for High Temperature, High Pressure Hydrogen Service *...Introduction This recommended practice applies to new heavy wall pressure vessels in petroleum refining, petrochemical and chemical facilities in which hydrogen or hydrogen-containing fluids are processed at elevated temperature and pressure. Materials covered by this recommended practice are conventional steels including standard 2-¼Cr-1Mo and standard 3Cr-1Mo steels, and advanced steels including enhanced 2-¼Cr-1 Mo, 2-¼Cr-1Mo-¼V, 3Cr-1Mo-¼V-Ti-B, and 3Cr-1Mo-¼V-Cb-Ca steels. The interior surfaces of these heavy wall pressure vessels may have an austenitic stainless steel weld overlay to provide additional corrosion resistance.... 22
Impact test - step cooling Additional to the PWHT condition impact tests are required after step cooling : on the base material (each heat) on welding consumables (each batch) on HAZ for the qualification of welding procedures and the verification on production welds What is step cooling and why is it applied? 23
impact transition curve impact energy before service after high temperature service 54J T test temperature 24
trace elements are responsible Parent material J = (Si + Mn) x (P + Sn) x 1000 Service embrittlement - step cooling Weld metal X = (10P + 5Sb + 4Sn + As) / 100 API 934 X < 15 harmful elements must be restricted to provide good toughness properties through the life time. 25
Step cooling - heat treatment Heating rate 56 /h 316 C 6h 1h 15h 24h 60h 100h 6h 1 6 C/h 2 6 C/h 3 6 C/h 4 3 C/h 5 28 C/h 26
Step cooling- impact transition curve impact energy initial after step cooling 54J T SC T tot after service T tot = 2.5 x T SC test temperature 27
4.6 Welding 28
HV10 400 HAZ hardness comparison of CrMo- and CrMoV-steel 2¼CrMo¼V as welded 250 usual range 2¼CrMo as welded cooling time t 8/5 29
Coarse grained HAZ microstructure as welded coarse grained HAZ t 8/5 22s - essentially Martensite For the usual welding conditions we obtain Martensite in the coarsed grained HAZ and high as welded hardness ~400 HB 30
Cold forming Bend test to check cold forming (cross section 200 x 50 mm) with severe deformation no cracks on the machined side even for bending at ambient temperatur a small crack in the flame cut edge after bending at 170 C 31
Hydrogen induced cold cracking Weld metal and HAZ in the as welded condition are susceptible to hydrogen induced cold cracking how to avoid this defect? dry and clean weld bevels select low hydrogen consumables and treat them properly to minimise hydrogen input (rebaking, storage, heated quivers...) keep the weld at sufficiently high temperatures until the weld is completed (>180 C) lower the concentration of residual hydrogen by heat treatment immediately after welding (300-350 C) lower the hardness and cracking susceptibility by PWHT (~700 C) or intermediate PWHT (~650-670 C) 32
HV10 400 HAZ hardness comparison of CrMo- and CrMoV-steel 650 C-10h 2¼CrMo¼V as welded 250 235 675 C-10h 700 C-10h 725 C-10h usual range 2¼CrMo as welded 650 C-10h 675 C-10h 700 C-10h cooling time t 8/5 33
Development of carbides during PWHT As welded no carbides 0,5µm TEM micrographs on carbon extraction replica 2 1 / 4 CrMoV Ref.: Lundin,C.D. and K.K.Khan, WRC Bulletin 409 620 C - 15 M 3 C few M 23 C 6 0,5µm 0,5µm 730 C - 8h M 7 C 3, M 23 C 6, fine V 4 C 3, M 2 C 34
5. Summary 35
Summary Parent metal toughness: sufficient safety margin against the requirements at -29 C and taking into account the step cooling. Limited step cooling embrittlement is achieved by extremely low level of trace elements. HAZ toughness: after PWHT impact at -29 C and after lifetime at +10 C satisfactory thanks to ultra low trace elements. HAZ hardness 248HV10 (235 HB) is achieved by proper PWHT at 705 C 235HV10 is difficult to achieve weld metal toughness: Very few potential suppliers. Rather important scatter of impact results at -29 C, and at +10 C after lifetime more difficult than for CrMo-Steel. (with regard to the lowest anticipated service temperature some relaxation should be possible). Development is ongoing. hydrogen induced cracking can safely be prevented -> needs good workmanship, careful personal and well controlled processing conditions PWHT for 8-10 hours 705 C - 710 C is experienced to be the best compromise for the properties in the welded construction. In case of repeated PWHT the sum of holding times shall not exceed 24 h. 36
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