SCC of Alloy 69, Alloy 152/52/52i Weld Metals and Dilution Zones Dr. Peter L. Andresen - GE Global Research Center (retired) Al Ahluwalia EPRI Project Manager International Light Water Reactor Materials Reliability Conference Chicago - August 216
Context / Perspective ASME codes rely on the concept of SCC immunity, which is not helpful. Despite widespread opinion a decade ago, Alloy 69 is susceptible to SCC initiation and growth, and CGRs can be high. Lore (opinion without data) has been repeatedly found inaccurate: 69 homogeneity, 1D rolling as unique, CRDM as immune, GB carbides as beneficial, no intentional cold work in plant components To date, only low CGRs of 69 observed at < ~1% cold work, but several materials that exhibit the highest CGRs have not been evaluated. Almost all CGRs are low in 152/52/5i weld metals, even with DDC or weld repairs or with high IG morphology. Exceptions occur primarily at one laboratory, where load fluctuations during testing may explain the difference. Excellent plant experience with 69 and 152/52 weld metals. 2
Context / Perspective High CGRs observed in some cases at ~ 12% cold work. High CGRs in best materials (CRDM) at 2% cold work. Despite < 5% intentional cold work policy, it is hard to ensure all components have <15 2% strain from incomplete annealing, fabrication / straightening and weld residual strain. Should employ 9 th percentile or similar. CGR evolution vs. time indicates susceptible paths exist; thus, some longer term testing is needed for evaluation. Temperature and H 2 dependencies vanish in high CGR materials, so very high CGRs can persist down to < 29 C. Comparisons of 6 vs. 69 at ~15% strain are limited but suggest an average of >1X difference in CGR and perhaps initiation. Expert Panel is creating an scored database that will be used to create CGR disposition curves for 69 & 152/52. Must pay attention to problem data 3
Testing Approach 69 cold worked by forging or 1-D rolling or weld HAZ aligned: used dcpd resistivity correction used anticipatory dcpd correction for better K control weld metal and HAZ-aligned and interface specimens evaluated.5t CT specimens in 36 ºC (29 36ºC) PWR primary water testing at 25 4+ ksi in, constant-k and Varying-K most H 2 levels are near Ni/NiO at the test temperature good water chemistry: ~2 volume exchanges per hour measured potentials of 69 & Pt vs. Cu/Cu 2 O/ZrO 2 Tests: 7 Alloy 69 base metal CTs 62,+ hours 26 Alloy 152/52 weld metal CTs 23,+ hours 13 Alloy 69 HAZ CTs 18,+ hours Totals: 19 CT Specimens 931,+ hours 4
5 Summary of GE Data on 69, HAZ & Welds GE CGRs for Alloy 69/152/52 can span a ~2,X range to values as high as ~2 x 1 6 in PWR primary water.
6 2X Evolution in CGR Over ~15 Hours 19.5 SCC#2 - c521-69, ANL NX3297HK12, As-Rec'd, 31% Forge, S-L.6 18.5 c521 -.5TCT of 69 AR, 31% Forge, S-L 3 ksi in, 36C, 6B/1Li, 26 cc/kg H 2 1.4 x 1-6.4 17.5 16.5 15.5 14.5 13.5 12.5 To 9s hold @ 549h Outlet conductivity x.1 3.3 x 1-7 To Constant K @ 1268h 6 x 1-8 Pt potential At 325C, ph = 7.74. At 3C, ph = 7.4 11.5 5 1 15 2 25 3 35 4 1.4 x 1 6 CT potential.2 -.2 -.4 -.6 -.8 Very high growth rates, very stable SCC response. Note continuing evolution of CGR vs. time.
All materials/microstructures 31% 1D-CR 69 CRDM, RE243 S-L SCC#5 - c471-69, RE243 As-Rec'd, 31% 1D Cold Rolled, S-L.6 12.4 12.38 12.36 12.34 12.32 12.3 To Constant K @ 24h c471 -.5TCT of 69 AR, 31% 1D CR, S-L 25 ksi in, 36C 6B/1Li, 26 cc/kg H 2 Outlet conductivity x.1 4.7 x 1-8 To 325C & 1.5 cc/kg H 2 @ 2311h 1.3 x 1-8 12.28 Pt potential CT potential -.8 At 325C, ph = 7.74. At 3C, ph = 7.4 12.26 2 22 24 26 28 3 32 Moderately high growth rates, very stable SCC response, normal (but somewhat low) temperature dependency. Very good agreement with PNNL data. To 36C & 26 cc/kg H 2 @ 2623h 5. x 1-8 5. x 1 8.4.2 -.2 -.4 -.6 7
8 3% 2D-Deform (Forged) 69 CRDM, S67743 Corrected Data S-L SCC#5a - c575-69, MHI CRDM, S67743, 3.3% Forge, S-L All materials/microstructures.6 2 c575 -.5TCT of 69 AR, 3% Forge, S-L 44 MPa m, 36C, 6B/1Li, 26 cc/kg H 2.4 19.8 19.6 19.4 K ~44 MPa m @ 131h Outlet conductivity x.1 7.6 x 1-7 7.6 x 1 7 Test End @ 1684h.2 -.2 -.4 -.6 19.2 -.8 Pt potential CT potential At 325C, ph = 7.74. At 3C, ph = 7.4 19 13 135 14 145 15 155 16 165 17 Very high growth rates, very stable SCC response.
9 CGR Response at Lower CW Astonishingly high CGR recently reported by Morton on 2% CW 69. Again demonstrating that we need to examine a diversity of materials and conditions as well as replicate specimens.
Corrected Data 21 2 19 18 17 16 15 14 13 SCC#2a - c521-69, ANL NX3297HK12, As-Rec'd, 31% Forge, S-L c521 -.5TCT of 69 AR, 31% Forge, S-L 33 MPa m, 36C, 6B/1Li, 26 cc/kg H 2 Outlet conductivity x.1 4.3 x 1 7 To 9s hold @ 549h 4.3 x 1-7 To Constant K @ 1268h 9 x 1-8 31% Forged NX3297HK12 S-L vs. µs Pt potential 12 5 1 15 2 25 3 35 4 1.1 x 1 6 4 MPa m @ 3h 1.6 x 1-6 CT potential At 325C, ph = 7.74. At 3C, ph = 7.4 1.1 x 1-6 Very low growth rates when Crack plane Forging plane 53 MPa m @ 4h Test End @ 4294h.6.4.2 -.2 -.4 -.6 -.8 S-L vs. µs T-L vs. CW S-L vs. CW Very high growth rates in the S-L orientation vs. µs & CW Crack plane = Forging plane Corrected Data 11.4 11.39 11.38 11.37 11.36 11.35 11.34 11.33 To 9s hold @ 549h Orientation vs. Deformation SCC#2 - c522-69, ANL NX3297HK12, As-Rec'd, 31% Forge in Width, S-L 3.1 x 1 8 3.1 x 1-8 To Constant K 29 MPa m @ 1268h 11.32 -.8 Pt potential CT potential At 325C, ph = 7.74. At 3C, ph = 7.4 11.31 5 7 9 11 13 15 17 19 21 23 ~1 x 1 ~1 x 1 1 Outlet conductivity x.1 K dropping due to crack advance in other CT specimen c522 -.5TCT of 69 AR, 31% Forge-W, S-L 33 MPa m, 36C, 6B/1Li, 26 cc/kg H 2 To Constant K 26 MPa m @ 1268h.6.4.2 -.2 -.4 -.6 1
16.25 Orientation vs. Deformation 31% Forged (Longitudinal) CRDM WQ199 S-L,, g,.6 12.4.6 16.2 16.15 16.1 16.5 16 15.95 15.9 To 9s hold @ 3643h c54 -.5TCT of 69 AR, 31% Forge, S-L 48 MPa m, 36C, 6B/1Li, 26 cc/kg H 2 Outlet conductivity x.1 2.8 x 1-7 To Constant K @ 4387h 5.7 x 1-8 5.7 x 1 8 Pt potential CT potential At 325C, ph = 7.74. At 3C, ph = 7.4.4.2 -.2 -.4 -.6 -.8 12.3 12.2 12.1 12 11.9 To Constant K @ 153h c619 -.5TCT of 69 AR, 31% Forge in C, S-L 33 MPa m, 36C, 6B/1Li, 26 cc/kg H 2 * 5% fall, 95% rise (~5s) Outlet conductivity x.1 7.8 x 1-8 7.8 x 1 8 Pt potential CT potential At 325C, ph = 7.74. At 3C, ph = 7.4.4.2 -.2 -.4 -.6 -.8 15.85 42 44 46 48 5 52 Very similar growth rates in all µs orientations when the Crack plane = Forging plane SCC susceptibility follows plane of cold work 11.8 15 2 25 3 35 4 12.6 12.55 12.5 12.45 12.4 12.35 12.3 12.25 12.2 12.15 To Constant K @ 153h Outlet conductivity x.1 5.2 x 1-8 12.1 15 2 25 3 35 4 5.2 x 1 8 Pt potential * 5% fall, 95% rise (~5s c62 -.5TCT of 69 AR, 31% Forge in R, S-L 33 MPa m, 36C, 6B/1Li, 26 cc/kg H 2 CT potential At 325C, ph = 7.74. At 3C, ph = 7.4.6.4.2 -.2 -.4 -.6 -.8 11
12 Must Be Clear on Orientation The intent of the ASTM orientation designations is to define the crack plane in relation to important processing conditions. This is true whether we re referring to the original mill processing or subsequent processing or welding. There is agreement on designating weld orientations as T-S completely independent of the product orientation, and the same approach should be taken with added forging or rolling or welding. 69 Database distinguishes orientation vs. product form and orientation vs. cold work or welding.
GB carbides not beneficial 31% 1D-CR 69 CRDM, RE243 S-L SCC#5 - c471-69, RE243 As-Rec'd, 31% 1D Cold Rolled, S-L.6 12.4 12.38 12.36 12.34 12.32 12.3 12.28 To Constant K @ 24h c471 -.5TCT of 69 AR, 31% 1D CR, S-L 25 ksi in, 36C 6B/1Li, 26 cc/kg H 2 Outlet conductivity x.1 4.7 x 1-8 To 325C & 1.5 cc/kg H 2 @ 2311h 1.3 x 1-8 12.26 2 22 24 26 28 3 32 5. x 1 8 To 36C & 26 cc/kg H 2 @ 2623h 5. x 1-8 Pt potential CT potential At 325C, ph = 7.74. At 3C, ph = 7.4.4.2 -.2 -.4 -.6 -.8 11.14 11.135 11.13 11.125 To 9s hold @ 847h SCC#2a - c472-69, RE243 C Modified, 31% 1D Cold Rolled, S-L c472 -.5TCT of 69 CM, 31% 1D CR, S-L 25 ksi in, 36C 6B/1Li, 26 cc/kg H 2 Outlet conductivity x.1 1.8 x 1-8 GB Carbides Removed To Constant K @ 163h 3 x 1-9 3 x 1 9.6.4.2 -.2 -.4 -.6 Pt potential 11.12 85 95 15 115 125 135 CT potential At 325C, ph = 7.74. At 3C, ph = 7.4 GB carbides are beneficial in susceptible materials like Alloy 6, but should perhaps be eliminated from Alloy 69 -.8 13
19.5 31% 2D-Deform (Forged) 69 Plate, NX3279HK.6 S-L SCC#2 - c521-69, ANL NX3297HK12, As-Rec'd, 31% Forge, S-L GB carbides not beneficial 18.5 17.5 16.5 15.5 14.5 13.5 12.5 To 9s hold @ 549h c521 -.5TCT of 69 AR, 31% Forge, S-L 3 ksi in, 36C, 6B/1Li, 26 cc/kg H 2 Outlet conductivity x.1 3.3 x 1-7 To Constant K @ 1268h 6 x 1-8 Pt potential At 325C, ph = 7.74. At 3C, ph = 7.4 11.5 5 1 15 2 25 3 35 4 1.4 x 1 6 CT potential 1.4 x 1-6.4.2 -.2 -.4 -.6 -.8 11.36 11.34 11.32 11.3 11.28 11.26 To 85,9s hold* @ 1529h SCC#3 - c621-69, ANL NX3297HK12, Soln Ann, 3% Forge, S-L Outlet conductivity x.1 1.9 x 1-8 GB Carbides Removed * 5% fall, 95% (~5s) rise, ~5s hold c621 -.5TCT of 69 SA, 3% Forge, S-L 33 MPa m, 36C, 6B/1Li, 26 cc/kg H 2 Pt potential 11.24 15 17 19 21 23 25 27 29 31 33 CT potential At 325C, ph = 7.74. At 3C, ph = 7.4 GB carbides are beneficial in susceptible materials like Alloy 6, but should perhaps be eliminated from Alloy 69 To Constant K @ 2747h 8. x 1-9 8 x 1 9.6.4.2 -.2 -.4 -.6 -.8 14
33% Cold Forged T-K 11492 S-L Hot deformation Corrected Data 16 SCC#4 - c546-69, T-K 11492, As-Rec'd, 33% Forge, S-L.6 15.5 15 14.5 14 13.5 To Constnat K @ 1416h c546 -.5TCT of 69 AR, 33% Forge, S-L 4 MPa m, 36C, 6B/1Li, 26 cc/kg H 2 8 x 1-8 Outlet conductivity x.1 13 14 19 24 29 34 39 44 41 MPa m @ 3h 9 x 1 7 4 x 1-7 9 x 1-7 47 MPa m @ 4h Pt potential CT potential At 325C, ph = 7.74. At 3C, ph = 7.4 Test End @ 4372h.4.2 -.2 -.4 -.6 -.8 11.17 11.16 11.15 11.14 11.13 11.12 11.11 11.1 Cold forged vs. To 9s hold* @ 61h SCC#2 - c617-69, 11692, 3% HForge @13F in Th, S-L Outlet conductivity x.1 1.5 x 1-8 To 28,3s hold* @ 1371h Hot forged 5.1 x 1-9 * 5% fall, 95% rise (~5s) c617 -.5TCT of 69 AR, 3% Hot Forge, S-L 33 MPa m, 36C, 6B/1Li, 26 cc/kg H 2 Pt potential CT potential To 85,9s hold* @ 259h 2.6 x 1-9 2.6 x 1 9.6.4.2 -.2 -.4 -.6 -.8 At 325C, ph = 7.74. At 3C, ph = 7.4 11.9 6 11 16 21 26 31 Low growth rates when hot forged, but residual strain is somewhat lower 15
16 Hot Forging vs. Cold Forging Hot deformation Low growth rates when hot forged, but residual strain is somewhat lower
17 Lower deformation 13% Forged CRDM WQ199 S-L 11.45 SCC#2a - c585-69, CRDM WQ199, As-Rec'd, 15% Forge, S-L 1 x 1-9.6.4 11.4 11.35 11.3 11.25 To 9s hold* @ 25h 1.4 x 1-8 To Constant K @ 1269h Pt potential 11.2 8 1 12 14 16 18 2 Outlet conductivity x.1 1 x 1 9 * 5% fall, 95% (~5s) rise c585 -.5TCT of 69 AR, 15% Forge, S-L 33 MPa m, 36C, 6B/1Li, 26 cc/kg H 2 CT potential At 325C, ph = 7.74. At 3C, ph = 7.4.2 -.2 -.4 -.6 -.8 Low growth rates at 13% cold forge
13% Forged Plate NX3297HK12 S-L Low growth rates at 13% cold forge. Other heats show medium & high growth rates at ~12% cold work. 18
19 16% Forged 133454 S-L 14.3 SCC#5 - c664-69, 133454, 16% Forge, S-L.6 14.25 14.2 14.15 14.1 14.5 14 13.95 13.9 To 27.3 ks hold @ 5573h 2.5 x 1-8 To 85.4 ks hold @ 6786h 2.3 x 1-8 To Constant K @ 8641h Pt potential 13.85 5 6 7 8 9 1 11 1.9 x 1-8 * 5% fall, 95% rise (~5s) Outlet conductivity x.1 c664 -.5TCT of 69 AR, 16% Forge, S-L 33 MPa m, 36C, 6B/1Li, 26 cc/kg H 2 CT potential At 325C, ph = 7.74. At 3C, ph = 7.4 1.9 x 1 8 Medium growth rates at 16% cold forge.4.2 -.2 -.4 -.6 -.8
2 2% Forged NX3297HK12 S-L SCC#7 - c67-69, NX3297HK12, 2%CF, S-L.6 14.58 14.53 14.48 14.43 To 44 MPa m, R=.6,.1 Hz @ 6259h 85,4s hold* @ 7975h Outlet conductivity x.1 3.1 x 1-8 Constant K @ 9661h 2.2 x 1-8 2.2 x 1 8 * 5% fall, 95% rise time c67 -.5TCT of 69 AR, 2% Forge, S-L.4.2 -.2 -.4 -.6 44 MPa m, 36C, 6B/1Li, 26 cc/kg H 2 Pt potential CT potential At 325C, ph = 7.74. At 3C, ph = 7.4 -.8 14.38 8 85 9 95 1 15 11 Medium growth rates at 2% cold forge
21 13% Forged NX3297HK12 S-L 14.94 SCC#7 - c671-69, NX3297HK12, 13%CF, S-L.6 14.93 14.92 14.91 14.9 14.89 To 44 MPa m, R=.6,.1 Hz @ 6259h 85,4s hold* @ 7975h Outlet conductivity x.1 4.6 x 1-9 Constant K @ 9611h 8.2 x 1-9 8.2 x 1 9 * 5% fall, 95% rise time c671 -.5TCT of 69 AR, 13% Forge, S-L.4.2 -.2 -.4 -.6 14.88 44 MPa m, 36C, 6B/1Li, 26 cc/kg H 2 Pt potential CT potential At 325C, ph = 7.74. At 3C, ph = 7.4 -.8 14.87 8 85 9 95 1 15 11 Medium growth rates at 13% cold forge
22 CGR Response at Lower CW 12% Bettis data below show medium, high & very high CGRs. 5 x 1-8 3 x 1-7 5 x 1-8 5 x 1-9 Medium, High, Very High GE GRC data show medium CGRs with 16% cold forged
HAZ of KAPL Narrow Gap Weld S-L 7 x 1 9 Medium growth rates in HAZ perhaps 1 2X faster than as-received Alloy 69 23
Weld Residual Strain Effects on SCC 11.9 11.8 288 C, 15 psi 2 ppb O 2, Pure Water Constant K = 27.5 MPa/m 2.18 x 1-7.4.35 Crack Length, mm 11.7 11.6 11.5 11.4 11.3 3.16 x 1-7 SCC of c111 -.5T CT of HEW Nb-SS 1.455S* FLW Pipe, HAZ Aligned 11.2 1 2 3 4 5 6 7 8 Time, hours Corrosion Potential of Pt Corrosion Potential of CT Outlet Conductivity High growth rates if align crack along SS HAZ Weld residual strain typically peaks at >2% equivalent room temperature strain To 2 ppb O 2 at 565h.3.25.2.15.1.5 Conductivity, us/cm or Potential, V she 24
25 Unsensitized Type 321 Stainless Steel Weld residual strain typically peaks at >2% equivalent room temperature strain, and SCC often follows these high-strain areas.
Weld Residual Strain in 69 & Welds: Steam Generator Divider Plate Mockup 26 Weld metal 69 composition Residual strains reach 4 5% in isolated dendrites of the weld metal, 18 21% in unmixed & partially melted zone, and ~14% in HAZ. Plate has ~8 1% retained strain (away from weld).
Alloy 6 + 15.8% Cold Forging 11.7 SCC#1 - c757 - Alloy 6, 93511, SA+15.8%CF, S-L.4 11.65 11.6 11.55 11.5 11.45 11.4 11.35 c757 -.5TCT of A6, SA+15.8%CF, S-L 27.5 MPa m, 36C, 15 ppm B, 2.5 ppm Li 33 MPa m, R=.6,.1 Hz @ 22.1h.1 Hz @ 23.7h 2.7 x 1-6 To 95s hold @ 35h 3.8 x 1-6 Outlet conductivity x.1 To 85,9s hold @ 44h 2.7 x 1-6 2.7 x 1 6 To Constant K= 27.5 MPa m @ 53h At 325C, ph = 7.22. At 3C, ph = 6.86 CT potential Pt potential.2 -.2 -.4 -.6 -.8 11.3 22 27 32 37 42 47 52 57 Consistent very high CGRs in 15.8% CW Alloy 6 (no GB carbides) perhaps 1X faster than most ~15% CW 69 27
28 Must Compare 69 vs. 6 Very high CGRs observed in 15.8% cold worked Alloy 6 without GB carbides Astonishingly high CGR reported by Morton on 2% CW 69. Reinforcing the need to examine a diversity of materials and conditions.
29 Weld Metals Have Very Inhomogeneous Strain Strain concentrates in isolated dendrites (red) This was avoided in MPR15 by requiring sufficient crack advance.
11.495 SCC#2 - c541 - Alloy 152 Weld, ANL, WC4F6, As-Welded, T-S.6 SCC of Alloy 152 Weld Metal C541, ANL, WC4F6 11.49 11.485 11.48 11.475 11.47 11.465 To ~1s rise time, 9s hold @ 1275h 1.7 x 1-8 To Constant K @ 1882h 8 x 1 8 x 1 1 Pt potential 11.46 15 2 25 3 35 4 Outlet conductivity x.1 c541 -.5TCT of 152 Weld, T-S 3 ksi in, 36C, 6B/1Li, 26 cc/kg H 2 CT potential At 325C, ph = 7.74. At 3C, ph = 7.4 Three SCC attempts covering 12,264 hours of testing low CGRs, moderate fraction IG.4.2 -.2 -.4 -.6 -.8 12.855 12.85 12.845 12.84 12.835 12.83 To 9s hold @ 52h To 85,9s hold @ 6528h 2.4 x 1-8 SCC#5 - c541 - Alloy 152 Weld, ANL, WC4F6, As-Welded, T-S 3 x 1-9 12.825 Pt potential CT potential -.8 At 325C, ph = 7.74. At 3C, ph = 7.4 3 12.82 64 66 68 7 72 74 76 78 To Constant K @ 7156h 7 x 1 1 7 x 1 Outlet conductivity x.1 c541 -.5TCT of 152 Weld, T-S 3 ksi in, 36C, 6B/1Li, 26 cc/kg H 2.6.4.2 -.2 -.4 -.6 3
31 C541: ANL Alloy 152 Weld Metal Three SCC attempts covering 12,264 hours of testing low CGRs, moderate fraction IG
32 SCC of Alloy 152 Weld Metal C555, MHI, 76447 Corrected Data 12.935 12.93 12.925 12.92 12.915 12.91 12.95 To 27,s hold @ 4937h SCC#5 - c555 - Alloy 152 Weld on Plate, MHI SMAW DM, 76447, As-Welded, T-S.6 1.2 x 1-8 To Constant K @ 5635h 4 x 1 1 12.9 Pt potential CT potential -.8 At 325C, ph = 7.74. At 3C, ph = 7.4 12.895 5 55 6 65 7 75 * 5% fall, 95% rise (~5s) 4 x 1 Outlet conductivity x.1 c555 -.5TCT of 152 Weld, T-S 33 MPa m, 36C, 6B/1Li, 26 cc/kg H 2 Test End @ 7499h.4.2 -.2 -.4 -.6 So far, one SCC attempt covering 7,499 hours of testing low CGRs Transitioned for.5 mm at slow rise times. Extensive IG morphology.
33 High Cr Welds in BWR Water All 52i / 52 / 152 welds show low growth rates despite being tested at high K, in 2 ppm O 2 and 3 5 ppb sulfate or chloride.
34 Key Findings Alloy 69 is susceptible to SCC initiation and growth. The best Alloy 69 (e.g., CRDM) is very homogeneous; but can still exhibit very high CGRs if cold worked >2%. 1-D cold rolling and forging give similar CGRs. GB carbides are not beneficial, at least when CW exists. 3% cold work is not very susceptible without GB carbides. CGR evolution vs. time suggests more susceptible paths exist. Temp & H 2 dependencies vanish in high CGR materials. When crack plane is not aligned with CW plane, much lower CGRs are observed even if aligned with microstructural banding. We see medium CGRs at ~15% CW; others see higher CGRs.
35 Recommendations We should focus on identifying vulnerabilities in alloys, then work hard to avoid them. The origin of very high CGRs in some heats of 69 need to be understood, and effects of 5 15% cold work evaluated. Weld interfaces esp. with SS and LAS need to be understood and SCC CGRs quantified. More characterization of weld residual strains, and composition & microstructures of weld interfaces is needed. Evaluation of higher SCC susceptibility from elevated hardness / yield strength in PWHT (tempered) low alloy steel welds & temper bead welds is needed. SCC in LAS is strongly accelerated at higher yield strength.