SCC of Alloy 690, Alloy 152/52/52i Weld Metals and Dilution Zones

Transcription

1 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

2 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

3 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

4 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 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 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 6 2X Evolution in CGR Over ~15 Hours 19.5 SCC#2 - c521-69, ANL NX3297HK12, As-Rec'd, 31% Forge, S-L c TCT of 69 AR, 31% Forge, S-L 3 ksi in, 36C, 6B/1Li, 26 cc/kg H x To 9s 549h Outlet conductivity x x 1-7 To Constant 1268h 6 x 1-8 Pt potential At 325C, ph = At 3C, ph = x 1 6 CT potential Very high growth rates, very stable SCC response. Note continuing evolution of CGR vs. time.

7 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 To Constant 24h c TCT of 69 AR, 31% 1D CR, S-L 25 ksi in, 36C 6B/1Li, 26 cc/kg H 2 Outlet conductivity x x 1-8 To 325C & 1.5 cc/kg H 2311h 1.3 x Pt potential CT potential -.8 At 325C, ph = At 3C, ph = 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 2623h 5. x x

8 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 c TCT of 69 AR, 3% Forge, S-L 44 MPa m, 36C, 6B/1Li, 26 cc/kg H K ~44 MPa 131h Outlet conductivity x x x 1 7 Test 1684h Pt potential CT potential At 325C, ph = At 3C, ph = Very high growth rates, very stable SCC response.

9 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.

10 Corrected Data SCC#2a - c521-69, ANL NX3297HK12, As-Rec'd, 31% Forge, S-L c TCT of 69 AR, 31% Forge, S-L 33 MPa m, 36C, 6B/1Li, 26 cc/kg H 2 Outlet conductivity x x 1 7 To 9s 549h 4.3 x 1-7 To Constant 1268h 9 x % Forged NX3297HK12 S-L vs. µs Pt potential x MPa 3h 1.6 x 1-6 CT potential At 325C, ph = At 3C, ph = x 1-6 Very low growth rates when Crack plane Forging plane 53 MPa 4h Test 4294h 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 To 9s 549h Orientation vs. Deformation SCC#2 - c522-69, ANL NX3297HK12, As-Rec'd, 31% Forge in Width, S-L 3.1 x x 1-8 To Constant K 29 MPa 1268h Pt potential CT potential At 325C, ph = At 3C, ph = ~1 x 1 ~1 x 1 1 Outlet conductivity x.1 K dropping due to crack advance in other CT specimen c TCT of 69 AR, 31% Forge-W, S-L 33 MPa m, 36C, 6B/1Li, 26 cc/kg H 2 To Constant K 26 MPa 1268h

11 16.25 Orientation vs. Deformation 31% Forged (Longitudinal) CRDM WQ199 S-L,, g, To 9s 3643h c54 -.5TCT of 69 AR, 31% Forge, S-L 48 MPa m, 36C, 6B/1Li, 26 cc/kg H 2 Outlet conductivity x x 1-7 To Constant 4387h 5.7 x x 1 8 Pt potential CT potential At 325C, ph = At 3C, ph = To Constant 153h c TCT 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 x x 1 8 Pt potential CT potential At 325C, ph = At 3C, ph = Very similar growth rates in all µs orientations when the Crack plane = Forging plane SCC susceptibility follows plane of cold work To Constant 153h Outlet conductivity x x 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 = At 3C, ph =

12 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.

13 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 To Constant 24h c TCT of 69 AR, 31% 1D CR, S-L 25 ksi in, 36C 6B/1Li, 26 cc/kg H 2 Outlet conductivity x x 1-8 To 325C & 1.5 cc/kg H 2311h 1.3 x x 1 8 To 36C & 26 cc/kg H 2623h 5. x 1-8 Pt potential CT potential At 325C, ph = At 3C, ph = To 9s 847h SCC#2a - c472-69, RE243 C Modified, 31% 1D Cold Rolled, S-L c TCT of 69 CM, 31% 1D CR, S-L 25 ksi in, 36C 6B/1Li, 26 cc/kg H 2 Outlet conductivity x x 1-8 GB Carbides Removed To Constant 163h 3 x x Pt potential CT potential At 325C, ph = At 3C, ph = 7.4 GB carbides are beneficial in susceptible materials like Alloy 6, but should perhaps be eliminated from Alloy

14 % 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 To 9s 549h c TCT of 69 AR, 31% Forge, S-L 3 ksi in, 36C, 6B/1Li, 26 cc/kg H 2 Outlet conductivity x x 1-7 To Constant 1268h 6 x 1-8 Pt potential At 325C, ph = At 3C, ph = x 1 6 CT potential 1.4 x To 85,9s 1529h SCC#3 - c621-69, ANL NX3297HK12, Soln Ann, 3% Forge, S-L Outlet conductivity x x 1-8 GB Carbides Removed * 5% fall, 95% (~5s) rise, ~5s hold c TCT of 69 SA, 3% Forge, S-L 33 MPa m, 36C, 6B/1Li, 26 cc/kg H 2 Pt potential CT potential At 325C, ph = 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 2747h 8. x x

15 33% Cold Forged T-K S-L Hot deformation Corrected Data 16 SCC#4 - c546-69, T-K 11492, As-Rec'd, 33% Forge, S-L To Constnat 1416h c TCT 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 MPa 3h 9 x x x MPa 4h Pt potential CT potential At 325C, ph = At 3C, ph = 7.4 Test 4372h Cold forged vs. To 9s 61h SCC#2 - c617-69, 11692, 3% in Th, S-L Outlet conductivity x x 1-8 To 28,3s 1371h Hot forged 5.1 x 1-9 * 5% fall, 95% rise (~5s) c TCT 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 259h 2.6 x x At 325C, ph = At 3C, ph = Low growth rates when hot forged, but residual strain is somewhat lower 15

16 16 Hot Forging vs. Cold Forging Hot deformation Low growth rates when hot forged, but residual strain is somewhat lower

17 17 Lower deformation 13% Forged CRDM WQ199 S-L SCC#2a - c585-69, CRDM WQ199, As-Rec'd, 15% Forge, S-L 1 x To 9s 25h 1.4 x 1-8 To Constant 1269h Pt potential Outlet conductivity x.1 1 x 1 9 * 5% fall, 95% (~5s) rise c TCT of 69 AR, 15% Forge, S-L 33 MPa m, 36C, 6B/1Li, 26 cc/kg H 2 CT potential At 325C, ph = At 3C, ph = Low growth rates at 13% cold forge

18 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 19 16% Forged S-L 14.3 SCC#5 - c664-69, , 16% Forge, S-L To 27.3 ks 5573h 2.5 x 1-8 To 85.4 ks 6786h 2.3 x 1-8 To Constant 8641h Pt potential x 1-8 * 5% fall, 95% rise (~5s) Outlet conductivity x.1 c TCT of 69 AR, 16% Forge, S-L 33 MPa m, 36C, 6B/1Li, 26 cc/kg H 2 CT potential At 325C, ph = At 3C, ph = x 1 8 Medium growth rates at 16% cold forge

20 2 2% Forged NX3297HK12 S-L SCC#7 - c67-69, NX3297HK12, 2%CF, S-L To 44 MPa m, R=.6, h 85,4s 7975h Outlet conductivity x x 1-8 Constant 9661h 2.2 x x 1 8 * 5% fall, 95% rise time c67 -.5TCT of 69 AR, 2% Forge, S-L MPa m, 36C, 6B/1Li, 26 cc/kg H 2 Pt potential CT potential At 325C, ph = At 3C, ph = Medium growth rates at 2% cold forge

21 21 13% Forged NX3297HK12 S-L SCC#7 - c671-69, NX3297HK12, 13%CF, S-L To 44 MPa m, R=.6, h 85,4s 7975h Outlet conductivity x x 1-9 Constant 9611h 8.2 x x 1 9 * 5% fall, 95% rise time c TCT of 69 AR, 13% Forge, S-L MPa m, 36C, 6B/1Li, 26 cc/kg H 2 Pt potential CT potential At 325C, ph = At 3C, ph = Medium growth rates at 13% cold forge

22 22 CGR Response at Lower CW 12% Bettis data below show medium, high & very high CGRs. 5 x x x x 1-9 Medium, High, Very High GE GRC data show medium CGRs with 16% cold forged

23 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

24 Weld Residual Strain Effects on SCC C, 15 psi 2 ppb O 2, Pure Water Constant K = 27.5 MPa/m 2.18 x Crack Length, mm x 1-7 SCC of c T CT of HEW Nb-SS 1.455S* FLW Pipe, HAZ Aligned 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 Conductivity, us/cm or Potential, V she 24

25 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.

26 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).

27 Alloy % Cold Forging 11.7 SCC#1 - c757 - Alloy 6, 93511, SA+15.8%CF, S-L c TCT 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, h h 2.7 x 1-6 To 95s 35h 3.8 x 1-6 Outlet conductivity x.1 To 85,9s 44h 2.7 x x 1 6 To Constant K= 27.5 MPa 53h At 325C, ph = At 3C, ph = 6.86 CT potential Pt potential Consistent very high CGRs in 15.8% CW Alloy 6 (no GB carbides) perhaps 1X faster than most ~15% CW 69 27

28 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 29 Weld Metals Have Very Inhomogeneous Strain Strain concentrates in isolated dendrites (red) This was avoided in MPR15 by requiring sufficient crack advance.

30 SCC#2 - c541 - Alloy 152 Weld, ANL, WC4F6, As-Welded, T-S.6 SCC of Alloy 152 Weld Metal C541, ANL, WC4F To ~1s rise time, 9s 1275h 1.7 x 1-8 To Constant 1882h 8 x 1 8 x 1 1 Pt potential Outlet conductivity x.1 c TCT of 152 Weld, T-S 3 ksi in, 36C, 6B/1Li, 26 cc/kg H 2 CT potential At 325C, ph = At 3C, ph = 7.4 Three SCC attempts covering 12,264 hours of testing low CGRs, moderate fraction IG To 9s 52h To 85,9s 6528h 2.4 x 1-8 SCC#5 - c541 - Alloy 152 Weld, ANL, WC4F6, As-Welded, T-S 3 x Pt potential CT potential -.8 At 325C, ph = At 3C, ph = To Constant 7156h 7 x x 1 Outlet conductivity x.1 c TCT of 152 Weld, T-S 3 ksi in, 36C, 6B/1Li, 26 cc/kg H

31 31 C541: ANL Alloy 152 Weld Metal Three SCC attempts covering 12,264 hours of testing low CGRs, moderate fraction IG

32 32 SCC of Alloy 152 Weld Metal C555, MHI, Corrected Data To 27,s 4937h SCC#5 - c555 - Alloy 152 Weld on Plate, MHI SMAW DM, 76447, As-Welded, T-S x 1-8 To Constant 5635h 4 x Pt potential CT potential -.8 At 325C, ph = At 3C, ph = * 5% fall, 95% rise (~5s) 4 x 1 Outlet conductivity x.1 c TCT of 152 Weld, T-S 33 MPa m, 36C, 6B/1Li, 26 cc/kg H 2 Test 7499h 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 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 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 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.