Review of Structural Material Corrosion in Liquid Li and Pb-Li
S. Sharafat and N. M. Ghoniem
The University of California at Los Angeles (UCLA) Los Angeles, CA. 90095-1597, USA
APEX Meeting Sandia National Laboratory November 15-17, 2000
SS-NG: Nov.'00 APEX-SNL 1 OUTLINE
• Liquid metal corrosion examples
• Review in conjunction with Na-Steel Data effects of: ∆ – Velocity, Tmax, T, Impurities – Product deposition rates – Rate of Temperature Rise – Coatings
• Systems: – Steel-Lithium – V-Lithium
– Steel Pb-Li –V-Pb-Li •Summary
SS-NG: Nov.'00 APEX-SNL 2 Examples of Liquid Metal Corrosion
MOLTEN LEAD: T = 700oC ∆T = 150oC V = 3 cm/s
ALLOYS: • Hasetlloy: – 70% Ni; – 8000 ppm at 700oC
•Croloy: N –2LQCr, 1Mo, 0.5Mn; – 8 ppm at 700oC
• Fecralloy: – 15Cr, 4Al
• Meehanite: – cast Fe, 3C, 1Si
R. C. Asher et al., 1977
SS-NG: Nov.'00 APEX-SNL 3 Example of Lithium-Steel Corrosion
• Formation of a ferritic layer on 316 SS: – Leaching of Cr, Ni, and Fe
• Nitrogen solubility in Li is high even at Tm (~1000 ppm): – Nitrogen must be removed for iron-based heat transfer systems – For Vanadium-based systems Nitrogen inhibits certain corrosions
• Austenitic 316 Stainless Steel in Li: o Tmax = 425 C R. C. Asher et al., 1977 N = 200 -500 ppm t > 3000 hr
SS-NG: Nov.'00 APEX-SNL 4 Corrosion Damage Zones
• Corrosion is often described in terms of a simple mass loss rate: – Mass loss rate (g/m2-year), or – Surface recession rate (µm/year)
Total Damaged Zone
• However, 3 processes constitute corrosion: – Surface Regression (wall thinning) J.H.DeVan, 1985 – Surface Degradation Examples of corrosion damage in SS – Intergranular attack (8000 h, Na:700oC, high ∆T) (IGA)
SS-NG: Nov.'00 APEX-SNL 5 Liquid Metal Corrosion Issues • Two major compatibility concerns: • (a) Corrosion/Mass transfer • (b) Degradation of mechanical strength • Corrosion, uniform or selective dissolution and/or intergranular penetration can result in: • wall thinning (mechanical strength) • corrosion products can restrict flow (pumping power) • Near-surface deformation behavior through: • Liquid metal embrittlement (LME) • Oxidation, nitridation, or carburization-decarburization • Bulk properties are affected by: • Compositional and microstructural modifications. • Selective corrosion, interstitial-element transfer, and/or thermal aging. • Most experience exists with LMFBR Na-Steel systems
SS-NG: Nov.'00 APEX-SNL 6 Experience with Li-Corrosion of Austenitic and Ferritic Steels
• Li and Pb-Li: Static, Thermal-Convection-Loop (TCL; v=0.05 to 0.3 m/s), and Forced-Circulation-Loop (FCL; 0.3 to 4 m/s) – (a) Austenitics develop ferritic layer (depletion of Ni and Cr) – (b) Ferritics show little or no surface degradation – (c ) Intergranular penetration with (> 1000 ppm N) in both
• Existing experimental data are insufficient to accurately establish corrosion behavior: – Experiment parameters vary significantly: • Velocity, ∆T, Area, and Purity
SS-NG: Nov.'00 APEX-SNL 7 Approach
Liquid Na corrosion has been studied extensively since the late 1940s
• Augment Li corrosion understanding by Na-data
Solubility of Metals:
Sodium Lithium Lead-Lithium Lead-bismuth (wppm @ 400 C) (wppm @ 400 C) (wppm @ 400 C) (ppm @ 500 C) Fe 0.04 0.94 35 2.3 -5 Cr 9x10 0.9 5 11 Ni 0.55 56.8 2360 25000 V low 0.008 low - Ti low low low 300 Mo 0.25 0.25 0.1 (Pb,700C) - W low low 0.1 (Pb,700C) - 5 Al 24.2 4x10 2000 - – In the absence of (O, N, C) dissolution of metals (except Al) is very low, unless driven by large ∆T in the loop.
SS-NG: Nov.'00 APEX-SNL 8 SS-Na Velocity Correlations
450 500 550 600 650 700 (oC) • SS-Na: Velocity and Oxygen 10 | | | | | | were identified as the two VELOCITY INDEPENDENT major variables: (V > 3 m/s) – Statistically corrosion rates were independent of velocity above 1
3-4 m/s m/year) µ – Corrosion rates were found to be directly proportional to oxygen concentration. Bagnall, 1975 0.1 Corrosion Rate ( For V> 4 m/s (1ppm O): 9 µ VELOCITY R = 1.69x10 exp(-18120/TK) m/year DEPENDENT (V = 1 m/s) 0.01
For V< 3 m/s (1ppm O): 1.41.3 1.2 1.1 1.0 R = (2.97x108 + 2.91x108 V) µ 1000/T(K) exp(-18120/TK) m/year Na-corrosion rate of 316SS at 1 ppm O (afer J. H. Devan, 1985)
SS-NG: Nov.'00 APEX-SNL 9 SS-Li Velocity Correlation (?)
700 600 500 400 (oC) • System parameters affecting 100 corrosion rates of ferrous alloys in TCL: Whitlow, 1979 Selle, 1976 Li are much more varied. FCL: Rumbaut, 1981
) Casteels, 1981 . -hr • Nitrogen effects are complex: 2 10 – In static tests: below 500oC significant weight loss even with low N levels (20- 50ppm). o – Dynamic tests: above 500 C 1 “nil” weight loss even with
high N levels (500 ppm). Dissolution Rate (mg/m
• Can not develop similar correlations for Steel-Li as for 0.1 Steel-Na. 1 1.1 1.2 1.3 1.4 1.5 1.6 1000/T(K) Corrosion rates of 304 and 316 SS after 1500 h
SS-NG: Nov.'00 APEX-SNL 10 Corrosion Product Deposition Rate
• Mass transfer affects: 600 – IHX performance Na-304SS, v=4m/s o – Radiation exposure Thot=740 C, >1500 h – Blockage 550 (Shiels, 1976)
• Deposition rates (DR) in a Na-steel loop have been 500 reported as a function of ∆T. Li-316SS • In Li-system only one study Temperature (C) 450 600oC; ∆T=150oC has looked at the deposition V=3 cm/s, >4000 h rates (Tortorelli, ’80): *(Tortorelli, 1980) o 400 –TCL, Thot = 600 C, ∆T = 150oC, 10 20 30 v = .03 m/s Deposition Rate (g/m2-year) • Initially 16-mm-diam channel was completely plugged: 2 – after 1000 h DR~70 g/m -y 2 – after 4000 h DR~30 g/m -y
15 mm SS-NG: Nov.'00 APEX-SNL 11 Effect of Heating Rate
500 550 600 650 700 (oC) • Rate of temperature 100 | | | | | Extrapolated on change (dT/dL) in the 9µm/yr at 700oC coolant as it flows along (250oC/m) a heated section. 9 µm/year
10
•For Na a high dT/dL m/year) 3 µm/year increases: µ
– Corrosion rate (Rc) in 1 µm/year austenitic steels – Ferrite layer thickness. 1 Corrosion Rate ( Rate Corrosion
• Corrosion rate is factor of 9 larger at 250oC/m T316 SS (40oC/m) o than at 40 C/m 0.1 (@700oC). 1.31.2 1.1 1.0 1000/T(K) Enhancement of corrosion rate for 316SS in Na, high dT/dL
SS-NG: Nov.'00 APEX-SNL 12 Summary of Steel-Li Corrosion Tests
Austenitic Steels: Ferritic Steels 304 and 316 (HT-9) Weight Loss W = ktn ; (n = 0.7) W is linear with time (mg/m2-h)
Dissolution rates FCL 5-20 > than in TCL FCL comparable to TCL
No internal corrosive attack Ferrite layer TCL: 55 µm/y at 570oC (low ppm N); Slight depletion formation FCL: 100 µm/y at 482oC of Cr near surface
Microstructure 20% cold worked has 2 times Effects larger than annealed
Insufficient data to derive correlations for Li Effect of ∆T and Corrosion (R) rates in Na increase with ∆T and Velocity Velocity Up to 3 m/s: R ∝ ( 2.97 + 2.91 V)
Lithium Purity Weight loss with 50 ppm N is 2-5 times lower than with (FCL) 200 ppm N. Findings: • N impurity plays a significant role (like O in Na). • For ferritic steels: No significant difference between TCL (v < 0.2 m/s) & FCL (v < 4 m/s) • Corrosion rate of Ferritic Steels 5-10 times < Austenitic Steels
SS-NG: Nov.'00 APEX-SNL 13 Summary of V-Lithium Tests
Type of Operating Experiment Alloy Primary Results Test Conditions Velocit y: 4 m/s; Forced- Pratt-Whitney Exposure: 1170 h; Corrosion rate: NIL Circulation Un-Alloyed V o ('50 - '60) T = 870 C (<0.1 mg/m 2h or 0.1 µm/y) Loop max ∆T = 220oC Corrosion rate: NIL High and low- Redistribution of Oxygen purity alloys: o was observed; Com pared ORNL ('60) Capsule tests Tmax=816 C V-15-Cr-5Ti, with Ta & Nb only small
V-10Cr penetration with O2 present. Velocit y: <1.5 m/s; High and low- Small wei ght changes; Forced- Exposure: 500 h, purity alloys: High-purity alloys show no ANL ('70-'80) Circulation & 30000 h; V-15-Cr-5Ti, o degradation in tensile Loop Tmax = 650 C V-10Cr properties, ∆T = 150oC
Force- V-4Ti-4Cr Velocity: 4 m/s; High corrosion resistance PRANA ('90) Circulation (Welds, Exposure: 1000 h; of V-Ti-Cr allo ys; Russian &Thermal- AlN-Coated); o Tmax = 870 C N and Al increase Federation Convection V-10Ti-5Cr; o ∆T = 220 C compatibility with SS. Findings: Loop V-9Ti-4Cr • No significant difference in corrosion rates between alloyed and unalloyed vanadium; • Corrosion rate of V-alloys is about factor of 1,000 lower than Austenitic Steels and about 100 lower than Ferritic Steels.
SS-NG: Nov.'00 APEX-SNL 14 Summary of Steel-PbLi Corrosion Tests
Austenitic Steels: Ferritic Steels: 304 and 316 HT-9 and Fe-9Cr-1Mo W = ktn W is linear with time (n = 0.5-0.9; 410 In flowing Pb-Li develop Little or no internal Ferrite layer formation very porous ferrite layers corrosive attack Microstructure PCA 4 times greater than Effects annealed or cold-worked 316 Effect of ∆T,Velocity NO DATA REPORTED Pb-Li purity NO DATA REPORTED Vanadium Pb-Li • Group V and VI refractory metals have low solubility in both Li and Pb. • Good corrosion resistance for Vanadium is predicted. • ANL scoping tests indicated no measurable corrosion of V-15Cr-5Ti after 2300 h in Pb-Li at 430oC: – Steels have a factor of 50 higher corrosion rate in Pb-Li than in Li – Take V-alloy corrosion rate to be a factor of 50 higher in Pb-Li than in Li. SS-NG: Nov.'00 APEX-SNL 15 Summary of Corrosion Data in Flowing Lithium 20 µm/y MASS TRANSFER LIMIT (remote) 5 µm/y Radioactive Mass Transfer Limit 0.5 µm/y Austenitic Steels Vanadium Ferretic Alloys Steels Increasing Velocity (0 – 4 m/s) SS-NG: Nov.'00 APEX-SNL 16 Summary of Corrosion in Pb-Li Austenitic 20 µm/y Steels MASS TRANSFER LIMIT (remote) 5 µm/y Radioactive Mass Transfer Limit 0.5 µm/y Ferretic Steels Vanadium Alloys Increasing Velocity (0 – 4 m/s) SS-NG: Nov.'00 APEX-SNL 17 Summary • Corrosion rates of ferrous and refractory alloys in liquid Li saturate at flow velocities of about 5 m/s. – No data available to make similar assertion for PbLi. • Nitrogen content must be controlled to below 50 ppm in Li for For ferrous alloys: – Addition of N and of Al minimizes corrosion rates in Vanadium alloys. • Deposition rates for Li-316SS have been measured to be 2 ∆ o o 30 g/m /year ( T=150 C, Tmax=600 C, 4000 h). • Rates of temperature-rise along heated sections might have significant impact on corrosion rates. SS-NG: Nov.'00 APEX-SNL 18 CONCLUSIONS • Based on Na-Steel experience, corrosion rates saturate at about v=4 m/s. • High corrosion resistance of V-Ti-Cr alloys has been experimentally confirmed in FCL (700oC, v=4 m/s, t >1000h) – Negligible weight change. • Bi-metallic tests with welds have shown some weight gain (0.8%) by V-Ti-Cr alloys: – Drastic reduction of weight gain (0.4%) by adding Al (~3 wt.%) and nitrogen (500 wppm) to the Lithium • Corrosion of refractory alloys, particularly with a ceramic coating may be negligible at blanket operating conditions. SS-NG: Nov.'00 APEX-SNL 19