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 Cr 9x10-5 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) - Al 24.2 4x105 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 Velocity: 4 m/s; Forced- Pratt-Whitney Exposure: 1170 h; Corrosion rate: NIL Circulation Un-Alloyed V ('50 - '60) T = 870oC (<0.1 mg/m2h or 0.1 µm/y) Loop max ∆T = 220oC Corrosion rate: NIL High and low- Redistribution of Oxygen purity alloys: was observed; Compared ORNL ('60) Capsule tests Tmax=816oC V-15-Cr-5Ti, with Ta & Nb only small V-10Cr penetration with O2 present. Velocity: <1.5 m/s; High and low- Small weight changes; Forced- Exposure: 500 h, purity alloys: High-purity alloys show no ANL ('70-'80) Circulation & 30000 h; V-15-Cr-5Ti, degradation in tensile Loop T = 650oC V-10Cr max 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 alloys; Russian &Thermal- AlN-Coated); T = 870oC N and Al increase Federation Convection V-10Ti-5Cr; max ∆ o compatibility with SS. Loop V-9Ti-4Cr T = 220 C Findings: • 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<T<460oC) Factor of 5-10 lower than Weight Loss linear at 500oC 316 SS (mg/m2-h) Lower in static Pb-Li than flowing for both Reaches constant value after 1000-3000 h Dissolution rates 10 times larger than in Li FCL comparable to TCL 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.