Environmentally Assisted Crack Growth in Cold Worked Alloy 690TT in Primary Water at Low and High Temperatures

Abstract

Environmentally assisted crack (EAC) growth in thermally treated Alloy 690 (Alloy 690TT) cold worked one-dimensionally to the thickness reduction of 25% was investigated by crack growth rate testing in the primary water at low and high temperatures. In water at 50 °C and a dissolved hydrogen (DH) of 2.7–2.9 ppm, the test results suggest that the crack growth rate is lower than 2.2×10−9 mm/s at a stress intensity factor of 35 MPa√m. Stress corrosion cracking (SCC) growth with a rate of <1×10−11 m/s was observed in the alloy in water at temperatures of 320 °C and 340 °C. Over a DH range of 0.37–2.6 ppm, the SCC growth in Alloy 690TT has a similar DH dependence as that in Alloy 600 and its weld metals. The magnitude of the DH dependence, however, is much smaller for Alloy 690TT. In water deaerated by N2 without DH, an extremely low SCC growth rate was observed. Increasing DH in water from 0 ppm to 0.38 ppm caused an active SCC growth, suggesting that hydrogen could promote SCC growth when increasing DH from a very low level. Results of the current work confirmed a general high resistance of 25% cold worked Alloy 690TT to EAC growth in the primary water at both low and high temperatures under moderate stress intensity factors.