Influence of cyclic load and environmental effects on stress corrosion cracking of sensitized stainless steel. Final report

An experimental stress-corrosion cracking (SCC) study has been conducted in order to mitigate SCC in stainless steel piping in BWR's. Effect of the temperature, dissolved oxygen, and cyclic loading was studied on furnace sensitized Type 304 stainless steel. Slow strain rate tests at 4 x 10-6 s-1 strain rate produced intergranular stress-corrosion cracking (IGSCC) at temperatures above 2040C, suggesting a threshold temperature for IGSCC of about 1300C at the 0.2 ppM oxygen level. Saturated solutions of AgCl produced IGSCC in slow strain rate tests in both aerated (8 ppM O2) and deaerated (< 0.06 ppM O2) tests at temperatures as low as 850C. Results suggest a potential hazard in using Ag/AgCl reference electrodes. IGSCC also was produced by trapezoidal cyclic loading (5 min load/unload, 10 or 75 min at load). Tests in 8 ppM oxygen water with the 75 min hold cycle, minimum load of 0.1 yield strength (YS) and maximum load greater than YS, indicated a threshold temperature for IGSCC of 1900C. Other cyclic load tests in 2880C - 8 ppM oxygen water with minimum load of 0.1 YS and maximum load less than YS, produced IGSCC at maximum loads as low as 0.7 YS in the rather high yield strength material studied (YS = 36.3 ksi at 2880C). Low increment load cyclic loading produced IGSCC with cyclic loads ranging between 0.5 and 0.6 YS and 0.8 to 0.9 YS, but not at 0.6 to 0.7 YS or 0.7 to 0.8 Ys. The short hold cycle (10 min at load) was much less aggressive in promoting IGSCC than the long hold cycle