Effect of Some Environmental Conditions on Stress Corrosion Behavior of Ni-Cr-Fe Alloys in Pressurized Water

Abstract

Abstract Stress corrosion tests have been run in pressurized water at 600 F (316 C) using double U-bends and double bent beam specimens. The tests were conducted in autoclaves for up to 3000 hours. The composition of the gas phase above the water and the pH were controlled. The materials tested were commercial heats of Inconel (1) 600, Inconel 625, lncoloy(1) 800 and stainless steel Types 304, 304L and 347; some Inconel alloy 600 weldments; and some experimental laboratory compositions. Several heat treatments were included. No attack was observed in specimens stressed at 90 percent of room temperature yield strength. No attack was observed when hydrogen constituted the gas phase. No attack was observed when crevices were absent. The combined action of a high stress, a high oxygen concentration and a crevice did promote intergranular attack and cracking in the crevice area in all alloys tested. The severity of the attack increased with the oxygen concentration. Many specimens heated for 2 hours at 1250 F (677 C) showed deeper attack than annealed specimens. Solution heat treatment, low carbon content or the presence of carbide stabilizers did not eliminate the attack. The behavior of weld metal deposits was not significantly different from that of base plate. Variations in composition within the normal range of Alloy 600 were unimportant. Differences in behavior among the several alloys tested were minor compared to those from environmental effects.