EFFECTS OF POTENTIAL AND ENVIRONMENT ON THE STRESS CORROSION CRACKING SUSCEPTIBILITY OF NICKEL-CHROMIUM-MOLYBDENUM ALLOYS

摘要

The effect of potential on the susceptibility to stress corrosion cracking (SCC) of Type 316L stainless steel (SS) [UNS S31603] and Alloy 22 [UNS N06022] was determined in hot, concentrated chloride solutions using precracked compact tension (CT) specimens. In the case of Alloy 22, constant deflection tests using single and double U-bend specimens were also conducted in hot, acidified and supersaturated PbCl_2 solutions. It was found that Alloy 22 is very resistant to crack initiation and propagation at an initial stress intensity of 47 MPa centre dot m~(1/2) [43 ksi centre dot in~(1/2)] in 9.1 molal LiCl solution at 95 deg C [203 deg F], confirming previously reported results. No crack growth was observed even when cyclic loading at a frequency of 0.001 Hz and a R ratio (R = K_(Imin)/K_(Imax)) of 0.7, with K_(Imax) - 47 MPa centre dot m~(1/2) [43 ksi centre dot in~(1/2)], was applied. Also, no SCC was detected in the chloride solutions containing lead species, even for thermally aged specimens. On the contrary, relatively fast crack growth was observed on Type 316L SS specimens in 9.1 molal LiCl solution at 95 deg C [203 deg F] when the potential was above the repassivation potential for crevice corrosion, even at a stress intensity of 20 MPa centre dot m~(1/2) [18 ksi centre dot in~(1/2)].