Evaluation of chloride stress corrosion cracking susceptibility of stainless steels

Abstract

Abstract The comparative chloride stress corrosion cracking (Cl-SCC) susceptibility for 304 L, 316 L, 317 L, and AL-6XN was evaluated using double cantilever beam (DCB) specimens in boiling MgCl2 by measuring the threshold stress intensity (KISCC), crack initiation time, and stage-II crack growth rate (CGR) for each material using in situ monitoring. Materials 304 L, 316 L, and 317 L were measured to have KISCC upper limit values of 2.5–5 MPa√m, substantially lower than previously measured for 304 L in DCB specimens in boiling MgCl2. The KISCC for AL-6XN was measured to be substantially higher, as would be expected in this more highly alloyed material. This work describes the challenge in measuring low KISCC values and how this was accomplished in the present work. More prototypical conditions were used to evaluate Cl-SCC behavior of 304 L using a DCB-like geometry with a smooth gauge area in a low humidity environment in the presence of MgCl2 salt. Finite element modeling (FEM) was used to establish the relationship between applied loads and stress and strain. Loading to 15 % strain led to low temperature creep that masked in situ Cl-SCC measurements. Below the yield stress (YS), no low temperature creep was observed, and Cl-SCC cracking could be distinguished using in situ methods.