Initiation testing is an important method of understanding Primary Water Stress Corrosion Cracking (PWSCC) susceptibility. Jacobs has previously conducted a program of work into the effect of surface condition on PWSCC initiation times. This work indicated that surface residual stress is an important factor influencing Alloy 600 PWSCC susceptibility. Differences in the manufacture of specimens (via changes in machining parameters or peening) have been shown to result in differences in the residual stress present and most importantly to their evolution upon straining. Therefore, it is important to understand the effect of straining on the evolution of surface residual stress to better relate testing strains to plant condition. This paper presents findings of a study into the evolution of surface residual stress on Alloy 600 specimens with increasing applied strain. X-Ray Diffraction (XRD) has been used to non-destructively measure the surface residual stress of unloaded specimens at room temperature before and after the application of increasing strains.
Four types of cylindrical tensile specimen, with different starting surface residual stresses (highly compressive, moderately compressive, peened compressive, and tensile) have been strained in increments to a total of 5% strain, and all follow an initial linear increase in surface residual stress with increasing applied strain, before reaching a plateau that is dependent upon the starting condition. Finite Element Analysis (FEA) modelling has been conducted which demonstrates that the theoretical understanding matches the experimental data well.