(A) study on the effect of environmental variables on the crack growth behavior in SA508Cl.3 pressure vessel steel

Abstract

In order to assess the susceptibility of the Environmentally Assisted Cracking (EAC) on SA508 Cl.3 steel in primary water condition, polarization test and Slow Strain Rate Test (SSRT) were conducted in a simulated crack tip condition with various environmental variables at room temperature. Corrosion potential shifted upward with the addition of oxygen, thus it facilitated EAC behavior. But the effect of sulfur was negligible. This explains the thermally activated reaction of sulfur. EAC susceptibility was dominant with the applied potential and acidity because of the pitting phenomenon as well as anodic dissolution. Ford-Andresen model to predict EAC growth behavior is applicable at high temperature condition because the model needs oxide/passive film ahead of crack tip. Thus it fails to explain the system where oxide/passive film were suppressed. Proposed simple dissolution model is a modification of the Hishida``s anodic dissolution model at the plastic zone. It has an assumption of the similarity between round-bar tensile specimen and tensile ligament at the crack tip. Finally, this model can be used regardless of oxide/passive film. Also it explains region II-K independent nature. Comparison with the actual data shows a good agreement