The Effect of Welding Residual Stress for Making Artificial Stress Corrosion Crack in the STS 304 Pipe

Jae-Seong Kim,Woong-Gi Hwang,Sung-Sik Kang,Bo-Young Lee

doi:10.1155/2015/932512

Abstract

The stress corrosion crack is one of the fracture phenomena for the major structure components in nuclear power plant. During the operation of a power plant, stress corrosion cracks are initiated and grown especially in dissimilar weldment of primary loop components. In particular, stress corrosion crack usually occurs when the following three factors exist at the same time: susceptible material, corrosive environment, and tensile stress (residual stress included). Thus, residual stress becomes a critical factor for stress corrosion crack when it is difficult to improve the material corrosivity of the components and their environment under operating conditions. In this study, stress corrosion cracks were artificially produced on STS 304 pipe itself by control of welding residual stress. We used the instrumented indentation technique and 3D FEM analysis (using ANSYS 12) to evaluate the residual stress values in the GTAW area. We used the custom-made device for fabricating the stress corrosion crack in the inner STS 304 pipe wall. As the result of both FEM analysis and experiment, the stress corrosion crack was quickly generated and could be reproduced, and it could be controlled by welding residual stress.

Highlights

Assisted crack, such as stress corrosion crack (SCC) of the NPP structural materials, has been one of the causes for the shutdown of the power plant resulting in a significant loss, incapacitating the production electric power
Stress corrosion cracking usually occurs when the following three factors exist at the same time: susceptible material, corrosive environment, and tensile stress
They have performed the SCC test on the austenitic SS using loading device and showed that the specimen of type 304L SS was fractured even when the applied stress was below 200 MPa which was less than 0.2% proof stress of type 304L SS [3]

Summary

Introduction

Assisted crack, such as stress corrosion crack (SCC) of the NPP structural materials, has been one of the causes for the shutdown of the power plant resulting in a significant loss, incapacitating the production electric power. Tani et al reported that chloride induced SCC of the austenitic stainless steel occurred independently of the tensile residual stress value. They have performed the SCC test on the austenitic SS using loading device and showed that the specimen of type 304L SS was fractured even when the applied stress was below 200 MPa which was less than 0.2% proof stress of type 304L SS [3]. The conventional method of manufacturing artificial stress corrosion cracks is difficult to imitate environmental conditions of the NPP because the resulting cracks are not obtained by using a pipe used for equipment of nuclear power plants but by using a simulation specimen. 3D FEM (Finite Element Method) analysis model is designed about STS 304 pipe and performed heat transfer analysis and residual stress analysis

Experimental Methods

Results and Discussion

Conclusions