Failure analysis of a hard-drawn water tube leakage caused by the synergistic actions of pitting corrosion and stress-corrosion cracking

摘要

Unalloyed high purity copper, deoxidized with phosphorus is widely used in tubing and fittings for sanitary installations due to its ease of use and corrosion resistance properties. Certain factors related to installation operating conditions on the one hand, and improper design/installation features on the other hand, often lead to unexpected failures. The case examines a Cu-tube that failed in a pump station after 2-3 years in-service. The investigation findings suggest strongly that the failure was the result of a complex mechanism involving corrosion-erosion process, facilitated by stress-corrosion cracking mechanism. Stress-corrosion cracking referred as a delayed failure mechanism resulted from the synergistic effect of corrosive environment, susceptible material and externally applied or residual - due to the manufacturing process-stress. In case of hard-drawn tubes, the development of tensile (circumferential or hoop) stress field at the outer surface area after cold drawing, enhances the propensity for stress-corrosion cracking (SCC), especially under the presence of corrosive environment.