Stress Corrosion Cracking of a Copper Pipe in a Heating Water Supply System

Abstract

Stress corrosion cracking behavior of a copper pipe and its mechanism were investigated in a heating water supply system using both metallurgical and mechanical analyses. The X-ray diffraction and energy dispersive spectroscopy measurements showed that uniform cupric oxide and cuprous oxide were formed during service on the inside surface of the pipe, while malachite and cupric oxide were the main corrosion products on the outer surface of the pipe. Many corrosion pits were observed around the cracking areas on the outer surface by optical microscopy. Finite element modeling highlighted a region with large hoop stresses mainly brought about by the bolt load, where it became susceptible to stress corrosion cracking (SCC). The morphology of the fracture surface revealed an intergranular mode towards the outer surface but a mixed inter- and trans-granular mode near the inner surface. Based on the obtained results, a phenomenological 4-stage fracture process is proposed to describe the failure process of the copper pipe, in which the SCC initiated from the corrosion pits on the outer surface, propagated along the axial direction and penetrated towards the inner surface until final fracture. Graphic