Metallurgical failure analysis of a closed recirculation system water cooling pipe

Abstract

Catastrophic failure is often associated with a large temperature rise. This situation may lead to a drastic deterioration in material strength where a cooling system is important for a smooth system plant operation to prevent catastrophic failure to its equipments, parts or processes. In this study, a part of a failed closedrecirculation system water cooling pipe in a steel manufacturing plant in Malaysia has been investigated for detailed failure analysis. A steam leakage of a water cooling pipe with a closed recirculation system operation made of ASTM A106/A (Carbon Steel Pipes for high temp service) was detected. The aim of this study is to explore the evidence related to the water cooling pipe leakage and to investigate the cause of failure. Detailed investigation was carried out by visual inspection, optical microscopy and hardness testing. With the evidence obtained, due to presence of water scale and prolonged overheating, decarburization had occurred. During decarburization, it was found that carbon elements from inner surface tube had depleted through the outer tube surface. The accumulation of carbon elements on the outer tube surface appears to show significantly higher brittle zone in the outer tube and with the presence of tensile stress developed from operating thermal cycle which subsequently resulted in crack. It can be concluded that the water cooling pipe leakage was due to thermal fatigue.