Long term overheating failure 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 closed recirculation system water cooling pipe obtained from a steel manufacturing plant in Malaysia has been investigated for detailed failure analysis. A steam leakage was detected on the ASTM A106/A pipe (carbon steel pipes for high temp service). The aim of this study is to explore the evidence related to the water cooling pipe leakage and to investigate the cause of failure. A detailed investigation was carried out by means of visual inspection, optical microscope examination and hardness test. Based on the evidences, the failure was caused by decarburization due to the presence of water scale and prolonged overheating. Based on microstructure examination, it was found that carbon elements from inner tube surface had depleted via carbon migration through the outer tube surface. The accumulation of carbon elements created a brittle zone on the outer tube surface. With the presence of tensile stress developed from operating thermal cycle had subsequently resulted in cracks. Based on all the findings, it can be concluded that the water cooling pipe leakage was due to long term overheating.