Effect of Post Heat Treatment to High Temperature Hydrogen Attack (HTHA) Corrosion of Decarburised Carbon Steel

Abstract

High Temperature Hydrogen Attack (HTHA) corrosion may occur on carbon steel when service at high temperature with hydrogen partial pressure. One micro pinhole crack may cause catastrophic if misleading of inspection. Pre-heat treatment was proven can control HTHA crack by release stress residue, however, some may remain to cause internal cracks. This research was aimed to reveal the effect of post heat treatment on failed HTHA. Results showed that crack length had reduced after post heat treatment at 900°C and holding time for seven hours. Visual inspection showed crack length had reduced from 13mm to 9mm which of ratio 30.77% reduction. SEM showed the corrosion pattern is to be intergranular and decarburization has occurred between the crack surface and the surface that is not having any cracks. The oxide film formed on the carbon steel after heat treatment is fragile. Characterization of corrosion product revealed that the oxide layer contains iron and oxygen elements only. The hardness value is increasing from before undergoing heat treatment and after undergoing heat treatment. The corrosion rate of carbon steel is determined through the electrochemical test. Heat treatment can be one of the possible option to undergo for carbon steel which the structure is failed by hydrogen attack.