Crack Healing of High Temperature Hydrogen Attack Corrosion by Heat Treatment

Abstract

Crack healing demonstrate as a ability of metal to repair physical damage by restructuring the carbon microstructure. High-Temperature Hydrogen Attack (HTHA) destruction happens when carbon steel equipment is exposed to hydrogen partial pressure at high temperatures. This will result in damage that severely degrades the mechanical properties of carbon steel. HTHA always happen at high-stress area in carbon steel such as a post-weld-heat-treated weldment and bending area in the form of the fissure exerted by methane gas inside the equipment. As more fissures are formed, it leads to form micro cracks and weaken the steel to cause a rupture. HTHA is difficult and challenging to inspect. In this research, the HTHA locations were identified by magnetic particle inspection (MPI) and heat treatment was performed by heating to annealing temperature and slowly cooled in the furnace. The early stages of attack with fissures or even small cracks detected are difficult to detect. When significant cracking detected, the particular point is already at higher possibilities of equipment to fail. Previous research has elucidated that there is a possibility of HTHA crack to reduce if undergoes for heat treatment. Heat treatment implies carbon diffuse into the matrix and hydrogen atoms escape. Therefore, diffusion plays an important part in the healing of HTHA crack as it plays a key role in the HTHA process. In this study, the specimen is 4-inch (10.16 cm) elbow pipe of the pipeline between distillation column and heat exchanger with a wall thickness of 1-inch (2.54 cm) had failed due to HTHA from pipelines which have been operating for 10 years. The failure occurs during operation on the pipelines between distillation column and heat exchanger. The crack length has reduced once the failed part was reheated to the annealing temperature of 850°C and slowly cooled in the furnace. The heat treatment by annealing also can be an alternative for altering the structure of the material in order to achieve desired properties and prepare the situation for further decision making by the process operation responsibilities. The conclusion for this research is to identify HTHA locations and restructure the microstructure of affected carbon steel by heat treatment. Results revealed that cracks length had reduced 3 to 10% by heating the failed pipe to annealing temperature and then slowly cooled for microstructure recover. However, the hardness had reduced and further research should be extended to overcome this problem.