Failure Analysis of Hydrogen Piping System
Background
A refinery plant has encountered the problem of damage to stainless steel pipes for transportation of hydrogen-containing gas in a hydrocarbon cracking unit after installed and serviced for nearly 21 months. A crack was detected on the outer wall surface resulting in leakage of hydrocarbon compounds and respective fire. This incident caused a malfunction in the oil refinery unit and the plant had to stop the operation of the 4 refinery units for 18 days. The economic impact is estimated to be approximately 800 million baht per year due to productivity loss during the shutdown. Therefore, the sections of the ruptured pipes were sent to Failure Analysis and Corrosion Technology Research Team of MTEC for root cause analysis. The improvement of refinery safety must be conducted in order to prevent the reoccurrence of such a severe accident.
Goal
To perform a metallurgical failure analysis and to acquire sufficient data for problem-solving of the ruptured pipe.
What does the research team do?
In order to determine the root cause of failure, various examination techniques including onsite examination, physical examination, thickness measurement, fracture surface analysis, microstructure analysis, corrosion product analysis, chemical composition determination, and numerical simulation of hydrogen diffusion were carried out.
Research results
The testing results indicated that the cracking of pipe was caused by hydrogen assisted cracking (HAC) due to the diffusion of hydrogen through the occurrence of slip bands. These defects were observed with a significant amount in austenite grains, especially in the subsurface of the outer wall. Also, the high degree of restraint in the T-joint weld area resulting in high tri-axial stress at the outer wall surface, which is the starting point of the crack. A numerical simulation of the distribution of hydrogen revealed that the concentration of hydrogen is uniformly distributed throughout the wall thickness of the pipe for more than 20 months. The final overload was propagated by a severe HAC as confirmed by the presence of intergranular cracking topography on the fracture surface. The diffusion time of hydrogen obtained from the simulation shows that it is related to the actual operating time.
Research status
The company is aware of the root cause of the problem and has improved the related processes. It is able to reduce the impact on the environment without leakage of hydrocarbon compounds. Moreover, the research team collaborated with experts from the Federal Institute for Materials Research and Testing (Bundesanstalt für Materialforschung und –prüfung, BAM) in simulating of hydrogen diffusion and also transfered the knowledge gained from this project by publishing an article in the Engineering Failure Analysis journal (E. Viyanit, S. Keawkumsai, K. Wongpinkeaw, N. Bunchoo, W. Khonraeng, T. Trachoo, Th. Boellinghaus. Hydrogen assisted cracking of an AISI 321 stainless steel seamless pipe exposed to hydrogen-containing hot gas at high pressure, Engineering Failure Analysis 2019: 100; 288-299)
Outlook
The research team will continue accumulating knowledge and support industries via metallurgical failure analysis services to acquire sufficient data for problem-solving of the failed parts. Besides, the knowledge will be transferred to the public via lectures and academic articles.
Research team:
Siam Kaewkumsai, Kosit Wongpinkaew, Nirut Bunchoo, Witsanupong Konraeng, Siriwan Auampan and Ekkarut Viyanit
Contact:
Siam Kaewkumsai (Senior Engineer)
Metal and Manufacturing Process Research Group
Tel: 0 2564 6500 ext. 4736
