Session: 15-06-01: Reliability and Safety in Transportation Systems I

Paper Number: 162947

An Investigation of Failure on the Crack in Hydrogen Gas Tank Flange 

Pressure vessels often operate in harsh conditions, including high temperature, high pressure, and corrosive media. The safe and stable operation of pressure vessels is closely related to both efficiency and safety of production. Flanges, as essential components of pressure vessels, are prone to internal defects due to production processes and they also withstand challenging operating conditions such as vibration, impact, and stress concentration additionally. Due to the influence of production processes and operating conditions, the reasons for the failure of vessel flanges vary, and most studies only analyze the causes of failure. Few studies start from the actual engineering situation and propose practical preventive measures.
In this paper, a hydrogen gas tank with leakage failure was studied, the analysis of the failure in hydrogen gas tank flange was conducted. In order to ascertain the cause of the leakage incident, macro-inspection, chemical analysis, mechanical property testing, metallographic analysis, scanning electron microanalysis(SEM) and energy dispersive spectrometer(EDS) were used to analyze the defects. 
Based on the comprehensive analysis of the above results, it is concluded that the failure mechanism of the flange involves hydrogen-induced chloride stress corrosion cracking, and fatigue cracking. The fatigue is considered one of the primary mechanisms for the initiation and propagation of the crack, because of the presence of roller marks and fatigue striations on the fracture surfaces of the crack initiation zone, propagation zone, and crack tip. Meanwhile, the fracture surfaces of both the crack initiation zone and crack tip exhibit high levels of Cl content, indicating that chloride stress corrosion cracking can be considered as one of the mechanisms contributing to crack propagation. In addition, the presence of alumina and calcium oxide inclusions on the fracture surface of the crack initiation zone suggests that inclusions may be one of the conditions leading to the initiation of the crack.
In the future, the operation of this equipment should be maintenance according to the following requirements:
•    Strictly control the quality of flanges to prevent the segregation and excessive inclusion of elements such as carbon, manganese, phosphorus, aluminum, and calcium. For example, the manufacturing unit strengthens the quality control when the material enters the factory for acceptance.
•    Identify the sources of alternating loads on the flanges and minimize them as much as possible. For example, the design unit should carry out the flexibility analysis of the connected pipeline and optimize the pipeline structure.
•    Monitor and control the chloride ions in the medium. For example, the user should regularly test the chloride ion content in the media to ensure that it is below 50ppm.

Presenting Author: Cong Deng Guangdong Institute of Special Equipment Inspection and Research

Presenting Author Biography: Special Equipment Inspection and Safety Assessment

Authors:

Cong Deng Guangdong Institute of Special Equipment Inspection and Research
Weijian Luo Guangdong Institute of Special Equipment Inspection and Research
Xufeng Li Guangdong Institute of Special Equipment Inspection and Research
Jin Guo Guangdong Institute of Special Equipment Inspection and Research
Wufei Yuan Guangdong Institute of Special Equipment Inspection and Research
Huasheng Hu Guangdong Institute of Special Equipment Inspection and Research
Shengzi Lu Guangdong Institute of Special Equipment Inspection and Research