Failure Analysis of the Cracked Synthetic Gas Pipe

Through macroscopic inspection, chemical composition analysis, metallographic examination, crack morphology analysis, fracture microstructure analysis, and energy spectrum analysis, the failure analysis of the cracked synthetic gas pipe was carried out to determine the cause of short-term cracking of the synthetic gas pipe, in order to avoid similar leakage accidents. The pipe was made of 20G material, with an outer diameter of 219mm and a wall thickness of 12.5mm. The medium inside the pipe was CO and H2 synthesis gas, with an operating pressure of 8.5MPa and an operating temperature of 135 °C. The analysis results indicated that the cracking type of the synthetic gas pipe was caustic stress corrosion cracking, and the crack originated from the outer wall of the pipe and gradually propagates to the inner wall. The main reason was that impurities such as water vapor and alkaline ions in the external environment seep into the damaged insulation layer. As these ions accumulated and concentrated on the surface of the pipe of the damaged insulation layer, an alkaline environment was formed. At the same time, local stress concentration was generated in the area of grooves and corrosion pits on the surface of the pipe. Under the combined action of these factors, caustic stress corrosion cracking was finally generated.