Failure Analysis of Leakage of X42 Line Pipe

The leakage cause of X42 line pipe was investigated by mechanical properties testing, nondestructive testing and SEM observation on corrosion pits and X-ray diffraction (XRD) analysis. Experimental results show that X42 line pipe has outstanding combination of strength and toughness, and the properties meet the requirement. Obvious corrosion features can be found at the 4 o'clock to 8 o'clock region of the inner surface, and several corrosion pits can be found at the 6 o'clock. Energy spectrum analysis and phase analysis of XRD show there were a high content of chloride ions at the corrosion pits, and the pits displayed the typical small-hole corrosion characteristics. Therefore, it can be assumed that the pipe leakage is due to a large amount of residual water containing high-concentration chloride ions. The chloride ions resulted in pitting corrosion and final leakage under test pressure. It is suggested that those line pipes that have been laid but not put into service should be fully drained to avoid the occurrence of similar accidents.