Failure analysis of leakage caused by perforation in an L415 steel gas pipeline

The reasons for the failure of a buried pipeline perforated during construction were investigated by a chemical composition analysis; a metallographic test; macromorphology observation; characterization of the corrosion products by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction; field medium characterization; and an analysis of the working conditions. The results revealed that the material composition and organization of the steel pipe conformed to API Specification 5CT. However, the reason for the perforation of the L415 steel pipe was an ultrahigh growth rate of pitting corrosion, as high as 14 mm per year. We confirmed that the synergistic effect of a high partial pressure of oxygen introduced by an improper packing process and concentrated Cl⁻ in the corrosion product layer, which originated from groundwater with a high salt concentration that was used for the water pressure test, were responsible for the failure process.