Incident involving failures of anticorrosion plastic alloy composite pipe which was used for oilfield gathering and transportation had caused serious burst after several years of usage.Investigations were performed to identify the most probable causes of the pipe failures.The study was conducted by reviewing the background of the incident, visual physical inspection, FTIR spectra and TG-DSC curves of inner plastic alloy and resin in outer GRP layer.Results revealed that additives in damaged plastic alloy may not be stirred enough before extrusion or the content of additives may exceed their normal range.The lower degree of cure for resin of GRP layer leads to decrease of glass transition temperature as well as its thermal stability, which will make the outer GRP structural layer have a relatively lower mechanical property, thus giving rise to final failure of the composite pipe under the long time service conditions.