Abstract: The analysis involves the failures of the φ127 mm×9.19 mm IEU S -135 drill pipe, including piercing-corrosion and outer surface corrosion of the pipe body. The result shows that the chemical composition, metallographic structure and mechanical properties etc. of the drill pipe are all up to applicable specification of API Standard and the technical requirements as specified in the order, and that the said piercing-corrosion failure is caused by the severe combined corrosive effect on the pipe inner surface by H₂S and oxygen, while the said outer surface corrosion is merely caused by oxygen.