Failure analysis of 127mm G105 drill pipe

One Φ127mm G105 drill pipe body washed out infrequently just after 126h of pure drilling time. This paper gives a systematic analysis in consideration of both material quality and loading condition on drill strings. Measurement and inspection were performed on configuration, chemical compositeon, mechanical performance, metallograghy and micro-fractograghy. It´s thought that the drill pipe failure accident was premature fatigue failure accident. Failure reason is the 0.35mm decarburization layer caused by improper heat treatment and mechanical damage because of improper operating on the out surface. Under the effect of fluctuating stress, fatigue cracks originated from decarburization layer and grew rapidly. When cracks propagated through the wall thickness, drill pipe washed out.