The failure cause of 0127mm G105 IEU drill pipe upset was investigated through mechanical properties testing, optical morphologies and fracture surface analysis. The result show that drill pipe upset's failure reason is the elephant hide and decarburization layer in its out-surface caused by improper upset treatment in forging process. Elephant hide and decarburization layer existing in drill pipe upset changed seriously reduced its strength and fatigue property. Under the effect of alternating stresses, the crack first initiated from the deepest position of elephant hide and developed quickly. In the end, it leaded the drill pipe to early piecing failure.
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