Abstract
This paper investigates the mechanism of failures of API-grade seamless pipes. Two failures occurred, the pipe with the first failure had a 4.7 m long longitudinal crack, which occurred catastrophically. The pipe with the second failure had a small leakage. Pressure in the pipes due to hydraulic oil remains at 30–140 bar. The occurrence of large longitudinal crack at such low pressure and 25–40 °C of ambient temperature in the seamless low carbon steel hydraulic pipe requires a very high strain rate exerting on the pipe or hydrogen-induced-cracking (HIC) etc. Chemical analysis, tensile testing, hardness, visual observations, optical and electron microscopy, and Energy dispersive spectroscopy (EDS) were used to thoroughly evaluate the root cause of this failure and its mechanism. Results showed hydraulic pipe failed by HIC due to the presence of severe Sulphide inclusions. The most probable source of hydrogen in the pipe was hydraulic oil. Some mitigation measures were also proposed to prevent such failures in the hydraulic pipes of the unit.
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