Failure Investigation of a Gate Valve Eye Bolt Fracture During Hydrotesting
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During preparation for a hydrotest on a 6-in. liquid discharge line of an onshore gas terminal, water was observed to be dripping from the gland packing on the isolation gate valve. On closer inspection, it was found that the gland eyebolt on the valve was fractured. The fractured sample was sent for metallurgical examination to determine the cause of the fracture. Results of this investigation suggest that the brittle fracture of the eyebolt was caused by hydrogen embrittlement (HE). The eyebolt was supplied with the wrong composition and hardness, thereby producing increased sensitivity to HE. This article illustrates the typical procedure for a metallurgical failure investigation and presents the results of the investigation, lessons to be learnt and remedies to be applied to prevent re-occurrence. The main recommendations are to; review the valve supplier’s quality assurance procedures and to ensure that new valves are supplied in the specified composition and hardness; carry out positive material identification tests on all existing stock of Class 600 gate valves and consider using tempered plated bolting for the high risk (hydrogen-rich environment) environment.
KeywordsCorrosion failure analysis Energy dispersive spectroscopy Failure analysis Hydrogen embrittlement
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