Failure analysis of local settlement induced Q345R bottom plate cracking of crude oil storage tank
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Published on: May 13, 2018
Zhang Shuxin1,2, Kang Chun3, Zhang Penggang3
1Tubular Goods Research Institute, China National Petroleum Corporation & State Key Laboratory for Performance and Structure Safety of Petroleum Tubular Goods and Equipment Materials, Xi'an, Shaanxi 710065, China.
Abstract:
A 5000m3 single deck floating roof crude oil storage tank was found to have a cracked Q345R bottom plate during an open tank inspection. To analyze the cause of the failure, a series of experiments were carried out. The results showed that the chemical composition of the failed crude oil storage tank bottom plate material Q345R had a slight excess of S, V, and Ti which causes the material to form a bainite structure, resulting in a hard and brittle material with poor toughness. Q345R is susceptive to H2S stress corrosion cracking according to SCC test. Based on the working condition investigation, the cracked plate was subjected to the local settlement and H2S contained corrosive medium. With the stress concentration induced by local settlement, the bottom plate cracked. In order to avoid such incidents, Q345R material should be avoided in H2S containing environment, and online monitoring should be carried out regularly to assess the overall condition of the tanks.
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