Comparison on the failure behaviour of the LPG spherical tank manufactured from different steels under the wet H₂S environment

Comparative studies on the failure behaviour of the liquefied petroleum gas(LPG) spherical tanks, which were manufactured from 16MnR steel and SPV50Q steel respectively and working under the wet H₂S environment, were conducted. By observing the crack feature of the samples cut from the severely corroded shell plates removed from the integral 16MnR spherical tank and the crack morphologies of the metallurgical replica photos made on the internal surface of SPV50Q tank on site, as well as analysing the hardness and welding residual stress measured on site, it was found that the failure of 16MnR tank was attributed to hydrogen - induced cracking(HIC) and the damages occurred on the base metal. While for SPV50Q tank, the failure was attributed to sulfide stress corrosion cracking(SSCC) and cracks mainly appeared in the heat - affected zone(HAZ) around the welded joints.