COMPARISON ON THE FAILURE BEHAVIOUR OF THE LPG SPHERICAL TANK MANUFACTURED FROM DIFFERENT STEELS UNDER THE WET H2S ENVIRONMENT

摘要

Comparative studies on the failure behaviour of the liquefied petroleum gas (LPG) spherical tank manufactured from different steels were conducted in this paper. One tank was fabricated from 16MnR steel that had been widely used as structure material in petrochemical plants. Another tank was built with SPV50Q steel that was specially designed to construct the spherical tank with larger volume and free PWHT (post-weld heat treatment) after its erection. Although these two steels belong to low-alloyed steel, they have different microstructures and mechanical properties due to different alloyed elements and heat treatment experiences. Therefore, when the tanks fabricated with 16MnR or SPV50Q were put into service to store LPG that sometimes contained water and hydrogen sulfide forming so-called wet H2S environment, the steels would suffer from the damages related to hydrogen. By observing the cracking samples cut from the severely corroded shell plates removed from the integral 16MnR spherical tank and the metallurgical replica made on the internal surface of SPV50Q tank on site, as well as analysing the hardness and welding residual stress measured on site for these two spherical tanks, it was found that the cracking of the 16MnR tank mostly occurred on the base metal in the form of hydrogen-induced cracking (HIC), while the SPV50Q tank failed in the heat-affected zone (HAZ) around the welded joints attributed to sulfide stress corrosion cracking (SSCC).