Study on cracking susceptibility of SPV50Q high strength steel weldment exposed to wet H₂S containing environment

SPV50Q steel of high strength and good ductility is often employed in construction of liquefied petroleum gas (LPG) spherical tanks. In general post weld heat treatment is not performed after welding of the steel and residual stress will be retained in the weldment. Service experiences and inspections indicate that higher H₂S concentration and welding residual stress may result in the environmental failure, such as hydrogen blistering (HB)or hydrogen-induced cracking (HIC), sulfide stress corrosion cracking (SSCC) and stress-oriented hydrogen induced cracking (SOHIC). The cracking susceptibility of SPV50Q steel weldment by manual electric arc welding has been investigated in various solutions with different concentrations of H₂S. The results of slow strain rate testing, performed at a strain rate of 1 x 10^-6s^-1, reveal the presence of SSCC and HIC in the zone of HAZ adjacent to weldment. The effects of temperature of post weld heat treatment on cracking are discussed. The appropriate post weld heat treatment (PWHT) procedure could enhance the resistance of SPV50Q weldment against SSCC or HIC and does not decrease the mechanical properties of SPV50Q weldment, in particular material ductility.