Engineering critical assessment to evaluate partial height hydrotesting of LPG storage tanks

This paper examines whether avoidance of full height hydrotesting by specifying additional toughness requirements can be justified using engineering critical analyses. The toughness requirements of BS 7777: 1993, the draft PD 7777:2000 and typical toughness data were used to derive representative toughness input parameters for LPG storage tank designs. Appropriate prior overload conditions for full and partial height hydrotest conditions were used to carry out fracture mechanics calculations to compare the two design scenarios. Whilst application of the draft PD is aimed at ensuring crack arrest, it is concluded that the more severe toughness requirements of the draft PD are considered to provide: i) adequate prevention of fracture initiation for partially hydrotested LPG tanks, ii) increased resistance to ductile tearing for the ferritic steels and weldments used for the LPG tanks. Furthermore, it has been shown that the tearing resistance of partial and full height hydrotest tanks is comparable when taking the additional draft PD toughness requirements into account. Postulated arrested flaws of reasonable dimensions have been shown to be stable with respect to ductile tearing.