Impact of Yield to Ultimate Ratio on the Reliability of Burst Limit States

In order to reduce arctic construction and transportation costs, high strength steels (> X80) have been advocated for use in high pressure gas pipelines. These steels differ from conventional steels by exhibiting lower work hardening capacity, lower strain to failure and possible softening of their HAZ. These differences can impact burst limit state and tensile limit state, in addition to crack arrest. In this paper, the impact of the variations in mechanical properties on the reliability of several pipe limit states involving burst is examined. The paper presents the results of burst limit state analysis using state-of-the-art plastic burst models of strain hardening pipe and considering all the uncertainties that impact the margin of safety of pipes subject to internal pressure. Intact pipes, corroded pipes and externally damaged pipes are considered. The analysis focuses on different design check equations (DCE) which “control” the safe usage of the pipe. In addition, the paper looks at how external or internal damage or corrosion affects the burst capacity differently for medium versus high-strength pipelines steels.