Risk-based design of a process component

Hasan, Sikder Mainul (2012) Risk-based design of a process component. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The production and transportation of hydrocarbon from a facilities involves complex process system. The components in such a process system are exposed to extreme operating and environmental conditions. To ensure safe and continuous operation, it is important to identify potential risk sources, and incorporate the risk factors in the designing of the process components. -- The present work develops a novel integrated methodology for the risk-based design of process components. It may be noted that there are lots of process component but specific consideration is given for oil and gas pipeline. Hence, the scope of the work is comprised of time dependent failure scenarios. The failure mechanisms considered here are: internal corrosion, external corrosion, stress corrosion cracking, fatigue failure due to corrosion fatigue and start up/shut down loading for a specific process component. The time independent failure mechanisms i.e. third party damage, earth movement, and material defects are not considered in this study. -- This research considered uncertainties associated with operational characteristics of the process component and included them in the risk-based design framework. The study reviewed different design codes/standards for a transportation system. In the internal corrosion analysis the defect depth was calculated from corrosion rate equations and failure probability was assessed considering the first order reliability method. A similar procedure was considered for external corrosion analysis. In the internal corrosion analysis, the study compared the performance of different codes and standards and listed comparative advantages of one over other. The external corrosion analysis identified the causes of the variability of probability of failure for recommended codes/standards. It is identified that the difference in parameter contribution in the bulging factor are responsible for variability in the bursting formulas. In the stress corrosion cracking (SCC) failure analysis, the stress based failure assessment diagram (FAD) was considered. The authors also proposed a strain based approach for the same analysis. The stress/strain based approach closely calculates the failure probability of the SCC defects. The corrosion fatigue analysis mainly considered the effect of variable amplitude loading (pressure fluctuation) on small weld defects. The Miners rule and Paris law are simultaneously considered for failure assessment. The Rainflow counting method is considered in the analysis for stress block and cycles counting. The failure probability is calculated from the damage caused by the pressure fluctuation. -- The failure probability obtained for an individual event is integrated using fault tree analysis to obtain the overall risk of the system -- The unified risk is minimized to design individual components to achieve the target safety level of the system.

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