Optimal design of buried pipelines considering failure by mechanical damage

Abstract

Mechanical damage by external interference can represent a serious threat to the structural integrity of onshore pipelines. International databases indicate that, nowadays, this failure mode is the main cause of spillages in pipelines. The present paper addresses the optimal design of buried pipelines considering failure by mechanical damage. Historical incident data relating failure rates with problem parameters are used to guide the optimisation process. The design objective is to minimise total costs over the lifecycle, which include costs of construction, inspection, and expected costs of failure and repair. The optimal wall thickness, depth of cover and surveillance interval are considered as design variables. Results of numerical examples are presented and discussed. Results show that operators should favour deeper depths-of-cover. In some cases, it is shown that the higher initial costs associated to larger wall thicknesses are compensated by reduction in expected costs of failure. Results also show that, for higher costs of failure, the optimal surveillance interval is significantly smaller than the commonly-practiced 15 days.

Keywords:

• Buried pipelines
• mechanical damage
• failure
• risk
• optimal inspection
• repair
• structural optimisation

Acknowledgements

Comments by the anonymous reviewers have significantly improved the article and are cheerfully acknowledged.