Pipelines form an integral part of energy resource transportation worldwide for over 150 years. The energy resources that are moved around include crude oil and natural gas. The typical service lives of operational pipelines are up to 50-70 years. The existing lines would subsequently be decommissioned and replaced with new lines. Decommissioned lines can be dealt with in two possible ways. The first method involves soil excavation along the existing line right-of-way and the pipe gets extracted. The excavated trench is backfilled at the completion of pipe extraction. The second method involves leaving the decommissioned line untouched in the ground. Despite the latter option being the most economical from a time and effort perspective, there exists uncertainty in the structural integrity of decommissioned lines under external corrosion over time. External corrosion could be local pitting and uniform. In pitting corrosion which is a localized form of corrosion, perforations are produced in the pipe material. Overburden soil has a tendency to migrate into and along the pipe under gravity and hydraulic gradient, thereby causing ground subsidence and possible formation of sinkholes. Uniform corrosion results in continuous thinning of the pipe wall thickness. The weaken pipe section eventually yields and collapses under soil overburden load.

 

This paper introduces reliability-based integrity assessment of decommissioned pipelines that remain in the ground. Two limit state functions are developed to quantify (i) formation of perforations under pitting corrosion, and (ii) thinning of pipe wall thickness under uniform corrosion and initiation of pipe yielding under soil and traffic loading. Corrosion occurrence and growth are modeled as stochastic processes to account for its spatio-temporal uncertainty. The reliability and safe remaining lifetime of an entire pipeline sections are determined using enhanced Monto-Carlo simulations. A sensitivity analysis is performed to identify the governing factors of the life expectancy. The proposed integrity assessment is illustrated on an example.


Life Expectancy of Decommissioned Pipelines Under External Corrosion - Probabilistic Modeling

Division / Sponsors: 
Pipeline Systems Division

Paper Proceedings: https://asmedigitalcollection.asme.org/IPC/IPC2020/volume/84447

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