An Engineering Assessment to Evaluate Integrity Options for Out of Class Pipelines

As population growth and development occurs along the pipeline right of way, the class location of pipeline segments could change to a higher class designation. A higher location class designation has a more stringent location factor according to Canadian Standard Association (CSA) Z662-11 Clause 4.3.7. For this situation, Onshore Pipeline Regulations (OPR) s.42 requires pipeline operators to submit a proposed plan in conformance with CSA Z662 requirements in Clause 10.7. Typically for compliance, a change to higher class designation leads to pipe replacement or operating pressure reduction (compliance options). Alternatively, the pipeline segment could also be subjected to an engineering assessment (EA) to develop other measures which are as safe as or safer than the compliance options. The CSA code requirements of pipeline replacement or pressure reduction for out-of-class pipe cater to generic cases, and essentially make the out-of-class pipe segment comply such that it is within class. In contrast, a site-specific EA considers the actual pipe conditions, the relevant hazards, and the case specific solutions. Therefore, the site-specific EA provides a more appropriate solution for the problem at hand and ensures a risk consistent approach for the class change site. This also provides a safety level that is equivalent or above the regulatory requirements. A three-level engineering assessment methodology was developed for an out-of-class EA. In the first level assessment, the design, construction, testing procedures and the location class development are reviewed to understand the regulatory constraints and compliance aspects. In the second level assessment, all the potential hazards are identified and assessed to determine the pipeline condition. Finally, in the third level assessment, quantitative reliability assessment techniques were utilized to determine the optimized mitigation activities that can make the pipe segments as safe as or safer than the compliant options. The class change EA used the above methodology to quantitatively compare mitigation activities with pipe replacement and reduced operating pressure scenarios. Some mitigation activities provided greater safety than pipe replacement and reduced operating pressure scenarios, thus providing safer options while avoiding pipeline service interruption; minimizing in-field disturbances and related risks of replacement; and providing cost-benefit optimization. The growth of urban areas and related encroachment on pipeline corridors is a common occurrence. Therefore this EA approach has industry wide applications in providing safer and more optimized solutions.

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