Arctic Pipeline Design Considerations

Abstract

Since the discovery of reserves in arctic regions, operators have been faced with a number of challenges, including assessing appropriate methods of transporting produced hydrocarbons to market. For pipeline systems, designers are required to deal with a number of unique environmental conditions not normally present in other regions of the world. These include ice scour, permafrost thaw and/or frost heave, leak detection and containment, and installation techniques. For offshore applications, novel design alternatives that have been considered to address these issues include pipe-in-pipe systems, non-bonded flexible pipes, composite wrapped pipes, and hybrid pipes. Each alternative offers strengths and weaknesses, depending on the specific hazards or failure event consequences that may exist at the location of interest. For buried onshore pipelines, the key design issue is the potential for high bending strains resulting from frost heave and thaw settlement. For both onshore and offshore pipelines, possible ways to address these issues includes the use of pressure and diameter combinations that lead to thick walls, integration of in-service inspection and maintenance within the design philosophy, stringent quality control for girth welds, and selection of materials with appropriate post yield behaviour. Because of the lack of traditional design solutions to these challenges, limit state, reliability-based and strain-based design methods are now preferred for arctic applications. The implementation of these methods requires a good understanding of linepipe material behaviour, soil loading conditions, ice loading mechanisms, and the consequences associated with product release. They allow the integration of analytical and experimental assessments into the overall design philosophy, which has been shown to improve design concept confidence and reduce overall uncertainty. This paper describes some of the key challenges facing the design of both onshore and offshore pipelines. It describes some of the current design options and how reliability-based and strain-based methods can be used to integrate essential information from a number of analytical and experimental sources into an overall framework that addresses the challenges and leads to optimal design decisions. It discusses the state of the art in this area and identifies knowledge gaps that need to be filled.