ABSTRACT

Production and delivery of hydrocarbons in remote locations of the world may involve traversing regions which could expose pipelines to geohazards. These geohazards may include fault crossings, landslides, liquefaction, ice gouging, and frost heave. ExxonMobil has developed a strain-based design (SBD) pipeline technology to design against these geohazards and to enable safe transportation of hydrocarbons across challenging terrain.

Integrity management of strain-based pipelines includes measures such as corrosion prevention, external damage prevention, ground movement monitoring, and geohazards mitigation. Despite preventive efforts, a pipeline may still become corroded or damaged. The damage may reduce the pipeline's strain capacity and a repair method to restore the pipeline's capacity will be required. This paper presents the qualification of the Type B split sleeve, a sealing repair methodology, for strain-based pipelines. The subjects addressed include selecting the Type B split sleeve as a repair candidate, finite element modeling of the repair, sleeve welding with in-service flow conditions, and full-scale proof testing of three repaired pipes.

INTRODUCTION

Production and delivery of hydrocarbons in remote locations often requires transportation of the hydrocarbons across challenging terrain. This may expose a pipeline to geohazards including faults, landslides, permafrost, earthquakes, and ice gouging. Pipelines are traditionally designed for pressure containment - a circumferential load - whereas most geohazards affect a pipeline by imposing loading in the longitudinal or axial direction. In extreme cases, the longitudinal loading can cause significant degrees of plastic deformation. Traditional pipeline design does not consider extreme longitudinal loading and the design methodology must be modified to ensure the pipe is able to withstand all loading conditions.

ExxonMobil has developed a SBD technology (Panico, et al. 2017; Fairchild et al., 2016, 2014; Tang et al., 2014; Macia et al., 2010) for building pipelines with the ability to sustain loads imposed by ground movement. Fig. 1 illustrates the principal difference between stress and strain-based pipeline design. A stress-based pipeline is designed for pressure containment considering hoop stresses such that at the maximum pressure, the stresses will remain below the specified minimum yield stress (SMYS) by a prescribed amount. The difference between the allowable stress limit and the specified minimum yield strength is the design safety margin. For SBD, the pipeline is designed to contain pressure and sustain loading imposed by potential ground movement. It should be noted that while pressure containment is constant, the loads caused by ground movements are typically upset events and often of long return periods; i.e., they are infrequent. When the ground movement does occur, it is allowed to cause yielding and plastic flow (straining) in the pipe up to the allowable strain limit.

This content is only available via PDF.
You can access this article if you purchase or spend a download.