Impact of Inline Isolation Tool on the Integrity of Onshore Pipelines

Abstract Inline pressure isolation tools are widely used for offshore pipelines for planned maintenance and emergency repair work, e.g. valve replacement, repair, tie-ins. Design and engineering analysis of such tools for offshore application have been well developed. Although inline pressure isolation technology is widely used in offshore pipelines, its use in onshore application is limited. However, because of its capability of providing reliable in-line isolation with significantly reduced blown-down length and methane emission for integrity and capital projects that traditionally require pipeline outages, the inline pressure isolation tools are getting increased attention from the onshore pipeline operators in recent years. Consequently, there is a growing need for better understanding of applicability and limitations of using established offshore design rules for onshore applications and developing engineering assessment workflow to ensure successful execution and prevent potential irreversible damage to existing assets. One of the challenges for the application of pressure isolation tools to onshore pipelines is to better understand the pipelines stresses that are exerted by these tools during their operation. This paper investigates the impact of these tools on the integrity of onshore pipelines from stress perspective through leveraging 3-D continuum finite element (FE) analysis using Abaqus FE software, with consideration of actual loading and boundary conditions that onshore pipelines could involve. The FE model was first calibrated with a full-scale test to ensure accuracy and validity of the simulation. Subsequently, a total of 137 FE models were developed for a wide range of pipe sizes (NPS 10 to NPS 48) and wall thicknesses (4 mm to 26.4 mm). The resulting stresses were compared with the allowable stresses for the pipelines. Furthermore, a sensitivity study was performed for various pipe material properties to ensure that an adequate factor of safety is maintained throughout the analysis. Outcomes of the investigative study was fed into a streamlined assessment workflow that includes a series of simplified graphs for determining the allowable pressure for various pipe sizes for future applications. The results demonstrate advantages of using FE based streamlined approach over conservative case-by-case analytical solutions. The outcome of this study provides insights on the various stress conditions that could result from the inline isolation tool for onshore pipelines and could potentially impact pipeline integrity.