State-of-the-Art Review of Performance Objectives for Legacy Gas Pipelines with Pipe-in-Pipe Rehabilitation Technologies

Legacy gas pipelines experience problems as they age. Pipe rehabilitation and replacement using internal pipes or liners is a trenchless renewal approach to address these issue-prone facilities. Here, a set of performance objectives is identified using data from both the field and the literature. First, observations of recorded pipeline incidents of cast/wrought iron gas distribution mains were analyzed to understand the causes of damage in host pipe systems. Natural force damage, including subsidence, frost-related deformation, and other earth movements, was identified as the leading cause of incidents in such systems. An internal-repair pipe would be expected to withstand such events. Secondly, a literature review of the mechanical behavior of rehabilitating internal pipes or liners was performed. Considerable work has been performed to understand how such systems behave under internal hydrostatic pressure, external pressure, surface loads, and external loads reflective of expected earth movements. Under internal pressure, stresses higher than that expected for an unconfined repair pipe or liner can develop at large holes in the host pipe. Studies to understand earth movements in rehabilitated pipelines often apply bending moments or axial loads to repaired specimens with joints or full-circumferential cracks. The literature demonstrated that the behavior of internal pipes or liners at discontinuities in the host pipe is critical for rehabilitated pipeline performance. Most available studies, however, have focused on nonstructural or semistructural repair systems, which may be unsuitable for full rehabilitation of deteriorating gas pipelines over an extended design life. The set of performance objectives described in this paper will help improve the understanding of structural pipe-in-pipe to enable effective design and implementation of trenchless repair systems for existing natural gas pipelines.