AbstractLegacy 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.Practical ApplicationsAging pipes can be repaired with internal rehabilitating pipes. This review provides insight into the causes of problems in gas distribution mains of cast/wrought iron, an important subset of legacy gas pipelines, by analyzing field observation records from between the years 1970 and 2020. Natural force damage was an important driver of damage; common subtypes of natural force damage are related to flexural deformation. Such deformation needs to be addressed by an internal repair pipe. Many researchers have studied the mechanical response of pipes repaired with internal pipes or liners. In these studies, the major loads are reflective of internal pressure, external pressure, surface loads, and soil movements. Interaction between the aging host pipe and internal rehabilitating pipe is an important factor. Performance objectives for internal rehabilitating pipes are outlined in this paper on the basis of field observations and existing work. The systematic identification of performance objectives most critical to these systems is intended to provide a pathway for future development and to qualify new pipe-in-pipe (PIP) system performance over a desired service life.