Experimental Assessment of Trenchless Rehabilitation for Pipeline Bends

Trenchless technologies are critical to extending the life of aging, deteriorated pipelines, particularly difficult-to-access areas where cut-and-cover methods are impractical or otherwise cost-prohibitive. Given their ideal use cases, internal replacement pipe (IRP) technologies must be capable of spanning host pipe joints and competently performing over their design life even when the host pipe experiences cracks or full deterioration. Past research efforts have tested these materials and analyzed their behavior under varying loading conditions, verifying the IRP's structural integrity and containment capacity. However, these previous studies have only assessed straight pipe specimens. For the first time, this study experimentally investigates the behavior of IRP technologies in specimens with bends by subjecting nominal 12-in. diameter steel pipes with 45° elbow fittings to external loading. Each specimen had two half-inch gaps where the bent fittings connected to straight pipe segments, simulating a realistic geometry encountered in the field. At the gaps, the IRP was exposed and required to accommodate various loading scenarios. In this study, specimens experienced flexural loading, while axial loading and a pull in tension until ultimate capacity are subsequently planned. Flexural loading consists of 500,000 modified 4-point-bending cycles to emulate 50 years of traffic loading and two large transverse displacements representative of adjacent excavation activities. The specimen was loaded at an orientation that was determined through numerical analysis to be most critical, hence, yielding worst-case results. The goal of this study was to assess the behavior of IRP repair systems under a complicated geometry that is representative of field conditions, ultimately providing pipeline owners confidence in the ability to repair pipelines in limited access areas. This research highlights the similarities and differences in material response between bent and straight specimens under equivalent external loading conditions. The proposed test methods are intended to fairly assess products under representative service life conditions, promote industry adoption of existing IRP technologies, and encourage further innovations in deposition methods, installation procedures, and material formulations.