This paper describes the results of a full-scale bend test of a 4.5-m-long section of NPS 24 X65 pipe. The pipe was instrumented using conventional strain gauges and a digital image correlation (DIC) system, pressurized, and subjected to axial and bending loads. The loading resulted in the pipe bending to a very high overall angle of 51.2° and the formation of a severe buckle. Post-buckle loading resulted in cracking and tearing of the pipe wall but without containment loss. The test data was used to validate the critical strain capacity of the pipe in support of future strain-based design applications for challenging real-world situations.
Pipelines may experience severe strains and extensive plastic deformation due to large bending loads caused by geohazards such as slope instability, seismic activity, water crossings, or frost heave. Strain-based design and assessment is an industry-standard approach that allows pipeline operators to better ensure that pipeline integrity is maintained if a pipe is subjected to these hazards. This approach requires a detailed understanding of the pipe's performance under severe loading conditions, while comparing the predicted strain demand to the strain capacity of the pipe. The critical strain capacity is generally determined using experimental approaches or experimentally benchmarked models. Full-scale testing may be performed as part of regulatory or operator-based pipe qualification requirements or as a means to support advanced techniques for the design and assessment of pipes. Full-scale testing under these conditions presents some clear challenges; however, it is generally considered the most accurate way to assess the pipe properties.
A full-scale bending test was performed to evaluate the behaviour of a 4.5-mlong section of a 610-mmdiameter (NPS 24) X65 electric resistance welded (ERW) line pipe with a 17.60-mm wall thickness (the "test specimen"). The primary objectives of this full-scale test program were to assess the compressive strain capacity of the pipe, evaluate the performance of the digital image correlation (DIC) system (described further by Johnson et al., 2023), and provide validation data for later numerical studies of this pipe material and geometry (described further by Tsuru et al., 2023). This paper describes the performance of the test specimen subjected to severe deformation caused by bending loads and axial displacement in a controlled and highly instrumented full-scale testing environment.
