Torsion-induced failure of a reinforced thermoplastic pipe used in a gas lift system

Abstract

After servicing for 4.5 years, a reinforced thermoplastic pipe utilized in a gas lift system experienced a burst failure. FTIR, visual inspection, TGA, tensile test, VST, pressure test, DSC, and torsion test were performed to investigate the root cause for the failure. The findings demonstrate that the failed pipe had suffered serious torsion. The torsion led to the significant performance deterioration of reinforced fibers and liner pipe. The liner pipe has multiple torsion morphologies. Tensile test results show that torsion led to the deterioration of the mechanical properties of the liner pipe, especially the modulus (14.7%). There was a 60–80% drop in both elongation at the break and tensile strength of the fibers. Results from the torsion-pressure test illustrate that torsion would lead to a decline in the pipe’s pressure capacity. The operating record indicates that this pipeline was a gas lift pipeline with long-term and high-pressure operations and weekly sweeping operations in winter. The pressure fluctuation was relatively frequent. The pipe failed when the instantaneous pressure exceeded the torsional pipe’s capacity.