Experimental Study on the Collapse of Mechanically Lined Pipe Under External Pressure

Abstract Mechanically lined pipes (MLP), known for their cost-effectiveness and reliability in transporting corrosive oil and gas, have increasing applications in offshore projects. The presence of the non-corrosive liner, although relatively thin, will increase the collapse capacity of MLP to some extent. In addition, the mechanical property changes induced by hydraulic plastic expansion during manufacturing are also expected to influence the buckling behavior of lined pipes. However, this problem is still less understood, and related studies about MLP collapse are mostly limited to numerical simulations instead of experiments. In this work, we conducted a series of small-scale experiments on the mechanically lined tubes. The lined pipes, made of carbon steel Grade GB45 (AISI 1045) and T2 copper, are manufactured using a custom hydraulic expansion facility. The products have finished diameters of 50 mm and an overall D/t of 16.5, with 1.0 mm thickness for the liner. Afterward, intact and minorly dented specimens were collapsed under external pressure in a sealed hyperbaric chamber. The collapse pressure and final configuration of the tubes were recorded. In addition, the experimental results were reproduced by finite element models, which takes account for both the manufacture and collapse stages, and good agreement was reached.