Fatigue of glass reinforced plastic pipes and joints for offshore applications

Abstract

In this thesis the static and fatigue characteristics of glass filament wound plastic pipes and joints are examined by experiments and numerical analysis. A hydraulic fatigue test rig, capable of exerting static or cyclic pressures of up to 70 MPa, was designed and built to enable pressure tests to be carried out on glass reinforced epoxy and glass reinforced vinyl ester composite pipes incorporating various joints. Static weepage and burst tests were performed on tubular specimens with and without rubber liners to determine their weepage and burst strengths under internal hydraulic pressure and to investigate the influence of the joints. Fatigue weepage tests were performed to determine the fatigue life and failure modes of glass fibre/epoxy and glass fibre/vinyl ester pipes and joints. For each material system, three types of specimen were tested. These were plain pipes, pipes with coupler-bonded joints (or laminate joints in the case of vinyl ester resin based pipes) and pipes with spigot/socket bonded joints. All specimens were commercial products with nominal diameters of two inches (50 mm). A family of curves showing pressure versus life was obtained. It was observed that weepage mostly occurred close to the pipe joints when pipes were subjected to internal pressure. Optical microscopy was used to investigate the damage initiation and propagation mechanisms in the specimens after testing. Finally, two-dimensional and three-dimensional finite element analyses were carried out to calculate the stress and strain distributions, to predict the strength, to interpret the experimental results and to examine the failure modes of the specimens. Ply-by-ply stress analysis and the Tsai-Wu failure criterion were employed for the strength prediction.