Failure Analysis of Glass Fibre Reinforced Plastic Pipe Produced by Filament Winding Technique.

The filament winding technique is the second popular process in basic composite manufacturing processes, which can provide an automated technique compared to traditional hand layup process. The continuous filament winding process is the manufacturing of glass reinforced polymer (GRP) pipes from continuously flowing glass fibre by winding it on an automatic machine. It is quick and reliable technology for making high performance parts. A big advantage of filament winding is that it uses continuous fibres which leads to very good material properties for both strength and stiffness. However, if there is any process abnormality it can cause defects such as voids, delamination, wrinkles, etc. which causes production loss or failure at customer loss leads to monetary and reputation loss. There was premature failure of GFRP composite pipes during hydrostatic (hydro) testing while laying out in the site were received. Two pipe samples, one referred as new or good pipe and another referred as leaked during hydro test, were investigated to find out the root cause of failure. The investigation consisted of field visits, studying the layout procedure, visual observation, microstructural characterization, thermogravimetric analysis (TGA) Fourier transform infrared spectroscopy (FTIR) and Raman analyses. Visual observations of the hydro test failed sample reveal some abnormal features like delamination of layers, circumferential cracks and white spots, while the leaked or used pipe shows features like air pockets, adherent foreign/ earthy materials, visible fibres and heterogeneity in colours. Adherence of earthy material on pipe's surface indicates that there is incomplete curing of polymer. Microstructural analysis exhibits that the volume fraction of fibres was very less (particularly in used pipe) in resin matrix and their distribution was also uneven. Raman, FTIR and TGA analysis suggest that impure or mixed resin material is used for production of pipe which failed during hydro test. Overall analysis suggests a defective manufacturing process and usage of expired polymer and sand along with non-prescribed fibre loading which might have initiated the failure of pipes during hydro test. [ABSTRACT FROM AUTHOR]