Failure analysis of glass fiber reinforced composite pipe for high pressure sewage transport

• Evaluation of a GFRP sewage pipe that failed after 15 years in an oilfield in China. • The analysis and research are carried out in three depths along the axial and radial directions of the composite pipe. • The microstructure and micromechanical properties of glass fiber reinforced composite pipes after failure were evaluated. • Degradation of amine curing agent and oxidative decomposition of epoxy resin occurred in the outer layer of the pipeline, and the resin content decreased. • The nano-hardness and elastic modulus of the resin deteriorated after the pipeline was aged, and the fiber-resin interface performance decreased significantly. The research was conducted on failed GFRP pipes used in sour oilfield gathering and transportation pipelines, with the matrix material being an epoxy resin of an aromatic amine system that destructively cracked after 15 years of operation. To determine the cause of the failure, the failure area of the GFRP pipe was compared to the undamaged area, and the pipe's micro-morphological structure, chemical composition, and mechanical properties were examined. The results show that there are cavity defects in the GFRP pipe with insufficient air bubbles and resin filling, that the overall resin content of the pipe is low, that the curing degree of the outer layer of the damaged area (DA-OL) is severely insufficient, and that the fiber bonding strength is weak. The degradation of the amine curing agent in the outer layer of the pipeline and the oxidative decomposition of the resin were characterized using Fourier transform infrared spectroscopy and X-ray electron spectroscopy, and an irreversible chemical degradation process occurred, reducing the performance of the fiber-matrix interface. The data from nanoindentation and dynamic thermomechanical characteristics confirmed the obvious reduction of nano-hardness and elastic modulus in the outer layer of GFRP tubes. The failure of the pipeline is caused by the interaction of the above factors.