Pressure response and life assessment of filament-wound composite pipes after impact

Abstract

This paper presents the results of drop-weight impact (5 J–150 J), quasi-static indentation, and post-impact internal pressure testing of a ±55°, filament-wound, glass fibre reinforced epoxy (GRE) pipe. The void content in the tested pipes was quantified by optical and stereo microscopy image analysis and ranged from 5% to approximately 13%. The void content was found not to influence the damage area, or the observed damage mechanisms, following impact loading. However, the void content was found to greatly affect the damage tolerance of the pipe during the pressure testing following an impact. It is established that impact damage area alone is not enough to determine the reduction in pipe failure performance under internal pressure. After impacts at low energies, a number of the tested pipes surpassed the operating pressure of the pipe during pressurisation (no leakage occurred). In these instances, an industry accepted regression gradient was used to determine the pipe's residual life, which estimated the reduction in service life from 20 years to less than two years. The quasi-static indentation testing confirmed that low energy impact behaviour (<20J) is largely equivalent to a quasi-static event under the tested constraints. Fabrication induced voids and their interaction with impact damage, are currently not considered by the existing testing standards (BS EN ISO 14692), but according to this investigation may influence the safe continued use of a GRE pipe subjected to internal pressure.