An underground Reinforced Thermosetting Resin (RTR) piping system used in firewater facilities experienced frequent ruptures from inside-out after 7 years of service at several locations. This work encompasses a material assessment study to potentially identify the root cause of the incidents. The assessment was conducted through a series of analytical and mechanical methodologies starting with visual inspection, Loss on Ignition (LOI), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), axial tensile testing and Environmental Scanning Electron Microscope (ESEM). Results revealed the presence of microdefects within the fiberglass/resin matrix, as well as unfilled spaces between fiber structures suggesting an uneven distribution of the resin throughout the pipe. These microdefects potentially resulted in a weakening of the mechanical, physical, and chemical properties of the RTR pipe leading to its overall performance degradation over time, which eventually led to its final rupture prior to its anticipated service life in the corresponding field operating conditions.