The objective of the project was to investigate the long-term hot/wet performance of Glass fibre Reinforced Epoxy composites used for industrial pipe systems. A large part of the work consisted of the development of test methods for both macroscopic and microscopic level. This resulted in new test methods that were found to be as discriminative as the proven internal ‘finger-print tests’ of FPI, a much more elaborative test. A series of glass fibre products was evaluated both for their resistance to storage in hot environments (‘thermal ageing’) and to long-term hot-wet exposure up to temperatures of 125 C. Furthermore, Carbon Fibre Reinforced Epoxy (CFRP) and Glass Fibre Reinforced Epoxy (GRE) were monitored for their response to long-term hot/wet exposure up to a temperature of 150 C.