Experimental evaluation of the long-term strength of reinforced plastic (GRP) pipes

The long-term mechanical strength of reinforced plastic (GRP) pipes is studied in internal pressure tests. The GRP pipes are industrially processed of polyester resin which is reinforced with glass fibre. The initial pressure resistance of the pipe structure and the strain in the pipe wall are measured. The longest running times of pressure tests reach nearly 40 000 h. The results of all pressure tests are extrapolated according to the procedure in ASTM standard to give an estimate of the strong of the pipe after an expected period under certain stressed conditions. Certain correlation is found between evaluations based on short and long-time measurements. Three different pipe structures also differ in their behaviour in the test. The pressure test does not necessarily do justice to all pipe structures.