Characterization of GRE Pipes Fatigue Failure Subjected to HTHP Loading Conditions

Abstract GRE composite pipes are a great substitute for Carbon steel, however, obstacles of introducing GRE composite pipes into oil and gas transmission lines have been primarily related to inadequate testing data to maintain materials’ extended performance and pipes fatigue failure characterization. Customized testing facility has been designed and fabricated to substantiate design of GRE pipes under controlled service conditions. The testing procedure was conducted based on ASTM and ISO Standards. Pipes filled with crude oil were placed in a thermal and pressure enclosure at a temperature of 65°C and an internal pressure of 130 bars for 1000 hours and fatigue failure behavior of the GRE pipes were investigated. Pipes with a surface crack a/t = 0.5 and 0.3 were exposed to alternating internal pressure of 25 cycles/min and a load ratio of R = 0.05. Fatigue tests were performed at two load levels: 50%, and 30% of the pipes strength under static internal pressure. Results show that the GRE pipes burst suddenly without any leakage when the internal pressure was high, however, the pipe exhibit leakage first and then fails when the internal pressure was low. The maximum fatigue life obtain for GRE reference and HTHP specimen pipes in the crack region were 72,237 cycles and 73,107 cycles, respectively, with applied 0.5 static internal pressure (102 MPa) and a/t = 0.3 ratio. The minimum fatigue life obtained in the crack region are 14,105 cycles and 13,627 cycles for GRE reference and HTHP specimen pipes, respectively, with applied 0.5 static internal pressure (170 MPa) for a/t = 0.3 ratio.