Fatigue Performance of Unbonded Flexible Pipes With Advanced Material Layers

This work investigates the fatigue performance of a novel hybrid flexible pipe (HFP) concept, designed for demanding oil and gas applications, comprising a thermoplastic composite pipe (TCP) core and conventional outer reinforcement layers including metallic armors and high strength tapes. Among all tests performed along the development program, one 3-inch HFP test was conducted simulating representative field conditions and subjecting it to approximately 1,600,000 cycles. The results demonstrated outstanding fatigue resistance with no visual evidence of damage nor degradation observed throughout the test, which had one last rupture block of 500,000 cycles. Axial and bending stiffnesses exhibited steady responses highlighting the HFP structural stability under cyclic loading. Post test dissection confirmed the integrity of the conventional layers and of the TCP core, which remained intact and undamaged with its surface appearing pristine and unchanged. These findings establish the HFP as a promising solution for demanding oil and gas applications offering enhanced durability and fatigue performance compared to traditional designs meeting the rigorous demands of the subsea environments.