Non-destructive testing techniques are not well-suited to complex parts with multi-layered structures like subsea pipes. Until now, there has been no reliable means of inspecting flexible subsea risers with multiple layers of steel rebar, for example. The IRIS (In-Service Riser Inspection System) R&D project, led by List in partnership with TechnipFMC, is combining several technologies to enable the detection of any defects in the various layers of reinforcements (breaks, cracks in the thermoplastic ducts, etc.) in real time. 

An ultrasonic NDT method developed by TechnipFMC is used to detect defects in the outer layer. This method is coupled with an electromagnetic wave technique developed by List to inspect the metal reinforcements. A sensor was designed and patented specifically for the project. It enables the NDT tools to see "through" the outer reinforcements to the inner ones. Another sensor uses capacitive measurement techniques to determine whether there is any water inside the thermoplastic ducts. Ultimately, a marine-grade X-ray source will be added to the system, giving it tomography capabilities. The entire package will be integrated into an ROV*-type system launched from the deck of a supply vessel and able to reach depths of 2,000 meters. The ROV will lock onto and move along the flexible riser independently. 

TechnipFMC plans to start using the new NDT system for several offshore oil and gas projects this year.

*Remotely-operated vehicle