The capability of the MEC-FIT™ flexible riser inspection technique has been successfully tested to demonstrate the following abilities:
Ability to detect the crack-like defects in both outer armour wire layers, indications differentiating the angle of cracking as well as providing gap determination of the cracks.
The inspection task relates to the detection of potential cracking in outer and inner armour layer of the 13’’ flexible risers located on a FPU. The inspection challenges include the 55° wiring angle structure with tight crack-like defects expected to run into the surface under an angle of 45°. Secondly, in addition to the thick outer sheath of 15.3mm, an anti-wear tape of 2.5mm is also present between the two armour wire layers.
A simulated test sample established by placing wires with various flaw types at different locations and wire layer positions was used. Blind tests were performed on four different assemblies of the structure - with defects in the near side (facing the sensors) of the top layer representing the outer first armour layer, with defects in the far side of the top layer and the same assemblies in the bottom layer representing the inner second armour layer.
The test results showed that all through-cracks in all the layers can be detected. Part-depth cracks are detectable in the outer layer. The detectable crack size in relation to the wire thickness is 30% for the near side top layer, 60-70% for the far side top layer and 100% for both the near and far side of the bottom layer. From the point of view of defect detection through the tight wire structure and particularly the thick sheath, this is considered a massive success.
In preparation for this inspection, the MEC-Hug Crawler tool for deploying the MEC-FITTM technique has been rebuilt to allow circumferential scanning to accommodate the scan requirements of the 55° flexible riser wiring structure. For the first time, the MEC-Hug Crawler tool will be deployed using an inspection-class ROV deployed from the installation. This would mean substantial savings for the Operator as compared to using a work-class ROV.