The interface between the flexible risers and I tubes installed in floating production units is being considered by the industry as a critical region regarding wearing due to its geometric characteristics and high contact loads between the flexible risers and I-tube interface equipment. During the past few years some instances of outer sheath damage were reported by the offshore industry.
Such occurrences have been responsible for the unplanned maintenance of flexible pipes and production loss. Based on this scenario, Wellstream has developed and incorporated into its regular supplies, a new model of riser interface equipment with a replaceable polymeric liner, which has been qualified through a full-scale test program and demonstrated to be adequate in protecting the flexible pipe’s outer sheaths .
Although the developed equipment was originally designed to allow the replacement of the polymeric liner, which acts as a sacrificial part, the planning of periodic inspections and the determination of the optimum liner thickness could not be reliably performed due to the lack of solid experimental data regarding the wear rates of the polymer pairs and the contact pressures expected for that region. As part of an internal research program, a FEA model has been developed and calibrated in order to allow the assessment of the contact pressure between the flexible pipe’s outer sheath and the I-tube interface equipment for the actual contact pressures generated by the field fatigue loads, supporting the development of a midscale test program to determine the wear rates of the polymeric materials pairs as a function of the contact pressure .
The determination of these two main variables allowed the definition and conception of a dedicated design tool and the generation of experimental data to the flexible riser interface equipment and its polymeric liner, increasing the reliability of the flexible risers installed in I-tubes.
This paper presents a discussion regarding the contact pressures experienced by the flexible pipe sample in service, the basis for the experimental test program and the concept of the developed design tool.