Design Issues with Repair

    The ability to repair in place, rather than replace, critical platform equipment systems like topside piping, flowlines and structural components is an attractive option for a platform operator. Composite piping is easily repairable using the same basic methods as the initial installation, says Kevin Schmit, manager of engineering at EDO Specialty Plastics (Baton Rouge, La., U.S.A.).

    “The most common method of repair for a composite pipe is a wrapped butt-type joint. This simply involves preparing the surface of the area to be joined just as you would for a new length of pipe, and applying layers of reinforcing fabrics wet out with the same resin used in the pipe construction,” states Schmit.

    In greater numbers, operators are turning to composites for repair of steel and other metallic structures as well. The concept is well documented for the repair of reinforced concrete and steel structures in civil infrastructure. In those applications as well as offshore, it is critical that repair personnel understand the design of the composite patch and then carefully execute the procedures prescribed for its application.

    Bjørn Melve of Statoil’s research center in Trondheim, Norway, says “Internal and external corrosion of steel pipe work is a common problem for all operators, both offshore and onshore, and can stop production. Composites provide a means to rapidly regain material strength without hot work, extending the life of the pipe until the next planned stop or turnover.” Pipework in particular lends itself to repair with composites, because defects tend to be localized. The fact that composites can be applied quickly, without welding, means that systems do not need to be shut down, which saves considerable cost.

    Composite repair technologies currently fall into two general groups: standardized, pre-cured kits simply applied with adhesive, and customized wet layup designs that are project-specific.

    A good example of the first group is the Clock Spring system supplied by Clock Spring Co. L.P. (Houston, Texas, U.S.A. and Huntingdon, Cambs, U.K.). Developed in the 1980s as an off-the-shelf kit for permanent repair of onshore corroded natural gas pipelines, it features uni-directional E-glass fibers, wet out with polyester resin and cured in a circular shape. The fibers are oriented in the hoop direction, or perpendicular to the pipe axis. The U.S. Department of Transportation (DOT), American Society of Mechanical Engineers (ASME) and other regulatory and code groups have approved the Clock Spring repair as an equivalent to a steel sleeve approach for pressurized pipelines.