Custom Wet Layup Repair Solutions

    In the second group are customized repairs, employing glass or carbon reinforcement, wet out with vinyl ester, polyester or epoxy resin and applied to the pipe by trained personnel, have been available since the mid-1990s. Selection of reinforcement material, wrap thickness and overlay length is dictated by the requirements of the particular situation and the severity of the pipe defect.

    “A repair system is the key,” says Dr. Simon Frost of AEA Technology (Abingdon, Oxon, U.K.). “The laminate, the surface preparation of the substrate and the adhesive all have to be qualified together to be successful.” Frost is a member of an industry forum that is developing documentation for the repair of pipework and pipeline systems using composite materials. The Composite Repair Workgroup includes representatives from Shell, BP, Saudi Aramco, Amerada Hess and Petrobras, and from several suppliers including Clock Spring, Devonport Management Ltd. (Plymouth, U.K.), SP Technologies Offshore (Ocean Village, Southhampton, U.K.) and Vosper Thornycroft (Southampton, U.K.) According to Frost, piping codes such as ISO 15649 are available for new pressurized piping systems, but they address neither equipment degradation nor repair or remediation options. The work group’s focus is to develop performance-based qualified repair systems for project-specific piping fixes.

    Input data used to determine the repair material and size include the pipe size (OD), the tensile modulus for the composite laminate in both the axial and circumferential directions, the tensile modulus of the underlying steel, the internal design pipe pressure and maximum allowable working pressure, the allowable circumferential and axial strains, and the sum axial tensile loads due to pressure, bending and axial thrust. If the pipe is leaking, the laminate is directly exposed to the material and the radial pressure inside the pipe. In such cases, a delamination factor can be added to the design equations to determine the repair patch dimensions.

    As with any composite fabrication process, training of the installers is critical, as is fastidious surface preparation of the pipe to be repaired. Ongoing inspection of the repaired pipe must also be taken into consideration. Frost says that while conventional ultrasonics have not been proven to be reliable for non-destructive testing, because the fiberglass laminate attenuates the signal, ultrasonic transducers can be placed beneath a repair in a critical region to ensure that health monitoring can occur. To date, AEA Technology has published three piping repair guides, based on the repair work group activities — one for design, one for installation procedures and a third for ND techniques for inspection of composite repairs (see below).