Composite riser repair materials

This chapter will first outline the conventional offshore riser repair techniques and their limitations which, in turn, provide the motivation for adoption of composite repair. A brief discussion about the application of FRPC in pipeline repair, its limitations, current practices, and material types will be given. A subsequent section provides information on the industrial design and safety standards used in designing and assessing the performance of offshore risers, corroded pipelines, and pipelines repaired with FRPC. The typical loading conditions of an offshore riser are also discussed so that the requirements of CRS can be understood. 

Additional information such as material and bonding properties between steel and composite can be obtained by reviewing literature related to composite patch repair on a steel structure. A comprehensive amount of studies have been conducted and can be used as a basis to model the bonding between the composite repair material and steel riser. 

In a CRS, the composite laminate is bonded to the steel riser surface such that effective load transfer from the weakened riser to the composite can take place. Within the FEA model, perfect bonding is assumed between the contact surface interfaces of the riser and the composite laminate. This is an idealization of the FRPC repair in offshore risers. However, variation in material types, installation techniques and parameters tend to result in localized microvoids between surface interfaces of the repair (i.e., between the riser-FRPC and between FRPC laminates) where less than perfect bonding is often observed. 

Leong, A.Yi., Leong, K.H., Tan, Y.C., Liew, P.F.M., Wood, C.D., Tian, W., Kozielski, K.A., 2011. Overwrap composite repairs for offshore risers at topside and splash zone. In 18th International Conference on Composite Materials, Korea. 

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