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Subsea structures

News International-French

16 Apr 2011

More than 80 large GRP covers were recently manufactured to protect undersea oil and gas pipeline equipment. With a total gross weight of 430 tonnes, some covers weigh up to 10 tonnes each.

(Published on July-August 2008 – JEC Magazine #42)


Most of the products were supplied to Acergy Norway AS for the Tyrihans project. The covers are designed to protect pipeline connection points from the impact of surface-dropped objects such as drill pipes. Pipeline expansion zones, usually an area of Zshaped pipework, are protected in a similar manner. The covers also protect seabed installations against commercial trawling operations. The GRP covers were manufactured using Scott Bader products.


They are typically 24 mm thick, sufficient to withstand a dropped-object impact force of 50 kN. Areas of thicker laminate (up to 80 mm) are also incorporated as lifting points for the heavier structures (maximum 30 tonnes). GRP is a material of choice for these protective covers as it is very competitive compared to fabricated steel and requires no anodic corrosion protection. Moreover, installation weight is only 1/3 of a comparative steel structure, while still providing high impact strength.


The Scott Bader Crystic 703PA used for this purpose is a pre-accelerated, DCPD polyester resin with low viscosity and controlled exotherm characteristics. The material is approved by Lloyds Register of Shipping for marine applications and is suitable for vacuum injection and other similar production techniques, particularly with large structures. It is also compatible with most reinforcements and provides excellent mechanical properties and impact resistance. On completion of the vacuum injection production process, the undersea mouldings are subject to an outer surface yellow gelcoat finish which ensures maximum visibility for seabed conditions. A final top gelcoat finish is also applied. Both products are manufactured by Scott Bader. Crystic 0209 SMK, an isophthalic gelcoat with low styrene content and good selflevelling properties, is used for the coloured finish, and Crystic X 103 KH, a preaccelerated orthophthalic gelcoat with a tack-free surface, is used for the final brushed topcoat. Both products are thixotropic polyester gelcoats designed for rapid cure and suitable for the production of high-quality mouldings.