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Riser arch trays

In 1999, we supplied the first composite primary structure for the offshore industry. The 42 subsea composite riser arch trays formed part of the flexible riser support system for the Norsk Hydro Troll C field. The trays are a critical part of the development, limiting the loads the risers apply to the floating platform above, and are subject to static, dynamic and environmental loads, which can be extreme in storm conditions. This project represented a major step forward in the use of composite materials for critical components in the offshore industry.

Composites were selected as they were cheaper than the steel option, one third the weight (which reduced the centre of gravity for the support structure during transportation), required no maintenance and the smooth moulded surface of the tray should extend the life of the riser. Each arch was 12m long, 5m high and 2m wide, and weighed 7 tonnes.

Design was carried out in-house by DML, with DNV completing the third party verification. Manufacture was carried out at our facilities in Plymouth over a period of 17 weeks.