Emerald Group Publishing Limited
Copyright © 2000, MCB UP Limited
Sub-sea pipeline protection
Sub-sea pipeline protection
Keywords: Sub-sea, Pipelines, Polyurethanes, Hyperlast, Avon Technical Products
For a material to withstand the elements and succeed in protecting sub-sea pipelines from the damage inflicted by extreme pressure, low temperature and corrosive sea water, it must demonstrate versatility and reliability in a harsh natural environment over a period of many years.
Hyperlast has, for over 30 years, been involved with the development and supply of customised polyurethane elastomer systems to the offshore industry, providing excellent thermal insulation, corrosion protection and impact strength to hundreds of kilometres of pipeline throughout the world.
Its manufacturer believes that the flexibility of Hyperlast® makes it suitable for a diverse range of other offshore applications, such as J-tube seals. Avon Technical Products was instructed by a major installation contractor to develop a sub-sea sealing system for the J-tubes offshore, west of Stavanger, Norway. These steel J-tubes are fitted to protect the flexible riser pipe from the risk of damage around the legs of the platform, where any accident would have catastrophic consequences.
J-tubes are used to protect flexible risers on bends. The J-tube itself is protected on the outside with a polyurethane coating. The interior is protected by filling the 200mm gap between the riser and the J-tube with water containing corrosion inhibitors, and this is held in place by J-tube seals at either end. These corrosion inhibitors can be harmful to the environment, therefore it is paramount that the J-tube seal prevents any leakage.
Under normal circumstances, this would be considered a standard procedure, by installing the J-tube seal to the riser. However, divers are not permitted to carry out such operations in Norwegian waters and so innovation was required to design a J-tube which when compressed would form the seal.
A large amount of analysis was directed at producing a seal unit. This analysis included a three-dimensional FEA model and extensive and rigorous testing which was carried out at the National Engineering Laboratory.
The J-tube seals were attached to a flexible pipe on the deck of the installation vessel, lowered to the seabed and then pulled in using the platform winch. An innovative interference fit sealing profile ensured that each seal was successfully pulled into its respective J-tube and pressure tested to ensure that no leakage of corrosion inhibitor occurred.
"It is testament to the innovation and technology of Avon Technical Products and Hyperlast, that since the Varg development, Avon Technical Products has successfully installed the same generic seal design on offshore installations worldwide including the Guffalks 'A' development and Cormorant Alpha in the UKCS", says Debbie Gardner of Avon.
The "Hyperlast" polyurethane range, which has found widespread approval from the international offshore industry, is used extensively by many of the industry's leading names including Texaco, Elf Petroland, Shell, Total and BP Amoco.
Hyperlast Syntactic 512, the pipeline insulating and protecting solution, is developed and supplied by Derbyshire based Hyperlast Ltd.
"Over the last decade Hyperlast has gone from strength to strength and is now considered to be a leading supplier of speciality polyurethane elastomers", comments Business Manager - Offshore, Stuart Carlyle. "Hyperlast is constantly evolving, undergoing rigorous development for use in higher temperature and deeper water-fields. It is thought that this determination, commitment and innovation that continues to attract an increasing number of contractors to Hyperlast and as a consequence, its use in offshore oil-fields around the world."
Details available from: Hyperlast Limited. Tel: +44 (0) 1663 746518; Fax: +44 (0) 1663 746605; e-mail: firstname.lastname@example.org