Repair kit has it all wrapped up

Improved composite materials and resins are enabling oil and gas companies to repair pipes whose replacement would once have stopped production for weeks.The technologies are the result of a new alliance between DML Devonport composites, formerly Devonport Royal Dockyard, and leak sealing specialist Furmanite International.

DML business development manager Jim Cuthill said it would end expensive and dangerous sub-sea welding operations, and surface and sub-surface pipe replacement: ‘We are in the final stages of validation testing for a resin for sub-sea use which will bond to wet surfaces and can cure underwater,’ he told TheEngineer.

DML and Furmanite have also been developing carbon fibre and epoxy resin technology to repair pipes above the surface, but in damp conditions such as on an oil rig.

The market for pipe repair in the UK oil and gas industry is thought to be worth £10m a year, and the system has been developed primarily with this sector in mind. However, projects have been undertaken in the power and pharmaceutical industries.The carbon fibre and epoxy resin composite materials used for the repairs are claimed to be up to 10 times as strong as steel and twice as stiff. It uses multi-directional carbon fibres to build axial and hoop strength. It is 20-25% lighter than steel and is not as susceptible to corrosion.

Because of the fibre’s innate flexibility it is also able to cope with areas of confined access and complex geometries. As such, repairs can be tailored on site.The technology was designed to cope with up to 70% humidity and a minimum temperature of 5°C. In this environment a repair can be completed in 12 hours. The resin can be used in temperatures of between 150°C and -50°C, but more time has to be allowed for it to cure.

Repairs in extreme conditions were carried out recently on the Shell Expro Dunlin Alpha oil platform in the North Sea. An inspection revealed significant external corrosion over an extensive section of pipework. Varying degrees of damage were discovered on two 24in steel water lines and one 12in fire water line.

More than 50m of strengthening was required, including numerous flanges, valves and tee-sections, much of it in severely restricted access areas.

To wrap the damaged pipe the surface was prepared using grit blasting to give the pipes a 75mic rough finish. This was followed by the application of a tie-coat of glass fibre fabric, impregnated with epoxy resin.

This provided an interface with the steel and insulated the carbon fibre from the pipe’s surface – and potential causes of further corrosion. Impregnated carbon fibre layers were then applied over the tie coat to give structural strength.

The application of this technology, which is being supported by industry-agreed guidelines, looks set to aid an industry whose ability to invest has been hampered in recent years by a drop in oil prices.