Polymer liner to protect block 31 riser off Angola

Offshore staff

ABERDEEN, UK -- Swagelining is to supply its polymer lining system for a 14-in. (35-cm) water injection riser for BP’s block 31 project offshore Angola.

The single line offset riser (SLOR), designed to operate at 555 bar (8,049 psi), will be installed by Heerema Marine Contractor’s Balder construction vessel in 2,000 m (6,562 ft) water depth. The contract was awarded by Heerema subsidiary Pipeline Techniques, which is responsible for delivery of the riser.

Swagelining is named after a technology developed in the UK by British Gas and United Utilities, mainly for the rehabilitation of buried onshore pipelines. Its debut offshore application came in 1995 on BP’s Foinaven field west of Shetland, and it has since been adapted by other operators of North Sea projects, including Statoil.

In recent years, BG’s R&D division in the UK, Advantica, has been responsible for taking development forward. Late last year, after Germanischer Lloyd acquired Advantica, a management team led by Stephen Barnes made a successful pitch to buy the Swagelining business, with the aim to re-energize the technology for wider application.

Swagelining involves placing a tight-fitting polymer line pipe inside the new or existing pipeline or riser. The liner has an outside diameter slightly larger than the inside diameter of the structure being lined.

For the installation, sections of the liner are pulled together to form a continuous pipe. The liner is then pulled through a reduction die that temporarily reduces its diameter, in turn allowing the liner to be pulled through the pipeline.

Once the liner is fully installed, the pulling force is withdrawn, causing the liner to expand towards its original diameter until it presses tightly against the host pipe’s inner wall. The tight fit ensures a flow capacity close to that of the original pipe design.

“Today the main application offshore is in water injection pipelines,” Barnes explains. “The polymer liner provides an internal corrosion barrier.

“In the North Sea, the phenomenon of failed water injection lines is well documented. The Groove Corrosion joint industry project, established in 1997, found that out of 23 water injection lines reviewed in the sector, only one had survived for longer than 15 years. For a pipeline operating water injection without a polymer liner, the average rate of corrosion is around 1.57 mm [0.06-in.] of wall thickness per year.”

An alternative to the use of polymer liners is to construct the pipeline from a corrosion-resistant alloy (CRA), or to apply a layer of CRA to internally clad a carbon steel pipe. However, this can add 30% to the cost, Barnes says.

BP has specified a 30-year design life for the block 31 SLOR. A qualification program is in progress for the polymer liner. “We are also finalizing the scope of individual tests with BP,” Roberts points out.

Fabrication is being managed by Pipeline Techniques at the Evanton spool base in northern Scotland. Swagelining will provide the WeldLink connectors for welding of the lined sections within the riser.

The company is working on a feasibility study for a land-based project in South America to apply polymer liner in 6-km (3.7-mi), 36-in. (91-cm) multiphase lines. “If this system is shown to work, there is no reason why in time it could not be transferred to multiphase lines offshore,” Barnes claims.

05/13/2010