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FlexGel Seals North Sea Annulus Riser Breach

10 February 2012

Flexlife says it has successfully applied its FlexGel product to tackle corrosion in a North Sea operation for a major oil company.

Flexlife had discovered the annulus breach during testing in a 4.5-in. (11.4-cm) gas main flexible riser, 4.5 m (14.7 ft) subsea.

The company applied 9,500 l (60 bbl) of FlexGel to fill the I-tube from 11.5 m (37.7 ft) above the sea surface to 33.5 m (110 ft) subsea. It was pumped in approximate meter increments to allow time for the product to settle and displace all water and air in order to fully surround the breach.

Flexlife’s Stuart Mitchell said: "It is common for the outer sheath of flexible risers and umbilicals to be damaged either during installation or even by regular friction caused during operation. If the problem is left un-addressed, it can lead to rapid corrosion of tensile armor layers and premature pipe failure.”

He said that the enclosed area inside a caisson is particularly problematic because there is restricted access for inspection, and damage usually occurs around the splash zone level where oxygenated seawater can cause accelerated corrosion.

The advantage of FlexGel, Mitchell said, "is that it can be deployed from topside or subsea without the need for costly intervention by rope access or diving teams and the associated health and safety risks of those types of operation.”

The oil-based product is non-soluble in water, with a density that can be adjusted to suit the application. In this case, the formulation was devised to halt corrosion of damaged areas of flexible risers or umbilicals within caissons.

FlexGel can be pumped into a caisson to envelop a riser with an annulus breach, displacing seawater and preventing further corrosion in the tensile armor wires of the flexible pipe. This in turn should increase the riser’s lifespan.