Solving oil platform corrosion problems

Paul Boughton

Global joint integrity specialist Hydratight has completed an intricate major contract using its mechanical connector (previously known as MORGRIP) to solve corrosion problems on an oil platform off the coast of Brazil.

Nine separate leaks in high-alloy, thin-wall duplex and super-duplex stainless steel pipelines had previously been repaired temporarily with standard split-sleeve clamps, but were at risk of leaking again due to galvanic corrosion.

Hydratight supplied 18 off flange adaptor connectors ranging from 6in to 20in diameter – crucially, built from the same alloys as the pipework – and which had to be designed, manufactured, tested and delivered in 17 weeks in time for a scheduled 10-day shutdown.[Page Break]

The project carried with it several significant challenges, both in manufacture and especially during installation.

During manufacture, the stainless raw materials were kept completely separate from standard carbon steel stock to avoid contamination that might lead to the same corrosion problems in later years. The material also had to be cut at far lower speeds than usual to avoid galling — meaning very tight workshop management to meet the delivery deadline.

Hydratight also supplied a liner kit for each flange adaptor, to strengthen the pipework internally so it could withstand the connector’s massive sealing forces and provide a permanent repair. The company also supplied all the installation and service equipment for the repairs.[Page Break]

Two teams marked, cut and repaired the damaged sections during the shutdown – the majority of the sections being in tight, hard to reach spaces.

The most challenging repair was to a 10in pipeline carrying cooling water for the platform air conditioning system. The connector was needed on a vertical pipe coming down over the side of the platform, over the open sea.

Scaffolding was erected over the side and the repair took place at night during good weather – at which point engineers found another problem: the pipe’s flow valve wouldn’t seal, which meant a constant flow of water in the affected pipe and a halt to the repair work.

While one team was solving that problem, the second team was attempting to work on a 16in pipeline with severely restricted access and a manufacturing fault at the point of repair. [Page Break]

The pipe could not be cut back any more because of the access problem, so the team had to fit the connector to pipe 9mm out of roundness. This defect, caused by the weld bead pulling on the pipe, was beyond even the wide tolerance of the Hydratight connector’s state of the art seals.

But having dealt with this type of issue before, the Hydratight technicians had a solution: they remounted the pipe cutter in a way that allowed its brace points to be tightened asymmetrically, to effectively distort the pipe and bring it back into tolerance.

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