North Sea platform felled by CUT’s diamond technology

CUTTING Underwater Technologies (CUT) has made a clean slice through the legs of a redundant North Sea platform, prior to it being lifted and shipped to Norway for dismantling and recycling.

Working on contract to Heerema, the firm used diamond-wire equipment to cut through the eight legs of the Norpipe 37/4A booster platform. The removal is part of the wider Ekofisk cessation project, located 240km (180 miles) south-west of Norway.

The 5,500 tonne platform, along with its sister Norpipe 36/22A, was installed in 1974, becoming operational the following year.

The platforms acted as booster stations between the main Ekofisk platform and the onshore reception facilities at Teesside, in the North of England.

Both platforms remained active until their final abandonment in 1983.

Two phases, one offshore and one carried out in the harbour at Merjarvik, in Norway, were completed during CUT’s mobilisation. All offshore and inshore work was carried out from the Heerema-owned and operated heavy lift vessel SSCV Thialf.

The first two cuts were carried out at 26m below the sea surface, on the main risers attached to legs A1 and B1, prior to both sections being recovered to deck. Thereafter, a further single cut was made to both risers to reduce their size and weight.

The 37/4A’s eight-legged jacket, which stood in some 85m of water, was then prepared for removal. Trenching operations were carried out in the vicinity of the jacket to expose the piles, to a distance of 2.7metres below the seabed.

CUT’s specialist 64inch diamond-wire cutter was then attached to the exposed jacket piles and the cuts performed. The equipment was hydraulically driven from the surface and a remotely operated vehicle used to locate it prior to each cut.

Once severance was completed, the jacket was lifted by the Thialf, and secured to the vessel with a specially-developed clamping system.

It was then transported to shore, where it was placed on a barge for removal of the top third, prior to removing the bottom section ashore for final reduction and recycling.

The reduction cuts were all carried out at a height of 62m from the barge deck. CUT had to develop a number of modifications to its equipment to complete the cuts.

While it was CUT’s Norway business unit that carried out the in-field and quayside work, the firm’s Aberdeen HQ provided significant back-up.