Simplifying decommissioning

An ILT being placed inside a pile.

IHC Handling Systems has a tool which may prove useful removing no longer required platform jackets. Elaine Maslin reports.

Operators are finally setting cessation of production (COP) dates on major assets, such as the mighty Murchison platform in the UK sector. Companies are also renewing facilities, and removing older structures as they do so, such as ConocoPhillip’s Ekofisk 2/4-s platform, which being removed as part of the field’s life extension.

How to remove the jacket structures left behind by these assets is being tackled by IHC Merwede group company IHC Handling Systems, using an internal lifting tool (ILT) design, which has already proven itself in the field of conductor removal.

The ILT was originally designed for lifting installation (skirt) piles, jackets and other offshore structures. It has since been developed into a range, starting at a range of 16in.-by-30in. with 200-ton capacity to a range of 60in.-by-96in. with 1200-ton capacity. These are available in the rental fleet with adjustable modes for every pile size. Last year they sold a special mode: 108in. with a capacity of 800-ton. One IHC Handling System’s ILT’s is being used by Saipem to lift out the 2/4-s 16,535-ton platform jacket, using the Saipem 7000.

“At the moment, the dominant lifting mechanism for jackets is slings. But the majority of removals so far has been small jackets and tripods, so removal methods have yet to be fully tested,” Peter Wempe, area manager, at IHC Handling Systems, says. Larger decommissioning projects are coming, such as Shell’s Brent field platforms, and the even bigger Murchison platform, operated by CNR international, with an eight-legged steel jacket.

Left: Two ILTs in place and ready to lift a jacket. Right: Jacket lifting operations using ILTs.

“Traditional methods (slings) are not possible any more. Putting stress on areas using slings will just rip pieces of structure off,” Wempe says. “Using external clamps or slings can also be difficult, due to uncertainties over how much load structures can take and the steel work around the outside of jackets, including anodes, railings, access points. In contrast, there is usually less steelwork inside jacket legs.

“I think contractors are looking for safer, more reliable options, with equal load transfer through the jacket.”

The ILT has already an established a track record, supporting installations of the KPOC jacket, BMB & CKD platforms, SHWE project, among many more installations of jackets and top-sides. ILTs, in combination with external clamps and aided by buoyancy tanks, were also used to lift out the eight-legged North West Hutton jacket in 2009. North West Hutton’s legs were 48in. diameter, weighing 1650-ton each, and requiring a 1930-ton capacity lifting tool with a 1500mm gripping length, and 250bar applied pressure. Two leg sections at a time were lifted using two tools (one for each leg), via a spreader bar from Heerema’s heavy-lift unit Hermod.

It is still a difficult job. “There are a lot of unknowns,” Wempe says. “These platforms are often more than 30 years old and there is uncertainty around the integrity of jacket steel thinness and so on. So a lot of engineering and calculation has to be done upfront.

“The biggest challenge is the quality of the steel that remains and its integrity. If the wall thickness decreases, we have to increase the tool length so it covers a greater area.”

Where there is marine growth, the firm also adjusts the tool so that it has a more aggressive grip, using teeth to cut through the marine growth.