ABLE, Swan Hunter assembling skills for platform destruction

(Top) One of the Viking jackets, covered in marine growth, at Swan Hunter's yard on Tyneside. (Right) Stanislav Yudin depositing one of the Viking A decks. Worldwide outrage over the planned deepsea disposal of the Brent Spar could work to the advantage of northern England's decommissioning industry. North Sea operators have to think seriously about removing redundant mid-depth installations altogether, and there will be plenty of these in the next century.

Deck hatch covers supplied to Amec Engineering for retrofitting to the Brent B and C platforms.

Mech-Tool Engineering has completed development of a range of composite passive fire protection systems rated from A60 through to H120. Designs include pre-manufactured panels that can span vertically or horizontally, according to span or penetration requirements.

Offshore construction contractors have had problems in the past achieving a neat fit with composite panels. As a solution, Mech-Tool has also introduced a patented self-leveling detail, which accommodates uneven decks, and an inter-deck movement joint which can expand vertically or horizontally. Both can also be used for upgrading existing bulkheads or disintegrating PFP coatings.

Applications can be performed on site, with no hotwork required. Pre-manufactured paneling can be retrofitted easily to existing structures: budget installation times are claimed to be on average 10sq metres per man-hour.

The new range was preceded last year by Mechlite 120, a lightweight composite blast relief system also suited to fire and blast walls, temporary safe refuges, control rooms and emergency shutdown valve enclosures.

In addition to the innovations offered by composites for walling systems, Mech-Tool has developed novel blast relief systems. Previously, single skin blast relief panels have been prone to relieve under the effects of wind suction. In decking/flooring blast relief systems they have also been known to relieve if a heavy weight were accidentally dropped on them. Mechlite 120 can be designed on a double skin system incorporating fully stabilised phenolic resins and waste organic fillers to withstand loads applied to the outer skin. It will only relieve from internal pressure applied to the inner skin.

The durability of the system was proven during repeated blast tests on individual panels at the Fire Research Station in Cardington, England. Following each blast, the panels were simply clipped back into position for the next set of tests. Irrespective of the explosion pressure/time profile, the panels open constantly at the same relief pressure. Mechlite 120 can be designed to relieve pressures as low as 0.01 bar upwards; panel sizes range up to 3.0 x 1.5 metres.

Mech-Tool's recent composite system deliveries include hybrid composite and steel blast relief deck hatch covers for Shell UK's Brent B and C platforms. Here the blast relief method is based on a cassette system designed by Shell and pre-assembled in Mech-Tool's Darlington factory. Other newer orders are 850 sq m of heat shields and additional fire walls for ETAP. Recent steel system orders include blast and fire walls, doors, heat shields and storage tanks for Britannia, and doors and blast walls for Armada.

Ship evacuation

When bidding recently for the Schiehallion FPSO escape tunnel, Mech-Tool advised Harland and Wolff that composites could work out 50% lighter in weight than steel; however, proving tests would have taken too long. Mech-Tool still won the contract (working with steel) as the only bidder to have all suitable blast and jet fire certification in place.

The tunnel is being designed to withstand jet fires at 300kW/metre for 30 minutes, at the same time limiting the mean internal air temperature to 50C. The tunnel must also remain functional following a blast overpressure of 500mbar. It will be equipped with communications, lighting, detection/protection systems and electrical cables - for normal daily movement of personnel, as well as an escape route.

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