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Decommissioning offshore platforms

As part of its work for the oil and gas industries TWI has carried out important testing work within one of Europe's first major research project into the controlled demolition of disused offshore platforms.

This work was won from the Platform Abandonment Technology Consortium (PATC) - a collaborative venture between SLP Engineering and John Brown Engineers and Constructors. It forms part of a joint industry project sponsored by major North Sea operating and regulatory organisations, including UK's HSE and the European Commission.

Platforms designed in the early 1960s were given a life expectancy of 30 years, to coincide with the gradual drying up of the oil wells. Consequently, a number of platforms became uneconomic to operate. A controllable and proven technology was needed for their abandonment.

TWI 2500 tonne test rig, designed to bend and buckle tubular specimens
TWI 2500 tonne test rig, designed to bend and buckle tubular specimens

An option for abandonment of deeper water platforms was to remove all environmentally unfriendly materials and topple the structural frame. This will then end up safely on the seabed. One technique was to cut the jacket into two halves and to use two of the four legs on each half jacket as structural hinges.

The aim of the project was to provide technology suitable for engineering practical toppling operations. It encompassed investigations into structural mechanisms and associated local buckling and fracture. Also the use of explosives for underwater cutting, hydrodynamic loading and motions associated with toppling trajectories and stability of seabed remains were explored.

A purpose built computer controlled test rig was constructed at Abington, designed by TWI's Martin Ogle. It was used for multi-axial loading tests - to buckle and bend tubular specimens. This rig can produce forces up to 2500kN in axial loading, 1200kN in shear loading and 660kNm in in-plane bending. Tubular specimens simulating offshore jacket legs, with diameters in excess of 0.3m were fabricated and crushed and bent through angles up to 45°.

TWI has been involved in all developmental and in-service aspects relating to oil platforms, working with the industry from cradle to grave.

For more information, please email contactus@twi.co.uk

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