Optimization of the shear tool deployment system for removal of steel piled jackets

Abstract

It is estimated that there are more than 200 steel piled platform installations in the North Sea which have reached the end of their life and have to be cut and removed. In comparison with other cutting methods, the shear tool cutting method offers the greatest potential regarding optimizing the time of the operation. However, the existing shear tool is susceptible to blade bending–related failures caused by heave motions of the heavy lift vessel to which the tool is attached. While there are many studies related to the operability and workability of sea surface structures, this study focuses on the operability and workability of an underwater structure, the shear tool system. In order to improve the performance of the existing shear tool, the new shear tool system has been designed as an equalizer with additional counter weights; thus, this system acts as a passive heave compensator. In total, six different design concepts have been assessed using a multicriteria sensitivity analysis, and the most promising concept has been selected. Afterwards, the performance of the new design was compared with the performance of the existing tool by calculating their operability and workability for the removal of the benchmark (Northern North Sea jacket) structure. The workability calculation was based on 15 years of environmental conditions and results indicate that the new design leads to 50% workability increase.

Keywords

Tool optimization passive heave compensation operability and workability shear cutting tool steel platform removal

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References

The United Kingdom Offshore Oil and Gas Industry Association Limited Trading Oil & Gas UK. The decommissioning of steel piled jackets in the North Sea region, October2012, http://www.oilandgasuk.co.uk/cmsfiles/modules/publications/pdfs/OP074.pdf (accessed 18 September 2014).

Rusu

Bernandino

. Estimation of the operability index of a container ship operating in the Black Sea. The Annals of University “Dunarea de Jos” of Galati Fascicle VIII 2009; XV: 215–220.

Tello

Ribeiro

Silva

Guedes Soares

. Seakeeping performance of fishing vessels in irregular waves. Ocean Eng 2011; XXXVII(5): 763–773.

Journee

JMJ

Massie

. Offshore hydromechanics. Delft: Delft University of Technology, 2001.

Van Zandwijk

van Dijk

Harmsen

. Deepwater lowering – a contractor weighing wires and winches. In: IMCA annual seminar 2013, http://www.imca-int.com/media/131935/abstract.pdf (accessed 18 September 2014).

Dalinga

van Daalen

Grin

. Scenario simulations in design for service. In: Proceedings of 9th symposium of practical design of ships and other floating structures (PRADS 2004), Travemünde, 12–17 September, 2004, vol. II, pp.604–611.

Det Norske Veritas (DNV). Recommended practice DNV-RP-C205: environmental conditions and environmental loads. Oslo: DNV, Schiffbautechnische Gesellschaft e.V., 2007.