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Content archived on 2022-12-27

ENGINEERED EXPLOSIVE UNDERWATER CUTTING USING MINIMUM EXPLOSIVE FOR SAFE RELIABLE PLATFORM REMOVAL

Objective

The aim of the project is to have commercially available a safe, reliable and proven explosive underwater cutting system to be used in the removal of fixed steel offshore production structures.
The proposed underwater cutting method uses explosives as an engineering, as opposed to a demolition tool. The innovative charge designs minimise the amount of explosive required to effect the cut by (i) exploiting the brittle fracture characteristics of steel; (ii) improving detonation procedure and jet formation; (iii) reducing sensitivity to hydrostatic pressure and stand off.L%
During Phase 1 of the project, it was possible to validate the charge designs by conducting numerous tests on small and large scale BS 4360 steel components in the form of plates and tubes of up to 65 mm thickness. Prototype charges were manufactured after modifications made to original designs. In order to make these precision tools, a new rolling machine has to be designed and manufactured for making the liners of the Radial Hollow Charge (RHC) a set of moulds for making the flexible waveguides of the Shockwave Focusing Charge (SWF).
The production methodology used in the manufacture of these charges is now established. The optimisation of key parameters of the process resulted in reliable cuts in different batches of BS 4360 steel. The optimisation included computer modelling as well as experimental tests. The underwater cutting tools have been successfully engineered to cope with the wide variation in batches of such steels.
The reliability and repeatabiliy of the prototypes tested so far give undoubted confidence in the ability of these charges to cut the tubular targets on land and in shallow waters (10 m). The RHC device however, proved to be better than the SWF device for fulfilling the programme objectives. The SWF device requires re-examination with particular emphasis on the initiation system underwater to induce a cut immediately below the initiation zone.
The project is in three phases : Phase 1 deals with the problem of optimisation of charge parameters and validation of the devices on land and nearshore. Phase 2 involves the design amendments and full documentation of the production methodology and the manufacture of a set of tools. Phase 3 concerns large scale offshore field trials, final specification and approval.
The explosive underwater cutting system to be used in the removal of fixed steel offshore production structures will have to demonstrate an ability to cut steel to BS4360 Grade 50D or equivalent to 65 mm thickness or greater in tubulars of approximately 3 m diameter at 10 m depth of water.
Based on many years of research and field experience, the promoters have selected two innovative explosive cutting systems for development within the project. The shock wave focussing charge (SWF) uses a convex shaped wave guide to generate focussed tensile stress waves in the material. The charge can be made in long strips joinedtogether and wrapped around tubulars internally or externally. The performance of this charge is independent of the hydrostatic head and is achieved using substantially less explosive than conventional linear shaped charges.
The Radial Hollow Shaped charge (RHC) is configured as a pie segment with the explosive initialed at the apex causing the curved liner to collapse instantaneously around the periphery thereby generating a radially flowing jet which fans out as it travels towards the target. Pewer charges are required per unit of length of cut.
The project will produce a detailed operational methodology and appropriate design information for the underwater cutting operation as a single hammock activity within total platform decommissioning and removal.

Call for proposal

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Coordinator

University of Salford
EU contribution
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Address
Coupland III Building
M13 9PL Manchester
United Kingdom

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Total cost
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