Hydraulic shears and diamond wire saw operations in MacCulloch field decommissioning


This project required the removal of eight risers, two umbilicals and one electrical cable connecting the MacCulloch field's subsea infrastructure to the FPSO.

This large-scale scope from client Bibby Offshore (now Rever Offshore) required the careful cutting of risers as close to the FPSO turret as possible. In addition to the risers, mooring chains securing the Mid Water Arch (MWA) were to be cut at both ends.

The solution

Requiring maximum cutting performance as well as user-friendliness, this scope relied heavily upon UCS’ own in-house engineered hydraulic shears. Both the MSD-4000 and MSD-4500 models were outfitted with rigging and ancillary equipment for both subsea and topside operations.

Cutting operations directly below the FPSO were undertaken with the UCS range of 22” and 42” diamond wire saws (DWS), with additional support provided by the Dual Cut Band Saw (DCBS). Both tools were set up to run directly from the ROV and their handling was improved by the use of a bespoke interface frame engineered by UCS. The 22” and 42” DWS also completed the MWA chain cuts.

Results

A total of 184 cutting operations were successfully completed during this scope, with 162 conducted by the hydraulic shear cutter, 17 via DWS and 5 by DCBS. During the course of operations, it was discovered that the bend stiffeners were made from vulcanised rubber as opposed to the Polyurethane as originally thought. As the DWS was unsuited to this type of cut, UCS cut the risers below the bend stiffeners before using the DCBS to successfully cut through the rubber bend stiffeners.

With a full range of cutting products available, UCS provided a versatile, high-performance and rapid solution for this decommissioning project.

Example cut times:

- Chain: 18 mins (22" DWS)

- 600mm OD bend stiffener with riser: 25 mins (DCBS)

- 8" production riser: 25 seconds (Hydraulic shears)

- 10" oil export riser: 27 minutes (42" DWS)