Subsea cutting solution for decommissioning work scope
Overview
Ashtead Technology was contracted to assist with the decommissioning of the Janice, James and Leadon fields.
With a strong focus on R&D and in-house fabrication and engineering, Ashtead Technology’s Mechanical Solutions team has considerable experience in supporting operators with decommissioning requirements worldwide.
Decommissioning works require a high degree of planning to ensure that the environmental impact is minimised and that operational safety is always prioritised. With the towheads and mid-line structure requiring to be cut free from the bundles in the Leadon field in the UK North Sea, Ashtead Technology commissioned a new size of diamond wire saw to effectively sever carrier pipes containing multi-string internals.
Solution
Our in-house experience and engineering capability allowed Ashtead Technology to design, test and manufacture a brand-new saw size in under 10 weeks. This 56in diamond wire saw was required to cut through Bundle Section A (42.5in OD carrier with a 46in OD carrier transition) and Bundle Section B (47.5in OD carrier plus 51in OD carrier transition). With the carrier pipe consisting of seven internal elements as well as a cable tray, considerable cutting performance was required.
As Ashtead Technology had innovated an entirely new size of diamond wire saw specifically to meet the challenge of this project, a rigorous test procedure was undertaken at our Inverurie facility, using test pipe bundles supplied by the client.
A representative 12m length of bundle was fabricated by our Mechanical Solutions specialists as part of the test process – demonstrating Ashtead Technology’s commitment to the highest standards of in-house engineering to support the client.
Benefits and value
The 51in OD x 30mm WT outer carrier, consisting of seven internal pipes and a length of flat bar, was successfully cut in less than two hours.
Having proved itself with an identical test specimen, the 56in diamond wire saw was soon dispatched offshore to complete the project – with the client reporting that it had exceeded expectations.
The DWS was deployed by vessel crane with ROV assistance, expertly locating the tool onto the cut location. Once at a depth of -145m, specialist Ashtead Technology technicians controlled the tool from topside via the Solenoid Control System.
On average, cutting operations took only 97 minutes for each of the six bundle cuts, proving the suitability of this in-house engineered solution for large bundle sizes.