Page 25: of Offshore Engineer Magazine (Aug/Sep 2013)

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Decommissioning Shears are used for many decommissioning projects including platform and pipeline removal, slot recovery, chain cutting, wire rope cutting, salvage work and well blow out intervention.

can provide solutions as these technical requirements and were not attempted. feasibilities studies are completed.” Operations for the cutting boat-to-boat times for the 10-in. pipeline included equipment deployment and reposition- ing, dredger setup, dredging, cutting, further reposition-

North Sea case study

A majority of Gulfstream’s work in the North Sea is pipe- ing, and hydraulic grapple recovery. The shear technology line-related. Recently, the company put its shear technology completed its tasks averaging 1 hour and 30 minutes with a to work decommissioning pipelines associated with the total of 8 cuts. The band-saw method averaged 2 hours and

North West Hutton platform in the North Sea. The platform 37 minutes with a total of 10 cuts. The chop saw averaged was the frst large fxed-steel jacket installation to be decom- 2 hours and 59 minutes with a total of 6 cuts. The abrasive missioned in the region after its feld production ceased in water-jet averaged 4 hours and 6 minutes while making 3 2003. cuts.

The steel platform stood at 140m water depth on Block The same operations conducted on the 20-in. line with 211/27a of the UK Continental Shelf. A 10-in. diameter the shear technology took 1 hour and 30 minutes with 56 pipeline had to be left mostly on site with some sections cuts. The abrasive water-jet took 4 hours and 6 minutes with removed, and a 20-in. pipeline had to be trenched and 4 cuts. Other methods were not used.

removed at three crossings, among other tasks in the work The operator learned that the intervention made to change scope. The seabed soil was very hard with medium to large the cutting technique used for the concrete coated pipelines boulders in various locations. was successful because, although the initial methods and

During the decommissioning, the operator compared tools that were used to make the cuts were effective, they hydraulic shear technology cutting methods to other cold were not time effcient, so consideration of other tools as a cutting methods such as dual band saws, chop saws, and contingency at an early stage is important. Other learnings abrasive water-jet cutting. included that operators should ensure that their acquired

The study found that the average actual pipeline cutting survey data is recent and accurate, and that accurate soil time using shear technology was 11 minutes on the 10-in. data is necessary to allow better engineering decisions to be line, compared to the dual-cut band saw, which took 21 made. An hour in the offce can save days offshore.

minutes. The chop saw took 49 minutes, while the abrasive According to the operator’s analyses, GSI’s shearing and water-jet cutting took 1 hour and 22 minutes. Working on grappling services typically reduce pipeline decommis- the 20-in. line, the shear cut in 8 minutes while the abrasive sioning cutting times by 200% to 300%, providing huge water jet cut in 1 hour and 2 minutes. The other methods cost savings to its customers. On three separate occasions oedigital.com August 2013 | OE 27 026_OE0813_Decom_1.indd 27 7/22/13 12:24 AM