DECOMMISSIONING & ABANDONMENT
SIGNIFICANT SUBSEA DECOM PROJECTS IN THE PIPELINE 17” outside diameter cutting capacity.
During the next seven years, it is estimated that nearly 2,400km of subsea pipeline is to be ‘made safe’ in the UK Continental Shelf. This is expected to peak in 2021 when almost a dozen assets are scheduled to be decommissioned.
The ‘making safe’ of pipelines involves depressurising the pipeline and removing any hydrocarbons until the next phase of decommissioning. These networks of pipe are then retired but may be reused by the operator for further projects, or recovered and removed permanently.
UES Seanic, a Centurion Group company, specialises in the supply of marine and subsea support equipment to the diving, ROV and decommissioning sectors within the offshore oil and gas, and renewables industries. The firm has been successfully supporting clients in the North Sea with decommissioning campaigns for more than a decade.
Centurion Group Business Development Director, Dave Grant, said the company’s successes have not gone unnoticed: “As the industry continues in its quest to find and embrace ways to improve efficiencies, interest in our decommissioning equipment and packages has continued to grow.
“Options for decommissioning include full removal, cutting in-situ, trenching and burial. Every case is unique and the approach adopted by UES Seanic is based on comparative assessments of these options as well as several factors including safety, environmental, technical feasibility, other sea users and cost. This method is reaping dividends for our clients.”
UES Seanic has built its reputation by being able to deliver the types of pipeline cutting activities required to remove pipes on site from either a topside position or subsea.
The business provides a wide range of equipment with material cutting capability encompassing slings, steel sections, flexibles, mooring wires, studs and bolts. This includes small hand held cutters through to large subsea shears with a
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Rigid and flexible flowlines Pipelines in the UKCS include both rigid pipe and flexible flowlines, and diameters can vary between two and 44 inches. Rigid pipeline is generally high strength encased in a concrete pipe wall or synthetically coated produced from different source materials to take advantage of the subsea conditions and ensure the desirable strength and chemical resistance are met.
Grant added: “In the 1980s, the industry began the move towards deeper water and using floating production storage and offloading (FPSO) platforms to process and store hydrocarbons in areas where no pipeline infrastructure existed.
“A typical flexible pipe may have many concentric layers of steel, plastics and spirally wound steel fibres, each performing a different function. These structures combine great axial and pressure containment strength with a high degree of bending and flexibility, making it ideal for the risers connecting FPSOs to subsea production wells.
“UES Seanic has built its solid industry position through having a deep understanding of the different requirements needed to decommission both, and being able to recommend the best equipment and techniques available to retiring clients’ tubulars.”
Powerful jaws
One decommissioning method best suited to the safe, quick and efficient cutting of pipelines and flowlines, whether made from rigid or flexible material, is the utilisation of large hydraulic shears.
“We house two types of cutting shear,” added Grant. “The first is the Verachtert hydraulic shear, (VHS 60) and is generally used for topside cutting but can also be configured for subsea deployment. This cutter has the largest mouth opening of the two with an 800mm opening jaw height and 830mm jaw depth. It delivers a crushing force of 9850kN, making it the most powerful cutting performer in our
Below: Cut pipeline on back of vessel.
extensive fleet.
“The alternative is the CAT S80 shear This can be used for topside and subsea decommissioning projects. With a jaw opening of 620mm and jaw depth 820mm, this has a crushing force of 8809kN. For subsea operations, the CAT S80 has two sets of lifting assemblies to enable it to carry out cuts either horizontally or vertically.
“Both cutters have dedicated transit frames which can also be used for deck cutting operations. The shears operate at a maximum of 350bar and therefore a suitable Hydraulic Power Unit (HPU) is essential to provide the necessary operating parameters. The business was built up by producing its own brand and client specific HPUs and hydraulic equipment and still operates in this way today, designing and manufacturing these in-house to insure the most suitable equipment is prepared for every project.”
Topside and subsea
As pipelines are varied, their removal will largely depend on the information provided by the operator on the type of material to be cut through and the outcome for the pipeline being removed.
“Subsea operations generally consist of either a single cut at the start and end of the pipeline which is then recovered onto the back of the vessel for disposal in its entirety or further cutting into sections. Multiple cuts may also be carried outsubsea to cut the pipeline into smaller manageable sections which will later be recovered.
“Topside operations are usually saved for umbilicals and flexible flowlines. Once they have been winched on-board, they are run
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