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Tried and tested, Part 1

Published by
Oilfield Technology,

Tony Davies, qedi, UK, outlines how proven industry techniques are supporting the successful management of major decommissioning projects.

The decision that an operator makes to decommission an asset is probably as large as the decision taken to build it in the first instance and the enormity is no less.

Comparing the build and removal processes

When building an asset in the first instance, a project goes through the stages of:

  • Concept.
  • FEED.
  • Detailed design.
  • Fabrication and construction.
  • Mechanical completion.
  • Commissioning.
  • Start-up.
  • Operation.

These project phases, depending upon the size of the asset, can take between three and five years in total and each phase may be performed by separate contractors, all using rigorous management systems to complete their work efficiently, safely and to a standard of quality expected by both the operator and the industry.

Decommissioning an asset is a similarly complex operation,going through the stages of:

  • Environmental planning, EIA (environmental impact assessment).
  • Engineering down.
  • Making safe equipment.
  • Shutdown, isolation, flushing, purging and venting of plant.
  • Cleaning and de-scaling of contaminated equipment.
  • Disconnection activities.
  • Removal.

Environmental planning and impact assessments are performed via the owner, the de-commissioning engineering contractor and specialist environmentalists to ensure that all activities being planned will meet the litigation and legal requirements.

Engineering down and making safe equipment - will be detailed by the de-commissioning engineering contractor, who will develop the scope of work and the appropriate documentation, deliverables and procedures.

Shutdown, isolation, flushing, purging and venting of plant will normally be the responsibility of the owner operations authority, with procedures and work packs developed by their own operations personnel. This is the better approach, as the owner operations group is intimately familiar with both the plant layout and the process, having lived with the installation for all of its life and is best placed both to advise and detail these activities.

The cleaning and de-scaling of contaminated equipment is carried out by specialist cleaning contractors. In conjunction with the de-commissioning engineering contractor, the specialist cleaning contractor will provide all the detailed procedures and work packs to take the cleanliness of the equipment being decommissioned to the required level.

Disconnection activities in preparation for module removal can either be part of the decommissioning engineering contractor scope or the scope of a separate disconnection engineering contractor. Procedures and work packs to cover disconnection activities will normally be the responsibility of these companies.

Finally, the removal of the asset itself, either whole or in parts, will more than likely be a separate contract again, since there will be heavy lift and transportation requirements and this equipment and service is only provided by a limited number of contractors.

For all of these activities there needs to be rigorous management systems required to complete the work efficiently, safely and to a standard of quality expected by both the operator and the industry.

Part 2 of this article will be available soon.

Adapted by David Bizley

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