Decommissioning and abandonment

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Decommissioning and abandonment

TRENCHING ISSUES

ƒ Remaining strength of pipeline ƒ Will it withstand trenching operation? ƒ Must avoid leakage – corrosion defects and welds ƒ No longer has high internal pressure ƒ Loss of concrete weight coating ƒ Especially at field joints ƒ Must avoid debris ƒ Loss of coal-tar epoxy ƒ Radioactivity ƒ Jetter arm/machine burial ƒ Lower stress than plough ƒ Slower in stiff clays

We need to assess how the pipeline will behave during the lowering process. Perhaps a less efficient option may be chosen, such as jetting. Ploughs may cause higher loads to be applied to the pipeline. Although coal-tar epoxy is not used nowadays for corrosion coating, there are many lines that used it historically. It may break off during the recovery of a corroded pipeline. Not only is coal-tar carcinogenic, but it contains natural radioactivity, which can cause concern should it be washed to shore.

DECOMMISSIONING IN-SITU SUMMARY

DECOMMISSIONING IN-SITU – SUMMARY

ƒ Preferred option for trunk lines and buried/ trenched pipelines ƒ Need to remove product and clean ƒ Exposed lines may require trenching ƒ Ensure pipe strength is sufficient to withstand trenching operation ƒ Avoid concrete break-up

Any questions?