The headings below represent further actions and procedures that might be implemented during the Initial inspection/investigation of an incident on a submerged pipeline. The need might arise from the initial inspection of a incident that the below criteria have to be met before any further work can be carried out, or that more information can be gained safely for a engineering assessment by applying some, or all of the following tasks:
- Pipeline Isolations.
- Pipeline depressurisation.
- Pipeline Flooding.
- Pipeline excavation.
- Concrete coating removal.
- Protective coating removal.
- Pipeline cutting.
- Ovality pipeline measuring.
- Pipeline deflection measurement.
Pipeline isolations
The type of isolation to be carried out, as these can vary and are dependant on the location and work scope involved. An engineering, production and safety analysis would confirm isolations and procedures.
Dependent on the repair or investigation/inspection needed, it might be that the pipeline will have to be isolated from the both platform/wellhead and/or terminal ends. Isolations on most occasions will be the closure of the main hydraulic flow line valves and the operation of the inline SSIV valves to a close position. All the isolations will have to be treated individually at the time of the incident, in accordance with safety risk and engineering assessment.
Barrier testing for divers
The diving company may wish to carry out barrier testing on the isolated hydraulic activated valves, including any manual valves that may have to be configured for the inspection or repair work. This can be time-consuming work especially if there are leaks involved. Sanction to test certificates can be issued to cover some individual valves or changes to the isolation certificate.
Pipeline depressurisation
The need to depressurise the damaged pipeline or reduce flow and pressure, will also need isolations in place to safely carry out further inspection or remedial actions as listed below:
NOTE: Category A: Leakage or high immediate threat of leakage.
- Severe weight coating damage leaking pipeline.
- Severe weight coating damage and damage to in-line pipeline flange.
- Severe weight coating damage and gouging of pipeline parent metal
- Severe weight coating damage and denting of the pipeline parent metal.
Pipeline Flooding
The extreme circumstances when a pipeline would need to be flooded would be severe damage inflicted into the concrete weight coating and penetration into the parent metal, causing ingress of water and total depressurisation of the whole pipeline. Further flooding and pigging would be needed to in order to confirm that no gas/pressure is present for or during the repair operations.
Flooding of the pipeline would also be the needed to change out an inline component such as tee-piece or flange connections, if no isolation valves are installed or may have been damaged or simply don’t work.
There are alternative to flooding the whole pipeline, which would be sending down the pipeline a pig train with a water slug to be positioned in the area of repair, the train would be propelled by chemical or product gas.
Pipeline excavation
There are various methods that can be utilised to excavate a pipeline or expose the area that needs to be investigated. During the initial call out for a suspected incident on a pipeline the inspection vessel would have to determine what will be needed to excavate or expose (if needed at all) the pipeline for damage or inspection assessment. This will fall into two main categories:
- Excavation for access for inspection assessment.
- Excavation for access for pipeline repair.
Similarly for inspection access using the same methods can be used to expose the area for a repair, this does depend on the depth and length needed to clear, in order to install a repair clamp or other repair method such as Hyperbaric welding habitat. The length of damage sustained on a pipeline can vary, dependant on what caused the damage in the first place. Dragged anchors can cause localised damaged or can continue down the pipeline, gouging with intermittent damage of varying degrees.
Backfill
During any excavation work the possibility of backfill will have to be taken into consideration, especially if the area will be left for the next phase of operations. Backfill will also be dependent on the type of seabed encountered; on soft sand/gravel with a tidal or current flow the likely hood of backfill would be high, on hard clay/coral low expectations for backfill. Both would benefit from lining the dredged area with grout/gravel bags.
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