PIPELINES AND SURVEY
Seabed Pipeline Route Surveys and their subsequent Inspection are the most mature of ROV activities in the Underwater Remote Intervention Oil and Gas market.
In the early 1970s such work was carried out by manned submersibles. This workscope readily lent bitself to workclass sized vehicles which had the payload to carry the special equipment needed to inspect the security of a seabed pipeline. Often a preliminary towed sonar “fish” survey was conducted as a low cost external overview of the whole pipeline, and this with interpretation of its sonic data could detect seabed anomalies, e.g. wrecks, boulders, lost anchors, trawl routes etc, which could threaten the pipeline security, also pipeline suspensions could be identified. Items of interest from this survey provide “targets” worthy of further investigation using a pipeline ROV spread.
Typical payload equipment for a Pipeline Survey Spread would consist of:
ACOUSTIC POSITIONING SYSTEMS
In association with radio or satellite navigation, allows accurate position fixing of the vehicle
on the seabed and the position of any pipeline features, e.g. damage or debris location,
position and length of suspended pipeline etc.
SECTOR SCAN SONAR SYSTEMS
Used for obstacle avoidance and seabed mapping.
TRENCH PROFILER
Can measure the cross-section lay of the pipeline in a trenched area.
PIPETRACKER
Can be used to follow a buried pipeline.
CP (CATHODIC POTENTIAL) MEASUREMENT SYSTEM
Where electrolytic cells are configured to survey the cathode protection given by the inbuilt pipeline anode systems.
COLOUR CCTV SYSTEMS
Used for high resolution video records of the pipeline condition. Special configurations of “boom” cameras and a wheel carriage under the ROV allow fast (typ 0.5knot) surveys of the top and sides of the pipeline simultaneously.
Pipeline Damage Inspection
The work method should be applied to the detailed inspection of a damaged area on a submarine pipeline caused by impact. Anchors wires trawl boards dropped objects etc. The work should include cathodic potential measurements, cleaning, UT wall thickness measurements, dimensional survey, mould profiles, video survey, photography survey and NDT methods.
The inspection should be capable of identifying the following:
- Damage to, or defect in, the pipeline.
- Change in the position of the pipeline.
- The extent of marine growth on the pipeline.
- The condition, or change in condition, of the seabed in the vicinity of the pipeline with particular reference to the presence of debris, boulders and scour.
- The presence of, and extent of, unsupported spans.
- The presence and extent of any loss of cover in buried lengths.
- The presence and extent of any loss of weight coating.
- Loss of wall thickness in the pipeline.
- Loss, movement or failure of any protection placed over or around the pipeline.
- Verification of satisfactory working of cathodic protection systems.
- Leaks from the pipeline.
- Deterioration in support and protection at pipeline crossings.
- ROV survey along pipeline route for any other signs of damage (the distance covered will have to be determined by reasons for the inspection /investigation such as trawl board, anchor dragging from other vessels).
- The ROV should locate and fix the positions of the incident/damaged area. Confirmation that no pipeline leaks or hazards that could endanger divers are evident, prior to deployment of the divers and DSV direct set-up over location.
Damage may be such that other inspection techniques and remedial works need to be carried out such as defect moulding, MPI, weld CVI procedures and profile grinding. The company engineer/ client should access these techniques if needed.
An engineering assessment would be correlated after the initial damage survey to determine the next step in regard to severity of damage reported and the need for further investigations in order to chose the repair or remedial scenario.
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