In the Azerbaijan sector of the Caspian Sea sixty per cent of BP’s 1,232 kilometres of offshore pipeline assets lie in water depths between 12 and 25 metres. In these waters, particularly in shallow parts, poor water clarity makes it difficult to carry out general visual inspection (GVI) of pipelines using ROVs. Delays due to poor visibility on the continental shelf of the Absheron Peninsula are compounded by restricted vessel availability, leading to increased costs.
The poor water clarity of this area, together with restricted vessel availability made it difficult to meet BP’s annual targets for GVI PINS. Investigation into alternative methods highlighted the “FlexMode” option in RESON’s 7125 multibeam echosounder (MBES), which was specifically designed for pipeline inspection operations.
Elaborating on a concept devised by BP we deployed two RESON 7125 MBES transducers on one vessel. Each transducer was mounted on an over-the-side pole, one on each side of the vessel. The transceiver heads were tilted inwards by 15˚ to provide an intersection point beneath the vessel’s hull upon which each systems’ dense sector could be centred. When robustly installed, accurately calibrated and heave-compensated this arrangement offers significant advantages:
- 8000 depth measurements per second
- Ability to ‘see’ beneath the pipeline where not in contact with the seabed
- 5 knot survey speed
In less than seven days, 740 kilometres of pipeline were fully surveyed. This time included all operations such as transits, line turns and re-runs.
BP concluded that the performance of the dual head, inwardly focused MBES configuration was “exceptional”. The raw data were processed using proprietary Fugro software, some of which was developed specifically for this project.
With the data in point cloud format, adjacent beams from each transducer were paired for analysis in three dimensions to provide pipeline position, pipeline and seabed levels and freespans. Modifying our ‘Starfix.Review’ visualisation and interactive application allowed viewing of point cloud data in 3D.
It was possible to view any 3D perspective of the pipeline, seabed or engineering feature. Manipulating and viewing the data and taking measurements in this way provides high levels of confidence in external pipeline integrity for pipeline engineers. It identifies seabed assets in the context of the seabed and each other, sees pipeline suspensions in full and detects and monitors precisely determined dislocations.
This data is of the highest quality I have ever seen from a vessel-mounted system. Even the ‘horns’ on the pipeline supports are visible.
HOW WE CAN HELP YOU
Based on the survey results, the frequency of BP’s acoustic pipeline inspection was increased to become an annual event, leading to a reduction in more costly and time-consuming ROV-based GVIs. Get in touch to see how we can apply our specialised technology to your pipeline inspection.