Aberdeen-owned MCS has just completed trials that could lead to BP adopting apparently more cost-effective inspection methods to establish the integrity of rigid subsea pipeline infrastructure associated with its deepwater assets.
Following a theoretical study to evaluate their integrity, the super-major decided it was necessary to validate the findings by measuring the wall thickness of rigid pipelines in order to quantify deterioration, if any, thereby determining what future intervention might be necessary.
MCS expects that the new inspection techniques will offer a safe and cost-effective alternative to operators needing to carry out future subsea rigid flowline inspections.
In essence, the John Wood Group subsidiary was appointed to investigate and evaluate non-intrusive inspection techniques and bring to trial the most cost-effective to validate the findings in the initial report.
As part of the evaluation and before undertaking wet trials, MCS selected companies against a set of criteria, including understanding of the demands of working in water depths of up to 500m; assessing track records using marine devices, and defining and quantifying the accuracy required to validate the wall thickness loss predictions.
Also recognising time constraints would be a key factor in performing this scope of work, therefore identifying technology that eliminated the need for coating removal was essential in the selection process.
Following the trials, undertaken at Subsea 7’s test facility in Aberdeen, MCS recommended the use of two companies with different techniques to allow for good comparable data recovery. As a result, Applus RTD and Tracerco were selected after the trials proved successful in quickly and easily detecting changes in wall thickness.
The tests were carried out on a 4.2m long section of 10in coated spare pipe of the same type used by BP. The pipe was machined internally to give different thicknesses at either end to test the inspection methods more fully.
Applus RTD used the RTD Incotest pulsed eddy current system, an electromagnetic method of inspection which saturates the whole cross-sectional tool footprint area of pipe to determine the average wall thickness. A key outcome was that Applus was able to detect a wall thickness with a 5% accuracy on a pipe with a nominal wall thickness of 21.6mm.
Tracerco used its Gamma Scan technique, which involves a gamma ray source transmitted through one side of the pipe section. The received intensity can then be plotted graphically to represent wall thickness loss.
This company also demonstrated that detecting 5% wall thickness loss was achievable and would therefore fulfil BP requirements.
According to MCS, the Tracerco technology has given added benefit in that it can identify changes to the internal condition of a pipe.
The gamma scan technique can, by measuring the received gamma ray intensity, identify changes in pipe content and thus condition.
Additional engineering was provided by Subsea 7 to aid the deployment of the RTD Tooling and Laser marking tool.
Dugald Cameron, who recently joined MCS as IRM (inspection, repair and maintenance) manager, said of the outcome: “The trials were successful in that the changes in wall thickness were detected. Both techniques identified the pre-machined wall thickness changes in the test piece.
“It is a clear advantage being able to carry out both methods of inspection, not only for live comparison of data but because both are quick and easy to use, which will allow BP to be more versatile in the field.”