Cost-effective techniques to be used on BP's rigid pipelines.

(Category: In Focus )

(Image: MCSTRIALS_008.jpg )

SUBSEA engineering company, MCS, a subisidiary of international energy services company, John Wood Group, has just completed trials to assess the capabilities of more cost-effective inspection methods to establish the integrity of subsea pipelines on BP's deep water assets.

Following a theoretical study to evaluate the integrity of these pipelines, BP wished to validate the findings by measuring the wall thickness of rigid pipelines. Measuring the wall thickness would allow BP to quantify deterioration if any and could influence future intervention on their rigid flow lines. It is anticipated that the new inspection techniques could be safe and cost-effective alternatives to future subsea rigid flow line inspection. MCS 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 500 metres. Assessing track records using marine devices, 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 and therefore identifying technology that eliminates 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. 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 4.2 m section of 10 inch 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 foot print area of pipe to determine the average wall thickness. Applus RTD was able to detect a wall thickness with a 5 per cent accuracy on a pipe with a nominal wall thickness of 21.6 mm. 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. Tracerco also demonstrated that detecting 5 per cent wall thickness loss was achievable and would therefore fulfil BP requirements. The Tracerco technology has given added benefit in that it can identify internal pipe line changes in condition. 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 with the deployment of the RTD Tooling and Laser marking tool. MCS has further enhanced its integrity management team with the appointment of Dugald Cameron as Inspection, Repairs and Maintenance manager. Cameron, who has over 30 years experience in the offshore oil and gas industry led this integrity project for BP. He said: "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 our 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. "We were pleased that BP chose us for this integrity project. Our engineering know-how and integrity management experience have enabled us to carry out a rigorous selection and evaluation of new techniques which will ultimately save time and money without compromising on integrity." Commenting on the success of the trials in early June, Philip Wickes of BP added: "Our integrity management strategy involves inspection, management and predictive engineering to ensure on-going integrity and assess life extension of the asset. Our focus is on diligence, rigour, discipline and procedure." MCS has been involved in over 90 per cent of the UK North Sea's FPSO projects involving flexible pipe. With over ten years experience in developing and implementing integrity management strategies for flexible and rigid pipe subsea systems in the North Sea and internationally, the company has also been involved in writing the industry guidelines on flexible pipe integrity management and leading a "Joint Industry Project" specifically focused on the subject. This extensive experience has positioned them as leading experts in integrity management strategies for subsea systems.

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