NDT Global Customer Case Study: Statoil: A Custom Solution for an Extreme Subsea Pipeline

December 2017

NDT Global, a leading service provider of ultrasonic pipeline inspection and data services, conducted a detailed and accurate baseline survey of Statoil’s Polarled gas pipeline, using ultrasonic technology to achieve highly accurate results of this varied wall thickness line.

When working with a gas pipeline, corrosion identification inspections are typically completed with magnetic flux leakage (MFL) technology, due to the absence of a liquid coupling medium. However, MFL depth sizing accuracy is reduced in direct proportion to the pipe wall thickness. As this pipeline has a varying wall thickness range of 28.9 mm to 37.5 mm (1.1″ to 1.5″) ultrasonic technology (UT) offered a solution, which was up to 80% more accurate for depth sizing than MFL.

UT inspection was feasible as prior to operation; the pipeline was filled with treated seawater. Polarled is the first pipeline on the Norwegian continental shelf that crosses the Arctic Circle, which brings both operational and environmental challenges. The Polarled pipeline is 482 km (299 miles) long and 36″ in diameter running from Nyhamna in western Norway to the Aasta Hansteen field in the Norwegian Sea.

To complete an accurate inspection, NDT Global used high-resolution pinhole and pitting (UMp) metal loss inspection technology to complete the inspection. The UMp offering delivered 0.4 mm (0.02 in) depth sizing accuracy and was the best choice for this thick-walled pipe. NDT Global provided a customized tool, fully certified to the harsh operating environment to ensure safe operation and a trouble-free project.

NDT Global’s Data Services team identified manufacturing baseline defects and delivered a thorough dataset to monitor the future corrosion thoroughly. Statoil now has the inputs required to improve integrity management over the lifetime of this strategic asset. The Polarled pipeline is now ready for operation.

This baseline inspection has collected data with the highest accuracy available today. Not only is the pipeline ready for operation but the operator now has the inputs required to improve integrity management over the lifetime of this strategic asset. Given the accuracy of the data, the baseline manufacturing defects are now known and corrosion growth can be confidently monitored.

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