Detecting and sizing pinhole features

Pinhole and pitting corrosion are localised forms of corrosion which can be caused by corrosion mechanisms such as internal/external MIC, or externally in areas of disbonded pipeline coating and CP shielding. Pinhole features can also be caused from third party activity such as ‘illegal taps’ for product theft, manufacturing anomalies and girth welds defects.

Pinhole corrosion is often considered to be more critical with respect to pipeline integrity than uniform corrosion due to the high growth rates, and because the traditional MFL and UT inspection technologies had difficulty in reliably detecting and sizing pinhole features, due to the low volume and small area of metal loss (ML). As defined by POF specification, a pinhole is a localised ML feature with surface dimensions smaller than 1 WT (1·t) or 10 mm whichever is greater in length and width direction. Frequently such features are too small to be reported, with a resulting challenge for pipeline operators to manage the associated integrity risk.

Pinhole features tend to cause small leaks and are difficult to detect in operation. Therefore, detecting and sizing of such features is of considerable interest to the pipeline industry. Modern ultra-high resolution (UHR) MFL technology has been demonstrated to be capable of detecting such pinhole features, giving an in-depth analysis of the pipe wall status and improved reliability in detecting and sizing pinholes features.

A ‘blind’ flow through test

At the end of 2021, Pipecare conducted a ‘blind’ flow through test using an UHR MFL tool to detect, size, characterise, and locate small diameter ML features (POF dimension class ‘pinholes’), in an 8 in. flow string (test loop) located at PRCI-TDC facility in Houston, Texas, USA.

After the completion of the MFL inspection and submission of the inspection report to the operator, the pipeline was sectioned and the ML features present were characterised and sized (depth, width, length) using laser scanning. The resulting database of 152 ML features in the test loop was provided to Pipecare to conduct a detailed review of the performance of the UHR MFL inspection …

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Read the article online at: https://www.worldpipelines.com/equipment-and-safety/16062023/detecting-and-sizing-pinhole-features/