Remote Nondestructive Testing of Unpiggable Pipelines

since 1999
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Nationalgrid Annual Report

Extract from “Gas Transmission E&D Programme Detailed Reports”

Magnetic Tomography Method (MTM) Pipeline Inspection System:
Evaluation & Validation

Uniqueness of the MTM Technique

None of the techniques, currently employed above-ground to assess the condition of buried pipelines, are capable of locating coating disbandment. However, the MTM technique is now claimed to be able to locate coating disbandment from above ground, and therefore provide similar information to that generated during an in-line inspection (ILI).

MTM technology has been developed to be an innovative, non-intrusive and non-contact method of inspection which can provide 100% inspection of a pipeline from above ground. It is said to be capable of locating pipeline material anomalies, characterizing these anomalies and forecasting the need for follow- up actions

How it Works

The MTM inspection technique has recently appeared in the UK market place and is currently being marketed by Transkor Ltd. The technique measures distortions in the earth’s magnetic field due to the presence of buried objects such as a pipeline. Areas of high stress in the pipeline, cause significant distortion of the earth’s magnetic field that surround the pipeline and these areas of distortion can be detected from the surface. Excavation of these areas can then be made to determine the cause of the distortion. The technique is claimed to have the following advantages over other above ground techniques:

  • No need for advanced preparation or change to the pipeline’s operating conditions.
  • Suitable for any pipeline regardless of type of construction, type of medium transported and presence of flow.
  • Does not magnetize the pipe.
  • Reveals metal loss features and cracking.

Potential for achieving expected benefits

Results from the first MTM trials were compared directly to In Line Inspection (ILI) tool results by overlaying both data sets onto an Uptime pipeline map. This enabled the results to be directly compared and confirmed that there was a correlation between both data sets.

The results indicate that the MTM system has the potential to inspect a buried pipeline from the surface and locate metal loss features and to identify stress deformed pipeline sections due to ground movement.

The MTM system is also a non intrusive method of pipeline inspection and, coupled with results obtained for this first set of site trials, it appears to have great potential for National Grid and other Oil and Gas majors for pipeline inspection.

Project progress [Year to End of March 2012]

Between February and April 2011, the MTM system was used successfully to inspect the 6 sections of chosen pipeline, having a total length of approximately 10km. The pipeline sections had previously been inspected with an In Line Inspection (ILI) tool and the ILI data was available for comparison with the MTM results.

Following completion of the onsite trails, an MTM inspection report was produced and the MTM results were overlaid on top of the ILI data using National Grid’s Uptime system.

All of the information and results obtained from the site trials was recorded and discussed in a GLND report No.13110, issued in December 2011. The report concluded that:

“These initial MTM trials suggest that the MTM system has potential to inspect a buried pipeline from the surface and locate metal loss features as well as to identify stress deformed pipeline sections due to ground movement. ”.

Based on these results and the potential of the MTM system to National Grid, and following discussions with National Grid, in March 2012, GL applied for further IFI funding to perform a second set of trials to inspect sections of National Grid pipeline where known ILI features were located.

© nationalgrid Annual Report 2011/2012