Got a thick pipe wall? Here’s how you can use magnetic pig signalling products

Nord Stream recently completed its first in-line operations to inspect for any indications of corrosion or changes in the shape of it’s dual Nord Stream pipeline. Monitoring the progress of pigs passing critical points on the pipeline was integral to the successful completion of the inspection. Online Electronics explains how it met the project’s challenges using its magnetic pig-signalling service.

Online Electronics specialises in the design and manufacture of innovative pipeline pig- monitoring/signalling equipment and advanced pipeline data-communications’ systems using acoustic, electromagnetic, magnetic, and ultrasonic technologies. This article describes the functionality of the company’s magnetic pig signallers that have been used for the Nord Stream pipelines.

Nord Stream consists of two 48 inch diameter, 1,224 km long pipelines running through the Baltic Sea, commencing at Vyborg, Russia, and terminating at Lubmin, Germany. The lines are fully operational and transport up to 55 Bcm/a of gas.

Last year Nord Stream completed its first in-line inspection (ILI) operation to examine the pipelines for any indications of corrosion or changes to the shape of the pipe, such as dents, buckles, or weld penetrations. The ILI procedures were undertaken in three stages using three different types of tool:

  • Gauging pig
  • Cleaning pig, and
  • ILI tool or “÷intelligent’ pig.

For operations such as these, it is of paramount importance to monitor the progress of the pigs as they pass specific critical points on the pipeline.

For Nord Stream, the specific purpose of pig signalling was to show when the pigs were approaching the receiver so the operators could accurately determine when to activate the valves at the receiver to allow successful receipt of the pigs. For this, Online Electronics used its MAGSIG model 4001D magnetic signaller.

The use of magnetic signallers presented several potential obstacles to successful indication of pig passage for Nord Stream. The technology is non-intrusive, and the equipment requires the device’s sensor to be mounted on the pipeline in order to detect magnetic signals through the pipe wall. The thickness of the pipe wall measured 41 mm, raising speculation with operators as to the viability of magnetic signals being detectable through such an amount of metal.

To alleviate concerns, Online Electronics conducted tests to verify that a magnetic signal would be detectable on the pipe wall’s exterior at a level substantial enough to be detected by the MAGSIG. Simulated job conditions were devised to evaluate the effectiveness of the unit operating through a 41 mm thick steel test sample. To confirm detection of the magnetic signal at strengths specified by operators, magnets of equivalent strength was mounted on a trolley 150 mm beneath the test sample, and the signaller was mounted on top of the sample and connected to a laptop. Since the signaler measures changes in magnetic flux and not an absolute value, the laptop was necessary to record specific values for changes in magnetic flux as they happened. The trolley with the magnets was then pulled underneath the sample so as to determine the signaller’s capability to detect the magnetic field through the steel wall. The test was then repeated with a 50 mm steel plate to allow for operational contingency.

Online Electronics’ MAGSIG units operating at a default setting will detect changes in magnetic flux of a minimum of 35 miliGauss (mG). Given the wall thickness of the Nord Stream pipelines, the units were configured to a more-sensitive setting to detect changes of 15 mG and above. During tests the change in magnetic flux detected for the 41 mm and 50 mm samples were above 2,000 mG and 1,300 mG respectively. From this information, Online Electronics could prove with certainty that the units were sufficiently sensitive to detect magnetic fields through the appropriate pipe wall thicknesses, as the changes in magnetic flux detected were substantially larger than the flux trigger level set at 15 mG.

The information derived from Online Electronics’ testing procedures was confirmed by the successful completion of ILI operations by Nord Stream, with each of the three pigs being detected upon arrival at the receiver in both pipelines. This project proved the reliability of the magnetic signallers functioning through pipe walls of substantial thicknesses.

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