NYSEARCH’s Validation Program Of Transkor’s Magnetic Tomography Method Of Pipe Inspection

By George Janega, NYSEARCH/Northeast Gas Association; Vitali Grigil, Transkor-USA and Igor Kolesnikov, Transkor-K Russia | June 2011 Vol. 238 No. 6

Figure 1.

NYSEARCH is leading a validation effort of a new non-contact method for inspecting steel pipelines known as Magnetic Tomography Method (MTM). MTM has been developed by Transkor-K of the Russian Federation and has been used for pipeline inspections worldwide.

Transkor-USA, Inc. is a U.S.-based company. More than 7,200 miles of various size pipelines in Russia, Saudi Arabia, Asia and South America have been inspected since 2002. Commercial service has been applied to gas, oil and water pipelines.

MTM inspection is unique to ECDA techniques because it passively measures the magnetic flux of a pipeline while simultaneously recording odometry. The technology is “passive” because electric signals or magnetic excitation are not applied to the pipe to accomplish an inspection. MTM primarily detects mechanically stressed areas of a pipeline (Figure 1).

These areas are a result of excessive mechanical loading, changes in structural conditions of the steel or a combination of such factors (Figure 2).

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Figure 2

MTM is intended to detect a range of stress-concentrating anomalies such as metal loss, cracks, dents, laminations and inclusions. Figure 3 illustrates possible earth related stress caused by erosion, seismic activity, or third party damage all of which are stress-causing conditions.

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Figure 3

Coating failures can also be detected by MTM although not as reliably as stressed areas. It is unique to ECDA techniques, yet similar to inline inspection, in that MTM detects metal defects despite good coating conditions. This technology is applicable to three inch or larger ferro-magnetic pipe and does not have limitations to pipe wall thickness, coating type, type of cover/backfill, the product transported or the presence of cathodic protection systems. However, there are a few limitations including the maximum distance from the pipe, minimum pipe diameter, etc., as well as possible interferences associated with transmission power lines, other buried steel structures and recent inline inspections.

The NYSEARCH validation program compares MTM predictions to actual findings using a third-party assessor. If deemed appropriate, the information may provide means for industry experts to support MTM as an “Other Technology” under PHMSA guidelines.

The MTM inspection proceeds as follows. A pipeline is scanned with an instrument called SKIF by walking above the section of interest. The SKIF houses on-board odometry which records the distance traveled while on-board magnetometers measure and record the pipe’s magnetic field. After the scan is complete, Transkor’s engineers, using its proprietary software, interpret the collected data and request one to three locations for calibration digs.

The suggested calibration dig locations may be negotiated in most cases. Once the pipeline operator provides the excavation(s), a Transkor technician inspects the pipe using a conventional magnetic flaw detector, UT and visual instruments. The purpose of the calibration dig(s) is to attain reference so that severity predictions may be assigned in the Final Anomaly Log. After the calibration operation is complete, Transkor sends the Final Anomaly Log to the operator within two to four weeks.