What is Non-Contact Magnetic Tomography?

6th Mar 2011 at 21:09

The technology that Argos Inspection utilise for non-contact (from the ground) magnetic inspection of pipelines was developed by the Transkor-K Centre in Moscow, and represents an innovative and highly effective alternative to the standard in-line inspection method. It was first demonstrated in 2003.

Non-Contact Magnetic Tomography is a non-contact, non-hazardous, highly accurate scanning procedure. It represents a real alternative to traditional methods of ultrasonic and radiographic inspection for pipelines

Using magnetic induction imaging techniques, pipelines are located and assessed without the need for energy input during testing. By examining each section of the pipeline in ‘slices’ the exact details of a defect can be determined and any potential danger identified.

The technology enables pipework to be effectively located and examined from above the ground. This highly sophisticated technique allows inspection to be carried out on a pipeline buried up to 15 times the pipes’ diameter, with assessment of defects based not on geometry but of the level of stress caused by them.

The data is collected by a non-contact scanning magnetometer and is subsequently analysed by a patented software, the non-contact nature of the process ensures that the pipeline remains in service throughout the survey thus eliminating cleaning, purging and downtime costs.

The survey report defines the location and extent of geometric and corrosion defects including:

  • Dents, corrugations, scores, out of roundness and differences in wall thickness
  • Loss of metal – including internal and external corrosion defects of any nature.
  • Delamination
  • Defects within welded joints eg cracks, pores, lack of weld penetration, displacement of edges and metal flakes
  • Crack-like defects in any orientation
  • Sections with deviations of a level of stress deformed conditions caused by, for example, sagging, landslips, washouts or transitions under roads.
  • Local corrosion under scaled insulating coating

The location of defects using this process are defined within an accuracy of +/- 1.5m thus facilitating further investigation or repair, with the final report defining the degree of danger of defects and recommending maximum safe working pressures and also the length of time it is safe to continue to operate defective sections of pipe at those pressures.

The system can be used to survey trunk pipelines (across any terrain including water) and service pipelines within cities. Accuracy is not affected by either the close proximity of other pipelines or city traffic

Fluctuations in magnetic field strength are used to automatically display, register and record in memory defects in the metal as the magnetometer is carried along the longitudinal axis of the pipeline by an operator.

All data is then subsequently analysed to produce an integrated indicator of the hazard level of the defects detected. This is presented in chart form and references an identification of each defect and its location (obtained using GPS).

Flaws in the metal are located by relating the magnetic permeability of the pipeline to stress raisers and are defined by analysing the interconnection of stress concentration with a change in the polarity of the components of the earth’s magnetic field.

The effect of interfering fields is minimised by equipping the magnetometer with high sensitivity converters and dedicated software with filtration algorithms.

The key benefits of Non-Contact Magnetic Tomography are:

• Much less invasive than traditional methods of NDT

• Requires minimum preparatory work

• No requirement to cease production

• No requirement to exclude personnel

• Time efficient

• Cost efficient

• Can be used where traditional methods/procedures are difficult

• Used in association with GPS technology whole pipelines can be planned and anomalies/defects listed and located

• Non-hazardous

• Highly accurate

• Proven

• Provides peace of mind

The technology has to date been used to successfully survey more than 20,000km of subterranean and submerged pipelines in the Russian Federation, Uzbekistan, Ukraine, Syria, Argentina, Brazil, Colombia, Mexico, Croatia, Saudi Arabia, Malaysia, Indonesia, China, UK and the USA.

Monitoring throughout this period has demonstrated an efficiency rate and reliability level of not less than 87%.

A first UK demonstration was carried out under the auspices of Argos Inspection on a ferromagnetic water main buried approximately 1.5 m and under various terrain, including water. The purpose of the demonstration was to validate the system by direct comparison with standard ultrasonic tests carried out in excavated pits by two different NDT Companies.

The testing proved conclusively that the Transkor–K magnetometric testing produced the anticipated results - confirmed by U/T examination - from the ground surface without costly excavation or in-line inspection procedures and all while the product continued to flow.

Magnetometric technology can be used for inspection of all ferromagnetic pipelines where in-line inspection is difficult, impossible or more costly.

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