MTM (Magnetic Tomography Method)

The basis of MTM integrity concept is the fact that it is not defects themselves that are dangerous for metal snd constructions, but local combination of defects and high stress is. MTM is capable ofremote detection of stress concentration spots in pipe metal by analyzing its magnetic field. It detects areas with stress concentrators (defects and locally applies forces) and determines the danger degree of these areas.
MTM is based on Villari effect (magneto-elasticity, of inverse magnetostriction).
MTM has undergone a successful industrial approbation at pipelines,
including those not subject to inline inspection – the total length of over 20 thousand kilometers buried at depthes up to 8 meters, with high rate of anomaly detection.

SCANNING AND CALIBRATION
1. Determining the pipeline axis position under the ground surface.
2. Pipeline scanning using a portable magnetometer SKIF that automatically records magnetic data and GPS tracks.
3. Preliminary processing and choosing 1-2 points for calibration.
4. Additional non-destructive testing is performed in the digs, involving contact methods,after that the calibration of the data is done.
5. Preparation of the final report, that includes a list of dangerous (anomalous) areas of the pipeline,matched with the map and having their respective danger degree reported.

INFORMATION FOR PIPELINE INTEGRITY MANAGEMENT:
1. The locations of all detected stress-deformed state anomalies.
2. Parameters for analyzing safety of all detected defect areas:
    • safe operation term Tsafe
    • safe operation pressure Psafe
    • estimated repair factor ERF
    • local internal stress values Si

MTM has been successfully tested in industrial pipelines, including those not subject to in – line inspection-more than 20 thousand km in depth to 26 m with a high probability of anomalies detection.
Sinopec Corp
29 control point
When subject to mechanical deformation (or stress), metal changes its magnetization.
Probability of detecting defective areas:
0%
The probability of interpreting the degree of danger:
0%
The probability of missing a dangerous defect:
0%
The advantages of MTM inspection are:

  • remote registration at a distance of up to 15 diameters from the pipe axis
  • it does not require any changes in the mode of operation of the pipeline
  • no impact on the pipeline (passive registration)
  • no prior preparation of the pipeline for controlling the detection of sags, deformation and bending of pipelines

Publications

Whole article

A ‘non-invasive’ stress test

Piping Up For Technology Series (Part 1)