Remote Nondestructive Testing of Unpiggable Pipelines

since 1999
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Magnetic Tomography Method

This unique proprietary method of pipeline inspection is based on the inverse magnetostrictive effect (Villari effect) - the change of the magnetic susceptibility of a material when subjected to a mechanical stress. Method uses “natural” magnetization of the ferrous pipes by magnetic field of the Earth.

Figure 1. Magnetic field in the absence of metal
defects

Magnetic tomography charts the attributes and characteristics of pipe sections by registering and analyzing changes in the magnetic field of the pipeline. These changes are related to stress which in turn are related to defects in the metal and insulation. Magnetic measurements data is collected from the ground surface and anomalies detected are a function of stress, mechanical loading and structural changes in the metal.
Figure 2. Measured magnetic field as it is recorded
by magnetometer device

Magnetic tomography does not measure the dimensions of geometric defects alone but instead it measures the stress caused by these defects and identifies their character, location and orientation in accordance with the location and orientation of the area of stress. Linear and angular coordinates of flaws in the metal and coating are defined within a tolerance of +/-0,25m.
Figure 3. Processed measurements allow detection
of flaws in the pipeline.

Measure Stress Not Geometry

MTM determines the comparative degree of danger of defects by a direct quantitative assessment of the stress-deformed condition of the metal. Conventional surveys only measure the geometrical parameters of a defect. Their subsequent calculations to assess the impact of the defect on the safe operation of the pipe do not take into consideration the stress caused by the defect. Therefore conventional surveys may fail to detect dangerously stressed areas of the pipe or, conversely, classify a defect as one which requires urgent attention when, in reality, the stress level may be low and the defect presents no immediate threat to the operation of the pipe. Since MTM directly measures the stress caused by defects it is an inherently more accurate guide to the safe operation of the pipeline than conventional survey methods.

MTM Identifies and analyzes magnetic field anomalies in areas with stress concentrators due to:

  • Defects or changes in structural conditions (such as metal loss, cracks, dents, lamination and inclusions)
    Corrosion caused defectDentInsulation defect
  • Excessive mechanical stress caused by erosion, seismic activity, or third party damage
    Seismic related defectThird party damage
  • Combination of the above

The method has the following advantages:

  1. Applicable for the unpiggable pipelines or other objects where in-line inspection method is inapplicable. This objects include but not limited to:
    • compressor stations pipelines;
    • pipeline inclusions;
    • water-supply pipelines in cities
  2. MTM doesn't require any preparation of the pipeline for testing such as cleaning, opening the pipe, or stopping pipeline operation. Magnetic field measurements are performed with pipeline operating as usual.
  3. Doesn't require magnetizing of the object's pipes;
  4. Method detects defects of various types including long crack-like defects of the pipe and the welding;
  5. Doesn't have limitation on the diameter, configuration, and method of protection of pipelines tested. These include:
    • change of pipe diameter and wall thickness,
    • pipeline turns and their directions,
    • transported product (e.g. gas, oil, or water)
    • pressure inside the pipline
    • pipeline protection (e.g. cathodic protection, etc)
  6. Method evaluates the degree of danger of defects by the level of concentration of mechanical tensions rather than defect geometry (e.g. length-width-depth)
  7. Method is optimal for running a database on condition certification of objects of any length and any monitoring period
  8. Method guarantees minimal customer resources use for monitoring preparation and repair works such as:
    • reduces work volume and total costs of pipe access works;
    • greatly reduces time of full diagnostic - repair evaluation - repair planning - repair cycle;
    • gives pipe corrosion prognosis and estimates levels of tense-deformed state of the pipeline under current operating conditions.

See Also