Flux Leakage Scanners

Corrosion Detection Using Flux Leakage Scanners

Applus RTD offers a full range of pipe and plate scanners covering diameters from 3 to flat plate. The scanner range includes the original Tank Floor Tester (TFT). All use the magnetic flux leakage method. This enables the scanners to detect corrosion pitting on the top and bottom surfaces of all carbon steel pipe and plate.

Brief Description

The tank floor tester was developed for rapid inspection of bulk storage tank floors.

The magnetic flux method allows detection of corrosion pitting in ferro-magnetic steel plates. Related Handscan and Pipescan™ scanners were developed on the same principle to inspect vessel walls, and pipe, from 3" diameter and above.

When an electromagnetic field is induced in a material, the magnetic flux generated tends to remain within that material. However, if a defect disrupts the magnetic field, some of the magnetic flux is forced outside the bounds of the plate. This creates a flux leakage field in the vicinity of the defect. "Hall Effect"? transducers in the scanner detect the flux leakage field and signal the location of the defect.

Once located, the area can be closely scrutinised, using ultrasonic or other techniques, to accurately measure corrosion damage. Equipment sensitivity depends on the material thickness.

Typically the lower bound sensitivity amounts to 30% wall loss in 6.4 mm thick material; 40% wall loss in 12.5 mm material and 60% wall loss in 19mm thick material.

Capabilities

  • Large scanning area: the Tank Floor Tester has a 280mm wide scan head; Pipescan and Handscan have up to 150mm wide scan heads.
  • Rapid scanning of large surface areas. As much as 1km of pipe may be scanned in four shifts.
  • Adjustable scan heads for Pipescan and Handscan allow scans of curved surfaces above 3"? diameter.
  • Scanning of plate up to 19mm thick.
  • An LED™ array allows the operator to locate areas of corrosion as they are traversed by the scanner. Such areas are then visually and ultrasonically examined to identify defective areas.
  • Sensitivity adjustable for different surface conditions.
  • Audible and visual alarm outputs.
  • Easily deployed.
  • Battery operated.

Limitations

  • Can only be applied to ferrous materials.
  • Does not provide actual remnant thickness.
  • Tank Floor Tester may be restricted where there is insufficient clearance below heater coil pipes and so forth. In such cases, supplementary scans with Handscan™ may be needed.

Preparation

  • The area to be tested should be free from loose scale, grease, oil and other product deposits. The equipment produces a strong magnetic field, loose objects such as nuts, bolts etc. should be removed from the test area.

Services Required

  • Adequate provision for personnel and equipment access.

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