Pulsed Eddy Current Testing (PECT) is an inspection technique used for corrosion under insulation (CUI)

screening on carbon steel structures as pipes, vessels, tanks and spherical tank legs without the need of contact with the steel surface.

PECT is a static technique able to measure spot percentage variations in steel thickness through any non-conductive

and non-magnetic material between the sensor and steel surface such as air, insulation material, concrete, plastics

coatings, paint, sea water, marine growth, deposits, oil, etc.

PECT is a comparative technique where the percentage variations measured on the specimen are compared with a calibration value which is always assumed to be the full wall thickness.

Advantages of PECT

When interpreting the PECT data, it is important to consider the strengths and limitations of the method. The advantages of PECT are as follow:

• Ability to measure the thickness of steel without surface preparation. There is no need to remove deposits,

      corrosion product or paint. This is obviously a key feature when inspecting the surface casing of an offshore

      well since surface preparation would be extremely difficult to implement due to the restricted access.

• Non-conducting and non-magnetic materials like insulation material, concrete, plastics, etc., do not influence the PECT signal at all and are therefore irrelevant to the PEC inspection. PEC can also measure through corrosion products (i.e. iron oxides), provided there is a gap between PEC probe and corrosion product of 20mm.
• PECT can even inspect through aluminum and stainless-steel insulation covers.
• PECT measurements are hardly influenced by variation in sensor lift-off.
• PECT can also be applied at high temperatures.
• PECT readings can be made highly repeatable. The high reproducibility makes PEC well suited for wall thickness monitoring.

Limitations of PECT

The limitations of the technique are as follow:

• Affected by the edge effect (about the size of a probe’s footprint) near metallic structures.
• Unable to discriminate between near-side and far-side defects.
• Impossible to detect small pitting.
• Under sizes flaws smaller than the probe’s averaging area (mitigated with the compensated wall thickness tool—see later in the training).
• Difficult to use on elbows smaller than 200 mm (8 in) in diameter.
• Difficult to use on very fast materials (with characteristic decay rates less than 3ms).