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Pulsed Eddy Current System - Incotest

INCOTEST (an acronym for INsulated COmponent TEST) formerly known as ARCO-TEMP, is a unique corrosion survey method that allows ferrous pipes and vessels to be surveyed without the time and expense of removing insulation, asbestos, fireproofing concrete or similar coatings.

Brief Description

A special eddy current probe is placed on top of insulation or component surface. This induces eddy currents in the material with a low frequency (pulsed) magnetic field. When the eddy currents reach the opposite face (back wall) their behaviour changes.

Material thickness is calculated from the strength of the eddy currents and the time taken before the deviation occurs at the back wall. By the application of different algorithms, the lift-off and the remaining average wall thickness can be calculated.

This thickness calculation gives the average thickness of the material within the enclosed magnetic field (probe footprint). The diameter of the footprint varies between 25 and 150mm and depends on wall thickness and thickness of the insulation.

Although originally developed for the detection of Corrosion Under Insulation (CUI), Incotest is well suited to detect internal wall loss such as Flow Accelerated Corrosion, again without removal of the insulation. The detection of corrosion through coatings, concrete and marine growths were also quickly identified as good applications. Surveying heavily corroded pipes where grinding for an ultrasonic survey would not be safe has also proved a successful application.

New applications are constantly emerging as people realise the benefits from this technology. One of the attractive features of Incotest is its tolerance with regard to coupling the signal to the object. Holding the probe at the right location is sufficient; as a result measurements can be taken in demanding circumstances. For example, on offshore risers and caissons, using rope access, or by divers or ROV underwater to a depth of 10m.

The equipment includes various types of probes, which can accommodate a range of lagging or protective coating thickness.

Capabilities

• Testing can be carried out through insulation up to 150mm thick.
• Can be used when insulation is wet.
• Testing can be applied at temperature from -100ºC to +500ºC.
• Can be applied to wire reinforced lagging.
• Testing can be carried out through stainless, aluminium and low alloy carbon steel cladding.
• Can be applied through heavy scale, encrusted or rough surfaces.
• A fast survey tool; an experienced two-man team can survey and store up to 1000 points per day depending on accessibility. The system is well suited to carrying out baseline surveys and has demonstrated excellent repeatability.
• Battery operated equipment.

Limitations

• The system gives an average thickness over the probe footprint and therefore should not be applied to search for small, isolated pits.
• The averaging effect means that the true minimum thickness may be less than that recorded.
• Variables such as temperature, lagging thickness and cladding may affect the results, but the system usefulness as a search tool is still retained.

Preparation

• Generally no requirements for surface preparation.

Services Required

• Adequate provision for personnel and equipment access.