Eddy Current Testing - Inspection Methods Using Eddy Current Technique

By Zul S Sadiq

Eddy Current Testing (ECT) or Eddy Current Technique as it's known was developed to test nonferrous metals originally. Development has been made to allow the testing of ferrous metals via Mag-Wave technology as well as automated scanning, and high speed probe mechanisms.

Eddy current technique has many applications from the inspection of condensers, to feedwater heaters, coolers, evaporators and chillers to name a few. It's utilised across a wide range of industries from chemical, to petroleum to power and offshore.

Some common scenarios involve the following equipment and technology, and showcase some of the new innovations within the industry.

ECT Tubular Inspection - This can be performed using a TX-4400, which features 8 standard channels with a multiple of mixing channels, a 1KHz to 1.2MHz frequency range, real time mixing, and a wide variety of data filters. It's compatible with bobbin, surface and magnetic saturation probes. It's main benefits include four frequencies for better flaw detection and sizing, automated and manual modes, signal suppression of unwanted signals, and the ability to deliver reports onsite via TS-MAP and AR-Wizard.

The second new application is a form of high speed inspection utilising the PD-6K. It's lightweight and fast. It connects to the TX-4400 and inserts probes quickly. It has the ability to adapt to different air fittings and only requires plant air. It's obvious benefit is it's speed, with speeds up to 5ft/second (1.52m/sec) achievable. It can inspect up to 8 tubes/minute and 2-3k tubes per team per 12 hour shift and can be used on ferrous or non-ferrous materials.

In follow up to the above technology, 'Ultra High Speed Inspection' was developed to produce even faster speeds. The piece of kit involved is called the PDP-22. Again it connects to the TX-4400 and can fit in a 16" (406mm) manway. It uses a modular design for easy repair, and holds probe inspection speeds constant. This kit can do inspection at speeds of 10ft/sec (3.05m/sec) and can inspect up to 12 tubes per minute, or 4-5k tubes per team per 12 hour shift.

The final technology involves the evolution to ferrous metals. 'Ferrous ECT Inspection' as it's known, and utilises the Mag-Wave ET (MWET) to test. MWET features a 1KHz to 500KHz frequency range, automated analysis, and automated insertion of probes. A variety of probe sizes are supported and connects to the TX4400 once again. The advantage of Mag-Wave is obviously the inspection of ferrous metals. Small pitting can be detected and quantified, large volume flaws can be detected and quantified, and saturation can be adjusted to eliminate signal noise due to finned tubes. It can also differentiate between ID (Internal Diameter) and OD (Outside Diameter) flaws.

As you can see the following technologies have different applications and uses, and have been largely developed to meet the changing needs various industries.

For more information on NDT or a recommended eddy current technique provider, visit TesTex NDT