Eddy Current Testing - An Introduction

John Hansen, Managing Director/CEO of Ether NDE Ltd, talks to AZoM about Eddy Current Testing.

What is an Eddy Current NDT?

Eddy Current Testing is one of the many Non-destructive Testing (NDT) methods. Well known methods include X-Ray and Ultrasonic testing. Eddy Current NDT uses the principle of electromagnetic induction to detect discontinuities in conductive materials.

A coil that is the sensing part of a probe is energized with an alternating current and scanned over the material to be tested, discontinuities cause very small changes in the coils impedance, which are displayed on the eddy current NDT instrument and are then interpreted by the operator to determine the quality of what is being tested.

It is a particularly appropriate method to apply if the material is coated by say paint (e.g. Oil Rig Welds or Aircraft), or the point to be inspected is difficult to access (e.g., bolt holes or heat exchanger tubes).

Widely used as part of a quality assurance program in all safety critical and high value asset inspections including Aircraft, Power Stations, Bridges, Amusement Rides, Automotive etc.

As with all NDT methods Eddy Current Testing has its own system of personnel certification including ASNT (USA) and PCN (UK).

Can you provide me with an overview on ETher NDE?

Ether NDE is an Eddy Current specific manufacturer of non-destructive testing NDT equipment, probes and accessories. ETher NDE offers the best in Eddy Current NDT specialists and knowledge for all your application issues.

Collectively the ETher NDE team has over 150 years of non-destructive testing experience and a vast amount of Eddy Current specific knowledge. We credit ourselves with being easily contactable and happy to offer advice to anyone with an Eddy Current NDT application question.

Talk to us about one of your products and how it works?

The SigmaCheck is ETher NDE’s Eddy Current Conductivity Meter. The best place to start to understand how it works is to look at the theory of conductivity.

Electrical conductivity is the measurement of a material's ability to conduct an electric current. This is the inverse of electrical resistivity, measuring a material's ability to resist an electric current.

Conductivity in metal is established using Ohm’s Law, which states that a current through a conductor between two points, is directly proportional to the potential difference across the two points. The resistance of the material, which is a constant for that material, allows the usual mathematical equation for this relationship to be true.

Conductivity is widely used to indicate the material type and determine the state of heat treatment. In order to give accurate readings the SigmaCheck uses a three-point reference method, the first measurement with the probe in the air and then two further measurements are required which span the range of interest.

The SigmaCheck is supplied with a detachable reference piece with two standards that span the range of commonly used metals.

The main advantages of the SigmaCheck include:

• High Resolution Colour Display (2.8”, 320 pixels by 240 pixels).
• Accurate Conductivity Range (0.5% IACS to 110% IACS, 0.28-64 MS/m).
• Wide range of Frequencies for testing thin materials (60kHz, 120kHz, 240kHz, 480kHz). Option of 960kHz.
• Non-conductive Coating Thickness Measurement display up to 0.5mm.
• Lightweight (350 grams/12 oz.). Ergonomic Slim-Line Case design and easy-to-hold Probe with adjustable finger-grip.

With the advantages in mind, the key benefits of the SigmaCheck include:

• User programmable display.
• 2GB of data storage. Able to store over one million data points.
• Uploaded data can be viewed using MS Excel.
• Intelligent charger via USB Port or AC Supply.
• Multiple languages available. E.g. English, German, French, Spanish.
• Excellent resistance to “edge effect”.
• Rapid Display of Conductivity Results.
• Battery life (up to 6 hours).
• Firmware can be upgraded in field.
• Different probes may be configured by loading the appropriate probe map from SD Card.
• Real-time clock for time and date so that readings can be “stamped”.
• Real-time PC control via USB or optional RS232 link.

The SigmaCheck takes advantage of the latest improvements in electronics and microprocessor technology as well as the ETher teams collective 150 years plus of experience in making eddy current instruments. We believe that the SigmaCheck offers the market a new modern perspective on Eddy Current Conductivity Measurement with all the functionalities an inspector demands from this type of instrument.

Can you discuss the main advantages to Eddy current testing?

The biggest advantage of Eddy Current NDT is that it is a clean NDT method. Unlike UT, Eddy Current NDT requires no fluid couplant; therefore, providing a faster scanning speed than conventional ultrasonic testing (UT).

The surfaces need minimal preparation as Eddy current testing can be used through several millimetres of coating and can detect very small cracks in or near the surface of the material.

Most Eddy Current testing equipment is portable meaning that it is easier for physically complex geometries to be investigated. There is also no need for the test probe to contact the component making Eddy Current NDT ideal for sensitive inspection areas.

Finally the Eddy Current NDT method often provides immediate feedback.

Are there any application areas that are emerging for Eddy Currents?

We have seen a great increase in demand for Eddy Current Weld Inspection Specific Equipment and Probes; especially within the Offshore Oil Industry. This is an application area of our business that we see growing rapidly and we are striving to make sure that we are recognized for our product quality, reliability and support within this industry.

Another growing area for NDT is Alternative Energy Sources including Wind Power and is an industry that will only keep expanding. We want to be visible to this market and make sure that our technology is complimentary to the needs of these industries in the future.

Can you discuss the advanced concepts for your technology?

There are five main advanced concepts for Eddy Current NDT applications:

Remote Field

This particular type of Eddy Current testing involves the use of ID probes, which helps indicate wall thickness changes on magnetic material and solves problems with using conventional eddy current methods on magnetic material.

Simultaneous Use of Multiple Frequencies

There are a range of frequencies that can help detect an array of surface and sub-surface defects, and so by using a range of these frequencies, it becomes possible to categorize difficult-to-detect defects. Being able to manipulate the phase separation and the x/y gain, it becomes possible to minimize unwanted signals, giving a more accurate reading on indications.

Simultaneous Use of Absolute and Differential Tests

Simultaneous testing for surface and sub-surface defects can also be in the form of an absolute and differential testing format. Absolute testing provides good sensitivity for small defects (i.e., cracks and small pits); whereas, differential testing is suitable for large defects including corrosion and material property changes.

Arrays

These are probes with multiple detection coils that allow wide areas to be covered in one pass rapidly and with improved reliability. The disadvantage is cost and the fact that complex geoemetries probes have to be tailor-made for each application.

Use of Imaging

Imaging to produce surface maps of the integrity of a material surface also add more value to an inspection especially when combined with multiple frequencies and/or arrays.

How do you plan on improving your services for your clients?

We plan to introduce more products enhancing customer choice while keeping the end-user in mind. We aim to to grow our business whilst retaining the personal relationships that we are building with all of our customers. As part of the ETher Core Principals, client-business relationships, client satisfaction and support are extremely important to ETher as we believe that happy clients are returning clients.

As well as offering quality products we are working to continue to expand our website content including more application-based information with a broadening focus on education in Eddy Current NDT. We are striving to be recognized as thought leaders in our field.

You are scheduled to exhibit at a number of conferences this year. What will be your main focus for these events?

This year has seen less exhibitions and conferences compared to 2012 where we were Gold Sponsors at the WCNDT in Durban as well as attending a further 14 exhibitions; however, this has meant that there has been a huge opportunity to be more creative with our stands this year.

As well as supporting our distributors worldwide at their local conferences, we did showcase at the Materials Testing 2013 conference in Telford in September. The main focus for this stand was to bring together all the companies that operate under the watchful eye of Mike Reilly including Baugh & Weedon and Imaginos NDE.

We were lucky enough to have a 48-meter squared stand at MT 2013 and the main emphasis was based around the theme of “movement”. We wanted to have a stand that was interactive and allowed our visitors to touch, feel and operate our equipment.

We are also due to attend the ASNT Fall Conference in Las Vegas in November. Due to the draw of its location, we expect this show to be very busy and made sure we got our booking finalised as soon as the spaces became available.

As with Materials Testing, I am due to give a presentation at the show on the advantages of using eddy current for weld inspection. This is something that we felt was important to cement our place in the market as a significant knowledge leader in Eddy Current NDT.

Where can we find further information on your products and services?

If you want honest answers from knowledgeable, down-to-earth Eddy Current NDT specialists then ETher NDE is the company for you. If you give us a call, you’ll go straight to Karen, who alone is an absolute fountain of product knowledge. She’ll be able to direct you to the right team member for your question. Within the ETher NDE offices we house the Hardware, Software, Applications, Probe Manufacturing, Electronics, Sales and Marketing teams so you will be sure to get the correct person for your needs.

Ultimately we like to keep it simple at ETher; the ability to speak to someone as soon as possible that can give knowledgeable answers to your questions.

There are a number of ways that you can get in touch with ETher NDE. Firstly you can email us at [email protected] or call +44 (0)1582 767912. You can also check out our site  for all the latest news and details of our products.

About John Hansen 

John Hansen was born in Africa. Studied Electronic Engineering at Southampton University, UK and since 1977 has been involved in the application of technology to help improve the reliability and safety of non-destructive testing.

In 1997 he joined Unit Inspection (an NDT company originally owned by state owned British Steel but the latter became Oceaneering UK) where he co-developed the original ACPD MicroGauge and then the U7 variant.

In parallel with developing products, John was also involved in the application of special NDT techniques such as Acoustic Emission, Automated UT, Thermography, Strain Gauging and Eddy Current tube inspection. In 1984 he joined the UK eddy current instrument and probe manufacturer Hocking NDT. In 2004 GE purchased Hocking outright.

Following the closure of the Hocking factory in December 2009 John co-founded with Mike Reilly ETher NDE - an Eddy Current Instrument and Probe manufacturer. Currently John is an elected council member and Vice-Chairman of the Trade Group for BINDT.