Eddy Current Inspection – The Best Non-Destructive Testing For You?

Most people are not familiar with Eddy Current or Eddy Current Testing but ECT has become a star in the field of non-destructive testing. Eddy Current Testing is the use of electromagnetic testing to find leaks and identify surface and sub-surface flaws in conductive materials. It is also used to examine non-ferrous tubing in condenser and heat exchangers.

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History of Eddy Current Testing, and Where It All Started

Eddy Current Testing, also known as ECT and not to be confused with Electroconvulsive therapy, is testing that started or derived from electromagnetism. François Arago is credited with observing eddy currents in 1824 but it was in 1855 when French physicist Léon Foucault was actually credited with the discovery.

 

There was very little use for ECT or development in the field of Eddy Current until WWII. A German professor named Friedrich Förster started to look at Eddy-Currents for industrial use. Friedrich started developing coils, testing conductivity and measured out ferrous materials, all to more accurately detect flaws in conductive materials.

 

Friedrich would ultimately go on to found the Foerster Group and continue development of ECT and other non-destructive testing techniques. The Foerster Group developed practical instruments used to carry out ECT testing for the masses and today it is a widely used and accepted technique for NDT.

The Basics of Eddy Current Testing and How They Apply to Today’s Testing

The most basic form of the ECT principal uses a single coil that is excited using alternating electrical currents. When the wire is excited, it produces an electromagnetic field around the coil. The electromagnetic field oscillates (spins) at the same frequency that ran through the coil. Introducing the coil to conductive material will create currents that are opposed to the ones in the coil and these currents are Eddy Current.

 

ECT uses Eddy Currents to produce an electromagnetic field using coils and detection instruments. When everything is normal and a conductive material is introduced to the magnetic field (normally rings) they stay circling around the coil like a stream.

 

If the conductive material has faults, breaks, or cracks, these streams start to jump off the typical Eddy-current magnetic field and causes the voltage that you are measuring change. These variants can be measured for fault detection in conductive materials allowing us to detect faults even if the eye cannot see them.

Eddy Current Testing by American Efficiency Services

To break everything down simpler, the coils produce a voltage that will be at a higher and different level than when introduced to Eddy-Currents. When Eddy-Currents are introduced the voltage steadies and will remain at the same level.

 

A fault or break stops the Eddy-Current’s oscillation and the voltage will spike back to the original levels before the Eddy-currents were introduced. The conductive material will not upset or change the spinning of Eddy-Currents but faults, cracks, and corrosion will so when the voltage jumps it typically means there is a fault in the material being tested.

 

Eddy-Current Testing is great for checking pipe’s surface area, checking for faults inside pipes, remote testing of carbon steel pipes, carbon steel weld inspections, and for clad thickness. Outside of our industry, the most common use of Eddy Current is in metal detectors.

American Efficiency Services employee checking eddy currents

The Benefits of Eddy Current Testing Compared to Other Non-Destructive Testing

  1. In favorable conditions, Eddy Current Testing can test fault in pipes up to 0.5 millimeters. With the proper equipment, the right type of conductive material, and properly trained professional, this test is extremely accurate at pinpointing even the smallest of faults.
  2. It can detect through coated materials. While other types of testing can be hindered or simply not work through paint, protective coatings, rust, and other materials, Eddy Current Testing is still accurate on coated materials up to 5 millimeters thick.
  3. No need to the clean surface area. Along the same lines as coated material, soils, uneven coatings, and rust will not affect the testing and therefore do not need to be cleaned for an accurate test.
  4. Testing is mobile and lightweight. Unlike other NDTs, Eddy-Current equipment is relatively small and portable. A proper Eddy-Current professional will have no problem coming to job sites, businesses, or even homes with the equipment and can test smaller areas compared to other non-destructive testing options.
  5. Testing through layers is no problem. Most Eddy Current professionals claim accurate testing through ten layers. We have found that we can still get accurate testing through 14 different layers without any interference due to the uniqueness of Eddy-Currents.
  6. For those looking for commercial testing, Eddy Current Testing can be automated using uniform parts. The testing is very quick and accurate. If you want to ensure quality production of conductive parts, this test can be streamlined with incredible accuracy.
  7. Lastly, this test provides accurate conductivity measurements. Instruments that are dedicated to conductivity testing use Eddy-Current. If you are not sure the material of the piping or metal in your wall you can have an Eddy Current test ran. The test will give you a conductivity reading and accurately tell you the materials in your wall.
eddy current testing equipment

The Disadvantages Compared to Other Non-Destructive Testing

  1. Eddy-Current testing can only be done on conductive materials. If there is no electrical current that flows through the material then Eddy-Currents are not present and without Eddy-Currents, testing is not possible.
  2. It will not detect flaws parallel with the surface. During testing, the flaws must interrupt the Eddy-current waves to register through testing tools. Eddy-Currents run parallel with the surface so any flaw that runs parallel on the surface will not interfere with the currents and therefore, will not register on the detection tools.
  3. Magnetic Permutations cause testing complications. Ferromagnetic material or any small changes in permeability can have effects on Eddy-currents. While testing is not impossible under such conditions, it makes it very difficult so the testing of welds and other ferromagnetic material are less accurate.
  4. Eddy-Current Testing is best suited for small areas with simple geometries. Large spaces are not the best area for this type of testing. While it is not impossible to do, it requires large expensive equipment and is less accurate than when done on a smaller scale.
  5. Also, different geometries make Eddy-Current Testing difficult. A trained professional will be needed to differentiate flaws from deflecting signals caused by different geometries.
  6. There is no real permanent record of testing. During automation of Eddy-Current tests, a print out might be available but only during automation testing. Manual testing will not have any record or lasting reports from the testing.
  7. Lastly, Eddy Current testing requires training and certifications. It is not something an unskilled person will be able to immediately pick up. Professionals are needed to read the testing material, differentiate from deflecting signals and faults, and be able to interpret data correctly on the fly and on-site.

ECA (Eddy-current Array) the All-Star of Eddy-current Testing and NDT

Eddy-current array technology uses multiple coils that increase electrical energy compared to your normal eddy current testing. The added coils create a more powerful testing area and stronger eddy-currents.

 

What do more powerful eddy-currents mean to NDT? In short, Eddy-current testing has its drawbacks: testing field size, issues with interference, and struggles with difficult geometric testing areas.

 

ECA technology is able to overcome those shortcomings in most cases thanks to its magnet field producing more kinetic energy.

 

Instead of performing tests with single element arrangments in a row, ECA covers a larger area in a single pass. No more pencil probing leading to inconclusive results. Eddy-current array probes use multiplexing for optimal results.

Eddy Current Array Benefits

Wider Testing Area for Faster Results

With ECA technology you get a much wider area of testing since you are not running items through coils. The wider area shows up on Eddy-current testing equipment giving larger sample sizes at once. The larger the test fields the quicker you get results from the testing. The best part of ECA is that you get the same accuracy as any other eddy-current testing technology.

 

Using Array Technology Makes Testing Less Depending On the Operator

ECA technology still needs an experienced tester to perform the ECA testing. An ECA professional is needed to read the results but the results are far less dependent on the tester. That means there is far less human error and provides more consistent results.

 

ECA Provides More Accurate Testing Results

Since Eddy-current Array technology is more powerful so is the accuracy of the test. More powerful arrays also give professionals an improved ability to detect flaws and increases the flexibility of testing areas. The highly concentrated Eddy-currents make ECA a superior non-destruction technology. With ECA, professionals detect more flaws and are able to test areas you could not before.

eddy current array testing machine    eddy current array testing machine

Our Go-To Guide’s Eddy-current FAQ and Answers

What types of damages can be detected with Eddy-current testing?

ECT can detect ID pitting, OD pitting, ID corrosion, and OD corrosion with near perfect accuracy. It is okay to use ECT for axial cracking and circumferential cracking but only in limited aspects.

 

What types of damages can be detected with ECA testing?

ECA is ideal for ID Pitting, OD pitting, ID corrosion, OD corrosion, axial cracking, and circumferential cracking. You can see a full chart comparison between ECA and ECT here, or check out our comparison chart below for a quick review.

 

When should ECT be performed and how often should it be performed?

ECT should be performed during your annual inspections of equipment. Equipment that has had no damage detection you can test every two to three years. Equipment that has already had faults, corrosion, or cracks should be tested annual or more often.

 

Why perform ECT and are there benefits to regular testing?

Detecting small flaws on a conductive object and minor erosion and corrosion will allow you to avoid major faults and damage. Think of ECT as preventative maintenance, detecting and monitoring flaws early will allow more accurate maintenance needed on machinery. If a piece of metal has regular ECT tests major damage can be avoided.

 

Who is the right person to perform or hire for ECT or ECA testing?

A properly trained analyst can provide you with all the information you need from ECT and ECA testing. Finding a trained and experienced analysts is important for accurate testing results. You should as for credentials, certifications, and experience before hiring anyone to perform Eddy-current testing.

 

A trained analyst professional will be able to report all issues found during the test. Experienced analysts will adhere to industry standards and will be able to give the severity of any detection flaws. A trained professional will also be able to detect smaller faults and track the faults progress. Trained analysts will be better suited condemning piping that otherwise might have been overlooked.

 

All analysts should have certifications from the area they test in. Applied technical services or ATS provides certifications and testing. You can find ATS certified analyst here.

 

ATS is not the only certification standard in the ECT field. It is important to ask for certifications and research the quality of those certifications before hiring a professional

Eddy Current Testing vs Eddy Current Array Comparison: What’s the Best Solution for You

eddy current testing and eddy current array comparison chart

Conclusion of ECA

Eddy-current technology as a non-destructive testing tool has many applications. ECT technology has only improved. Today, ECT and ECA a far more flexible and accurate form of testing.

 

An ECT professional can help you perform eddy-current testing during an annual inspection. Annual inspections help avoid major problems and monitor erosion and corrosion. If you are unsure if ECT or ECA is applicable to your business check the list below or above.

 

If you have any titanium, aluminum, stainless steel, conductive materials, copper alloys in your machinery or pipping then ECT can be used to detect and track flaws. If you have any questions about how ECT or ECA can help your business fill out our contact form. We will have one of our professionals contact you and answer any of your questions.

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