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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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 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 Currents.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 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.