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NABL ISO17025 Accredited Eddy Current Testing Center.

Crack Detection, Material Sorting & Heat Exchanger Tubes using Eddy Current Testing

Eddy Current testing (ECT) NDT Labs. Crack detection, Sorting & Heat Exchanger Tubes Corrosion Inspection Services.

Eddy current testing is a surface and subsurface Nondestructive testing method. It is helpful for detecting cracks in ferrous & nonferrous metals. It can be applied on Aluminium, Magnesium, Stainless Steel, titanium and almost all conducting materials. Generally, the method is used in Aerospace, automotive and heat exchanger tube testing. Also, a reliable method for material mix-up sorting, measuring wall thickness in manufacturing and in-service inspection of thin wall tubes and pipes.

Beyond Surface and Subsurface Crack Detection...

NABL and NADCAP Accredited Lab ISO17025
NABL, ISO17025:2017 and NADCAP Accredited Lab in Bangalore India

Eddy current is an NDT method for surface and subsurface crack testing. This method finds surface and subsurface flaws in any conductive material. Many applications are existing that use Eddy current principles. Present Eddy current NDT method has applications in Aerospace Component Inspections, Heat exchanger tube inspections in Oil Gas companies. Also, real time non-contact wall thickness testing, Material sorting, mixing, paint and non-conductive coating thickness testing.

Demand for eddy current testing is steeply rising due to increasing usage of nonferrous materials. For example, Aluminium alloys for aerospace cannot be tested using magnetic particle method, thus tested easily using this method. In fact, it can detect fatigue cracks effectively.

Crack and Other Flaw Detection using Eddy Currents

Eddy Current testing Crack detection
Eddy Current testing Crack detection

Crack detection on ferrous materials such as iron, nickel, cobalt based alloys is easy. Because, all ferro magnetic materials can undergo crack detection using magnetic particle inspection method. 

Then, what about other non-ferro magnetic materials? Such as Aluminium, or other non magnetic materials? Is there any NDT method to detect cracks on these materials? Answer is YES, Eddy current testing is one of the effective means of detecting cracks. 

The method can detect both surface and subsurface crack without even contacting the surface. Therefore, in many areas eddy current crack detector have replaced magnetic particle testing where speed and accuracy is vital.


For example, eddy current machines detects cracks on railway tracks at steel plants. Also, as the method is contact less, high speed inspections are possible. In addition, unlike ultrasonic testing, no couplant is necessary.


Our Eddy current labs can provide you crack testing services both onsite across India and at our labs in Peenya, Bangalore.


Depth of Flaw Detection in Eddy Current Inspection

Like Ultrasonic testing-UT, this method can detect depth of cracks with good accuracy. Depth of crack detection in Eddy Current depends on conductivity of materials and frequency of currents. To clarify, less is the conductivity of the material, better is the depth of penetration. Therefore, in highly conductive materials, depth is very minimal and limited to surfaces. However, in less conductive materials deeper cracks are detectable. In any case, usually depth of detection is three times the skin depth.


In conclusion, to improve the depth of penetration in high conducting materials we use lower frequencies.


Solutions to material mix-up problems - Sorting Based on Hardness, Composition and Heat Treatment.

Material sorting or mix up is a common issue in workshops. As there are varieties of materials machined and heat treated, mix up commonly happens. If the mix up is based on chemistry variation, there are methods such as wet analysis, PMI etc., But these methods are time consuming and not cost effective. Then, which is the best NDT method for materials sorting? It is Eddy Current sorting.


Automobile components manufacturers are processing varieties of components. There could be variation in design, chemistry, heat treatment or other properties in materials. The most common issue in work floors is mix up of various grade of materials. 

Mix up could be either different chemistry or mechanical properties or metallurgical structures. Eddy current sorting is the cost effective and less time consuming means of arriving at right conclusion. Therefore, it is increasing becoming common to sort out the materials, using Eddy current sorting machines.


Portable as well as stationery type eddy current machines are available based on the volume of sorting and speed of sorting needed. Sorting could be based on chemistry, hardness variation or heat treatment condition. 

Eddy current sorting machines can do the job precisely. It could be manual sorting or fully automated machines for shop floor sorting. We have complete solutions on material sorting.


Quick Solution for Measuring Electrical Conductivity of Metals. Now measure using eddy Current Probes.

For a given material, conductivity depends on purity of metal. Therefore, by measuring conductivity we can estimate the purity of metals to a reasonable extent. Eddy current machines comes with conductivity test probes. %IACS ( International Annealed Copper Standard) is the unit for measuring conductivity of metals. Accuracy of testing depends on accuracy of calibration prior to testing.


We use NPL calibrated conductivity samples to establish the procedure. Do you need conductivity value or do you need sorting based on conductivity? Our ET labs have eddy current probes to test %IACS.


Now accurately measure Conductive and Non-conductive Coating thickness using Eddy Current Machine

Measuring coating thickness is important to ensure the quality of coating. It could be during manufacturing or during in-service inspection. In the sense, there could be conductive coating on conductive metals or non conductive coating on conductive metals. 

For example, paint or insulation on pipe lines or nickel or chromium plating on metals. Eddy current machines can help to estimate the thickness of these coatings. In fact, its a very good method for the purpose. There is still one limitation, that is the conductivity of coating and base material should have greater variation to get good results. Thus, ET is good to detect coating thickness using eddy current principles.


At our Eddy Current test centre, we have coating thickness samples traceable to national standards.


Heat Exchanger Tube Inspection for Corrosion

Corrosion causes loss of wall thickness in heat exchanger tubes. This can lead to sudden failure of tubes in petroleum refineries. Eddy current bobbin probes helps to detect corrosion damages using dual frequency probes. By inter mixing the frequencies, suppression of signals due to noise or support plates is possible. Inner surfaces of tubes shall be clean to proceed for testing. Modern eddy current machines are highly reliable for testing corrosion during in-service inspections of heat exchanger tubes. We have eddy current machines and bobbin probes suitable for corrosion monitoring of heat exchanger tubes.

Procedure for Eddy Current testing of Heat Exchanger tubes

Eddy Current Inspection Heat Exchanger Tubes
Eddy Current Inspection Heat Exchanger Tubes in India

Eddy current testing of Heat Exchanger tubes involves the following procedure (usually followed by our Eddy Current Level II technicians):

  1. Preparation: The first step is to prepare the equipment and materials needed to perform inspection. This includes setting up the eddy current testing equipment, probe, power supply, and display or recording equipment. It is also important to ensure that the surfaces of heat exchanger tubes are clean and free of debris such as corrosion deposit, as this can affect the accuracy of the test results.
  2. Calibration: The eddy current testing equipment must be calibrated to ensure that it is functioning correctly and providing accurate results. This typically involves using a corrosion reference standard or sample with known properties, and adjusting the ET equipment settings as needed.
  3. Testing: Once the equipment is set up and calibrated, the eddy current testing can start. The technician will move the probe over the surface of the heat exchanger tubes in a systematic manner, making sure to cover the entire surface. As the probe passes over the surface, it generates eddy currents in the material, which create their own magnetic fields that interact with the probe’s magnetic field. The change in impedance of the probe’s coil due to this interaction is measured and used to determine the properties of the material being tested.
  4. Information/Data analysis: The data collected during the eddy current testing process is typically displayed or recorded on a computer or other device. The Level II technician will review the data to identify any abnormalities or defects that may be present in the heat exchanger tubes. This may include comparing the data to known flaws, reference standards or using specialized software to analyze the data.
  5. Reporting: Once the eddy current testing is complete, the Level II technician will prepare a report detailing the results of the inspection. This report will include any defects or abnormalities that were detected, as well as recommendations for repair or further testing as needed.

Important Note: It is important to note that eddy current testing is typically performed by only qualified, trained and certified Level II technicians who have a thorough understanding of the principles of eddy current testing and the characteristics of the material being tested. It is also important to follow established and ASNT Level III approved testing procedures and guidelines to ensure the accuracy and reliability of the results. Check for more NDT procedures and report formats free download.

Trinity NDT – Testing Labs have the equipment, experienced technicians and ASNT Level III experts to ensure accurate and reliable test results. Contact us today to schedule inspection right at your plant across India. In addition, our NDT services are NABL accredited as per ISO17025:2017 International standard.

Online and Offline Tube Wall Thickness Measurement using Eddy Current Principle

Eddy current wall thickness is a modern NDT inspection method suitable for measuring low thicknesses. It could be in the order of few millimeters on conductive materials. For instance, ET is an accurate method, where there is a limit on using Ultrasonic machines.


Eddy current inspections can be either contact or non-contact type tests. Non- contact methods are suitable for online automation. This is to control thickness of wall, during making of Pipes,Tubes, Plates in real time. Of course, proper setup is the need of the hour to get accurate test results.


In-service Inspection - Aircraft, Helicopter Structures and Bolt hole Inspections

Magnetic particle testing(MPI) is impossible to carried out on non-magnetic materials such as Aluminium and Titanium. In aerospace, Eddy current testing is common to find fatigue cracks on aircraft skins, fastener holes and turbine components during in-service inspections. The method is highly reliable. In addition, eddy currents can pass through even from some surface coatings. This reduces removal of coatings and restoring. Also, save time and thus cost of testing.


Further, for aerospace, speed of testing is vital. Therefore, high speed rotating scanners fitted to eddy current machines can perform bolt hole crack detection in a minimum of time. Our eddy current labs in Bengaluru, India have machines and probes for inspection of Aircraft structures.


NABL Accredited, ISO17025, ISO9001 certified Eddy Current NDT Testing Facility

NABL, Delhi provide accreditation of testing labs on Nondestructive testing services. Eddy Current Testing labs have accreditation for eddy current testing as per ISO17025:2017. Download NABL Certificate | Scope of NABL

Impedance plane display machines have built in defect recording makes testing and printing reports easy. It could be crack detection or material sorting or heat exchanger tube inspection, we are ready to serve you from our NDT labs in Bangalore, India.

We at ‘Trinity NDT’ provide reliable inspection services on Eddy current testing fine tuned to the client needs. Our ET NDT Level II Inspectors are ready to carryout testing in house and onsite. Working under ASNT Level III gives the best view of inspections. Therefore, our NDT inspectors have good skills to give you the best solutions on eddy current testing.

In addition, we also give you ASNT NDT Eddy current testing ET Level III services for procedure preparation and approval. If you need any NDT procedure preparation for your jobs or setup lab contact us today. Find more details about our NDT testing services.

Training and Certification Course for Level I, II in Eddy Current testing. Learn from Top Class Experts.

We offers the best courses and training to certify for Eddy current ET Level I and ET Level II.  The courses will be as per ASNT SNT TC 1A. Training is through our training centre at Bangalore – India. We can offer you the same training or specific training at your location. Contact our training department today for more details. Our services at pan India available in Chennai, Kochi, Hyderabad, Vizag, Mangalore and Hosur.

Find more about Eligibility Criteria, NDT Level II training schedule and Register for course online.

Download Free Eddy Current procedure and Test Report formats

Are you looking for free eddy current test procedure or report format? Here, we give you useful NDT procedures and test report formats for free in pdf. Download free Eddy current testing procedure and Test report Format in PDF.

Know more about Eddy Current Testing


When a test conducting object is brought close to the AC field of test coil, flux causes electrons to circulate in a swirling eddy-like pattern in the object; thus the term ‘eddy currents’. In other words, eddy current behavior depends on the properties of both the flux and the object itself. Therefore, eddy currents are circular AC currents caused by a varying magnetic field. It works on the principle of ‘EM induction’. If there is a change in current flow path, that will provide an indication on screen.

How it works?

In Eddy current testing, the test component is placed in a varying magnetic field of a coil carrying Alternating Current(AC). The AC magnetic field (primary) induces eddy currents in the test component. The eddy currents, in turn, produce an secondary magnetic field. As per Lenz’s law, this secondary magnetic field opposes the primary magnetic field which caused it to produce. Finally, by scanning and measuring the changes in impedance in an area of test object, cracks and material properties can be evaluated.

Major Limitation

Eddy Current testing is only suitable for electrically conducting materials such as Aluminium, Steel, Brass, Bronze, Gold etc., Testing is not possible on wood, plastics, glass and other non conducting materials. It is one of the major limitation in this NDT method.

Also, Alternating currents (AC) can only be used to generate and perform inspection. Because, to generate eddy currents, changing magnetic field is needed.

Maximum Depth of Penetration

Eddy current has skin effect, there the maximum depth of penetration is limited to three skin depths only. Beyond that current density deminishes rapidly thus reducing crack detectability exponentially. Therefore, it can detect cracks up to maximum 3-4mm based on conductivity and permeability of the material.

Industrial Applications

Eddy current testing has numerous applications. It is used in manufacturing and in-service inspections of heat exchanger tubes for oil, gas and landing gear inspection on aircraft applications. Usage includes,

  • crack detection,
  • material sorting  
  • Wall thickness measurement
  • Coating thickness
  • Conductivity
  • Second layer cracks detection
  • Corrosion damage
  • Case depth

Difference between Ultrasonic and Eddy Current Testing

  1. Ultrasonic testing(UT) uses sound waves and eddy current(ET) uses electromagnetic waves.
  2. Frequencies: In UT, above 20KHz and up to 25MHz. ET uses from 50Hz up to 15MHz.
  3. Couplant is essential for UT testing, whereas, eddy currents do not need couplant.
  4. Contact is mandatory in UT, whereas, ET do not need contact.
  5. Speed of inspection in ET is much more higher than in UT
  6. UT is for internal flaws, whereas ET is suitable for surface and subsurface flaws.
  7. Any object that conducts sound can be a candidate for UT testing, for eddy current testing, material shall be an electrical conductor.


ECT Over PMI for Material Sorting

Though Positive Material Identification (PMI) testing is widely used, eddy current testing is increasingly becoming popular NDT technique for materials sorting. Because, PMI is comparatively expensive and also, time consuming. However, the former method gives actual chemistry of material, whereas in later method, it is comparison of known with unknown, similar to go and no-go type gauge inspection.
Eddy current testing is preferred for sorting due 3 reasons;
  • Speed of inspection
  • Economy
  • Portability of ET equipment
  • less initial equipment cost


  • Sensitive to small cracks
  • Detects surface and near surface defects
  • Gives quick results
  • Portable machines
  • Can be used for much more than flaws
  • Minimum part preparation
  • Probe need not contact the part
  • Finally, Tests complex shapes



  • Suitable for only conductive materials
  • Surface must be accessible to probe
  • Skill and training required is more than other methods
  • Surface finish and roughness may interfere
  • Need of Reference standards
  • Depth of penetration is limited
  • Flaws that lie parallel to the probe coil winding not detectable.



Want to learn more about Eddy Current testing & Join our ET Level 1, 2 training Course today? Contact us for information on courses eligibility, fee structure and training schedules.