Eddy Current testing is a method of nondestructive testing that is based on the principles of electromagnetism. When an eddy current probe is energized at a given alternating frequency while in close proximity to a conductive test specimen eddy currents are induced in the test specimen by means of electromagnetic induction.
What Is Eddy Current Testing?
This inspection technique does not require couplant or constant contact with the material being examined. The presence or absence of flaws in the test specimen can be determined by monitoring changes in the impedance of the eddy current coil. Changes in coil impedance are displayed as voltage changes in terms of signal amplitude and signal phase. These variations in phase angle and/or signal amplitude are correlated to flaw conditions, such as percent wall loss and volumetric wall loss. Therefore, ET is a comparative method as opposed to an absolute method. It’s a widely used and well-understood inspection technique for flaw detection and can provide information on a relative part or coating thickness and specimen conductivity.
Need Eddy Current Testing Services?
How often should Eddy Current Testing be performed?
Maintaining high levels of heat exchanger and condenser performance and system reliability
requires regularly scheduled maintenance and inspections.
Performance of eddy current inspections in a consistent manner allows trending of inspection results which permits accurate forecasting of maintenance and repair or replacement activities. The actual amount of time between testing periods will rely on a number of factors, such as the amount of damage that was identified in the heat exchangers or condensers. Ideally, testing will occur approximately every 3 to 5 years, possibly more frequently if there is active damage occurring that should be monitored. Including eddy current testing in an annual inspection ensures that testing occurs with the proper regularity.
Our expert staff can assist you by utilizing the latest technology coupled with extensive experience and knowledge to determine the condition of components and provide guidance for operational and maintenance activities to improve system performance and reliability.
Our Eddy current testing and maintenance services include:
The Merrick Group Difference
The Merrick Group offers Nondestructive Examination Services (NDE)
as part of our catalog of capabilities.
To know more about our testing services or any other service feel free to contact us OR alternatively you can call us at +01.570.455.0600! Our Friendly executives will be happy to help you to understand our services.
How does Eddy Current Testing work?
Eddy currents are created when an energized A/C coil nears a conductive
material and opposing currents (eddy currents) are formed.
When there is a defect in the material, the flow of the eddy currents change, and this way the defect can be detected by measuring the impedance changes that occur in the A/C coil. This method of testing is a very efficient non-destructive method for finding defects in the heat exchanger and condenser tubing.
What is Eddy Current Testing of Tubes?
A common application for eddy current testing is tubing inspection in heat exchangers and condensers.
Eddy current testing of tubes is a non-destructive method for discovering defects in the tubing, is effective on a number of different tubing materials, and can detect defects that can create larger issues for the heat exchangers and condensers. It’s extremely sensitive, can detect extremely small defects in the tube wall, and is only one type of Nondestructive testing (NDT). Other NDT testing techniques include visual testing, liquid penetrant examination, ultrasonic testing, magnetic flux leakage, and magnetic particle testing.
Several types of defects can be detected in tubing with this testing method:
- Inner-diameter (ID) and Outer-diameter (OD) pitting
- Wear (from support structures, other tubes, and loose parts)
- OD and ID Erosion
Eddy Current Testing Applicability
What kinds of Materials can be
Tested with Eddy Current Testing?
Eddy current testing can successfully test any conductive, non-magnetic, or mildly ferromagnetic materials.
This would include materials such as nickel alloys and ferritic chromium-molybdenum stainless steel.
What kind of Inspections can be performed
using the Eddy Current Testing method?
Eddy current inspection techniques include. but are not limited to:
- Inspecting the integrity of welds and bolts
- Checking heat-treated materials by testing conductivity
- Inspecting metal surfaces for defects
- Determining whether the metal has corroded
- Inspecting metal tubing
This is very useful for testing the integrity of structures made of conductive material like copper, steel, and aluminum metals because the results are immediate and you do not need to touch the actual metal. Eddy Current is used to detect flaws in the metal. If you need to verify that a conductive material like a pipe is not cracked, pitted, or corroded, these testing techniques will get the job done. You can use them to determine how thick a non-conductive coating, such as paint, is and determine metal hardness. Verifying that heat exchangers are not corroded is an example where eddy current testing is often used.
How effective is Eddy Current Testing?
It’s extremely sensitive to defects in the tube wall and is the
most efficient method for detecting and depth sizing tubing flaws.
Accurate depth sizing requires the use of calibration standards that mimic the damage mechanism. Eddy current testing is best used as a method to assess the condition of a component, particularly the tubing in a component, but other information on component condition can be identified. As part of the condition assessment program, degradation detected by eddy current testing can be re-inspected over time to determine if degradation is ongoing and to trend degradation through the life cycle of the component.
What Types of Probes are used
in Eddy Current Testing?
Simple single-coil probes can be used for simple surface or bolt hole exams while array probes with over 50 coils
are often used for tubing and surface inspections. The expected damage mechanism and the geometry of the
test specimen determine the coil configurations that are used.