Electromagnetic testing
Encyclopedia
Electromagnetic Testing as a form of nondestructive testing
, is the process of inducing electric current
s or magnetic field
s or both inside a test object and observing the electromagnetic
response. If the test is set up properly, a defect inside the test object creates a measurable response.
The term "Electromagnetic Testing" is often intended to mean simply Eddy-Current Testing
(ECT). However with an expanding number of electromagnetic and magnetic test methods, "Electromagnetic Testing" is more often used to mean the whole class of electromagnetic test methods, of which Eddy-Current Testing is just one.
Nondestructive testing
Nondestructive testing or Non-destructive testing is a wide group of analysis techniques used in science and industry to evaluate the properties of a material, component or system without causing damage....
, is the process of inducing electric current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
s or magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
s or both inside a test object and observing the electromagnetic
Electromagnetism
Electromagnetism is one of the four fundamental interactions in nature. The other three are the strong interaction, the weak interaction and gravitation...
response. If the test is set up properly, a defect inside the test object creates a measurable response.
The term "Electromagnetic Testing" is often intended to mean simply Eddy-Current Testing
Eddy-current testing
Eddy-current testing uses electromagnetic induction to detect flaws in conductive materials. There are several limitations, among them: only conductive materials can be tested, the surface of the material must be accessible, the finish of the material may cause bad readings, the depth of...
(ECT). However with an expanding number of electromagnetic and magnetic test methods, "Electromagnetic Testing" is more often used to mean the whole class of electromagnetic test methods, of which Eddy-Current Testing is just one.
Common Methods of Electromagnetic Testing
- Eddy-Current TestingEddy-current testingEddy-current testing uses electromagnetic induction to detect flaws in conductive materials. There are several limitations, among them: only conductive materials can be tested, the surface of the material must be accessible, the finish of the material may cause bad readings, the depth of...
(ECT) is used to detect near-surface cracks and corrosion in metallic objects such as tubes and aircraft fuselage and structures. ECT is more commonly applied to nonferromagnetic materials, since in ferromagnetic materials the depth of penetrationSkin effectSkin effect is the tendency of an alternating electric current to distribute itself within a conductor with the current density being largest near the surface of the conductor, decreasing at greater depths. In other words, the electric current flows mainly at the "skin" of the conductor, at an...
is relatively small.
- Remote field testingRemote field testingRemote field testing is an electromagnetic method of nondestructive testing whose main application is finding defects in steel pipes and tubes. RFT may also referred to as RFEC or RFET...
(RFT) is used for nondestructive testing (NDT) of steel tubes and pipes.
- Magnetic flux leakage testingMagnetic flux leakageMagnetic flux leakage is a magnetic method of nondestructive testing that is used to detect corrosion and pitting in steel structures, most commonly pipelines and storage tanks. The basic principle is that a powerful magnet is used to magnetize the steel. At areas where there is corrosion or...
(MFL) is also used for nondestructive testing (NDT) of steel tubes and pipes. At present RFT is more commonly used in small diameter tubes and MFL in larger diameter pipes over long travel distances.
- Wire rope testing is MFL applied to steel cables, to detect broken strands of wire.
- Magnetic particle inspection (MT or MPI) is a form of MFL where small magnetic particles in the form of a powder or liquid are sprayed on the magnetized steel test object and gather at surface-breaking cracks.
- Alternating Current Field MeasurementAlternating Current Field MeasurementAlternating Current Field Measurement is an electromagnetic technique for detection and sizing of surface breaking cracks. It works on all metals and, not requiring direct, electrical contact, works through coatings.-Use:...
(ACFM) is similar to eddy current applied to steel. Its most common application is to detect and size cracks in welds. Description from the company that developed it.
- Pulsed eddy currenthttp://www.ndt-ed.org/educationresources/communitycollege/EddyCurrents/AdvancedTechniques/background.htm enables the detection of large-volume metal loss in steel objects from a considerable stand-off, allowing steel pipes to be tested without removing insulation.