Remote Field Eddy Current Testing (RFECT)
Remote Field Eddy Current Testing (RFECT) term is often used to describe Remote Field Testing (RFT) and is associated with eddy current testing. Although RFECT applies the same electromagnetic principal as Eddy Current Testing, there are still major differences between the testing in terms of coil-to-coil spacing. In Eddy current Testing, the field created within the coils is only able to measure the response within a small area while RFECT has a wide spaced coil to pick-up the through-transmission field.
RFECT probe consist of two different functions of coil, where one of them is known as an exciter (transmitter) coil while the other one is called a detector (receiver) coil. A low frequency Alternating Current is driven through the exciter coil which in turn emits a magnetic field. The produced magnetic fields then travel outwards from the exciter, through the pipe thereby inducing eddy currents which extend both axially and radially through the tube wall. The eddy currents then cause the wall to create its own magnetic field which is opposite to the field produced by the probe. The consistency of the voltage produced by the tube wall’s magnetic field then is able to be measured by the detectors, which is located a distance away from the exciter coil. Any flaws present in the tube wall, such as cracks, corrosion or pitting can be identified through the inconsistencies of the voltage (changes in the magnitude and phase) received by the detector coil.
Remote Field Eddy Current Testing is applied mainly to inspect ferromagnetic tubing, including some ferritic stainless steel. Nowadays, RFECT is commercially used in a wide range of industries such as water and gas distribution lines. It is used to inspect pressure tubes, boilers and heat exchangers, where lots of elbows and tees that are difficult for any other tool to negotiate are present. The inspection can be used to identify size wall loss at baffle locations, isolated pitting, corrosion, cracks, and mechanical damage.
Operating RFECT has the same concept as ECT where the probe does not need to have a direct contact with the parts being inspected, making it suitable to inspect complex areas. The probe is also very flexible and enables it to inspect U-Bend areas. Coil-to-coil spacing between the probes allow large areas of discontinuities to be detected. Besides, RFECT is capable of detecting any small defect present at both the inner and outer surfaces of a ferromagnetic tube. This method is highly sensitive to distinctions in wall thickness and tends to be less sensitive to fill-factor changes between the coil and tube. RFECT can be used to inspect any conducting tubular product, however it is generally considered to be less sensitive than conventional eddy current techniques when it comes to inspection for non-ferromagnetic materials.