Remote field testing


Remote field testing is a method of nondestructive testing using low-frequency AC. whose main application is finding defects in steel pipes and tubes. RFT is also referred to as remote field eddy current testing. RFET is sometimes expanded as remote field electromagnetic technique, although a magnetic, rather than electromagnetic field is used. An RFT probe is moved down the inside of a pipe and is able to detect inside and outside defects with approximately equal sensitivity. Although RFT works in nonferromagnetic materials such as copper and brass, its sister technology eddy-current testing is preferred.
The basic RFT probe consists of an exciter coil which sends a signal to the detector. The exciter coil is pumped with an AC current and emits a magnetic field. The field travels outwards from the exciter coil, through the pipe wall, and along the pipe. The detector is placed inside the pipe two to three pipe diameters away from the exciter and detects the magnetic field that has travelled back in from the outside of the pipe wall. In areas of metal loss, the field arrives at the detector with a faster travel time and greater signal strength due to the reduced path through the steel. Hence the dominant mechanism of RFT is through-transmission.

Main features

The main differences between RFT and conventional eddy-current testing is in the coil-to-coil spacing. The RFT probe has widely spaced coils to pick up the through-transmission field. The typical ECT probe has coils or coil sets that create a field and measure the response within a small area, close to the object being tested.