GENERAL DESCRIPTION

XRFT is an electromagnetic testing technique used primarily for in-service ferromagnetic tubing and pipe inspection.

The conventional remote field test produces a great amount of noise, coming from any unwanted signature, or electrical source, that masks the desired flaw response by much larger amplitude than the flaw response.

Some sources of the noise are aluminum fins in air cooler fin fan application, carbon steel fins, in economizers, or waste heat boiler tubes.

These external structures of the tube cause a disruption to the natural magnetic field flow path known as the ‘through wall transmission effect.’ This disruption causes, or induces, a large offset in the sensor coils, especially in the absolute coil of an RFT probe.

In piping applications, the long runs often result in drifting due to permeability changes. To eliminate this noise, a second probe is placed in a stationary reference tube. The tester now compares, or differentiates, the test probe input to the reference probe input, creating a more balanced system with reduced unwanted noise.

It is important to have the reference probe placed in a tube that is comparable to the tube under test, so the noise can be eliminated.

It is important to have the reference probe placed in a tube that is comparable to the tube under test, so the noise can be eliminated.

A near balanced system is created as the naturally unbalanced condition, as generated by the induced voltage of an RFT test probe, is now being saturated by an identical induced voltage from the reference probe.

Now, as the test probe transverses a flaw, it will no longer be masked, instead it can be seen on the output display in differential and/or absolute modes.

The RFT technique dictates the test parameters – frequency, probe drive and gain, as well as traverse speeds, and field adjustments. Sensitivity and resolution will need to be determined, as most XRFT applications cannot be successfully conducted using the standard RFT methods.

LIMITATIONS

• Has limited sensitivity for detecting cracks.

• Magnetic properties will affect the inspection.

• Reduced sensitivity at the support and tube sheet.

• Slower procedure than eddy current.

• Provides amplitude information only.

• Requires a second probe for reference.

For additional information please contact us.