remote field testing (rft)
Remote Field Testing is an electromagnetic examination which utilizes the through transmission effect to produce a resulting field that is affected by anomalies. It is measured a few or more tube diameters away from the AC excitation source without any tube magnetization or saturation. The remote field phenomenon is an electromagnetic testing technique used primarily for in-service, baseline, or QC inspection of ferromagnetic tubing and piping.
We at Horizon Testing Inc. utilizes the Zetec MIZ-28 in conjunction with Carbon Steel Inspection (CSI), advanced design probes, remote field amplifier, and software. This inspection consists of a full-length examination performed from the inside of the tubes with equal inner and outer surface discontinuity detection and sizing. An alternating current is applied to an excitation coil which generates a strong electromagnetic field that propagates out of, and extends away from, the exciter along the tube length. The field then re-enters the tube wall axially from the exciter.
The inducer voltage is measured through the use of a detector coil, bobbin, or pancake that is placed in the remote field zone providing for a volumetric inspection with equal sensitivity to ID and OD anomalies of the tube. The sensor coils pick up the disturbance of the field due to the presence of any anomaly caused by corrosion, stress, foreign object, or mechanical vibration. The signal is measured relative to the X-axis in degrees which equates to flaw depth. The technology has the ability to display in a (X-Y) format.
This allows the data analysis to use pattern recognition for characterizing the signals. Typically, the analysis parameters are established where the phase or angular relationship of the signal is measured relative to the X-axis in degrees, which equates to flaw depth.
The tube exit signal, baseline and tube support/baffle establish certain reference points for nominal conditions and is used to determine the defect phase envelope. Based on this, the instrument parameter can then be adjusted to obtain a certain resolution.
Resolution is the phase separation between flaws of varying depths and will vary with operating frequency.
Multi frequency testers provide greater capability for a broader range of tubing inspection.
Sensitivity is dependent on various conditions such as the type of material, grade, wall thickness, residual stress, operating conditions such as aging, ambient temperature, tube cleanliness, and location.
External material such as support, baffle, tube sheet, and weld attachment, aluminum fins can short or shunt the field that prevents the field from reaching the pick-up coils and therefore reducing sensitivity.
Probe traverse speed is dependent upon the data sampling rate which can never be more than the lowest operating frequency.
At Horizon Testing Inc. we strive to provide the best selection of RFT probes for specific applications. RFT probe design is affected by many considerations and variables.
Probes are designed for specific applications and may, or may not, be suitable for testing other materials, sizes, or wall thickness.
Preparation is advisable, and customers should consult and discuss component history with the inspector prior to the inspection.
Not sensitive to circumferential cracking
Magnetic properties affect the inspection
Reduced sensitivity at the support and tube sheet
Slower speed than eddy current
For additional information please contact us.