How do you validate and document your RFT results and procedures?

1 Choose the right probe

The first step is to select the appropriate RFT probe for the tube size, material, and defect type. RFT probes consist of an exciter coil and a detector coil, which are separated by a distance greater than the tube diameter. The exciter coil generates an alternating magnetic field that induces eddy currents in the tube wall. The detector coil measures the changes in the magnetic field caused by the eddy currents. Different probe designs have different sensitivity and resolution characteristics, so you should consult the probe manufacturer's specifications and recommendations before choosing a probe.

2 Set up the instrument

The next step is to set up the RFT instrument according to the test parameters and conditions. The instrument is the device that controls the probe, displays the signals, and records the data. The instrument settings include the frequency, gain, phase, filter, and calibration mode. The frequency determines the depth of penetration and the signal-to-noise ratio of the eddy currents. The gain adjusts the amplitude of the signals. The phase rotates the signals on the complex plane. The filter removes unwanted noise and interference. The calibration mode defines the reference signal and the defect response.

3 Calibrate the probe

The third step is to calibrate the probe using a standard tube with known defects. The standard tube should have the same size, material, and configuration as the test tube, and should have artificial defects such as notches, holes, or pits that simulate the expected defect types and sizes. The probe is inserted into the standard tube and moved along its length. The signals from the defects are recorded and compared to the reference signal from the defect-free section of the tube. The calibration process ensures that the probe is working properly and that the signals are normalized and aligned.

4 Verify the calibration

The fourth step is to verify the calibration using a different standard tube or a different section of the same standard tube. The verification process is similar to the calibration process, except that the instrument settings are not changed. The verification process checks that the calibration is consistent and reproducible, and that the probe can detect the defects with the expected amplitude and phase.

5 Perform the inspection

The fifth step is to perform the inspection on the test tubes using the calibrated and verified probe and instrument. The inspection process involves inserting the probe into each test tube and moving it along its length at a constant speed. The signals from the test tubes are recorded and displayed on the instrument screen. The signals are analyzed for any anomalies or deviations from the reference signal that indicate corrosion or wall thinning.

6 Document the results

The final step is to document the results of the calibration, verification, and inspection processes. This documentation should include the probe type, serial number, frequency, and configuration; the instrument model, serial number, settings, and software version; the standard tube specifications, defect types, sizes, and locations; the test tube specifications, identification numbers, and locations; the signal plots, defect indications, and defect measurements; as well as the date, time, operator name, and client name. This provides a record of the test procedures, results, and quality assurance measures. Moreover, it facilitates the interpretation, reporting, and communication of the RFT findings.