Method and apparatus for determining the health and remaining service life of austenitic steel reformer tubes and the like

A method of testing an austenitic steel reformer tube comprising:

• providing a sample austenitic steel reformer tube to be tested;
• choosing one or more testing positions on said an austenitic steel reformer tube;
• transmitting two sinusoidal electromagnetic signals, each having a different frequency F1 and F2, into a test position on the austenitic steel reformer tube;
• receiving a response signal from said test position;
• and
• analyzing said received response signal's fundamental and intermodulation frequencies to determine the state of the austenitic steel reformer tube at said test position;
• wherein said step of receiving a response signal from said test position includes receiving an analog response signal on a receiver coil;
• wherein said step of receiving a response signal from said test position further includes the step of converting said analog response signal to a digital response signal, using an analog to digital converter;
• wherein said analog to digital converter has a sampling frequency Fs;
• and
• wherein said step of converting said analog response signal to a digital response signal, using an analog to digital converter includes combining a multiple of samples into a single representative sample, the number of samples which are combined into said single representative sample being designated the sample size Ss.