# US RE48,734 E1 · Method and apparatus for determining the health and remaining service life of austenitic steel reformer tubes and the like > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US RE48,734 E1 - Document ID: USRE48734E1 - Status: Granted - Kind: E1 - Application number: 15/936,649 - Filed: 2018-03-27 - Granted: 2021-09-14 - Earliest claimed: 2012-12-10 - Assignees: ArcelorMittal - Applicants: Arcelormittal - Inventors: Michael A. Masleid; Zofia E. Niemczura; George B. Tsvik - Web page: https://patentgrep.com/patent/USRE48734E1 ## CPC - G01N 27/9046: {by analysing electrical signals} - G01N 27/82: for investigating the presence of flaws - G01N 27/83: by investigating stray magnetic fields - G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q) ## Abstract Testing methods and apparatus for testing the health of steel tubes used in reformers and other tubes and pipes used in other high temperature applications. The method includes the steps of transmitting two sinusoidal electromagnetic signals, each having a different frequency F1 and F2, into the reformer tube, receiving a response signal, and analyzing the received response signal's intermodulation frequencies to determine the state of the steel reformer tube. ## Claims ### Claim 1 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. ### Claim 2 (depends on 1) The method of claim 1, wherein said step of receiving a response signal from said test position includes receiving an analog response signal on a receiver coil. ### Claim 3 (depends on 2) The method of claim 2, 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. ### Claim 4 (depends on 3) The method of claim 3, wherein said analog to digital converter has a sampling frequency Fs. ### Claim 5 (depends on 4) The method of claim 4, 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. ### Claim 6 (depends on 5) The method of claim 5 1, wherein said sample size Ss is a is an integral power of 2. ### Claim 7 (depends on 6) The method of claim 6, wherein said sample size Ss is a number selected from the group consisting of 4096, 8192, and 16384 samples. ### Claim 8 (depends on 7) The method of claim 7, wherein said sampling frequency Fs is 44100 samples per second. ### Claim 9 (depends on 5) The method of claim 5, wherein said step of transmitting two sinusoidal electromagnetic signals includes the step of defining a base frequency F0, wherein F0=Fs/Ss. ### Claim 10 (depends on 9) The method of claim 9, wherein said step of transmitting two sinusoidal electromagnetic signals further includes the step of choosing said two frequencies F1 and F2 such that: F1=N×F0; F2=P×F0; where N and P are integers with N not equal to P, and N and P are chosen such that none of the intermodulation frequencies, F(Q,R)=Q×F1+R×F2 are equal to an integral multiple of F1 or F2 for small, non-zero, integer (positive or negative) values of Q and R. ### Claim 11 (depends on 1) The method of claim 1, wherein said step of transmitting two sinusoidal electromagnetic signals comprises transmitting both of said signals from a single transmitter coil. ### Claim 12 (depends on 1) The method of claim 1, wherein said step of transmitting two sinusoidal electromagnetic signals comprises transmitting each of said signals from individual transmitter coils. ### Claim 13 (depends on 12) The method of claim 12, 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 transmitting two sinusoidal electromagnetic signals comprises transmitting each of said signals from individual transmitter coils; and wherein said transmitter coils have a larger diameter than the thickness of the sample tube to be tested. ### Claim 14 (depends on 1) The method of claim 1, wherein said step of transmitting two sinusoidal electromagnetic signals comprises creating analog sinusoidal electromagnetic signals using at least one digital-to-analog signal generator. ### Claim 15 (depends on 14) The method of claim 14, wherein said two sinusoidal electromagnetic signals are created by two signal generators. ### Claim 16 (depends on 1) The method of claim 1, wherein said step of analyzing said received response signal's fundamental and intermodulation frequencies comprises analyzing the first order fundamental and the third order intermodulation frequencies of said received response signal. ### Claim 17 (depends on 16) The method of claim 16, wherein said fundamental is F2 and said third order intermodulation frequencies are 2F1+F2 and F1+2F2. ### Claim 18 (depends on 16) The method of claim 16, wherein said step of analyzing the third order intermodulation frequencies comprises converting the amplitude of said third order intermodulation frequencies into decibels dB relative to the amplitude of said fundamental. ### Claim 19 (depends on 18) The method of claim 18, wherein the strength of said third order intermodulation frequencies which have been converted into decibels dB is compared to the same measurement of brand new and end of service life austenitic steel reformer tubes, said comparison providing a qualitative measure of the health of said austenitic steel reformer tube. ### Claim 20 (depends on 19) The method of claim 19, 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 analyzing said received response signal's fundamental and intermodulation frequencies comprises analyzing the first order fundamental and the third order intermodulation frequencies of said received response signal; wherein said step of analyzing the third order intermodulation frequencies comprises converting the amplitude of said third order intermodulation frequencies into decibels dB relative to the amplitude of said fundamental; wherein the strength of said third order intermodulation frequencies which have been converted into decibels dB is compared to the same measurement of brand new and end of service life austenitic steel reformer tubes, said comparison providing a qualitative measure of the health of said austenitic steel reformer tube; and including the further step of estimating the remaining service life of said austenitic steel reformer tube as a fraction of the present service life of said austenitic steel reformer tube by the following formulas: fractional life remaining Lr=|Se−Sn|/|Se−S0|; and estimated lifetime remaining Tr=(Lr/(1−Lr))×Tn where: Lr is the estimated percentage of life remaining; Se is the third order intermodulation frequencies signal strength converted into decibels dB of an austenitic steel reformer tube at the end of service life; Sn is the third order intermodulation frequencies signal strength converted into decibels dB of the test sample now; S0 is either the third order intermodulation frequencies signal strength when there is no tube present under the probe, or the third order intermodulation frequencies signal strength of a new tube that has been heated to operating temperature for a few hours, whichever is higher; Tr is the estimated service lifetime remaining for the test sample; and Tn is the present service life of the test sample.