Ultrasonic inspection method utilizing resonant phenomena

An ultrasonic inspection method utilizing a resonance phenomenon of continuously transmitting a wideband ultrasonic wave by a transmission probe and receiving a wideband ultrasonic wave from an inspection target by a reception probe,

• wherein a measurement is performed with the transmission probe and the reception probe being located on a surface of a cylindrical pipe on a cross-section perpendicular to a direction along a cylindrical axis of the pipe, where the length of a line segment connecting the centers of the pair of probes is labeled as “a” and the line segment is matched to the direction along the cylindrical axis of the cylindrical pipe;
• the method comprising:
• executing a first step of transmitting a wideband ultrasonic wave from the transmission probe toward the central point of the cross-section of the cylindrical pipe by an externally specified number of times (nB);
• receiving a wideband received wave by the reception probe each time when the transmission is performed;
• and adding the nB number of the wideband received waves G1(t) obtained in accordance with the specified number of times at a position of the receipt and averaging the addition result with a time area;
• executing the first step each time when the line segment connecting the pair of probes is translated with respect to the direction along the cylindrical axis of the pipe on the surface of the pipe on the cross-section perpendicular to the axis of the pipe by a predefined or externally given predetermined value ΔL while the pair of probes are kept as distanced by the interval “a”;
• and executing a second step of performing the first step by an externally given predetermined number of times nA and thus obtaining all the wideband received waves Gj(t) (j=1 through nA);
• executing a third step of calculating a longitudinal primary resonant frequency f1 which has a relationship with a thickness of the inspection target by:
• ∫1=106/(2W÷VP) [Expression 16]
• where the thickness of the inspection target is W (mm), the longitudinal wave sonic speed is VP (mm/gsec) and the sonic speed ratio of a transverse wave and the longitudinal wave is γ1, and calculating a primary resonant frequency fS1 of the transverse wave generated by mode conversion by:
• ƒs1=γ1·ƒ1 [Expression 17]
• ;
• and
• successively performing analyses of step 4, step 5 and step 6 shown below using sizing coefficients ns1, ns2, ns3 and ns4 for inspecting, at high precision, presence/absence of a flaw of the inspection target and time-wise development of the flaw, and using a comparative display of the obtained component waves GAj(t) to analyze the presence/absence of the flaw in a thickness in a radial direction of the cross-section of the pipe on a line extended from the line segment connecting the centers of the transmission probe and the reception probe and to analyze a position of the flaw in the direction along the cylindrical axis of the pipe:
• step 4:
• step by which Gj(t) is processed by Fourier transformation to find Fj(f), n is an integer of 1 or greater, fST=n·f1 or fST=n·fS1 is found to create an arbitrarily-defined frequency function S(f) which has an increasing function of f=0 through fST, is 1.0 when f=fST,
• has a decreasing function of f=fST through 2fST and is 0.0 when f≧2fST, an FAj(t) function is found by:
• FAj(f)=S(f)S4·Fj(f) [Expression 8]
• using the sizing coefficient ns4, and the corresponding component wave GAj(t) is found by:
• GA
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• step 5:
• step by which a maximum amplitude of each component wave GAj(t) (j=1 through nA) obtained in step 4 is found and labeled as Aj, the maximum value among Aj is labeled as Amax, the component wave GAj(t) which fulfills Aj≧(1/ns1)Amax is replaced with (Amax/Aj)GAj(t), a G Aj(t) wave calculated by:
• G{tilde over ( )}Aj(t)=(1/Amax)GAj(t) [Expression 6]
• is created, and the component wave GAj(t) is replaced with G{tilde over ( )}Aj(t);
• step 6:
• step by which an ns3·GAjns2(t) wave is created using the sizing coefficients ns2 and ns3, and the GAj(t) wave is replaced with the ns3·GAjns2(t) wave.