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Three Gorges power plant row of ultrasonic testing of steel sand

The following reasons: (1) the process of sound wave transmission. Thick as grass-roots side, the speed of sound changes and the impact of the grain scattering attenuation will be relatively improved. (2) The welding process in the transition layer and complex layer of grass-roots very different physical properties, stainless steel core resistance welding large (about 4 ~ 5 times carbon steel), could easily lead to cracking of drug skin redness, affect the welding process stability and weld quality, welding, such as the strict control of the cooling rate, compared with the control fusion inappropriate, improper operating practices welder, there is bound to increase the interlayer slag, not fusion, the probability of welding defects such as crack,[link widoczny dla zalogowanych], the other under the substrate groove surface is so large, face detection can be effective at the grassroots level to use a wave (ie direct wave) scan found defects in the transition layer, is conducive to location, nature of the accuracy and reliability of the welding quality assurance Secondly, stratified side wall inspection. Mainly for purposes of expansion joints. Because the welding joints in the concrete pouring is completed,[link widoczny dla zalogowanych], the form of V-groove weld with a plate, so the testing only when the inner wall of stainless steel from the face of it for testing. At this time most of the second wave to take advantage of defects in the transition layer carefully observed. Speed should not be too fast, suspicious waveform, should be used first and second waves comprehensive judgments. However. Should not be ignored in the first wave appears waveform. Especially in the beginning of the phenomenon of pulse waveform near the swimming. Because in the case of the right way, a wave can also be found near the surface defects in 5 ~ 8mm. 3.2 The volatility of the curve from the production of a drawing from an amplitude curve in the front, after the reference block with a self-velocity test of the composite board was informed that the longitudinal wave velocity is 5945m / s, the shear wave velocity of about half of the longitudinal wave velocity, so shear wave velocity is 3260m / s. Reference to JB4730-94 standard ultrasound examination papers, with the CSK Ⅲ A test block of a drawing from a volatility curve, the curve by the evaluation line (EL),[link widoczny dla zalogowanych], quantitative line (SL), sentenced to waste line (RL) consists in the thickness is greater than 15 \~ 46mm range of the assessed line is l × 6-9dB, quantitative line is l × 6-3dB, sentenced to waste line is l × 6 +5 dB, considering the surface acoustic energy compensation 4dB, drawn from a volatility curve as shown in Figure l instructions. Evaluation of the sensitivity testing is not less than cable, the actual testing, the use of a reflection method for evaluation of line j2 『l × 6-15dB, as the detection sensitivity, when the defect is discovered,[link widoczny dla zalogowanych], the difference is again a wave or secondary wave found defects. Then the endpoint 6dB 6dB law or length measurement and classification methods. 3.3 examples of instruments: Hs 400 digital ultrasonic flaw detector for a probe size: 2.5P13Xl3K2 a D, detection sensitivity: 1 × 6-15dB, the surface of Compensation: 4dB19l was ll Example 1 (wall testing):. Flaw in the movement of expansion joint (see Figure 2) found that a defective weld in the reflected wave (see Figure 3) on analysis (see Figure 4) to determine the defect as a crack,[link widoczny dla zalogowanych], with the endpoint 6dB its length measurement method, location parameters are as follows: H = 5 ~ 8mm, △ L a 350mm, SL +13.5 dB. And retesting with the second wave got the same results (Figure 5, Figure 6, Figure 7), supplemented by anatomy coloring test to prove that the defect is intermittent crack. Consistent with the results of ultrasonic testing. Flow Figure 2 Figure 3 Figure 420 NDT (bimonthly) 3 2002 Figure 5 Figure 6 Figure 8 slag (substrate layer) Figure 9 Example 2 cracks (primary side testing): In the inspection of girth in the other that the surface of the flaw from the grass roots movement, can effectively discover the substrate, transition layer and stainless steel weld defects (see Figure 8 and Figure 9, Figure 10, Figure ll, Figure 12), the latter confirmed by anatomical defects in basically meet the determined results. Figure 11 to fusion (transition layer) Figure 12 slag (over set layer) 4 Concluding remarks by the above method for detection of composite welds. Longitudinal seam measured four hundred articles (both with primary side detection), girth more than two hundred articles. Determination of weld defects, and autopsy were consistent with the facts. Effectively ensure the steel lining of the Three Gorges row of sand bore pipe welding quality. But in the testing process there are several issues worth noting: (1) pay special attention to the underside of the waveform and the reflected wave in the wall near the detection, the pulse near the beginning of the waveform, prevent undetected. (2) easy fast moving speed, moving the process of moving strictly to do the interval between two probes to ensure that the width of at least 10 overlapping probe and the probe for 10. 15. Rotation, tilt weld defects prevent undetected. Therefore, as long as the right way, strict implementation process of order, with the wave angle probe testing, but also can effectively guarantee the quality of the welding seam compound.

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