Discussion on precautions during flaw detection
Abstract:
Rail defects are easy to threaten the stability and safety of train operation, so it is necessary to do a good job of detection, so as to accurately judge the quality situation, so as to take measures to deal with the defects. At present, ultrasonic technology as a non-destructive testing technology, has been widely used, it can complete the testing work in a more convenient way, and the obtained results are accurate, short operation time, has the feasibility.
Welding quality is directly related to the quality and safety of engineering construction. In order to meet the needs of railway construction, transportation and convenient use, steel structure welding will be adopted to become a 50m-200m long rail. Therefore, it is necessary to clarify the technical requirements of non-destructive testing and relevant matters need to be paid attention to in the application process, and rational use of calibration instruments.
Comprehensive weld inspection:
1. Weld rail head flaw detection
To accurately determine the detection range of the top surface of the track, the probe can be moved longitudinally to scan there. Considering the limitation of the small contact area of the probe, it is appropriate to adopt the way of deflection longitudinal movement in order to comprehensively scan the weld rail head. In the detection work of the weld rail head, the distance between the probe and the weld center should be 80mm. When the diameter of the weld defect is smaller than the width of the ultrasonic beam, the ultrasonic beam reflection phenomenon can occur synchronously in the two places of the defect and the steel bar, and corresponding to the fluorescent screen, the defect wave and the welding rib contour wave can be displayed simultaneously. When the weld defect diameter is larger than the ultrasonic beam width, the display results will be different, and the fluorescent screen only displays the defect wave. The position of the two inclined probes is more suitable for the two sides of the rail head, that is, the two probes through synchronous longitudinal movement to complete the detection of the cross section.
n order to ensure the accuracy of the inspection results, before the formal operation, information such as the width of the weld and the width of the acoustic beam of the probe should be collected, and the scanning frequency and the location of the incident point can be determined after calculation, so as to carry out the detection work efficiently and ensure the reliability of the results. When there is no defect in the weld seam of the rail head, there is no echo display on the fluorescent screen. The sound wave of probe A reflects on the side of the rail head, but probe B cannot receive the echo. If the rail head has A flake defect, the ultrasonic wave of probe A is reflected at the defect and can be received by probe B. If the weld defect is outside the probe scanning area, there will be no echo display on the fluorescent screen.
2. Weld rail waist inspection
(1) The straight probe is placed in the longitudinal middle area of the rail surface, and the probe is moved along the longitudinal. This method can be used to detect the defect that the reflection surface is parallel to the detection surface in the weld.
(2) The scattering phenomenon occurs when there are defects in the rail weld, which makes it difficult for sound waves to form enough reflection energy at the bottom of the rail. If there is a slanting defect, the bottom wave of the orbit will disappear in the detection results.
(3) The tandem reflection method is a more suitable method for the vertical rail plane flaked defects. It can realize the full-section scanning by placing two probes on a probe surface and making them move longitude-synchronous at the same time, and adjusting the probe distance properly during the process. After the probe collection, the summary of rail reflection echo, can not identify rail defects. Through the application of wavelet analysis method, it can achieve the effect of simultaneously analyzing signal visual area and frequency domain. Therefore, the method of wavelet analysis can be used to reconstruct the characteristic signal of the defect, during which the refined spectrum analysis combined with Hilbert demodulation can generate more comprehensive rail defect information, and the location of the defect can be accurately judged according to the obtained information.
3. Weld rail bottom flaw detection
The bottom of the rail can be divided into two main areas, the two sides of the rail bottom and the connecting part of the rail waist and the rail bottom. According to the corresponding relationship between the bottom Angle of the rail and the sound beam, the bottom Angle of the rail can be further divided to form six detection areas. The probe can be moved longitudinally to complete the detection work.
Scanning the bottom Angle 1-3 area of the rail, taking the center of the weld as the reference, the distance between the probe incident point and it is 65mm, it can be found that the detection results at this time show the contour wave on the welding rib. When the distance between the two increases to 90mm, the content displayed will change, that is, the lower contour wave is displayed. Scan the bottom Angle 4-6 area of the rail, when the spacing is 95mm, the contour wave on the welding rib will be displayed. From the Angle of defect diameter and ultrasonic beam width, the analysis is divided into two cases: when the former is smaller than the latter, the welding rib wave and the defect wave are displayed; When the former is greater than the latter, only defect waves are displayed.