| Small-diameter austenitic stainless steel tube is widely used in petrochemical industry and nuclear power industry, the weld of it has a characteristic of structural heterogeneity, thin wall, large curvature, it makes ultrasonic testing to be a technical problem, therefore developing a kind of UT technology for austenitic stainless steel butt weld in small-diameter tube, to improve the ability of defect detection is very necessary.In order to enhance ultrasonic testing effect of austenitic stainless steel weld, improve sensitivity and signal-to-noise ratio, based on theory analysis, a new detection method is proposed——critically refracted longitudinal wave(LCR)method.First,Three kinds of tube specimens with different welding methods of austenitic stainless steel and carbon steel are prepared, through metallographic analysis and ultrasonic testing on the samples, the influence of microstructure of austenitic welds on ultrasonic detection is studied.To verify the application feasibility of this method, LCR probe with narrow pulse and double crystal is developed. At the same time, the frequency spectrum characteristic of the probe is tested.Calibration block, reference block, and defect analog sample are designed and made out which meet the demand of testing defects. LCR probes are tested on the calibration block, with the performance and sound field characteristic of probes studied. Then probes are tested on reference block to detect artificial defects, furthermore, probes are tested on analog sample to detect analog defects. With comparison of radiographic testing on analog sample, detection effect of LCR probes is analyzed.Experimental results show that coarse crystal characteristic of austenitic welds has certain effects on the ultrasonic detection, and LCR probes can achieve the purpose of testing austenitic stainless steel butt weld in small-diameter tube, with accuracy and detection rate improved, the defect detection sensitivity and the signal-to-noise ratio is also improved. |
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