Ultrasonic inspection of thin wall tubing

Keywords:ultrasonic inspection, thin wall tubing
Ultrasonic inspection of thin wall tubing is as follows:
(1) Detection method. Ultrasonic inspection of thin wall tubing is mainly carried out by automatic detection. The forms are:
① The probe is fixed, and the steel pipe is spirally advanced by the mechanical transmission device, so that the probe moves relative to the axis of the pipe. A single-wafer water immersion line focusing probe and a single-channel A-type pulse reflection ultrasonic flaw detector are usually used to detect the longitudinal (distribution along the axis of the tube) defects in the inner and outer walls of the tube.

② The pipe is rotated by the mechanical transmission equipment. The probe is driven by the drive trolley to move at a uniform speed along the axis of the pipe. The probes, instruments and detection defects used are the same as ①. 

③ While the probe is rotating, the pipe is fed straight by the mechanical transmission equipment. Generally, multiple probes with different functions and different forms are used. The multi-channel ultrasonic flaw detector is used to simultaneously detect the longitudinal, lateral and layer defects of the inner and outer walls of the pipe. At the same time, the wall thickness of the tube is measured and the ellipticity is checked.

The detection method has a high degree of automation, and can simultaneously detect multi-directional defects, and can be combined with a micro-processor or an automatic multi-recorder for automatic print recording, quality sorting and the like.

(2) Detection frequency. Due to the thin wall thickness of the tube and the small size for effective pairing. The defects are detected and generally use a frequency of 5 MHz or higher.

(3) Acoustic coupling.
Regardless of the detection method used, water-treated water is used as a coupling agent in the ultrasonic testing of small-diameter thin-walled tubes. The basic requirement is to ensure that the water is sufficiently wetted on the surface of the steel pipe without generating blisters and reducing the corrosion of water on the steel pipe material. 

(4) Acoustic wave incident angle adjustment. 
① Horizontal offset method: the axis of the probe is adjusted parallel to the central axis OP of the tube, and the distance from the OP-segment is translated, which is called the eccentricity X (determined by the incident angle of the acoustic wave), so that the sound wave is inclined to the surface of the tube. After being refracted, it is transmitted inside the pipe material and is guaranteed to reach the inner wall of the pipe.

② Deflection method: the axis of the probe coincides with the central axis OP of the tube, and the pivot point on the probe is deflected by a certain angle, so that the sound wave is inclined to the surface of the pipe, and is refracted and transmitted to the inside of the pipe material.