In order to detect LSAW longitudinal weld defects in the weld total length of horizontal or vertical use jet (water column) coupled ultrasonic flaw detection. Jet (water column) ultrasonic flaw detection is between the probe and the pipe coupling by jet, so that the longitudinal wave probe beam emitted by the incident to the interface of water or steel pipe, a steel pipe weld inspection by pure shear wave conversion. Therefore, to achieve the weld pure shear testing, the incident angle of the probe must be between Ⅰ critical angle and the critical angle II, drawn by the law of refraction. Can be obtained by calculating the longitudinal wave is incident from the water to the steel in the first critical angle I and II were critical angle 14.5 ° and 27.3 °.

Longitudinal ultrasonic testing: non-destructive testing is on-site detection, rapid non-destructive, without having to reach the lab, greatly improving efficiency. Analysis speed is much faster than desktop spectrometer, only a few seconds to display the results of the analysis. Small size, light weight, easy to carry.

NDT ultrasonic flaw detection for very many, testing principle Longitudinal not divided: ultrasonic testing, X-ray testing, testing film. Testing methods are: single-sided double-sided testing, double-sided double-sided testing, single-sided unilateral testing.

The choice of which depends on the testing straight seam steel pipe wall thickness and width of the weld, the weld testing if too wide on one side of the double-sided double-sided or double-sided testing (generally used for thick seam width) of Implementation of the standards: GB 11345-89 (most common), GB / T11345-2013. DW1.1 standard inside a two minute testing, usually less demanding steel structure is three testing no matter what standard testing must meet the requirements of customers in accordance with the national standard steel pipe testing to a weld two.