In the ultrasonic detection of DSAW tube, how to identify and determine the echo is a key problem. By analyzing the characteristics of actual ultrasonic inspection of double-sided submerged arc welded pipe seam, including segregation, the influence of ultrasonic defect signal or non-defect signal and pipe curvature radius on defect location is analyzed. Inclusions, cracks and base metal layers in ultrasonic echo signals. This paper summarizes the causes and identification methods of four kinds of pseudo-defect wave, such as the reflection wave of coupling agent, the reflection wave of welding surface, the reflection wave caused by dislocation of upper and lower weld seam, and the accuracy of identification of non-defect wave caused by weld height or undercut, which provides a new idea and direction for the actual ultrasonic testing of yaw pipe.


In the ultrasonic inspection of steel pipe welds, due to the characteristics of steel pipe welding process, besides the initial wave and defect wave, the oscilloscope screen will also have some other pseudo-defect echoes, which interfere with the defects. The following are the reasons for making four kinds of pseudo-defect waves and their identification methods.
(1) Coupling agent reflection wave
In theory, the thickness of the coupling layer needs to be an integral multiple of the radius. Coupling agent is too thick and fluidity is not good; the thickness of coupling layer is too thick to accumulate in front of the probe, and part of longitudinal wave reflected from piezoelectric wafer is converted into surface wave, which generates reflection signal, coupling agent, wave will disappear.


(2) Trace Reflected Waves on Welded Surface
This kind of reflection wave appears more frequently in the butt weld of steel pipe. Because of the deviation of the length of steel pipe and the cumulative error of multi-layer structure, the weld width of steel pipe is too large, and the road welding fraction is formed by multi-pass welding on the weld surface. When the ultrasonic scanning to the welding, it will cause weld marks, the reflected wave signal is not strong, slow, generally occurs in the first and second bottom wave slightly backward position. The identification method is to fix the probe, tap the weld seam lightly with a hand-immersed coupler and tap the wave lightly.


(3) Welding caused by dislocation of reflected wave
This reflected wave mainly occurs in the field butt weld detection of steel pipe, which is caused by the deviation of the axis when the pipe is connected up and down.


(4) Too high weld seam or bottom cutting formed by defect-free waveform
When the weld seam is too high or undercut, it is easy to form corner reflection, which affects the discrimination. The method calculates the distance of vocal tract accurately, determines the depth of defect or the horizontal position of defect wave according to the data displayed on the display screen, and taps the weld seam with hand-immersed coupler, such as reflected wave signal. There is a jump, and then the reflection of the wave is due to the welding height caused by the corner reflection, not the defect wave. Third, the weld height or scar is polished by manual grinding and then tested. If the reflection wave disappears, the reflection wave is a defect-free wave.