Root defect detection method for thick-wall large-diameter pipe butt weld

Abstract

The invention discloses a method for quantitatively and qualitatively detecting root defects when the butt-jointed seam of the prior thick-wall (the thickness is more than 40mm) big-diameter tube can only be detected from a single side by adopting one-vertical one-horizontal high-frequency and narrow-pulse double probes based on a digital ultrasonic defect detector. For a thin-wall tube or tube on which the two-side detection is allowed, the digital ultrasonic wave based defect detector also can be used in reference. The horizontal wave inclined probe is moved, a main acoustic beam can generate the strongest diffracted waves when hitting the top part of the root defects such as crack, incomplete fusion, lack of fusion and the like or root shape defect aberration serious parts such as welding beading, inward depression, misaligned edges and the like, and the vertical wave straight probe on the welding seam receives the strongest diffracted waves; the horizontal wave inclined probe can read out the depths of top points of the defects, and the thickness of the wall of parent metal on the side of the inclined probe can be measured by moving the vertical wave straight probe; therefore, the quantitation on six types of typical root defects is realized; and simultaneously, by combining the quantitative data such as heights and horizontal positions of the defects, which is measured by a one-vertical one-horizontal double probe strongest diffracted wave method, with the characteristics of the diffracted waves generated when the horizontal wave inclined probe rotates to detect, the qualitation on the six types of typical root defects is completed, thereby solving the problem that the root defects are difficultly judged when the butt-jointed seam of the thick-wall big-diameter tube can only be detected from the single side.

Description

technical field [0001] The invention relates to a detection method for butt weld root defects when thick-walled and large-diameter pipes in service can only be detected on one side. Quantitative and at the same time qualitative for root defects. For thin-walled pipes and those who allow double-sided detection, it can also be used as a reference. Background technique [0002] Butt welds of thick-walled large-diameter pipes in boilers in thermal power plants generally adopt the welding process of manual argon arc welding for bottom sealing, electric welding for covering, and single-side welding and double-side forming. Common root defects of welds mainly include cracks, unfused, unwelded There are three types of root forming defects: welding tumor, indentation and misalignment. During the ultrasonic inspection of pipeline butt welds, the judgment of root defects has always been a major problem, and these dissimilar steel welds connected to valve bodies, tees, etc. are the mo...

AI Technical Summary

Problems solved by technology

However, TOFD technology also has the following disadvantages: on both sides of the weld, there must be a position where the transmitting and receiving probes for TOFD detection can be placed; affected by side waves and bottom reflected waves, there are blind areas near the upper and lower surfaces; Since the intensity of the root defect diffraction signal is much smaller than that of the reflection signal, in order to improve the accuracy of detection, it is necessary to use a pre-amplification circuit to amplify the diffraction wave signal, but this will increase the noise at the same time; training and experience in

[0006] For the ultrasonic inspection of welded joints of thick-walled and large-diameter pipes, the pipe wall is thick and the sound path is long. Due to the effect of scattering and absorption, the sound beam attenuation is large, which affects the ability to detect defects.

At the same time, when ultrasonic waves are incident on workpieces with complex structures such as thick-walled and large-diameter pipe dissimilar steel welded joints, many interference signals will be generated, which will bring great difficulties to the correct judgment and location of defects.

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