The wave detection technology of straight seam steel pipe weld is a detection process that has gradually emerged in recent years. It is of great significance to improve the stability of straight seam steel pipe. Regarding the specific application and common problems of wave detection of straight seam steel pipe, we will bring you a specific content introduction:

First, what are the common welding defects in welds? How are they formed?
Common defects in welds include pores, slag inclusions, incomplete penetration, incomplete fusion, and cracks.
1. Porosity is the cavity formed by absorbing excessive gas or gas produced by the metallurgical reaction when the welding pool is at high temperature during welding, which does not have time to escape and remains in the weld metal before cooling and solidification. The main reason for its formation is that the welding rod or flux is not dried before welding, and the dirt on the surface of the weld is not cleaned up.
2. Incomplete penetration refers to the phenomenon that the parent material at the root of the weld joint is not fully melted. The main reason for the occurrence is that the welding current is too small, the rod feeding speed is too fast or the welding specification is improper.
3. Incomplete fusion refers to the lack of fusion between the filler metal and the parent material or between the filler metal and the filler metal. The main reasons for the lack of fusion are unclean grooves, too fast welding speed, too small welding current, improper welding rod angle, etc.
4. Slag inclusion: refers to the slag or non-metallic inclusions remaining in the weld metal after welding. The main reasons for the slag inclusion are too small welding current, too fast welding speed, and unclean cleaning, which causes the slag or non-metallic inclusions to float up in time.
5. Crack: refers to the local crack in the heat-affected zone of the weld or parent material during or after welding. Cracks can be divided into hot cracks, cold cracks, and reheating cracks according to their causes. Hot cracks are caused by improper welding processes during welding; cold cracks are caused by excessive welding stress, too high hydrogen content in the welding rod flux, or too large a difference in weld rigidity. They are often generated after the weld cools to temperature, so they are also called delayed cracks; reheating cracks are generally cracks caused by reheating the weld after welding (stress relief heat treatment or other heating process).

Second, why is shear wave testing often used in weld wave flaw detection?
Porosity and slag inclusions in welds are three-dimensional defects with less harm. Cracks, incomplete penetration, and incomplete fusion are planar defects with greater harm. In weld flaw detection, due to the influence of the reinforcement height and the fact that dangerous defects such as cracks, incomplete penetration, and incomplete fusion in welds are often perpendicular to or at an angle to the detection surface, shear wave flaw detection is generally used.

Third, when using shear wave flaw detection on welds, what principles should be followed to select the probe K value?
The selection of the probe K value should be considered from the following three aspects:
1. Make the sound beam able to scan the entire weld cross section.
2. Make the center line of the sound beam as perpendicular as possible to the main dangerous defect.
3. Ensure sufficient flaw detection sensitivity.
4. When testing welds, what are the basic scanning methods of oblique probes, and what are their main functions?
Sawtooth inspection is a scanning method that uses front and back, left and right, and corner scanning at the same time, and the probe moves in a zigzag shape. It can check whether there are defects in the weld.

Fourth, scanning method
Left-right scanning: a scanning method in which the probe moves parallel to the direction of the weld. The length of the longitudinal defect in the weld can be inferred.
Front-back scanning: infer the depth of the defect and its height.
Corner scanning: determine the directionality of the defect.
Front-back, left-right, and corner scanning are performed simultaneously to find the relatively large echo of the defect, and then determine the defect location.
Circular scanning: infer the shape of the defect.
Parallel, oblique parallel inspection and cross scanning: detect transverse defects in the weld and heat-affected zone.
Serial scanning: detect planar defects perpendicular to the inspection surface.

Fifth, how to determine the position of the defect in the weld during weld inspection?
After the defect wave is found in the weld inspection, the position of the defect in the actual weld should be determined according to the position of the defect wave on the oscilloscope screen. The defect positioning methods are divided into:
1. Sound path positioning method: when the instrument adjusts the scanning speed according to the sound path 1:n, the method of determining the defect position is used.
2. Horizontal positioning method: when the instrument adjusts the scanning speed according to the horizontal 1:n, the method of determining the defect position is used.
3. Depth positioning method: When the instrument adjusts the scanning speed according to the depth 1:n, the method used to determine the defect position is adopted.

Sixth, what are the methods for determining the defect indication length in weld flaw detection? What situations are they applicable to?
During flaw detection, defects located at or above the quantitative line should be determined to determine the indication length of the defect wave. The JB/T4130.3-2005 standard stipulates that when the defect wave has only one high point, the 6dB method is used to measure its indication length. When the defect wave has multiple high points and the endpoint wave height is located in zone II, the endpoint 6dB method is used to measure its indication length. When the defect wave is located in zone I, if there is, the evaluation line can be used as the sensitivity to measure its indication length.