First, how are the welds of these welded steel pipes formed?
Common defects in welds include pores, slag inclusions, incomplete penetration, incomplete fusion, and cracks.
1. Porosity is a cavity formed by absorbing excess gas or gas generated by a metallurgical reaction when the welding pool is at a high temperature during the welding process. It has no time to escape before cooling and solidifying and remains in the welded metal. The main reasons are that the welding rod or flux is not dried before welding, and the dirt on the surface of the weldment is not cleaned.
2. Incomplete penetration refers to the phenomenon that the base metal at the root of the welded joint is not penetrated. The main reasons are that the welding current is too small, the bar transport speed is too fast or the welding specifications are improper.
3. Not fused means that the filler metal and the base metal or the filler metal and the filler metal are not fused. The main reasons for the lack of fusion are that the groove is not clean, the rod transport speed is too fast, the welding current is too small, the angle of the welding rod is improper, etc.
4. Slag inclusion: refers to the slag or non-metallic inclusions remaining in the weld metal after welding. The main reason for slag inclusion is that the welding current is too small, the welding speed is too fast, and the cleaning is not clean so that the slag or non-metallic inclusions have no time to float.
5. Crack: refers to the gap that partially breaks in the heat-affected zone of the weld or base metal during or after welding. Cracks can be divided into hot cracks, cold cracks, and reheat cracks according to their causes. Hot cracks are caused by improper welding technology during welding; cold cracks are caused by excessive welding stress, excessive hydrogen content in the welding rod flux, or excessive difference in the rigidity of the weldment. They often occur after the weldment has cooled to temperature. Therefore, it is also called delayed cracks; reheat cracks are generally cracks caused by reheating the weldment after welding (stress relief heat treatment or other heating processes).
Second, in weld wave flaw detection, why is transverse wave flaw detection often used?
The pores and slag inclusions in the weld are three-dimensional defects and are less harmful. Cracks, incomplete welding, and incomplete fusion are planar defects that are very harmful. In weld flaw detection, due to the influence of high reinforcement and dangerous defects such as cracks, incomplete penetration, and lack of fusion in the weld, which are often perpendicular to or at an angle to the detection surface, transverse wave flaw detection is generally used. When conducting shear wave flaw detection on welds, what principles should be used to select the K value of the probe?
The selection of probe K value should consider the following three aspects:
1. Enable the sound beam to scan the entire weld cross-section.
2. Make the center line of the sound beam as perpendicular to the main dangerous defects as possible.
3. Ensure sufficient flaw detection sensitivity.
4. During weld flaw detection, what are the basic scanning methods of angle probes, and what are the main functions of each?
Zigzag inspection is a scanning method that uses front and rear, left and right, and corner scanning at the same time, and the probe moves in a zigzag shape. The welds can be inspected for defects.
Left and right scanning: A scanning method in which the probe moves parallel to the direction of the weld. The length of longitudinal defects in the weld can be inferred.
Front and back scanning: infer the depth of the defect and its height.
Corner scan: Determine the directionality of defects. By performing front-to-back, left-right, and corner scanning at the same time, relatively large echoes of defects can be found, and then the location of the defect can be determined.
Orbital scan: Infer defect shape.
Parallel, oblique parallel inspection and cross scanning: detect lateral defects in welds and heat-affected zones.
Tandem scanning: detects planar defects perpendicular to the detection surface.
Third, during weld flaw detection, how to determine the location of defects in the weld?
After the defect wave is found during weld flaw detection, the location of the defect in the actual weld should be determined based on 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, this method is used to determine the location of the defect.
2. Horizontal positioning method: When the instrument adjusts the scanning speed horizontally 1:n, this method is used to determine the location of the defect.
3. Depth positioning method: When the instrument adjusts the scanning speed according to the depth 1:n, this method is used to determine the location of the defect.
Fourth, in weld flaw detection, what are the methods for measuring the defect indication length? In what situations does each apply?
If defects located at or above the quantitative line are found during flaw detection, the indicated length of the defect wave must be measured. 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 indicated length. When the defective wave has multiple high points and the endpoint wave height is located in Zone II, use the endpoint 6dB method to measure its indicated length. When the defective wave is located in Zone I, if there is, the evaluation line can be used as the sensitivity to measure its indicated length.
Post time: Feb-19-2024