LSAW Steel Pipe Weld And Ultrasonic Testing

1 What kinds of welding defects are common in welds? How are they formed?A: Common defects in welds are pores, slag inclusions, incomplete penetration, unfused and cracks.1) Porosity of the lsaw steel pipe is a gas generated by absorbing excessive gas or metallurgical reaction during welding of a molten pool at a high temperature during welding, and which is left in the weld metal before it is cooled and solidified. The main reason for the formation is that the electrode 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 of the welded joint is not completely penetrated. The main reason for this is that the welding current is too small, the speed of the moving rod is too fast, or the welding specifications are improper.3) Unfused means that the filler metal and the base material or the filler metal and the filler metal are not fused together. The main reason for the unfused is that the groove is not clean, the speed of the moving bar is too fast, the welding current is too small, and the angle of the welding rod is improper.4) Slag inclusion: refers to slag or non-metallic inclusions remaining in the weld metal after welding. The main reason for the slag inclusion is that the welding current is too small, the welding speed is too fast, and the cleaning is not clean, resulting in slag or non-metallic inclusions not being able to float.?5) Crack: refers to the gap that is partially broken 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. The hot crack is caused by the improper welding process during the welding; the cold crack is caused by the excessive welding stress, the hydrogen content in the flux of the welding rod is too high or the difference in the rigidity of the weldment is too large, often after the weldment is cooled to a certain temperature. ProducedLate crack; reheat crack is generally a crack generated by the weldment being reheated after welding (stress-relieving heat treatment or other heating process).

1. In the ultrasonic inspection of welds, why is it often used for transverse wave inspection?Answer: The pores and slag inclusions in the weld are three-dimensional defects, which are less harmful. Cracks, incomplete penetration, and unmelting are planar defects, which are highly harmful. In the weld flaw detection, due to the high impact of the reinforcement and the high-risk defects such as cracks, incomplete penetration and unfusion in the weld are often perpendicular or at a certain angle to the detection surface, transverse wave inspection is generally used.
2. When the transverse wave is inspected for welds, what are the principles for selecting the K value of the probe?A: The choice of probe K value should be considered from the following three aspects:1) Enable the sound beam to scan the entire weld cross section.2) Make the centerline of the sound beam as perpendicular as possible to the main dangerous defect.3) Ensure sufficient detection sensitivity.
3. What are the main functions of the oblique probe when the weld is flawed? What are the main functions?Answer: The zigzag inspection is a scanning method in which the front and rear, left and right, and corner scans are used together, and the probe is moved in a zigzag shape. You can check for defects in the weld.Scan left and right: A scanning method in which the probe moves in parallel along the direction of the weld. The longitudinal length of the weld can be inferred.Scan before and after: Infer the depth of the defect and its height.Corner scan: Determine the directionality of the defect.The front, back, left and right, and corner scans are performed simultaneously, and the maximum echo of the defect can be found to determine the defect position.Surround scan: Infer the shape of the defect.Parallel, oblique parallel inspection and cross-scan: detect lateral defects in the weld and heat affected zone.Tandem scan: Detects planar defects perpendicular to the flaw detection surface.
4. In weld flaw detection, how to determine the position of the defect in the weld?Answer: After the flaw detection wave is found, 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 positioning method of the defect is divided into:1) Sound path localization method: When the instrument adjusts the scanning speed according to the sound path 1:n, the method of determining the defect position is adopted.2) Horizontal positioning method: When the instrument adjusts the scanning speed by level 1:n, the method of determining the position of the defect is adopted.3) Depth positioning method: When the instrument adjusts the scanning speed by depth 1:n, the method of determining the position of the defect is adopted.
5. What are the methods for determining the length of the defect indication in weld flaw detection? What is the applicable situation?Answer: Defects found above the quantitative line or the quantitative line in the flaw detection shall be determined by the indicated length of the defect wave.The JB/T4130.3-2005 standard stipulates that when the defect wave has only one high point, the indicated length is measured by the 6dB method. When the defect wave has multiple high points and the endpoint wave height is in the II zone, the indicated length is measured by the end point 6dB method. When the defect wave is located in the I zone, if necessary, the evaluation line can be used as the absolute sensitivity to measure the indicated length.