Analysis of Common Weld Quality Defects and Detection of Grids
Welding quality defects are common in many construction projects, and they can significantly affect the structural integrity of a joint. One of the most noticeable issues is an improper weld height—either too high or too low. A well-executed weld should have a smooth transition from the base material, ensuring even distribution of stress. If the weld is too high, it may lead to stress concentration, while if it's too low, it could result in insufficient tensile strength. These issues can be identified using a weld inspection ruler, which helps determine whether the weld meets the required standards.
In cases where automatic gas-shielded welding is used, problems can arise if the groove angle is not properly adjusted or if the wire’s centerline is misaligned with the groove. This can cause incomplete fusion on one side of the weld, a defect that is more severe than undercut. The lack of proper wire oscillation during the process often leads to such issues, reducing the cross-sectional area of the weld and weakening the overall structure. Another serious issue is false soldering, where the base material isn't fully melted, and molten metal flows across the joint without actual fusion. In tension members, this can lead to catastrophic failure if the weak spot is pulled apart.
Other common defects include porosity, slag inclusions, crater cracks, and undercuts. While some undercuts are allowed within specific limits, other flaws must be completely avoided. Any weld that doesn’t meet the required standards should be repaired before final approval. These internal defects—such as lack of fusion or cracks—are typically detected using ultrasonic testing, which is essential for ensuring the safety and reliability of critical joints.
Due to the small diameter and thin walls of grid members, weld flaw detection can be challenging. When the entire grid structure is completed and ready for acceptance, it's important to check the height difference between adjacent supports. The difference should not exceed the allowable limit. However, when many supports are closed or difficult to access, physical measurements may not be feasible. In such cases, engineers rely on completion data for analysis and judgment.
Grid deflection and dimensional accuracy are also crucial indicators of the quality of the structure. Vertical and horizontal dimensions, along with deflection values, reflect the processing precision, installation accuracy, and design quality. Accurate measurements are necessary, especially for existing grids. Traditional steel tape measures may not be suitable for vertical or horizontal checks, so laser measuring tools are often preferred due to their speed, convenience, and precision.
To detect potential issues in ball joints, a ray vertical projection method is commonly used. This involves taking a film of the sleeve part of the joint, which clearly shows the number of threads on the bolt inside the sleeve. Since bolts of the same specification have standard thread lengths and numbers, this allows for quantitative calculations of how deep the bolt is screwed into the ball. By examining the image, it’s possible to determine if there is any gap between the bolt head and the cone sealing plate, which would indicate insufficient screwing depth.
The error calculation principle emphasizes minimizing negative deviations in readings to ensure a positive deviation in the bolt’s screwing depth. This approach ensures that the bolt meets all required specifications and maintains the structural integrity of the joint.
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