How to solve the misalignment problem of large-diameter steel pipes and improve welding quality

First, what are the causes of misalignment in large-diameter steel pipes?

1. The nominal outer diameter of large-diameter steel pipes has an allowable positive and negative deviation in the specifications at the time of manufacture. When the positive deviation meets the negative deviation, the total deviation will be the maximum. Or, the nominal outer diameter itself exceeds the specification, and the "nominal outer diameter" does not meet the standard.

2. Large-diameter steel pipes may undergo certain deformation during manufacturing, transportation, hoisting, and handling, resulting in "out-of-roundness" not meeting the standard.

Given the above-mentioned reasons related to the large-diameter steel pipes themselves, and given that the materials have already been delivered to the site and must be used, how can the construction be carried out to ensure quality?

Second, what measures can be taken to solve the misalignment problem of large-diameter steel pipes?

1. Optimize alignment measures and improve alignment equipment: Conduct tabletop exercises on how to correctly use external alignment tools for large-diameter steel pipes and combine them with current hoisting and positioning construction techniques and processes for large-diameter steel pipe connections. In other words, using a pipe alignment tool for correction is suitable for misalignments of 3mm or less, allowing for simultaneous correction and welding.

2. If the misalignment is greater than 5mm, or even exceeding 20mm, a pipe alignment tool cannot correct it. In this case, the pipe end of the large-diameter steel pipe needs to be cut to the size of the smaller end before welding. This requires an on-site plasma cutter, followed by mechanical correction using shavings. After correction, the cut opening is welded together.

3. Finally, during the welding of large-diameter steel pipe joints, attention must be paid to welding current, voltage, welding speed, and weld shape to avoid porosity, slag inclusions, concavity, incomplete penetration, cracks, etc. 24 hours after welding, ultrasonic or radiographic testing should be performed to ensure the quality of the treated area and joint.

Thirdly, the acceptance inspection of large-diameter steel pipe materials upon arrival must be strict.

Before the large-diameter steel pipes arrive on site, the laboratory thoroughly reviews and verifies the purchase contract and quality certification documents, including product certificates, material lists, anti-corrosion layer test reports, and weld quality test reports, ensuring that substandard materials are prevented from entering the project at the source. Visual Inspection: A comprehensive visual quality inspection is conducted on the large-diameter steel pipes. Surface quality is checked to ensure there are no serious unevenness; weld quality is crucial, and the welds of spiral submerged arc welded steel pipes should be uniform and continuous, free from defects such as porosity, slag inclusions, and cracks. The outer anti-corrosion layer should be intact and undamaged, without bubbles or peeling. Simultaneously, the out-of-roundness of the large-diameter steel pipe ends is checked to facilitate subsequent installation and connection. Dimensional and Geometric Accuracy: Using calipers, thickness gauges, and other tools, key dimensions such as the outer diameter, wall thickness, and length of the large-diameter steel pipes are accurately measured to ensure compliance with design specifications.