When welding pipes, the wall thickness grades of the main pipe and the branch pipes are different; how should a tee be selected?
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This post was last edited by dpclove21 on 2017-11-25 at 11:10. During the on-site piping work, it was found that the wall thickness grades of the main pipes and branch pipes were different: the main pipes had a SHC30 grade, while the branch pipes had an SCH40 grade. The tees used were of SHC40 grade. When matching the flanges of the main pipes, it was observed that the misalignment between them was 1-2 mm. Question: 1. Is a deviation of 1-2 mm between the edges acceptable? Can grooving be done for treatment? 2. If the wall thickness grades of the main pipe and branch pipes are different, how should a tee be selected? There are also cases on site where the grades differ even more, with the main pipe being SHC30 while the branch pipes use SCH80 – how should this be handled?
It is normal for wall thickness grades to vary; when the wall thickness grade remains the same, the larger the diameter, the thicker the wall thickness. Therefore, in low-pressure pipelines (where corrosion and stiffness considerations are important), different wall thickness grades may occur when the same wall thickness is chosen. This is reasonable.
The problem is that the wall thicknesses are also different, and the misalignment when installing the pipes is 1-2 mm
Select the tee SCH according to the supervisor’s specification; it’s normal for the SCH values to differ, as some pipe diameters don’t have a corresponding SCH value, so a higher one is chosen. For walls with different thicknesses, grooves can be made in accordance with the specifications and then welding can be carried out directly – there is no problem with that
An error of no more than 3 mm is acceptable