How do people handle the cutting of the cylinder shells for pressure vessel equipment and the reservation of gaps for assembly?
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When welding the longitudinal seams and performing seam alignment before welding the circumferential seams of carbon steel and stainless steel pressure vessel shells, there is a problem of weld shrinkage. I would like to ask how others handle this issue. When cutting the cylinder sections using marking lines, by how many millimeters should the perimeter of each section be increased, or should the cutting be done based on theoretical values? Weld shrinkage occurs whenever cylinders are fitted together (that is, at the circumferential welds); how many millimeters of gap should be left when using TIG welding for the root pass?
It is included in the 2020 version of the HG202580 six-in-one standard, but it is also based on empirical cutting methods
When cutting the material, we also need to add a certain amount of process allowance; this is mainly based on experience and takes into account the thickness of the head plate. The alignment gap shall be determined in accordance with the welding procedure sheet, or the welding joint diagram on the drawings, or 20583
A theoretical calculation is carried out based on the diameter, and then a small amount is added empirically, but not too much. For TIG welding, 2–5 mm is generally reserved, depending on factors such as thickness, location, and the welder’s skill level.
Material should be cut according to the theoretical values, with a weld gap of two millimeters and moderate shrinkage. Generally, it does not exceed two millimeters