Issues regarding the final circumferential weld of pressure vessels and the welding of nozzles at the vessel’s openings
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It’s been a long time since I’ve worked with manufacturing processes. Recently, I encountered a problem in my design and would appreciate some guidance from those who are more experienced. Thank you! Problem: A separation tank with dimensions of φ500×1500, made entirely of S30408 material. The pressure is 0.65 Mpa, the temperature is 60℃, and the wall thickness is 8 mm. There are openings on the tank body: one with a diameter of DN 100, two with a diameter of DN 200, and two with a diameter of DN 20. Question: 1. Regarding the opening at the joint, is welding carried out before or after the final ring weld? This is related to whether the fillet welds at the joint can be welded on both sides and achieved with full penetration. 2. If the final circumferential weld is carried out after the butt welding, will the cylinder deform, thereby affecting alignment and the quality of the welds?
1. The opening for takeover and welding are generally carried out after the welding of the final ring seam; TIG welding can be used as a root pass to ensure full penetration. 2. If the final circumferential weld is carried out after the takeover welding, the cylinder may deform, affecting alignment and weld quality.
For a container of φ500×1500, it is extremely difficult, and practically impossible, to achieve double-sided welding on the corner welds of the cylinder shell. Of course, from the perspective of ensuring the quality of the backside formation, it is possible to first weld a head or not weld any heads at all (this depends on the location of the openings and the size of the holes closest to the head); after that, the openings are made, the tubes are butt-welded, and a bottom weld is performed on the outside of the cylinder. If the backside formation is not satisfactory, appropriate repair welding can be carried out on the inside. After the head assembly welding is completed, the remaining passes of the nozzle fillet welds are welded.
L=1500, it’s that short. . 500 inner diameter; the circumferential weld is reserved for welding last. . . Weld the pipe fittings first. . For any type of takeover, with your insert-type design, achieving single-sided welding with double-sided formation results in almost 0 error. . . It’s achievable if using a saddle. . The problem is that many designs are not chosen. .
1. TIG welding can be used for the root pass； 2. Yes, the last circumferential weld should be welded first