Welding process for the circumferential weld between the head and the cylinder of pressure vessels
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For storage tanks that do not have manholes but require flaw detection, there are generally two welding methods for the circumferential weld seam between the top head and the tank body: The first method involves filling the tank with argon gas (inert gas shielded welding), allowing for single-sided welding with double-sided completion. The second method: a gasket is placed between the upper head and the cylinder, with single-sided welding. I would like to ask everyone: from a cost perspective, at what volume level or below for equipment is the first option generally considered appropriate? At what volume in liters should one consider the second option?
There is no fixed answer to this question, as the volume of the equipment is not the main factor determining the choice of welding process. In fact, factors such as equipment design, types and properties of materials, and safety requirements have a greater impact on the selection of welding processes. The advantage of inert gas shielded welding is high weld quality, but the cost is also high; it is suitable for small devices or those with strict requirements regarding weld quality. The gasket welding method, on the other hand, has lower costs and is suitable for large-scale equipment or those where the requirements for welding quality are relatively low. However, the welding method to be used cannot be determined solely based on volume; a comprehensive evaluation taking into account actual conditions is necessary. If you need specific advice, it is recommended that you consult professional welding technicians or consulting firms. .
These two types of joints are independent of volume. The joint with a lining ring has limited applications: it cannot be used in environments with high stress, in cases of stress corrosion, or when the material is prone to delayed cracking; it also cannot be used in low-temperature containers. Moreover, the welding coefficient for joints with a lining ring cannot be set to 1. For less critical equipment, if it is permissible and one has experience in welding gaskets, using gaskets is cheaper; however, those without such experience are not advised to use them, as it is easy for depressions to form at the root of the weld due to the contraction that occurs as the molten pool solidifies.
Carbon steel equipment does not require argon filling; today’s TIG welding techniques for root pass welding are now quite common. Using shims affects the weld joint efficiency, so such practices have been largely abandoned
It is also possible to use TIG welding for the final circumferential weld as a backing layer, and to incorporate ultrasonic testing.
Stainless steel storage tanks need to be filled with argon; otherwise, they won’t pass the flaw detection
Currently, there is a self-shielded welding wire for TIG welding that does not require argon gas; you can ask your welding materials supplier about it.
Currently, TIG welding is generally used for the root welding; the second method has too many limitations and is not recommended.
Gas cylinders use liners inside them, and submerged arc welding is employed; pressure vessels generally do not require liners. According to the 150 standards, those with a pressure below 800 cannot be tested and thus do not need to undergo inspection.