How is the groove made for the opening in the cylinder?
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When welding the cylinder body of a pressure vessel to its nozzles, full penetration is required. But how should the groove at the opening be prepared in order to achieve maximum precision and ensure full penetration? This post was last edited by Lan Meng on 2009-3-19 09:15]
Small pipes can be drilled, but large pipes probably can only be cut with gas.
The small nozzles on the small cylinders can be drilled using a drilling machine, while the rest can only be cut by gas cutting; however, gas cutting makes it difficult to ensure precise dimensions. However, the groove must be ground, and where possible, welding on both the inside and outside should be performed to ensure full penetration.
Due to the issue with cracks, workers find it difficult to achieve full penetration, which affects the quality of welding. Is there any good way to solve this problem?
Building on what was discussed on the 3rd floor, a welding method that uses TIG welding for the root pass and shielded metal arc welding for the cover pass can be employed to ensure good penetration.
What we do now is to use gas cutting to create the holes and then grind them, which is time-consuming and labor-intensive. Moreover, the quality of full penetration welding is not satisfactory; it’s better when welding on both sides. But in cases where welding must be done on only one side, it’s possible to detect that full penetration has not been achieved simply by putting a hand inside the pipe connection, and this is a difficult problem to resolve!
Thin-walled sheet cylinders can be shaped and polished using an angle grinder or an electric shaping tool, while larger openings can be created with specialized pipe hole cutters or cutters for intersecting pipe ends.
Hole machining is generally done manually or mechanically; it’s quite difficult, so double-sided welding should be preferred whenever possible.
I’ve seen that in foreign pressure vessel manufacturing plants, holes are made in flat sheets and bevels are created using specialized machines, after which the sheets are rolled up (of course, the precision of the rolling machines must be high)
For those that can be welded on both sides, cleaning the back side first and then welding; for those that cannot be welded on both sides, TIG welding is used for the root pass.
TIG welding is costly and not fast either
Some manufacturers also employ advanced CNC cutting technology; after using software such as FastCAM for computer programming, the cutting and drilling of the flat sheets are carried out in one step, followed by the rolling of the cylinder shells. This approach ensures the quality of the grooves, laying a solid foundation for welding the joints.
Our factory uses gas cutting, so the quality is probably a bit lower