Is it necessary to ensure proper welding for pipeline valves?
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It’s a project I’m new to. The design institute requires that all valves on the gas pipelines be of the flanged type. However, for the actual connections, there is no need to use matching flange bolts; instead, the pipes are directly welded to the valves’ flanges, as welding is said to provide better sealing than flange connections. I was wondering if this is unreasonable? :In my opinion, this will cause two problems: 1. The valve body must be disassembled and the valve core removed during welding; otherwise, the valve core is likely to get damaged during the welding process. However, disassembling and reassembling it reduces the reliability of the valve. 2. Future maintenance will be a major problem; once it breaks, it cannot be disassembled and fire cutting will be necessary. I really don’t know why such a requirement exists. You all have broad experience; share your views.
Looking at the structure of the valve, if it is three-piece, this problem does not exist.
It’s true that welding provides better sealing than flange connections, but welding the pipe directly to the valve’s flange isn’t reasonable – at least it wouldn’t pass inspection.
According to the standards, as long as it meets those standards, it is considered qualified. However, welding is definitely better than flange connection; welded valves are typically used in high-pressure pipelines, and there is no need to disassemble the valve core in such valves.
The problem lies in the gas pipelines at normal pressure
Flanged valves must be connected using matching flanges of the appropriate type; it is not permissible to weld the pipes directly to the flange on the valve body. Especially for gas valves under high pressure, with a DN50 size or larger, this welding method of socket welding is not permitted.
If the valve is damaged, it’s difficult to remove, and it’s also not possible to install a blind flange.
I don’t understand the sentence ‘The pipe is directly welded to the valve’s flange’. What kind of procedure is this? How is it welded on?
This post was last edited by 690840741 on 2021-6-17 08:50. It’s definitely unreasonable; not only will it not meet the standards and thus fail acceptance, but... Grooves at welding sites are difficult to handle, resulting in poor stress distribution.