How can an electric gate valve with DN400 flange connections be converted to a welded version?
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Valve for the heating steam pipeline, DN400, with P=4.0 MPa and T=350°C; it is currently connected by flanges. Due to frequent steam leaks, the owner now requires that it be replaced with a welded connection. How can this be done? The cost of repurchasing is also high.
Study the latest case carefully; the design elements have already been included
Check the original design to see whether the pipeline installation with flange gaskets meets the design requirements. If no issues are found, have the design team review the pipeline setup again to determine why leaks occur frequently and how to eliminate pipeline stress; redesigning the pipeline is the fundamental solution. If replacing the valve is not desired, a long-term pressure-containing leak-sealing clamp can be considered (as it poses little risk from steam, subject to the owner’s approval). Furthermore, the design could be modified to use gaskets of a sealed-weld type, with the sides of the gasket being sealed by welding after the flanges are tightened; the downside is that it will be difficult to remove these gaskets when the valve needs to be repaired in the future.
There are 2 options: 1 is to replace the welded valve, and 2 is to change the material of the gasket and check whether its thickness meets the requirements; it must comply with the design specifications for pressure pipelines, and no arbitrary changes should be made.
How can this flange connection be changed to a welded connection?
Look at what was said last above. How to weld.
First, identify the cause of the leak, then contact the designer to seek a solution. Any changes to the design of the pressure pipeline must be handled carefully, and it is not possible to simply follow the owner’s requests. :lol
. Check whether the original flange is connected to the valve body by welding. If so, it is possible to cut away the flange along the weld or at the root of the flange, then grind the bevel before welding it to the pipe ； If not, it is necessary to check whether the valve housing is suitable for welding. When welding, care should be taken to ensure that heat is not applied too quickly. If the valve core material is not heat-resistant, it needs to be removed before welding. .
When leaks occur frequently, it’s necessary to find the cause of those leaks – whether it’s an inappropriate selection of gaskets, or unevenness or stress at the flange connections. Rough and careless welding is nothing but trying to cover up the problem
It seems that the pipe expansion joints might not be installed properly, which leads to temperature changes and stress on the pipes; this makes leaks more likely to occur at the flange connections. Additionally, it’s possible that the sealing gaskets chosen are not suitable – wave-shaped gaskets could be considered as an alternative