Seeking advice on flange material issues
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The process pipes are made of PN25, grade 20 steel, and the valves are wafer butterfly valves made of 316 material. The medium involved is hot air at 1.2 MPa and 400 degrees Celsius. I would like to ask everyone, what material is suitable for the flanges used in welding valves and pipes? Should it be consistent with the valve or with the pipeline? Similar to valves, the flanges and pipes involve welding of dissimilar steels. Similar to pipes, at the sealing interface where the flange meets the valve, due to differences in material and thus different coefficients of thermal expansion, could there be variations in deformation leading to leaks? In such a situation, how should one make a choice?
The material of the flange should be the same as that of the pipe.
It is recommended to use the same material for the pipes
The difference in deformation between carbon steel and stainless steel can be fully absorbed by the gaskets. I think you should consider another issue related to thermal expansion: wafer-type butterfly valves require long bolts, and the temperature of 400°C inside the pipe can cause expansion that may lead to leaks.
The main consideration is the long-term use of pipelines, as there are many uncertainties associated with welding dissimilar steels
The question you raised is something that needs to be considered, but it seems there’s no good solution for it at the moment It can only be tightened again after the system is running. Fortunately, it’s not a fluctuating temperature, so there’s little need to worry about it after tightening it once.
Pipe welding should avoid welding of dissimilar steels
Pipe welding should avoid welding of dissimilar steels
The disadvantages associated with welding dissimilar steels can be avoided through appropriate welding techniques; this is especially true for carbon steel and stainless steel. However, we shouldn’t overlook another issue: thermal deformation When two rights conflict, which one should be given priority?