What are the requirements for installing switches on pipeline valves?
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Valves are installed on pipelines; valves connected by flanges or threads should be in a closed state, while those connected by welding should be in an open state. Why is this?
It seems like they should all be in the open state, to prevent foreign objects from entering and damaging the spherical surface
Article 10.2.16 of the \"Technical Specifications for the Construction of Petrochemical Instrumentation Projects SH/T 3521-2007\" specifies that, in accordance with the GB/T 20801.1–6-2006 standards for pressure pipelines – industrial pipelines – valves connected by flanges should be closed during installation, in order to prevent impurities from entering during the installation process; such impurities could otherwise fall onto or stick to the valve seals, leading to seal leakage. It should be opened when installed via welded connections. Due to thermal expansion and contraction, the high temperatures during welding cause the gas inside the valve cavity to expand.
Flanges and threads are vulnerable to the intrusion of impurities, which can damage the seal； Welding should be done with the gas turned on, as the gas expands during welding
I don’t quite understand it. When the ball valve is open, impurities can’t get into the sealing surface anyway. If it’s closed, the spherical surface is more likely to get damaged. Also, when welding, it’s not a problem if impurities get in when the valve is open