Process connection of field instruments and transmitter pressure tapping valves in the chemical industry
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Question 1: Recently, while working on design selection, I encountered an issue. Regarding the process connections at the root valve where the pressure gauge and transmitter are connected on-site, the automation installation manual only provides options for socket welding and butt welding; in other words, the root valve is fixed to the branch pipe support through welding. Another design firm that can work with us has proposed another method of threaded connection. In other words, a single-threaded short connector is welded to the process pipeline, and it is connected to the externally threaded stop valve via threads. So I would like to ask the experts here: is this type of threaded connection feasible? If unavailable, please specify which standard indicates it. Question 2: Also, regarding the installation of pressure gauges and transmitters on equipment storage tanks, how is the installation method generally chosen? Is a flanged gate valve being used? Should the pressure gauge nozzle still be welded to the equipment? The method we have been using is to prepare the equipment by creating flange holes and using flanged gate valves. I’m not sure if this type of pressure gauge nozzle can be used on equipment storage tanks. Similarly, if there is a standard source, please indicate the name of the standard. I would like to thank everyone here.
1. Strictly speaking, there should be three types of connections: welding, threading, and flanging. The primary valve falls under the category of process valves, while the control valve is considered a secondary valve. For low pressures, threading is a viable connection method; for higher pressures, flanging or welding is used, with welding being preferred in cases of very high pressures. 2. For flanged pressure transmitters or pressure gauges, flanged gate valves should be used; if the medium is prone to condensation or scaling, flanged ball valves are recommended. Can we use a short nozzle referring to the answer to the first question? In any case, it’s best for the instrument to be equipped with two valves, namely a primary valve and a secondary valve