Instrument issues, process interface problems – seeking help
Thread Content
In accordance with the requirements of Article 4.2.5 of the \"Code for Installation and Design of Petrochemical Instruments\" (SHT 3104-2013), instruments used to measure toxic media shall not employ threaded process connections. I have a question: 1. What is a process interface? 2. Can’t threaded connectors be used for the pressure gauge ports of those pressure vessel equipment? If the gauge port of the equipment is fitted with a flange, but most of the gauges use threaded connections, there are still threads after all. 3. According to the Fixed Volume Regulations, a needle valve or a three-way stopcock is required in front of a pressure gauge. However, what should be done in cases where the needle valve has flange connections for both the inlet and outlet? Use a stop valve?
1. A process interface refers to the part that connects the process piping and instrumentation, used to enable the transfer of media from the piping to the instruments. 2. For pressure gauges used to measure toxic media, threaded connections should indeed be avoided, and flange connections can be used instead. Although pressure gauges usually have threaded connections, the interface type can be changed by using adapters or connectors with flanges to meet regulatory requirements. 3. Regarding the valve in front of the pressure gauge, if there are no needle valves or three-way plug valves that meet the specifications available on the market, globe valves or other types of valves can be considered, provided that their safety and suitability are ensured. It is also necessary to consult relevant engineers or experts to confirm whether they meet the required usage conditions and safety standards. .
Regarding the second point, conversion through an adapter – after all, a wire connector is still present in this connection process. For example, as shown in this diagram:
In cases involving toxic media, special attention must indeed be paid to the sealing and safety of the interfaces. Even when changing from a threaded connection to a flanged connection using an adapter, the threaded portion still poses a potential leakage risk. Regarding your concerns, here are several possible solutions: – Use high-quality sealing materials and techniques to ensure the tightness of the threaded connections, such as special sealants or sturdy custom-made gaskets. - A fully welded process interface is used to eliminate the risk of leakage caused by threads, especially in applications involving high-risk media. - Consider redesigning the piping and instrumentation connections, using flanges or other threadless connection methods whenever possible. In short, it is important to ensure the integrity and sealing of all connection points; especially when dealing with hazardous or toxic substances, relevant regulations and safety standards must be followed, and expert advice should be sought when necessary. .
You’ve chosen the wrong picture; a flanged diaphragm pressure gauge looks like this – it has a diaphragm filled with silicone oil at the bottom, which means it is a single-flange pressure gauge. In practice, this is also the way people handle flammable materials on site. Also, who said that flanged needle valves don’t exist? I’ve seen tons of them on site; you just need to search for flanged globe valves. Furthermore, most suppliers prefer welding root valves, as they meet the requirements and are also cheaper.
Flanged globe valves and flanged needle valves are not exactly the same, right?
If we stick strictly to the literal words, then it’s definitely different. The appearance and principle are the same; it’s just the valve core that differs. It’s difficult to find pictures of flanged needle valves, so it’s better to look for pictures of flanged globe valves – their appearance can help you understand them better.
This interface refers to the connection point between the process and the instrumentation. Section 3.14 of SHT 3104-2013 contains definitions of terms. In fact, the first valve that connects the process to the instrument must be a welded valve.