Regarding the material selection for instrument air pipelines

If possible, it is of course best to use stainless steel; however, the cost is several times higher, and it also helps prevent issues such as rust from affecting the quality of the air used in the instruments. Using welding is certainly no problem; it’s best to require TIG welding in all cases, as this prevents the formation of slag

Galvanized pipes will do; use threaded joints for the connections – using stainless steel would be a bit too expensive

Ordinary industrial galvanized steel pipes are sufficient. But in the food industry, stainless steel must be used.

The main pipes and branch pipes of the instrument air pipeline are basically made of galvanized steel pipes, while the actuators of the control valves are generally made of stainless steel. It would be ideal to use 304 or 316 instead, but the cost is too high. As for welding issues, TIG welding is no problem as long as the pipes are thoroughly purged after piping.

For general chemical and petroleum applications, galvanized pipes are sufficient; there is no need to use stainless steel pipes. As for the use of threaded connections, it is done for safety reasons, to prevent weld slag and other debris from getting inside the pipes and jamming the instruments. Although TIG welding can be used, it is too slow, and the cost is relatively higher compared to the threaded version.

Galvanized pipes can be used; there is no need to use stainless steel, unless the instruments have special requirements.

As long as the requirements are met, that’s enough; the standards are set too high on purpose, which results in unnecessary extra costs

Under normal circumstances, galvanized steel pipes are sufficient to meet the requirements; in special cases, stainless steel can be used, welded by TIG welding, and cleaned thoroughly before use. However, the cost of using stainless steel is far too high compared to galvanized steel pipes.

Made of stainless steel: lol :lol :lol

Generally, the manufacturing cost of galvanized steel pipes is much lower than that of 304 or 316 steel pipes. However, whether to use galvanized steel pipes or 304/316 steel pipes in engineering projects depends mainly on various factors such as process requirements, the type of instruments, and the importance of the facilities. :lol

Galvanized pipes will suffice; if stainless steel is used, that’s certainly fine as well, and welding is possible.

The reason why galvanized pipes are used for instrument air lines instead of stainless steel is that the air itself is not corrosive, and the required grade and strength are not high; galvanized steel pipes are sufficient for this purpose. Moreover, stainless steel is quite expensive. Threaded connections are used instead of welding because the air used for instruments needs to be clean, and welding can easily contaminate this clean air, so welding is not feasible. In special cases where welding is necessary, the weld joint must be treated specially, such as by using TIG welding.

For instrument air pipelines, domestic owners generally use galvanized pipes. Some foreign owners require 304, while others even demand 316. On site, I found that the instrument air pipelines included with foreign instruments are all made of stainless steel.

Hehe, it seems that in current engineering projects, 304 stainless steel is used for instrument air pipelines; anyway, not a large amount of it is used.

The key issue is to prevent foreign objects from entering the pipeline and causing instrument failures; therefore, it doesn’t matter what material is used, as long as it is not prone to rusting. The connection method should also be such that it is unlikely for foreign objects to get in

The original poster’s analysis is correct. Stainless steel is too expensive, while galvanized steel pipes can meet the requirements

Hehe! I firmly advocate the use of stainless steel as the material for pipes carrying instrument air. The reasons are as follows: 1. Using stainless steel for such pipes ensures that the purity requirements for the air supply to control valve actuators are met right from the pipeline stage. Modern chemical plants aim to operate continuously and safely over long periods; if a control valve fails due to issues with the air supply, it can lead to abnormal system operation or even safety accidents, with significant financial losses as a result. Other materials such as carbon steel or carbon steel coated with zinc cannot guarantee that their anti-corrosion layers remain intact during installation and use, so rusting is inevitable, and rust particles may end up reaching the end-users of the instrument air. 2. Using stainless steel ensures better quality in on-site installation. For carbon steel or carbon steel-coated pipes, threading is often used for connection at the installation site, which involves a lot of work, and the quality and speed of completion cannot be guaranteed. With stainless steel pipes, TIG welding can be used on-site to ensure cleanliness inside the pipes, and the construction process is simpler and faster. 3. In general, for medium to large-scale installations, based on the number of control valves used, the diameter of the main pipes carrying instrument air is usually below DN100. In contrast, with carbon steel-coated pipes, threaded connectors must be added at regular intervals to achieve connections, and a large number of threaded fittings are required. Sometimes, to repair any damage to the galvanized layer of the pipes during installation, additional hot-dip galvanizing is necessary. In humid and corrosive environments, galvanized pipes require frequent replacement and maintenance during normal operations. Considering overall costs and maintenance needs, using stainless steel as the material for instrument air pipes offers advantages over traditional 20#+Zn materials.

In our previous company, the main pipes used were carbon steel pipes, while the branch pipes were stainless steel pipes. I’m not sure if this is a problem