Find out first, what is "toxic medium"?
Not all toxic gases or liquids deserve this name. In the chemical, pharmaceutical and petroleum industries, such as chlorine, hydrogen sulfide, benzene and hydrofluoric acid-once leaked, it is not a problem of equipment damage, but human life. Therefore, when choosing the expansion joint, the conventional general-purpose corrugated expansion joint is afraid to use at all. What about that? Look down.
Three core demands: zero leakage, high corrosion resistance and long life
The requirements of toxic media for metal expansion joints are these three points. However, in reality, in order to save money, many projects use ordinary stainless steel bellows to deal with them, and as a result, they are worn in half a year. Let me tell you a real case: a chemical plant used 316L bellows to transport chlorine-containing media, and the weld cracked for three months. Later, we changed the PTFE-lined hose and PTFE compensator in our station, and the problem was completely solved. Why? Because PTFE can carry almost all strong corrosive media. Chlorine and hydrofluoric acid are side dishes in front of it.
The products that can be used on this site are listed clearly for you
PTFE-lined hose、PTFE compensator、Metal hose(Custom lining required), andDesulfurization flue gas baffle door(for sulfur-containing exhaust gas). In addition, general-purpose corrugated expansion joints can also be used if the right materials are chosen-such as Hastelloy and Monel-but the cost is doubled. Let's focus on the PTFE-lined metal hose: it is lined with PTFE in the metal bellows, which not only retains the strength of the metal, but also makes the contact surface of the medium become PTFE, and the corrosion resistance is directly drawn.
Don't just look at the material when selecting the type, but the structural design should also be realistic
Toxic media pipelines usually have low pressure, but the temperature fluctuates greatly, which easily causes stress concentration. At this time, you can considerExternal pressure single axial expansion jointOrStraight pipe pressure balanced expansion joint-They can absorb axial displacement and reduce thrust on pipe end equipment. There is also the guide tube. As mentioned in the question and answer, the guide tube can prevent high-speed media from washing the bellows, which is especially important for toxic media with particles. Don't underestimate this detail, without it, the bellows life is directly cut in half.
Installation and operation and maintenance shall not be careless
The tie rod nut of the expansion joint is locked during transportation and installation, and must be loosened before commissioning-the question and answer specifically mentioned "Does the screw of the expansion joint need to be disassembled?" The answer is yes, otherwise the compensation function will fail. In addition, it is recommended to install leak monitoring interfaces, such as pressure gauges or sensors, for expansion joints on pipelines with toxic media. In case of seal failure, you can call the police at the first time, instead of waiting for on-site personnel to be poisoned. This is no joke.
Finally, let's tell you the truth
Toxic media plumbing is not a place to save money. According to the statistics of a German chemical enterprise, the shutdown loss caused by leakage accident is more than 20 times the procurement cost of expansion joints. Think about it, 20 times! Instead of gambling on luck, it is better to directly line PTFE hose or PTFE compensator with the correct installation method (refer to the correct installation method of large tie rod expansion joint). This is a serious life-saving plan. Don't wait until something happens to regret it, it's too late.
By the way, by the way: if your pipeline has sulfur-containing exhaust gas, remember to use the desulfurization flue gas baffle door of our station, double seal design, leakage rate is almost zero. In short, you can't have a fluke when you treat toxic media.