Question: Corrosion of titanium by chlorine gas!
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The chlorine supply pipes used in our company’s hypochlorite production are of TA2φ32*3 type; there is severe corrosion inside these pipes, whereas the cooling coils show no signs of corrosion. What is the reason for this? ? Thank you!
Titanium is not corrosion-resistant in an environment of chlorine (anhydrous).
What was said upstairs is correct: dry chlorine cannot form a protective layer on the titanium surface, so it causes corrosion, whereas wet chlorine has the opposite effect. For dry chlorine gas (if it contains no other substances), carbon steel can be used.
The media outside the cooling coil are sodium hypochlorite and sodium hydroxide, and titanium exhibits excellent corrosion resistance in both of these media. The chlorine gas inside the chlorine delivery pipes may be dehydrated and dry; titanium is not resistant to corrosion in chlorine environments with a water content of less than 0.5%, so non-metallic materials such as PVC/FRP and FRP can be used.
Titanium’s corrosion resistance relies on the formation of a titanium oxide protective film on its surface; dry chlorine gas can easily destroy this film, which is why titanium is prone to corrosion.
If there is alkali outside the tube, using fiberglass may not be suitable (unless a high-quality resin is used), while PP can withstand alkali solutions with a concentration of less than 70%, at temperatures below 100 degrees Celsius.
Dry chlorine is non-corrosive, but once water vapor gets in, it’s hard to say
Titanium is fine for wet chlorine gas, but not for dry chlorine gas. Use carbon steel instead.
What the friends upstairs said is right! Titanium is not resistant to dry chlorine gas, but it is resistant to moist chlorine gas: lol! It’s better to use graphite equipment instead! That one has good corrosion resistance:victory:
Wet chlorine, due to the chloride ions formed by its dissolution in water, possesses strong oxidizing properties; this enables a titanium oxide passivation layer to form on the surface of titanium, preventing corrosion. In contrast, dry chlorine has both strong oxidizing and strong reducing properties, making it difficult for a titanium oxide passivation layer to form on the surface of titanium
In wet chlorine gas, a titanium dioxide protective film forms on the surface of titanium, serving to prevent corrosion； Titanium chloride ignition occurs in dry chlorine. Titanium is not resistant to pure sodium hydroxide solutions, but it has no problem with hypochlorite; a protective film also forms on the surface of titanium in hypochlorite solutions. Therefore, it is essential to maintain a certain proportion of hyposodium in the solution during operation.
Dry chlorine causes severe corrosion of titanium materials. In our facility, the chlorine pipelines are made of fiberglass-reinforced plastic; plastic-lined carbon steel is also an option – you might want to give that a try