How long can a stainless steel wet acid removal tower last?
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Hello, friends in the group! Recently, the company plans to restart a production line that has been idle for about 1.5 years, and the wet acid removal tower (spray type) is one of the equipment in this system. The material and operating conditions of the wet acid removal tower are as follows: Material – 316L, thickness – 5 mm. Sodium hydroxide solution with a pH of 8–11 is used during operation; the temperature inside the tower is 60–80°C. The anions present in the solution include Cl- (10–20 g/l) and F- (2–8 g/l). Below are photos of the inner wall of this deacidification tower. Please take a look at this condition and assess how long the tower can withstand operation under these conditions.
Looking at the first image, the pitted corrosion is almost forming a continuous area; it probably won’t hold much longer. Keep watching closely.
If the system equipment needs to be put into use right away, and the corrosion in the images is severe, it is recommended to carry out rust and corrosion removal on the equipment. The use of chemicals is not advised as it may exacerbate the corrosion; instead, physical methods for rust and scale removal are suggested – devices that can be directly attached to the pipes will do. Within 1–3 months, the corrosion and rust inside the equipment should be significantly reduced or even eliminated. In fact, this equipment can still be used for some time, provided it wasn’t properly maintained before it was taken out of service
Let’s use an anti-corrosion agent; I’ll recommend a suitable product for you.
Our chlorine- and fluoride-resistant heavy-duty anti-corrosion coatings can be used
With my limited knowledge, I’m wondering why the inner wall of the wet acid removal tower is shaped like that. Ours is corroded, but it has a shiny stainless steel surface.
The material for the deacidification tower must be chosen based on the fluid that is used within it. In your process, there are two issues: firstly, the F content is too high, and almost no metallic material can withstand such conditions; it is recommended to use a non-metallic lining. Secondly, there are also too many Cl ions; even in the absence of F, with such a high amount of Cl ions, 316 should not be used for the equipment casing. Cl ions cause severe corrosion in austenitic stainless steels; it is not acid corrosion in the usual sense, but intergranular corrosion. For Cl ions, carbon steel is a better choice than austenitic stainless steel. In summary, the biggest problem is an excess of F ions; it is recommended to use a metal casing with an anti-corrosion lining. The temperature here isn’t high either, so there should be no problem.
For internal anti-corrosion, it is best to use fiberglass-reinforced plastic material