Sulfuric acid delivery pipeline
Thread Content
I really don’t know if this question will be laughed at, but I’m truly facing a problem. I have been working with sulfuric acid for over a decade; I only use it, I don’t engage in its production, and I don’t understand the processes related to sulfuric acid. What we were taught in school is that concentrated sulfuric acid can be transported through carbon steel pipes, as it forms a passivation layer on the surface of carbon steel, which prevents corrosion. This is more or less what I’ve seen in my professional experience as well. I’m currently working in Ningbo, and I’ve noticed a problem: all the pipelines used for concentrated sulfuric acid in this facility are lined with PTFE. So when the reason was asked, the answer was: Carbon steel cannot be used; it usually runs out in half a year. So after investigating the reason carefully, it turned out that when the factory was built in 2008, carbon steel pipes were used to transport sulfuric acid with a concentration of over 91.5%, and they could last for a year; but after being replaced, those carbon steel pipes could no longer be used – they would break down within a few months ； The large amount of maintenance work was exhausting, so everything was replaced with steel-lined PTFE. It is suspected that the quality of the carbon steel pipes is not as good as before. I’m completely puzzled; I wasn’t able to figure out the reason even when discussing it with a colleague today. I just remember that at the original factory, a large amount of concentrated sulfuric acid was produced and stored; generally, the acid produced had to wait two or three days before it could be used ； In modern factories, the acid is generally used as it is produced; could this be the reason? I’m really puzzled by it. I’ve come here specifically to ask for help. Thank you all!
The concentration of sulfuric acid, temperature, and so on all affect the service life of pipes. For carbon steel pipes, it is even related to their wall thickness as well; those with a greater corrosion allowance can last longer. The lining made of PTFE is resistant to corrosion; it’s just that too many flange connections pose some difficulties.
(⊙o⊙)… Thank you to the person above. You mean it can be ruled out
Temperature, flow rate, and impurities in the acid all affect the corrosion of carbon steel by sulfuric acid. Using lined pipelines does indeed work well in the initial stage. However, the manufacturing of lined pipelines is relatively complex, and the more complex the process, the greater the decrease in reliability. Mechanical integrity cannot be guaranteed. Moreover, the flange should be isolated using a flange guard to prevent sulfuric acid splashing.
Sulfuric acid at 98% should work better. Our company uses carbon steel everywhere.
The acid concentration is not an issue; however, carbon steel is used as storage equipment, and it is unreasonable to use carbon steel for transporting sulfuric acid. The flow of sulfuric acid prevents the formation of a passivation layer, which leads to corrosion； It is scientifically sound to use pipes lined with PTFE or stainless steel. You should be able to find the relevant charts in the sulfuric acid production manual.
We use 304 steel pipes to transport sulfuric acid
When designing for 98% acid applications, the use of carbon steel pipes is based on the following conditions: first, the temperature of the acid is usually reduced to around 40°C (with 50°C being the upper limit); second, the flow rate of the acid through the pipe should be kept at around 0.6 m/s (as the corrosion rate increases rapidly above 1 m/s). When using carbon steel pipes, a higher value is typically assigned as the corrosion allowance when calculating the wall thickness.
b] Welded carbon steel pipes can be used, but their lifespan is short; this is because factors such as the geographical location of each factory and the wall thickness of the pipes used vary. Generally, they suffer severe corrosion within less than a year. If one does not want to incur additional costs, low-chromium cast iron or high-chromium cast iron can be used, or stainless steel pipes along with PTFE-lined pipes can be employed instead
Unified reply: Thank you all up there!
The key factor to consider when using carbon steel pipes to transport concentrated sulfuric acid is temperature. Thicker carbon steel pipes can be used to transport concentrated sulfuric acid at temperatures below 45 degrees, or cast iron pipes can also be employed.