Selection of pipeline material?
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On the flowchart of our plant, why was carbon steel used previously as the material for the pipes carrying the acidic water resulting from sulfur recovery? Yet the pipeline section before the air intake tower is made of stainless steel. Why is that? Why not use the same material?
The ones made of carbon steel are also sulfur-resistant pipes. As for why they were replaced, whether it was after passing through a certain device, and whether the temperature and pressure conditions changed – it’s quite simple to state that, but it’s not easy to answer
There’s no change at all! It comes from the sulfur recovery scrubber tower and is pumped into the stripping tower to strip acidic gases. The part where the material changes is through a check valve, located near the stripping tower
Probably to match the material of the stripping tower itself.
Does it matter if they’re different? Is it to avoid corrosion?
For design issues, the same is true for our air ducts. The materials are different, but they are altered after passing through the filter.
Yeah, so I was wondering why? I’d appreciate some advice from those who are more experienced
My understanding is that the high temperature in the stripping tower increases the corrosion of the material by sulfur; and due to concerns about backflow of the material, the material composition changes after the check valve.
I think it’s mainly a cost issue; also, it’s necessary to check what specific grade of steel it is and whether the inner surface has been specially treated. The corrosion resistance of carbon steel… Steel is widely used in industry for manufacturing metal structures and equipment. Carbon steel is widely used in construction, transportation, petroleum, and chemical processing equipment, among other fields. In terms of corrosion resistance, various grades of carbon steel and cast iron are roughly similar. Since carbon steel rusts in the atmosphere and water, it is often not considered a corrosion-resistant material. In fact, aside from highly corrosive media, carbon steel generally possesses a certain degree of corrosion resistance against a wide range of corrosive media. At the same time, carbon steel has a low cost, being about 1/3 of the cost of Pb and Zn of the same weight, 1/5 of Al’s cost, 1/8 of Cu’s cost, and 1/15 of Ni and Sn’s cost. Carbon steel equipment can be protected against corrosion using coatings, corrosion inhibitors, and electrochemical methods. Low-alloy high-strength steels, which are obtained by adding small amounts of alloying elements to carbon steel, can also improve the corrosion resistance of the steel in certain environments, and thus have a very wide range of applications. The manufacturing cost of low-alloy high-strength steel is only about 20% to 30% higher than that of ordinary carbon steel, so it is also widely used. As a structural material, low-carbon structural steel is the most commonly used, so in future discussions on the corrosion behavior of carbon steel, low-carbon steel will be the main focus.
I have also noticed this phenomenon, and I don’t understand the reason behind it. I would appreciate some guidance from those who know more.
It’s probably a cost issue; it’s to match the material of the tower
For such weak acids containing sulfide ions, ordinary 304 stainless steel is not suitable; it is better to use ultra-low carbon austenitic stainless steel.
It is common in engineering design to change the material grade at the check valve: firstly, to facilitate connection at the valve flange, and secondly, to prevent or reduce corrosion under the corrosive conditions present in the same tower.