The austenitic stainless steel is at the optimum temperature and has the properties of good resistance to any phosphate corrosion. So this steel is extremely useful and extremely economical in the production and processing of phosphoric acid. Martensitic and ferritic stainless steel is much less able to corrode than austenitic stainless steel, so it is generally not used in phosphoric acid. 302 and 304 stainless steel are satisfactory at room temperature for the corrosion resistance of various concentration phosphate. At higher temperatures, especially when the acid concentration is high, 316 steel is required. Using the limit of 316 steel temperature about 316 ℃.
If fluoride or chloride is present in a hot phosphate solution, corrosion of stainless steel will be greatly increased, and if nitric acid is present in the concentrated solution, the corrosion will be reduced. The phosphoric acid can cause corrosion of the stainless steel, which is treated by sensitization, so it is best to use stainless steel with low carbon content.
The sulfuric acid can cause 302 and 304 steel points, but the corrosion of molybdenum stainless steel is mild. So 316 stainless steel is very useful in the flue gas that contains sulfur dioxide exhaust. In the sulfite pulp and paper industry, 316 and 317 stainless steel are used for heat exchangers, cooking pot lining, and circulating system of thermal sulfite solution.
Source: China Steel Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)