Acetic acid is an important raw material for organic synthesis and is widely used in chemical industry, light industry, medicine and food industry. It is relatively easy to solve the corrosion problem of acetic acid with stainless steel. For example, in pure acetic acid, general Cr17 ferritic stainless steel can withstand dilute acetic acid below 80 degrees Celsius and concentrated acetic acid with a concentration higher than 70%; general 18-8 Cr-Ni austenitic stainless steel can withstand 50 degrees Celsius Below, acetic acid with a concentration of <=99% and acetic acid vapor with a concentration of 100%, with the increase of Mo content in the steel, the acetic acid corrosion resistance of Cr17 ferritic stainless steel and Cr-Ni austenitic stainless steel improves, such as , stainless steels such as Cr18Mo2 and Cr17Ni12Mo2 containing Mo~2% can withstand any concentration of acetic acid below the boiling temperature under normal pressure. When there are Cl ions in acetic acid, the corrosion rate of stainless steel will be significantly accelerated. For example, when there is 1% NaCl in concentrated acetic acid, the corrosion rate of general chromium-nickel austenitic stainless steel will increase by 50 times; when the content of Cl ions in acetic acid with a concentration of 99% is increased from 0.0002% to 0.002%, the corrosion rate will be Increased from 0.001mm/a to 1.8mm/a. Therefore, in order to solve the corrosion problem of acetic acid containing Cl ions, according to the concentration of Cl ions in acetic acid, Cr17Ni12Mo2 containing Mo2%~3% and Cr19Ni13Mo3 containing Mo3~4% and high Mo stainless steel, such as 00Cr18Ni16Mo5, 00Cr20Ni25Mo4.5Cu, can be selected according to the concentration of Cl ions in acetic acid. And duplex stainless steel 00Cr25Ni7Mo3N and so on.
When acetic acid contains formic acid, its corrosiveness increases with the increase of formic acid concentration. Tests in 50% acetic acid show that the corrosion rate of stainless steel and some corrosion-resistant alloys increases with the increase of the amount of formic acid. However, the dual-phase steel 00Cr25Ni7Mo3N and the nickel-based corrosion-resistant alloy 00Cr16Ni60Mo16W4 in the stainless steel are hardly corroded, so they are ideal corrosion-resistant materials. Formic acid is a widely used organic acid. The choice of formic acid-resistant stainless steel is basically the same as that of acetic acid. However, because formic acid is more corrosive than acetic acid, the alloying degree of the selected stainless steel grades is higher than that of acetic acid, and even some stainless steel grades are more corrosive than acetic acid. In this case, nickel-based alloys should be used. In formic acid, 00Cr17Ni14Mo2 (316L) and 00Cr20Ni25Mo4.5Cu (904L) have quite good corrosion resistance, while the corrosion resistance of duplex stainless steel 00Cr25Ni7Mo3N is better, not only surpassing nickel-based alloy 00Cr16Ni60Mo16W4, but also being comparable to high-nickel corrosion-resistant stainless steel 00Cr27Ni31Mo3Cu is similar.Obviously, in pure formic acid, corrosion-resistant stainless steel can be selected in the order of 00Cr17Ni14Mo2, 00Cr20Ni25Mo4.5Cu, 00Cr25Ni7Mo3N and 00Cr27Ni31Mo3Cu. However, in the presence of chloride ions in formic acid, the corrosion of stainless steel will be significantly accelerated. In formic acid containing 2000ppm of Cl ions with a concentration of 40% and 99%, the aforementioned formic acid corrosion resistance 00Cr25Ni7Mo3N and another duplex stainless steel 00Cr22Ni5Mo2N and Comparison of corrosion resistance of several nickel-based corrosion-resistant alloys. Obviously, under the condition of 99% formic acid plus 2000ppm Cl ions, the two duplex stainless steels still have good corrosion resistance, and 00Cr25Ni7Mo3N is better than 00Cr22Ni5Mo2N, but under the boiling condition of 40% formic acid and 2000ppm Cl ions, the The corrosion resistance of the above two duplex stainless steels can no longer meet the requirements.
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