Urea grade stainless steel is a kind of austenitic stainless steel specialized for use in the urea industry. Derivatives such as CO2, NH3, NH2COONH4, (NH2)2CO during the urea production process are not highly corrosive when they are present alone, but the reactants that form when they are mixed together are equipment Cause strong corrosion. Urea methyl ammonium solution contains ammonium carbamate and ammonium cyanate. It contains 2% to 3% Mo Cr-Ni austenitic stainless steel because it is highly corrosive under high temperature and high pressure of stainless steel and may destroy the passive film of stainless steel. It is difficult to resist corrosion. In addition, the urea synthesis column linings, strippers, and methylammonium condensers are easily corroded by methylammonium.
In the 1950s, the Dutch company Stamicarbon proposed using 18-8 austenitic stainless steel under conditions of carbon dioxide and oxygen protection for the urea industry, but there is still severe corrosion. With the development of ultra-low carbon stainless steel smelting technology, the purity of the steel has been greatly improved, and finally it became stainless steel for urea production. The chemical composition, microstructure and corrosion resistance of urea grade stainless steel are clearly defined with the aim of completely suppressing the ferrite content of the steel and obtaining a complete austenitic structure with as little intermetallic precipitation as possible. Corrosion resistance and selective corrosion ability of steel. All urea grade stainless steels must pass the Huey and Selective Corrosion tests. In addition, a metallographic examination of the material is required. Sigma phase and metal inclusions are not allowed. These stringent test conditions make it difficult to meet common stainless steels such as 316L.
310MoLN (S31050/725LN/1.4466/2Re69) and 316L mod (724L/316LN) are the most widely used urea grade stainless steels. 310MoLN is a urea grade ultra low carbon austenitic stainless steel with a density of 7.9g/cm. Its corrosion resistance is similar to that of 904L steel, especially ammonium carbamate and nitric acid, which provides excellent corrosion resistance. 316L modified stainless steel has a low carbon content, a very low silicon content and a fairly high molybdenum content. The modified 316L is designed to improve corrosion resistance in urea-carbonate environments.
Urea grade stainless steel provides excellent weld hot cracking resistance and intergranular corrosion resistance, with good corrosion resistance especially to sulfurous acid, sulfuric acid, phosphoric acid, acetic acid, formic acid and chlorine salts, halogens and sulfites. It has been successfully applied to urea, production equipment such as full cycle method of urea equipment such as synthetic tower such as high pressure separator, also widely used in pulp and paper, chemical fertilizer, chemical industry, pharmaceutical, synthetic fiber industry and other industries. Is being used.
