〣What is the relationship between urea and stainless steel? What is urea grade stainless steel?

We all know that there are many kinds of stainless steel, according to the structure can be divided into austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, duplex stainless steel, precipitation hardening stainless steel; According to the chemical composition can also be divided into chromium manganese nickel stainless steel, chromium nickel stainless steel, chromium stainless steel; Individual stainless steel has many names, such as molybdenum stainless steel, low carbon stainless steel, non-magnetic stainless steel and so on.

There is a kind of stainless steel, we must not know, that is urea grade stainless steel.

What is urea? What does it have to do with stainless steel? What is urea grade stainless steel?

Urea has two definitions, one definition is the main nitrogenous substance in the urine of people and some animals, is also a protein metabolite; Another meaning is an important chemical fertilizer containing nitrogen (the meaning specified in this article).

It is very corrosive in the process of urea production. It contains methylamine solution, which contains ammonium carbamate and ammonium cyanate, which corrodes urea production equipment such as synthesizer lining, stripper and ammonium methonium condenser.

Stainless steel has excellent corrosion resistance, good oxidation resistance, not easy to rust, stable comprehensive performance, long service life and other advantages, and no secondary pollution, is a green environmental protection material. Among them, 316L stainless steel contains molybdenum, which can be used in urea production equipment.

However, urea is synthesized by carbon dioxide and ammonia under the conditions of high pressure (140~250 atmospheres) and temperature (180~210 degrees), and the intermediate product ammonium carbamate is strongly corrosive to 316L stainless steel, which cannot meet its corrosion resistance, so the development of urea grade stainless steel such as 316Lmod stainless steel.

316Lmod is modified316L, meaning improved 316L, specially used in urea industry, so it is called urea grade 316L. The difference between 316mod and 316L lies in the chemical composition. The chemical composition of 316Lmod is adjusted in order to suppress the ferrite structure in the steel, obtain the austenitic structure as much as possible, and improve the corrosion resistance of the steel.

Urea grade stainless steel is austenitic stainless steel specially used for urea production, steel types are 316UG and 00Cr25Ni22Mo2N (2RE69). According to Xiaobian, the metallographic structure of urea grade stainless steel is austenite, and the ferritic content is not more than 0.6%. It must be tested by Hugh's test and selective corrosion test, and the test conditions are very harsh.