What is urea grade stainless steel?

 　　1. It is a special type of austenitic stainless steel, which is mainly used for urea production. Urea grade stainless steel mainly includes 316UG, 00Cr25Ni22Mo2N (2RE69). Urea production is synthesized from carbon dioxide and ammonia under high pressure (140-250 atmospheric pressure) and temperature of 180-210 degrees Celsius. The intermediate products such as ammonium carbamate have strong corrosion resistance to stainless steel. Generally, stainless steel such as 316L cannot meet its corrosion resistance. The special steel bell developed from this is called urea grade stainless steel

　　2. The specialized stainless steel used in urea production is called urea grade stainless steel, specifically, it should meet the following requirements:

　　1. The grades are 316L UG and 00Cr25Ni22Mo2N, and their chemical composition and mechanical properties should meet the national standard requirements for urea equipment and materials. 2. The metallographic structure of the material is austenite, with a ferrite content not exceeding 0.6%.

　　3. The material must undergo a rest test, and the test results should meet the national standards requirements for urea equipment and materials.

　　4. After the rest test, a selective corrosion test should be conducted, and the test results should comply with the national standards for urea equipment and materials. 5. The material should also undergo metallographic examination and should not contain sigma phase or metal inclusions, and other requirements.

　　3.316L mod is a modified 316L modified 316L, specifically used in the urea industry, hence it is called urea grade 316L. The main difference from 316L lies in its chemical composition. The purpose of adjusting the composition is to fully suppress the ferrite content in the steel, obtain a fully austenitic structure as much as possible, and improve the resistance to intergranular corrosion and selective corrosion of the steel. Urea grade stainless steel requires Hugh's test and selective corrosion test. The test conditions are very strict, and ordinary stainless steel is difficult to pass.

　　The chemical composition difference between 316mod and 316L is not significant. 316mod needs to pass the Huey test, and it is required that during the 48 hour boiling corrosion test period, the corrosion values of all 5 samples should not be less than 0.54gr/m2hr (3.3 microns/48 hours). The composition is roughly as follows:

　　316mod: C max0.03, Cr17.0-18.5, Ni13.0-15.0; Mo2.20-3.0; Si max1.0 Mn max2.0; Pmax0.045，Smax0.22; Physical performance:

　　Density: 7.90g/cm3 Modulus of elasticity: 200GPa coefficient of thermal expansion (20 - 10C): 15.0 a10-6K-1

　　Main features: It has excellent resistance to welding hot cracking and intergranular corrosion.



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