1. is a special austenitic stainless steel, designed for urea production of urea-grade stainless steel mainly 316UG, 00cr25ni22mo2n (2re69), urea production is in high pressure (140~250 atmospheric pressure) and temperature 180~210度 conditions,by carbon dioxide and ammonia synthesis, Among them, ammonium carbamate and other stainless steel has strong corrosive, the general stainless steel, such as 316L can not meet its corrosion resistance. The special steel Bell developed here iscalled Urea grade stainless steel.
2. The special stainless steel used in urea production is called urea grade stainless steel, in particular, the following requirements should be met:
1.316L ug and 00cr25ni22mo2n, the chemical composition and mechanical properties of urea equipment and materials should be qualified for the national standard requirements.
2. The metallographic microstructure of the material is austenite, and the ferrite content is not greater than 0.6%.
3. Materials must undergo a trial test, the test results should meet the requirements of the national standards for urea equipment and materials.
4. The selective corrosion test should be carried out after the trial test, and the test results should conform to the national standard of urea equipment and materials.
5. Materials should also be metallographic examination, should not contain the Six Sigma phase and metal inclusions, and other requirements.
3 316L mod is modified 316L, modified 316L, specifically for the urea industry, it is called urea-grade 316L. The main difference from the 316L is the chemical composition. The aim of the adjusting composition is to restrain the ferrite content in steel and to obtain all austenite microstructure as much as possible so as to improve the resistance between intergranular corrosion and selective corrosion of steel. The urea grade stainless steels are required to carry out the test of both the Hugh and the selective corrosion. Test conditions are very harsh, general stainless steel difficult to pass.
316mod and 316L chemical composition is not very different, 316mod to pass the test (Huey), the 48-hour boiling corrosion test period, 5 samples of the corrosion value is not less than 0.54gr/m2hr (3.3 microns/48 hours).
The ingredients are 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;
Elastic modulus: 200GPa
Coefficient of thermal expansion (20-100°c): 15.0 a10-6k-1
Main features: excellent resistance to weld thermal cracking and intergranular corrosion resistance.