STUDY OF THE CORROSION RESISTANCE OF STRUCTURAL MATERIALS WORKING IN CONDITIONS OF SULPHATE SOLUTIONS OF COKE-CHEMICAL PRODUCTION

Abstract

The article presents the results of the study of the corrosion resistance of austenitic and austenitic-ferritic steels in the environments of the sulfate department of PJSC “Zaporozhkoks”. Now in the coking industry, the problem of corrosion protection of welded joints in the equipment of sulfate sections is most acute. Aggressive medium sulfate compartments are mother liquors, which include: sulfuric acid, ammonium sulfate, chlorides. In the mother solution with the acidity of 3-6%, the following ions are present, g/l: sulfates – 400-450; chlorides – 0.2-2.8; cyanides – 0.065-0.16; rodanid – 0.1-1.2; total iron – 0,002-0,05; pyridine bases – 10-20. The presence of pyridine bases in the working solutions of the sulfate separation somewhat reduces the aggressiveness of the solutions. However, at a concentration of 10-20 g/l in 6-10% H2SO4 at 60°C, their protective effect does not exceed 50-60%. According to researchers, the content in process solutions of mineral salts and in coke oven gas with the almost complete absence of O2 makes it difficult to form protective passive films on the surface of nickel-chromium steels, leading to the occurrence of local types of corrosion damage (ulcers and pitting). In addition, the occurrence of corrosion processes stimulates increased temperature and velocity of movement of the solutions.It has been established that the corrosion resistance of materials depends on the acidity of the mother liquor and when applying strong sulfuric acid in these zones, it is necessary to use lined materials, enameled pipes or steels of alloy type 943 (0Х23Н28М3Д3Т) capable of withstanding increased acidity (10-15%) of the mother liquor. Avesta 254 SMO stainless austenitic steel containing slightly more than 6% molybdenum (Mo) – (АКС 254 SMO (X20Н18AM6D) shows the highest corrosion resistance in sulphate separation environments.