Metals & Mining

Corrosion in Steel Industry

Steel making involves reduction of iron ore to iron which is the principal ingredient of steel. This is accomplished by carbonaceous inputs derived from coal either in solid or gaseous forms. Apart from being one of the largest emitters of carbon dioxide, steel manufacturing liberates sulphur contained in the ores as well as in the fossil fuel in the form of sulphur and nitrogen oxides together with ammonia, etc. Hydrogen sulphide (H2S) however is the major corrosive pollutant released during steel manufacturing and slag handling processes. While all these oxides form acids in the presence of moisture, sulphur products cause maximum destruction to infrastructure through sulfidic corrosion.As is well known this is one of the worst forms of attack which may cause severe internal stresses in steel infrastructure. Downstream processes like cold rolling employ hydrochloric acid which goes through acid regeneration process to restore its strength. In addition fluxing agents and molten zinc used in galvanizing plants cause high emissions. All such processes emit extremely corrosive acid vapour that affect all steel structures in the vicinity. Further, multiple tank pre-treatment of coated steels prior to coil coating necessitate corrosive liquid discharge and chromate based aqueous streams which are known carcinogens.