Development of 216L for Conservation of Nickel & Molybdenum and its Application in Sugar Refinery Instead of 316L

Abstract

Development of an austenitic Fe-Cr-Mn-Ni-Mo-Cu-N alloy 216L to substitute AISI 316L for saving a part of expensive nickel and molybdenum is described. Nickel content is reduced by 40% and molybdenum by 25% with the help of nitrogen, manganese and copper additions. Corrosion tests in boiling solutions in a variety of acidic media including oxalic, nitric, phosphoric, sulfuric and chromic acids and polarization curves in acidic and chloride environment indicate similar behaviour of both grades. There is also striking similarity in pitting corrosion resistance and inter-granular corrosion resistance of the two alloys as per ASTM G-48 and ASTM A262 respectively. Both alloys exhibit excellent resistance to any staining in prolonged salt spray test. Produced by conventional EAF-AOD-CC-Steckel Mill route, the alloy exhibits surface quality comparable to AISI 316L in both hot and cold rolled conditions. Like 316L, it is equally amenable to fabrication and welding. Higher yield strength of 216L confers potential for material saving in use as compared to 316L. In the process of extracting refined sugar from raw sugar a number of chemicals are used. Accumulated scale from the equipments is periodically removed by using hot solutions containing caustic soda and soda ash followed by rinsing in solutions containing dilute hydrochloric acid and finishing with water rinse. The steel generally used is 316L and based on comparative performance of 216L this new alloy was successfully used in sugar refinery columns where it is subjected to periodic cleaning by hot salt & caustic soda solution and hot dilute hydrochloric acid.. Key words: nickel conservation, 216L austenitic stainless steel; corrosion resistance, sugar refinery