New Duplex Stainless Steel Optimized for the Urea Process

摘要

Corrosion of stainless steels is a known problem in the high-pressure section of urea plants. A particularly demanding part of the plant, which often has the highest passive corrosion rates, is the high-pressure stripper. The reason is that the corrosion is strongly temperature dependent. This paper presents the development program of UNS S83071, a new improved duplex stainless steel customized for this environment. The key for the successful development was alloy screening in ammonium carbamate solution corresponding to stripper conditions. It was shown that there is a clear difference between screening in the ammonium carbamate environment compared to screening in the standardized corrosion tests that were used during the development of UNS S31050 and UNS S32906, two stainless steels that are commonly used in the urea industry today. The new material, which will shortly be available for use in urea plants combines good mechanical properties with improved corrosion resistance and enables extended life time of the high-pressure stripper.