2015 06 Guldberg SMT Materials for Nitric Acid Service
Much of the nitric acid produced is used for the production of Fertilizers. The fertilizer industry uses acid at a concentration of 60-65%. Stainless steel is used for almost all equipment that comes in contact with the process media. The most common material is AISI 304L. However, corrosion of heat exchanger tubes and shells has caused much costly down time and maintenance in several nitric acid plants. The selection of more advanced stainless steels can be a solution for many of the corrosion problems in a cost effective way. The choice of material is critical for the performance of the plant and needs to be made carefully taking into account the local service conditions. A selection of stainless steels is presented which can be used in nitric acid plants to solve problems caused by nitric acid and chloride induced corrosion.
Corrosion problems may vary from plant to plant because of local service conditions. It is important to carefully select material in order to avoid corrosion. The initial cost for a more advanced material may be higher, but a later change to a corrosion resistant material is always more expensive. For nitric acid service Sandvik 2RE10 is recommended if there are problems with 304L type materials due to condensation or evaporation of nitric acid droplets. Sandvik 2RE10 is expected to increase the service life several times compared to 304L. If there are problems caused by chlorides, for instance in the cooling water Sandvik SAF 2304 can be a suitable material with better resistance to both chlorides and nitric acid compared to 304L. For cases when a combined resistance to both chlorides and nitric acid is needed Sanicro 28 and Sandvik SAF 2906 are the best options.