The corrosiveness of phosphoric acid during the wet-process concentration is quite complex and dependent on several influencing factors. The factor, which has the most significant impact, is the presence of impurities. For example, at a given concentration, the presence of fluorine, calcium oxide, sodium and chlorine in the process will crease the corrosivity of phosphoric acid whereas iron, alumina and magnesium will have the opposite affect. This paper discusses the general aspects of the corrosiveness of phosphoric acid produced via the wet-process method. Additionally, information exploiting the benefits of stainless steel metallic heaters versus graphite will be detailed. Finally, several case references are documented describing twenty years of successful application experience of Sandvik Steel's Sanicro 28 used as a material of construction for metallic heaters for phosphoric acid evaporation.
El Kayar, K., & Perrot, V. (2014). Metallic heaters for phosphoric acid evaporation. In Procedia Engineering (Vol. 83, pp. 291–301). Elsevier Ltd. https://doi.org/10.1016/j.proeng.2014.09.009