Development of automatic analyzer for sulfuric acid, mixed nitric acid, and hydrofluoric acid in stainless pickling process

Stainless steel is pickled in pickling bath with the sulfuric acid and a mi xture of hydrofluoric acid and nitric acid. Suitable equipment based on spe edy and accurate chemical analysis for actual production lines has not been developed yet. The concentration of sulfuric acid can be analyzed by using the neutralizat ion titration method. As a method of analyzing hydrofluoric acid in the mix ed acid, the iron-acetylacetone complex discoloration absorbance method was adopted. For the concentration, of nitric acid, the method of subtracting the concentration of hydrofluoric acid from the total mixed acid amounts ob tained by neutralization titration is adopted. Furthermore, the iron-salicy lic acid complex absorbance method is adopted as a method of analyzing the iron content. By adopting these methods, the fully automated analyzer is developed. Compl eting analysis work can be shortened to 40 minutes by automated sampling fr om the acid pipes. The fully automated acid supply and exhaust system is eq uipped to enable suitable pickling conditions from these results.