Application of 316L Stainless Steel and Technical Improvement on Large Evaporators of Five-effect System in Acrylic Fiber Process

316L stainless steel is generally chosen for the equipments contact with feed solution in five-effect system by NaSCN wet spinning two-step method for acrylic fiber.But with the increase of service life and adjustment of process parameters,the body defects expose consecutively,and the other material is used in manufacture and application of similar systems,the applicability of 316L stainless steel on the working condition has be doubted.The leakage reason of a two-effect evaporator in use was analyzed and the technique was improved.The results showed that the material properties could be improved greatly by means of increasing molybdenum content in 316L stainless steel to insure the applicability of 316L stainless steel in NaSCN solution.