Q. General corrosion rates of castings?
Austenitic stainless steels (300 series) are very resistant to caustic in concentrations up to 50% and temperatures below 200oF (95oC). Type 316 L shows improved overall performance over type 304 because of increased resistance to pitting and sensitization.
In caustic service, corrosion is due primarily to caustic stress corrosion cracking (caustic embrittlement) and occurs in the area above the SCC boundary curve. Care must be taken to avoid service conditions within this caustic SCC region. In neutral and acidic services, chloride induced SCC is of major concern. The effect of chlorides is not generally a concern in caustic service where the solution is sufficiently alkaline (e.g. a solution of 0.5 g/L NaOH with a pH of 12).
Cast stainless pumps and valves have performed very well in caustic service and tend to be more resistant to caustic SCC than their wrought equivalents. Minimization of SCC is due to the nature of the cast product. General corrosion rates of castings are similar to those of wrought products.