DCI implements use of Duplexes
The most common metallic material of construction for product contact surfaces in BioPharm applications continues to be 316L stainless steel. In more demanding and corrosive environments, higher alloyed Super-Austenitic (6-Moly) stainless steels, such as AL6XN® (N08367) and 254SMO® (S31254) or Nickel-Chrome-Moly alloys such as Hastelloy® C-22® (N06022) have been successfully used. Now, more than ever, the fluctuating costs of these higher alloys, mainly due to surcharges of nickel and molybdenum, have made these choices increasingly difficult.
End users must look at corrosion resistance, product contamination risks, cleanability, etc. when they choose a material of construction. One potential solution currently being used is the use of duplex stainless steels. Generally, duplex alloys have a higher Chrome composition, a lower Nickel content and precise additions of Nitrogen, as compared to conventional 316L. The most common duplex stainless steel is 2205 (see figure 1 for a basic chemistry comparison). Since duplex 2205 contains a much lower nickel content than 316L, one of the main cost drivers is lowered, thereby making it a cost effective alternative to the higher alloys.
The most critical issue in using duplex stainless steels is in the fabrication process. The main issues are maintaining the metallurgy during welding and potential special tooling. Knowledgeable and experienced fabricators who understand duplex stainless steels should be utilized.
Compared to 316L, generally duplex 2205 is more corrosion resistant, especially in chloride containing environments, and is very resistant to chloride pitting and stress corrosion cracking. The material can be finished, polished, electropolished and passivated to the industry’s highest standards. Duplex 2205 and other duplex stainless steels are a viable option for many applications in the BioPharm industry.