By Michelle M. Gonzalez
Stainless steels are uniquely qualified for bioprocessing applications not only because of their long service life, availability, and fabricability, but also because they are non-corroding, non-contaminant, can be polished to very smooth finishes, are strong and rigid, can withstand heat and chemical sterilization treatments, and are easily welded. With more than 70 standard types of stainless steel produced, the industry’s workhorse is the austenitic group which includes types 304 and 316 and their L or low carbon content variations. With concerns for higher corrosion resistance, the low carbon superaustenitic stainless steel AL-6XN (6% Molybdenum) and the Nickel-based alloys, Hastelloy C (C-22, C-276), are becoming notoriously important in the fabrication of vessels, piping, tubing, and fittings (see Table 1). Finally, the cast stainless alloys such as CF- 8 (similar to 304), CF- 8M (similar to 316), and CF-3M (similar to 316L) utilized in pumps, various types of valves, (particularly ball type), and fittings occupy a prominent position in the industry.
In some biopharmaceutical industry circles, there is the belief that the stringent specifications that rule biopharmaceutical processes have no comparison with the food and dairy industries. Actually, almost the reverse is true; the present standards and specifications for tubing fabrication and their product/solution contact surfaces, as well as the installation of systems, have their origin in the dairy industry through the 3-A Sanitary Standards and Accepted Practices, now known as 3-A Sanitary Standards, Inc. (3-A SSI). Published by the International Association for Food Protection (IAFP) and the Milk Industry Foundation (MIF), these standards dealt first with the sanitary aspects of polished
metal tubing used to conduct dairy products in processing lines or systems that also included sanitary fittings, and secondly, with the cleaning of rigid solution lines and the clean-in- place (CIP) units used to circulate the pre-rinse, rinse, cleaning solutions, and post-rinse liquids used for cleaning and sanitizing the product pipelines and process equipment.