By Michelle M. Gonzalez
Chemical services of any kind may require special alloys for corrosion resistance, freedom from metal ion contamination, or both. Bioprocessing applications can have even more stringent requirements, due to the high degree of cleanliness required to convey sterile and non-sterile products or solutions. Tubing and/or piping systems, must, therefore meet these requirements in their fabrication, particularly when it applies to their product or solution contact surfaces. Stainless steels are uniquely qualified not only because of their long service life, availability and fabricability, but also because they are non-corroding, non-contaminant, they can be polished to very smooth finishes, they are strong and rigid, they can withstand heat and chemical sterilization treatments, and they are easily welded.
There are more than 70 standard types of stainless steel and many special alloys. These steels are produced in the wrought form (AISI - American Iron and Steel Institute - types) and as cast alloys (ACI - Alloy Casting Institute - types). Generally, all are iron based, with 12% to 30% chromium, 0% to 22% nickel, and minor amounts of carbon, columbium, copper, molybdenum, selenium, tantalum, and titanium.