Grades of Stainless Steel in Pharmaceutical Equipment
Equipment used in the pharmaceutical industry is highly specialized and must maintain a cleanable exterior. This equipment is likely located inside a strictly environment controlled area such as a clean room. Clean rooms have extreme sterility requirements. Their cleaning procedures often use strong chemicals that corrode and even damage most materials. Materials such as stainless steels and high performance plastics are commonly used in the manufacturing of pharmaceutical equipment due to it’s resistance to these chemicals.
304 and 316L Stainless Steel
304 stainless steel is often used for the exteriors of machines and for protective coverings. It can be very useful for skirting and trimming around and between the areas of a clean room that are difficult to sanitize and clean. 304 stainless is an economical grade of stainless used widely across industries.
316L stainless steel is a special grade of stainless being adopted in the pharmaceutical industry. 316L is very similar to 304 for fabrication purposes. It welds, polishes, cuts and bends much as 304 does. However 316L stainless has a greater corrosion resistance and is therefore used when manufacturing product contact parts and associated equipment.
Stainless Steel Treatments
Pharmaceutical manufacturing requires that all parts contacting medicine or product maintain the highest levels of sterility. One way to ensure this is to reduce a parts surface roughness. On a microscopic scale materials have peaks and valleys on it’s surface. The greater the difference in a materials peaks and valleys will increase it’s surface roughness. A rough surface is likely to harbor microorganisms and is therefore unfit for pharmaceutical production. A few treatments that enhance the corrosion resistance and surface quality of stainless steel are Electropolishing and Passivation.
Mechanical polishing or buffing can greatly reduce the surface roughness of stainless steel. However electropolishing can further smooth a stainless surface on a microscopic level. We can measure how smooth a surface is with the use of a profilometer. This device measures an items Ra (Roughness Average) and allows us to compare how smooth or rough a surface is.
Stainless steel forms a passive film on its surface once presented to the open air. During the manufacturing of stainless parts there are several processes that disturb this passive film such as polishing, cutting, welding, etc. The passivation process reintroduces this passive film and provides further corrosion resistance to the stainless parts.