Pharmaceutical industry is governed by strict regulatory norms. With time these norms have just got stringent. In order to comply with the regulations, high performance alloys containing chromium, nickel, molybdenum are used extensively throughout processes. Higher composition of these alloys imparts greater resistance to adverse environments. Stainless steel is used in Pharmaceutical industry for manufacturing of tanks, pressure vessels, pipe works as well as more intricate parts like orthopaedic implants and hypodermic needles. Material used in the industry needs to interact with corrosive chemicals, high temperature, high pressure and withstand frequent fierce cleaning regimes. These adverse operating conditions are major concern for the industry as they may lead to various types of degradations like chloride stress-corrosion cracking, pitting corrosion, crevice corrosion and corrosion of weld heat-affected zones.
Food and Drug Administration (FDA) states the rules for equipment construction in its CFR – Code of Federal Regulations Title 21
“Equipment shall be constructed so that surfaces that contact components, in-process materials, or drug products shall not be reactive, additive, or absorptive so as to alter the safety, identity, strength, quality, or purity of the drug product beyond the official or other established requirements.”
Austenitic grade 316L/1.4404 meets most of the industry requirements, as a result it is used extensively in manufacturing of components. Presence of higher percentage of Nickel and Molybdenum improves resistance to pitting corrosion and corrosion from exposure to salts. For higher resistance to corrosive environments, super austenitic grades containing higher percentage of nickel and molybdenum are developed. However, high molybdenum content increases the overall cost of equipment.
Another austenitic grade 304L/1.4307 is used for less critical applications where moderate levels of corrosion resistance are desired. It has wide acceptance as it offers good corrosion resistance with ease of cleaning and sterilizing. It has overall good performance at modest cost, making it ideal for variety of applications.
Super austenitic grades containing high Nickel and Molybdenum are expensive. In order to keep costs low, duplex grade 2205 with about 3% molybdenum can be preferred. It offers similar corrosion resistance at economical cost. 2205 has higher nitrogen content and finer microstructure resulting in higher strength than austenitic 316L. Increased strength results in reduced wall thickness of components. It is especially beneficial in manufacture of intricate parts with design constraints. Duplex stainless steel offers higher resistance to Stress Corrosion Cracking credit to its 50% austenitic and 50% ferritic microstructure.
To enhance passivity and clean-ability of stainless steel equipment, most of the stainless steel equipment are electropolished and passivated. These processes develop a thin passive film over metal surface thereby increasing its corrosion resistance. Electropolishing and Passivation also helps to remove surface imperfections, which may have developed during various manufacturing stages. This ensures, that the surface is microscopically featureless and clean.
Equipment used in Pharmaceutical industry are highly customised and expensive, hence decision with regard to equipment design and material needs to be prudent. Use of inferior grade material may lead to frequent contamination of production batches, which need to be discarded. Such frequent incidents impact operational cost and it is also not feasible to replace installed equipment over short period of time. Stainless steel and other high alloy grades involve substantial up-front cost. However, considering better longevity of these products, the overall life-cycle cost is substantially lower. All the above mechanical properties with added financial benefits make stainless steel a popular choice in the Pharmaceutical industry.