Stainless steel and types of Stainless steel in Pharma Industries
Stainless steel in pharmaceutical applications, such as food and beverage manufacturing, require structural materials to maintain structural integrity (i.e., corrosion resistance and sufficient strength to withstand the conditions of use), as well as inert surfaces (i.e., (low release of contaminants within the product) is also required. Stainless steel is widely used in the pharmaceutical industry due to its corrosion resistance, inert (easy to clean) surface, and ease of manufacturing.
Although grade 1.4401 (AISI 316) and its derivative stainless steels are most widely used in pharmaceutical applications and are considered by many to be the industry standard, the materials for each application vary in their corrosion resistance in the specific operating environment. Selected based on. Choosing the right grade of stainless steel also requires consideration of the cleaning routine and cleaning products used within the facility.
In addition, material selection can also be influenced by the operation of the equipment, whether it is continuous operation with a cleaning-in-place system or periodic operation with stops to clean the equipment.
Austenitic stainless steel grade 1.4031 (AISI 304) and its derivatives are used in soft environments with a chloride content of less than 200 mg/l, and grade 1.4401 (AISI 316) and its derivatives are used in soft environments with a chloride content of less than 500 mg/l. Can be used up to /l. mg/l.
Duplex stainless steel grades 1.4462 (2205) and 1.4362 (2304) are used because of their high chloride content and resistance to stress corrosion cracking, especially at high operating temperatures.
For more severe operating conditions, super-austenitic (e.g. 1.4547) and super-duplex (e.g. 1.4410) grades may be required. Common uses for stainless steel in pharmaceutical manufacturing include process vessels, reaction vessels, tanks/storage vessels, pumps, piping and tubing, heat exchangers, scrubbers, faucets, and valves.
Stainless steel is typically classified into five types:
Ferritic: – These steels are based on chromium with a small amount (usually less than 0.10%) of carbon. These steels have microstructures similar to carbon steels and low alloy steels. Their use is usually limited to relatively thin sections due to insufficient weld strength. However, it offers a wide range of applications when welding is not required. It cannot be strengthened by heat treatment. High chromium steels with molybdenum additives can be used even in very harsh conditions such as seawater. Ferritic steels are also selected for their resistance to stress corrosion cracking. Not as ductile as austenitic stainless steels. They are magnetic.
Austenitic: – These steels are the most common. Their microstructure is determined by the addition of nickel, manganese, and nitrogen. This is the same structure found in conventional steel at much higher temperatures. This structure gives these steels a distinctive combination of weldability and formability. Corrosion resistance is improved by adding chromium, molybdenum, and nitrogen. Although it cannot be strengthened by heat treatment, it has the advantage of being strengthened to high strength while maintaining the necessary ductility and toughness.
Austenitic steels with higher nickel content have increased resistance to stress corrosion cracking. Although they are nominally non-magnetic, they typically exhibit some degree of magnetic response depending on the composition and work hardening of the steel.
Martensitic steels: – These steels are similar to ferritic steels in that they are chromium-based, but have higher carbon levels of up to 1%. This allows it to be hardened and tempered in the same way as carbon steel or low alloy steel. It is more common in roll products than in sheet or plate form. Usually has poor weldability and formability. They are magnetic.
Duplex steels: – These steels have a microstructure consisting of approximately 50% ferrite and 50% austenite. This gives it higher strength than ferritic and austenitic steels. Resistant to stress corrosion cracking. So-called “lean duplex steels” have corrosion resistance comparable to standard austenitic steels, but with increased strength and resistance to stress corrosion cracking. “Super duplex” steels have increased strength and resistance to all forms of corrosion compared to standard austenitic steels. It is suitable for welding, but care must be taken in selecting welding materials and heat input. It has moderate formability. It is magnetic, but not as strong as ferrite or martensite.
Distributed reinforcement. These steels can achieve very high strength by adding elements such as copper, niobium, and aluminum to the steel. Proper “aging” heat treatment forms very fine grains in the steel matrix, imparting strength. These steels can be machined into very complex shapes and require good tolerances before final aging treatment to minimize deformation during final machining. This is in contrast to traditional hardening and tempering of martensitic steels, where distortion is a major issue. Corrosion resistance is comparable to standard austenitic steels such as 1.4301 (304).
Austenitic stainless steels: – These are stainless steels containing chromium and nickel with very low carbon content. It is not magnetic, but may become slightly magnetic due to cold working. Cold working also increases strength. Austenitic stainless steel has excellent corrosion resistance. Good formability. It has good weldability and excellent mechanical properties over a wide temperature range. Additionally, these steels are easy to clean, which has led to their increasing use in hygienic and sterile environments.
Common uses for the different grades include:
304/304L: – Reservoirs, storage tanks and pipelines for aggressive liquids. Technical equipment for the mining, chemical, cryogenic, food, pharmaceutical and beverage industries. These stainless steels are also used to make cookware, cutlery, building products, and sinks.
309/310: – These grades have higher chromium and nickel content than grade 304. Due to their high oxidation resistance, these steels are used in high-temperature applications such as furnace components, kilns, and catalytic converters.
318/316L: – Tanks, pressure vessels, piping and components for harsher environments and special applications, such as the manufacture of tank containers for bulk transport of chemicals and corrosive liquids. Containing molybdenum improves corrosion resistance.
321/316Ti:- These are “stabilized” grades. They are resistant to sensitization and therefore to the possibility of intergranular corrosion. It is also used in parts that require improved heat and corrosion resistance, such as afterburners, super-heaters, expansion joints, and bellows.
Ferritic stainless steels: Ferritic stainless steels are simple chromium stainless steels that typically have a low carbon content. It is magnetic, highly ductile, and resistant to corrosion and oxidation. They are generally resistant to stress corrosion cracking. However, it has weldability limitations that limit its use in thinner gauges. 3CR12 is a special grade developed and patented by Columbus Sustainable that significantly solves this problem.
Common uses for the different grades include:
409:– Automotive exhaust pipe and catalytic converter housings.
430: – Kitchen sinks, troughs, cutlery, kitchen and catering equipment and appliances.
1.4509 (441): – This grade is specially manufactured by Columbus Sustainable for use in automotive parts. Good mechanical strength at high temperatures (up to 850°C) makes it an ideal material for the front end of exhaust systems (near the engine). It can also be used to manufacture heat exchanger tubes.
AISI 444: – The PRE (pitting resistance equivalent) of the AISI 444 grade is very similar to the 316 grade, meaning its corrosion resistance is similar even in harsh environments such as outdoor environments. On the coast. 444 tubes can be ground, bent, and welded using conventional methods, and the inside of the tube is clearly marked. PRE is defined as %Cr + (3.3%Mo) + (16%N) and indicates the resistance of steel to pitting corrosion.
3CR12: – This is a cost-competitive, corrosion-resistant, general-purpose weldable ferritic stainless steel with particular advantages in wet grinding applications. Unlike other ferritic stainless steels, it can be welded up to a thickness of 30mm. It is widely used in the mining, material handling and sugar industries due to its resistance to atmospheric and wet abrasion corrosion.