For a number of years now, stainless steel has enjoyed widespread popularity in the pharmaceuticals industry, simply because it matches up very well with the criteria established in the industry for the requirements of industry-specific products. It’s very important in pharmaceutical usage that any metals used are highly resistant to corrosion, that they can be easily manufactured, and that they can be quickly and easily cleaned without surface particles coming off in the process.
Some specific examples of how stainless steel is used in the pharmaceutical industry include the areas of pumps, processing and reaction vessels, storage tanks, heat exchangers, tubes and pipelines, and valves and taps. All of these products are easily made, easily cleaned, and are highly resistant to corrosive action, but there are even more uses for the various types and grades of stainless steel in the pharmaceuticals industry.
Grades of steel and how they’re used
The most widely used grouping of stainless steels in the pharmaceutical industry is grade 1.4401 and its derivatives. This grouping has become the de facto standard of the industry, although other specific grades of stainless steel will still be chosen on the basis of their suitability to a particular service or action being performed.
In some cases, the grade of stainless steel selected is closely associated with the type of cleaning agents and the method of cleaning used in a particular facility. It’s also possible that the operational mode of a facility will influence stainless steel grade selection, because some facilities operate continuously while using a clean-in-place method, whereas others will close the facility down for a comprehensive all-at-once cleaning.
In mild environments where chloride content does not exceed 200 mg/L, an austenitic stainless steel grade such as 1.4031 might be used, while chloride content up to 500 mg/L might indicate a grade of 1.4401. When chloride content exceeds 500 mg/L, it’s very common to see duplex stainless grades such as 1.4362 and 1.4462 chosen, because they offer high resistance to stress corrosion cracking. For service environments which are even more aggressive, it may be necessary to use the super-austenitic stainless steel grade 1.4547, or the super-duplex grade of 1.4410.
Types of stainless steel
The most common types of stainless steel are the austenitic types, whose structure is comprised of nitrogen, nickel, and manganese. This kind of structure is responsible for imparting characteristics such as formability and weldability to the finished product. The resistance to corrosion which stainless steel naturally has can be supplemented by adding more nitrogen, along with chromium and/or molybdenum.
These stainless steels do not get any harder with treatment, but they can be processed to extraordinary levels of strength. While austenitic steels are susceptible to stress corrosion cracking, they can be made more impervious by including a higher nickel content. Some of the most common applications which austenitic stainless steel grades are used in, include the following:
- 304/304L – these kinds of stainless steel are generally used for producing cutlery, sinks, hollow-ware, architectural products, storage vessels, tanks, and pipes intended for use with corrosive fluids.
- 309/310 – higher nickel and chrome content gives this grade of stainless steel greater resistance to oxidation, making it suitable for applications where high temperatures are involved, such as in furnaces, catalytic converters, and kilns.
- 318/316L – a higher molybdenum content increases resistance to corrosion, making this grade of stainless steel ideal for use in pressure vessels, pipework, and tanks where the transportation of corrosive liquids and chemicals is indicated.
- 321/316Ti – considered to be the stabilized grades of stainless steel, these are resistant to inter-granular corrosion, so they can be used in components which require high temperature strength and resistance to corrosion, for instance in super-heaters, expansion bellows, compensators, and after-burners.
Ferritic steels are largely comprised of chromium, with small amounts of carbon mixed in. They are structurally similar to low-alloy steels and carbon, and since they are not particularly useful for welding, they are mostly used in thin sections where welding is not required. Ferritic steels are also known for being magnetic, but lack the powerful resistance capabilities of austenitic stainless steels. Some of the applications where ferritic steels are most commonly used include the following:
- 409 – this grade of ferritic steel is commonly used in catalytic converter casings, and sometimes in exhaust tubing.
- 430 – often used in wash troughs, cutlery, catering equipment, and kitchen sinks, Grade 430 is considered quite versatile.
- 1.4509 – a special grade produced by Columbus Stainless, this grade is frequently used in automotive components because of its mechanical strength at high temperatures. It’s also frequently used in heat exchanger tubes.
- AISI 444 – this stainless steel grade has similar characteristics to Grade 316, in that its resistance to corrosion is very strong in aggressive outdoor environments.
- 3CR12 – this is another special grade developed by Columbus Stainless for the purpose of overcoming problems with weldability. It has high resistance to corrosion and is particularly useful in wet or abrasive applications. Unlike most other types of ferritic stainless steel, this special grade can be welded, even to higher thicknesses. It is frequently used in material handling, mining, and in the sugar industry, because of its increased resistance to atmospheric and abrasive corrosion factors.
The structure of duplex steels is comprised of approximately 50% ferritic and 50% austenitic, and this composition gives them greater strength than either of their sources, as well as high resistance to stress corrosion cracking. The subcategory known as lean duplex steels are manufactured to approximate the standard corrosion resistance of austenitic steels, but with greater resistance to stress corrosion cracking and with increased strength. The subclass known as a super duplex steels have greater strength and greater resistance to all kinds of corrosion, compared to ordinary austenitic steels. Duplex steels can be welded, if care is taken with heat input and welding consumables.
Martensitic steels are much like for ferritic steels in that their primary ingredient is chromium, although they have a greater carbon content than do the ferritic steels. This being the case, they can be tempered and hardened in the same fashion as carbon or low-alloy steels. Their usage comes in play primarily in settings where moderate resistance to corrosion is necessary, but high-strength is a solid requirement. Martensitic steels are more commonly manufactured into long-ish products, rather than in plates or sheets, and have relatively low formability and weldability.
Precipitation-hardening steels can achieve extraordinary strength when components such as aluminum, niobium, and copper are added in. These types of steels are often machined into shapes that are fairly intricate and delicate, because they sustain very minimal distortion during the final treatment process. This is in stark contrast to more conventional martensitic steels, where greater distortion typically occurs during hardening and tempering.