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Peer-Reviewed Topical Review: The Importance of Quality in Corrosion-Resistant Alloys in Biopharmaceutical Manufacturing
In this topical review, the authors discuss the rationale behind microstructural requirements for biopharmaceutical equipment and problems that may be encountered during the fabrication of high-performance corrosion-resistant equipment.
The fabrication of vessels made of austenitic stainless steels and the higher corrosion-resistant materials such as the superaustenitic
and nickel alloys are the same in many ways, but there are some differences. The obvious difference is the higher value of
the raw material being used to fabricate the vessels. There are also the basic welding, forming, and polishing differences.
The more important issue, however, is that the vessels made of these higher alloys are generally used in more critical applications
with regard to corrosion resistance, some of those being final product or "payload" vessels where the value of the product
in these vessels are much higher than any other. The vessels made of these higher alloys are expected to be at a minimum equivalent
in surface-finish characteristics to austenitic stainless steels. By meeting this requirement, the cleaning and sterilization
will be equivalent to known practices and the higher corrosion resistance will be automatic. Overall, the surface-finish quality
and corrosion resistance must be at a premium. If there are any problems encountered during manufacturing of the vessels that
do not allow this premium quality to be achieved, it hampers fabrication schedules, which can in turn affect a company's schedule
of getting a drug to market. There are also major cost effects of raw materials and shop labor that the vessel manufacturer
has put into the product.
Figure 1: (COURTESY OF DCI INC.)
The fabrication of these high-alloy vessels begin with the normal purchase of raw materials. The lead times of these raw materials
are generally longer than the austenitic stainless steels, and it is important to have the correct material specifications
at this stage. Raw materials are received into the fabrication shop normally in the mill hot-rolled, annealed, and descaled
condition, but on occasion are in a cold-rolled 2B type finish. The material is thoroughly inspected. Raw-material markings
are checked, and material certifications are received and reviewed for compliance. Positive material identification is performed
to verify the correct material chemistry. After inspection, components such as vessel heads, liners, heat-transfer coils,
and heat-transfer jackets are cold-formed and prepared for welding. Welding is performed in compliance with the applicable
code and customer specifications; typically for the American Society of Mechanical Engineers' (ASME) Section VIII, Division
I code vessels, ASME Section IX is required (3, 4). Welding of the shells, heads, nozzles, and heat-transfer surfaces are
performed. After welding, many forms of mechanical polishing steps are performed to remove any mill hot-rolled, annealed,
and pickled finish, weld beads, and weld-heat tint to achieve a uniform, flush, and smooth surface finish. Much of this work
is performed at the component and subassembly stage. Many inspections of welds and surface finishes are performed during this
process to comply with customer requirements and the ASME bioprocessing equipment standard (5).
Figure 2: (COURTESY OF DCI INC.)
The final stage is electropolishing of the vessel components and subassemblies. At this stage, the final surface finish is
achieved and inspected. If it does not meet the requirements and if it is found to be a raw-material metallurgical issue,
the surface finish generally cannot be changed. This situation becomes a major issue for the vessel manufacturer, raw-material
suppliers, and mostly the vessel purchaser. Depending on the vessel, 70–90% of the fabrication costs may be already performed
at this point. Normally there are only a few final fabrication steps left such as installation of components and subassemblies
into the vessel and finally the insulation and exterior sheathing. In addition, there may be some final factory-acceptance
testing to be performed. Figure 1 shows the highly electropolished heat-transfer coils for a vessel. A completed biopharmaceutical
vessel is shown in Figure 2.
Hira Ahluwalia, PhD, is president of Material Selection Resources, Pennington, NJ 08534, hira@doctormetals.com.
Articles by Hira Ahluwalia
Brian J. Uhlenkamp
Brian J. Uhlenkamp is vice-president of engineering and research and development at DCI Inc., 600 North 54th Ave., St. Cloud, Minnesota 56303, tel. 320.252.8200, bjuhlenkamp@dciinc.com.
Articles by Brian J. Uhlenkamp
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To select processes for both new and legacy products
