Peer-Reviewed Topical Review: The Importance of Quality in Corrosion-Resistant Alloys in Biopharmaceutical Manufacturing - Pharmaceutical Technology

Latest Issue
PharmTech

Latest Issue
PharmTech Europe

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.


Pharmaceutical Technology
Volume 3, Issue 32

The need for electropolishing


Figure 5: (COURTESY OF AUTHORS.)
The 300-series type stainless steels are often electropolished and passivated primarily to improve their corrosion resistance and cleanability. It can be argued that the high performance corrosion-resistant alloys do not need to be electropolished and passivated because the higher alloying content provides adequate corrosion resistance. Passivation procedures that are used to form a uniform passive film to enhance corrosion resistance are not necessary with the higher alloys. Electropolishing, however, is often specified for the high-performance alloys. Mechanically finished surfaces produce a cold worked surface and damaged layer that includes scratches, lapping, and gouges with possible embedded abrasive compounds. Electropolishing is used to remove this layer and impart a surface that is microscopically featureless and clean. It substantially reduces product contamination and adhesion as electropolishing reduces the effective active surface area on the metal surface and removes material imperfections such as inclusions. Overall, electropolishing allows better cleaning, sanitization, and sterilization, thereby, lowering cleaning costs, allowing easier validation that minimizes the potential for product contamination, along with lowering future maintenance costs.


Figure 6: (COURTESY OF AUTHORS.)
Since electropolishing is a form of corrosion, any microstructural defects are preferentially corroded leading to an undesirable surface finish.

Microstructure quality deficiency


Figure 7: (COURTESY OF AUTHORS.)
Over the past few years, several cases have been reported where vessels fabricated using the high-performance alloys showed a visual "hazing," frosting, or whitening of the surface (6). Figures 5 and 6 show some of the extreme cases of inadequate surface characteristics obtained after electropolishing the nickel–chromium–molybdenum alloy UNS N10276 plate. Figures 7 and 8 show the surface of an UNS N08367 plate after electropolishing. It is clear that the surface appearance in all these cases is due to the preferential corrosion of secondary phases in the microstructure. The defects have been observed on various product forms, including sheet, plate, tube, pipe, bar, and forgings. The defects are not limited to alloy N10276, but have been observed in UNS N06022, UNS N06200, UNS N06686 (Alloy 686), and UNS N06059 (Alloy 59) and also the superaustenitic stainless steels UNS N08367, UNS S31254, and UNS N08926 (Alloy 25-6Mo).


Figure 8: (COURTESY OF AUTHORS.)
To determine the root cause of the deficiency observed during electropolishing, samples from the various alloy plates were cross-sectioned, and the microstructure evaluated. The montage of photomicrographs shown in Figure 9 show the microstructure of the various nickel–chromium–molybdenum alloys that cause undesirable electropolish quality and make these microstructures unacceptable for fabrication of biopharmaceutical equipment.


ADVERTISEMENT

blog comments powered by Disqus
LCGC E-mail Newsletters

Subscribe: Click to learn more about the newsletter
| Weekly
| Monthly
|Monthly
| Weekly

Survey
FDASIA was signed into law two years ago. Where has the most progress been made in implementation?
Reducing drug shortages
Breakthrough designations
Protecting the supply chain
Expedited reviews of drug submissions
More stakeholder involvement
Reducing drug shortages
70%
Breakthrough designations
4%
Protecting the supply chain
17%
Expedited reviews of drug submissions
2%
More stakeholder involvement
7%
View Results
Eric Langerr Outsourcing Outlook Eric LangerRelationship-building at Top of Mind for Clients
Cynthia Challener, PhD Ingredients Insider Cynthia ChallenerRisk Reduction Top Driver for Biopharmaceutical Raw Material Development
Jill Wechsler Regulatory Watch Jill Wechsler Changes and Challenges for Generic Drugs
Faiz Kermaini Industry Insider Faiz KermainiNo Signs of a Slowdown in Mergers
From Generics to Supergenerics
CMOs and the Track-and-Trace Race: Are You Engaged Yet?
Ebola Outbreak Raises Ethical Issues
Better Comms Means a Fitter Future for Pharma, Part 2: Realizing the Benefits of Unified Communications
Better Comms Means a Fitter Future for Pharma, Part 1: Challenges and Changes
Source: Pharmaceutical Technology,
Click here