The Importance of Passivated Stainless Steel for Biopharmaceutical Applications

Reviewed by Jordan Schaecher
  • January 8, 2021

Contamination is the bane of almost any manufacturing process, but when the product being made is pharmaceuticals, even a small amount of contamination can have disastrous results. Because of its high resistance to corrosion, austenitic stainless steels such as 304L and 316L are frequently the go-to materials for construction of tanks, supply lines and other portions of the production system.

Stainless steel alloys contains at least 11% chromium and when free iron has been removed from the surface, it naturally forms a chemically inert passive layer that protects the underlying base metal. But, this layer can become damaged or compromised over time, even by the natural movement of iron atoms through the structure of the metal itself. As a result, the metal needs to be proactively cleaned and re-passivated on a proactive driven schedule. If left untreated, the most common visible version of corrosion is called rouge.

Rouge is the name for a variety of iron oxides, with the most common being ferric oxide or simply, “rust”. It can form in water systems, including in water for injection (WFI) equipment, but also in process tanks and in the piping that runs throughout the system. It is an unfortunate irony that the high-purity water systems that are integral in the production of medications can be the source of contamination that ruins an entire production lot.

Beyond the risks of the ferric oxide itself, its presence increases the difficulty of effectively cleaning the surfaces between batches. Further, microbes can find haven within the rust particles themselves adding the risk of biologic contamination of the product.

Preventative Maintenance Preempts Problems

Obviously, the best way to prevent contaminated product is to reduce the factors that could lead to such a situation. Chemical passivation strengthens the passive layer far beyond what it can achieve through natural means, increasing its resistance to corrosion. Additionally, once an analysis of the operating conditions of the system has been completed, a data-based schedule of preventative maintenance can be put in, which unlike an emergency shutdown, can be planned well in advance.

Preventative maintenance itself allows for an extended period between downtimes. Because of the stronger passive layer, the average time between failures is greater than it would be for a naturally passivated surface. Moreover, because the maintenance occurs before rouge can form, the risk of such failures, along with possible structural damage caused by rouge buildup is significantly reduced. It should also be noted that the period of non-operation for a planned service is most likely to be shorter than the time needed to track down the source of such contamination, clean, and repair any damage.

Such data-based servicing of the equipment can also prevent problems of a different kind. Over the years, rouge contamination has prompted numerous FDA warning letters for pharmaceutical manufacturers, producers of denture resins, and others as violations of good manufacturing practices (GMP). Not only will planned maintenance forestall instances requiring the FDA’s attention, but as reputable companies provide documentation to show that their passivation services have been performed to meet ASME and other standards, and that the metal has been tested, this helps establish compliance with GMP.

It All Comes Down to Money

Ultimately, production is about generating revenue and cost considerations are usually top of mind for any operator. When looking at a spreadsheet, it is easy to see regular passivation treatments as nothing more than a simple cost of doing business. But, that would be overlooking the broader return on the investment. As noted above, a proactive schedule of servicing provides these benefits:

  • Reduces risk of product contamination resulting in rejected production lots
  • Reduces risk of unplanned outages
  • Extends operational periods
  • Reduces costly repairs
  • Demonstrates compliance with GMP requirements

Any one of those above factors can result in unexpected expenditures. Individually, the costs associated with an incident can far exceed the cost of a preventative treatment. Considering, for a moment that more than one of those factors can come into play from a single incident, a scheduled passivation treatment can be seen as an investment that turns savings many times more than the financial outlay. As an example, the cost in lost materials of a bad lot can be equaled by the expenses involved in retasking another production line to make up for the shortfall in production to meet a delivery deadline.

Going one step further, passivation treatments offer the cost savings of efficiency. Looking beyond the simple axiom of “time is money”, planned downtime can be used to perform similar maintenance services up and down the production chain, whether it’s changing filters, adjusting the packaging or anything in between. And because it’s scheduled, people and resources can be pre-tasked elsewhere as needed, as opposed to an “all-hands-on-deck” moment while critical personnel are off-site.

The Bottom Line

In reality, it is all about the bottom line. The expenses of an unplanned outage, the lost time and materials, and the procedural hurdles required to once again demonstrate regulatory compliance each constitute an unplanned, and highly variable expense.  On the other hand, a schedule of passivation treatments, custom-tailored to a specific system greatly reduces the risks of such occurrences and replaces them with predictable investments into the health and longevity of the equipment that far exceeds any outlay.