Choosing among the wide variety of stainless steel and specific alloys available can be challenging when you need sanitary processing equipment. However, the consequences of corrosion-related system failure can be significant, and you can’t observe what’s happening inside your system daily to determine whether corrosion might be beginning.
The fact that so many stainless steels and alloys’ primary selling point is corrosion resistance complicates matters further. The science of corrosion is complex, but the reality of how it manifests in your equipment over time is even more so because it is highly situation-specific, and unanticipated factors, such as the presence of pollutants, can have a significant impact.
Hastelloy C-22 Or Hastelloy C-276 Are Both Tough Alloys
Hastelloy C-22 and Hastelloy C-276 are two highly corrosion-resistant alloys. These alloys are frequently used in processing which puts a lot of strain on the machinery since it requires harsh chemicals, high temperatures, and constant cleaning to maintain product purity and avoid contamination.
Sanitary processing, whether for foods and drinks, household goods and pharmaceuticals or personal care and cleaning products, belongs firmly in the “demanding” category. It has to do with the chemistry of the materials used to build the processing system and the chemistry of the products used in and produced by the equipment.
Around 20 high-performance alloys with nickel as their main component all fall under the “Hastelloy” brand.
Chromium Provides Critical Corrosion Protection
Whereas C-22 is commercially accessible from stock in sanitary or high purity tubes while C276 is not, both C-276 and C-22 have exceptional corrosion resistance—considerably more than any stainless steel.
Corrosion resistance is often increased directly by the amount of chromium added. Even though other substances, such as molybdenum, are frequently used to boost chromium protection, chromium is still essential for this protection.
When a system is first put into service, chromium reacts with oxygen to generate an incredibly thin, stable coating of chromium oxide (Cr2O3) on the interior surface of processing equipment. This coating is crucial to corrosion resistance.
Processing Environments And Corrosion
To avoid corrosion and damage, choosing suitable materials when building your sanitary processing system is essential. Still, everything depends on the system’s internal environment, or the processing environment, in which it runs. Although the technology exists to peer inside processing systems to check for potential corrosion, it will only catch corrosion after it has started and won’t stop it from developing. Corrosion starts from the inside.
In essence, corrosion is damage resulting from metals interacting with aggressive species in the environment, transforming the metal into dissolved metal ions and accumulating corrosion products. Corrosion is a chemical reaction that occurs when gases or liquids that have access to metal surfaces attack them. Usually, the more active the corrosion, the higher the temperature.
Since we process wet materials and liquid cleaning solutions frequently at temperatures below the boiling point, we concentrate on “wet” corrosion concerning the interior of processing equipment because the corrosive chemicals are suspended or dissolved in water, which contributes to the process known as aqueous corrosion.
Which Is Best For Your Sanitary Processing Environment?
Compared to all other stainless steels, C-276 and C-22 both have exceptional corrosion resistance; however, C-22 is readily available for purchase in sanitary or high-purity tubes, but C276 is not.
In decreasing conditions, C-22 and C-276 offer nearly the same level of protection. Due to its increased chromium concentration, C-22 offers stronger general corrosion resistance and significantly improved localized corrosion resistance in chloride-containing conditions, which are much more typical in sanitary processing.
Below are the critical temperatures for crevice corrosion and pitting for C-22 demonstrated. Sodium chloride (NaCl), hydrochloric acid (HCl), sulfuric acid (H2SO4), and sodium hypochlorite are examples of common strongly oxidizing media. In hygienic processing, all of these are routinely utilized.
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