Hastelloy® C-22® or Hastelloy® C-276®: Which Is Right for Your Processing Environment?

The availability of so many stainless steels and special alloys can be daunting when there’s a choice to be made for your sanitary processing equipment needs.

However, the costs of system failure due to corrosion can also be formidable, and on a day-to-day basis, you can’t see what’s going on inside your system to find out if corrosion might be starting.

Adding to the complication is the fact that corrosion resistance is the main selling point of so many stainless steels and alloys. The science of corrosion is complicated, but the reality of how it plays out over time in your equipment is even more so because it’s highly specific to each situation, and unforeseen factors like the presence of contaminants can play a huge role.

Hastelloy® C-22® Family Shot

Hastelloy® C-22® vs C-276®: Both made for tough conditions

Here we’ll explore two highly corrosion-resistant alloys - Hastelloy C-22 and Hastelloy C-276. These alloys are often used in processing that places heavy demands on equipment – involving harsh chemicals, high temperatures, and the need for continuous cleaning to ensure product purity and prevent contamination. 

Sanitary processing, whether it be for food and beverages, personal care and cleaning products, or pharmaceuticals, falls squarely in the “demanding” category. It has to do with the chemistry of the products used in and made by the equipment, and the chemistry of the materials used to construct the processing system.

Hastelloy” is a trademark name that applies to around 20 high-performance alloys that all have nickel as a primary ingredient. 

Many are highly resistant to corrosion by hydrochloric, sulfuric, phosphoric, acetic, and formic acids, and to chlorine – all of which are common in sanitary processing.

The Hastelloys fall into two groups:

  • Nickel-molybdenum (Ni-Mo) alloys
  • Nickel-molybdenum-chromium (Ni-Mo-Cr) alloys

Both C-22 and C-276 are Ni-Mo-Cr alloys. Let’s first look at the critical role of chromium in enhancing corrosion resistance.

Chromium provides critical corrosion protection

All stainless steels, including the 304 (18% Cr) and 316 (16% Cr, 2% Mo) stainless steels commonly used for sanitary processing equipment, contain at least 10-11% chromium. It is why stainless steel is called “stainless.”

In general, the greater the amount of chromium added, the higher the corrosion resistance. Although other elements such as molybdenum are often added to enhance the chromium protection, the chromium is key to providing this protection.

Chromium is critical to corrosion resistance because when a system is first put into service, it reacts with oxygen to form an extremely thin, stable coating of chromium oxide (Cr2O3) on the inside surface of processing equipment.

When this protective layer is formed, the alloy surface is referred to as “passive” because it’s unlikely to react chemically or electrochemically with what’s put through the processing equipment.

It is also chemical and electrochemical reactions between processor contents and the equipment construction material that leads to corrosion.

Not only does the passive layer itself not react, but it also acts as a barrier between the contents inside the processor and the system’s underlying metal, preventing it from corroding. Passivation can be removed with strong reducing agents that destroy the protective oxide layer on the metal.

In nominal terms, C-276 is 16% chromium, and C-22 is 22% – a significant difference. We’ll discuss the practical differences this makes to their respective performances below.

Nickel: strength and stability

Over two-thirds of all the nickel produced goes into making stainless steel, and about three-quarters of all stainless steels, including 304 (about 8% nickel) and 316 (10% nickel), contain it. Nickel lends formability, weldability, and ductility. 

It also adds resistance to: 

  • Reducing acids
  • Caustic solutions
  • Stress corrosion cracking

Under certain processing conditions, including the presence of chlorides, the protective chromium passive layer can become chemically reactive and begin to break down, exposing the inside of the system to localized corrosion - particularly pitting and crevice corrosion. Nickel has no role in initiating that process but slows down the progression once it has begun. It also allows more chromium to be incorporated into an alloy, thereby increasing corrosion resistance.

Molybdenum: versatility in enhancing alloy qualities

Molybdenum is a key alloying element in high-performance nickel-based alloys that fall into two categories:

In sanitary processing, temperatures, in general, don’t exceed boiling (212°F/100°C), so the temperature-resistant qualities don’t really apply. Corrosion resistance is the quality with which sanitary processing is primarily concerned. 

These are some of the main corrosion-fighting benefits of molybdenum:

  • It resists non-oxidizing conditions (reducing acids where the primary corrodent is the hydrogen ion rather than dissolved oxygen), including hydrochloric and sulfuric acids, common in sanitary processing.
  • Molybdenum doesn’t provide corrosion resistance to oxidizing environments - in fact, it typically results in a higher corrosion rate. Because of this, nickel alloys that contain high levels of Mo and little or no Cr are not recommended for oxidizing acids or solutions containing higher levels of oxidizers such as chlorine.
  • In oxidizing environments, it joins with chromium to protect against localized s such as pitting and crevice corrosion, especially in the presence of chlorides and non-oxidizing acids.
  • It dramatically enhances the resistance of nickel to reducing agents such as oxalic acid.


Tungsten’s primary benefits (increased resistance to oxidation, nitridation, carburization, halogenation, and stress corrosion cracking) apply in temperatures above those involved in sanitary processing. At temperatures applicable to sanitary processing – generally between room temperature and boiling – it performs many of the same functions as molybdenum, including supporting metallurgical stability.

Nominal quantities (percent by weight) of Cr, Ni, Mo and W in C-22 and C-276

Chromium %

Nickel %

Molybdenum %












C-22 vs C-276 Corroded Pipe

Processing environments and corrosion

Proper choice of material for constructing your sanitary processing system is critical to prevent corrosion and damage. Still, it all depends on the processing environment in which it operates – the environment inside the system. Corrosion starts from the inside, and while the technology exists to see inside processing systems to determine whether corrosion may be happening, it will only detect corrosion once it has initiated and won’t prevent it from happening.

That makes choosing the right material for your specific environment even more important.

Corrosion is essentially damage that happens when metals react with aggressive species in the environment to turn the metal into dissolved metal ions and accumulated corrosion products. It occurs when gases or liquids chemically attack metal surfaces they have access to, and typically the higher the temperature, the more active the corrosion becomes.

With the inside of processing systems, we focus on “wet” corrosion because we’re dealing commonly with processing wet products and liquid cleaning solutions at temperatures below the boiling point. This is also referred to as aqueous corrosion because the corrosive agents are dissolved or suspended in water, and the water itself also plays a role.

Oxidation and reduction: the foundation of corrosion

We discussed earlier how chromium reacts with oxygen to form the protective passive layer, and after that, has a tendency to stabilize and stop reacting with other elements in the environment and thereby stop corrosion. We would think of this as beneficial oxidation, while corrosion is harmful oxidation. Creating the conditions for the stability that preserves the passive layer is a lot about choosing the right alloy for the environment.

When metals react with their environments, two basic electrochemical processes are going on – oxidation and reduction - which result in atoms leaving the metal surface as ions and either remaining as dissolved metal ions in the process stream or combining with other substances to form accumulated corrosion products.

Oxidation is the process of an atom or lower valance ion giving up one or more electrons. It will only occur when the electrons from the oxidation reaction can be transferred to another atom or ion by a corresponding reduction reaction. A typical example of this is the corrosion of iron in moist air or a neutral water environment. 

Under these conditions, the Fe will oxidize to form a soluble Fe2+ion and two electrons. The dissolved O2 in the water will accept the electrons and be reduced to form OH- ions. The reactions for this corrosion process are summarized below.

Fe = Fe2++ 2e- (oxidation reaction)
O2 + 2H2O + 4e- = 4OH- (reduction reaction)
2Fe + O2 + H2O = 4OH- + Fe2+ (overall corrosion reaction)

When products of this corrosion reaction, OH- and Fe2+, become sufficiently concentrated, they will combine and precipitate out as ferrous hydroxide Fe(OH)2, which in the presence of oxygen will oxidize to Fe(OH)3, which is the final corrosion product known as rust.

The species in the reduction reaction that accepts the electrons is the oxidant or oxidizing agent. It’s being reduced and becoming more negative because it accepts the electrons from the oxidized species. The two most common oxidants responsible for the corrosion of stainless steels and nickel alloys are dissolved oxygen in neutral and basic solutions and the H+ ion in acidic solutions.

Which is best for your sanitary processing environment?

Both C-276 and C-22 have outstanding corrosion resistance — substantially more than any of the stainless steels — however, C-22 is commercially available from stock in sanitary or high purity tube while C276 is not.

C-22 and C-276 provide about the same protection in reducing environments. In non-reducing and oxidizing environments — which are much more common in sanitary processing — due to its higher chromium content, C-22 provides better resistance to general corrosion and much better resistance to localized corrosion in the presence of chlorides.

This is shown by C-22’s critical pitting and crevice corrosion temperatures below. Common severely oxidizing mediums include sodium chloride (NaCl), hydrochloric acid (HCl), sulfuric acid (H2SO4), and sodium hypochlorite. These are all frequently used in sanitary processing.

C22 vs C276
Comparison of the Aqueous Corrosion Resistances of C-22 and C-276
(in acidified 6 wt.% ferric chloride)

Nominal content of chromium, nickel and molybdenum (% by weight)

Critical Pitting Temp C°/F°

Critical Crevice Temp C°/F°


22Cr/56Ni/ 13Mo/4W

>150/ >302



16Cr/57Ni/ 16Mo/3W

>150/ >302


The C22 alloy also provides corrosion resistance over a much broader range of oxidizing and reducing environments, and using it to construct your processing system will give you a highly robust system for resisting corrosion in a wide range of chemical environments.

Next Steps

It's clear to see that the science of corrosion is complicated, but the reality of how it plays out over time in your equipment is even more so because it’s highly specific to each situation. Therefore, to protect your system, you need to make the right material choice! We’re here to help!

The sanitary and high-purity processing experts at CSI have decades of collective experience selecting the right materials for the job. Contact us today to consult on your processing system needs. We’ll help you pinpoint the best materials for your demanding processes and guide you through the steps to ensure your system operates safely for years to come.

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Central States Industrial Equipment (CSI) is a leader in distribution of hygienic pipe, valves, fittings, pumps, heat exchangers, and MRO supplies for hygienic industrial processors, with four distribution facilities across the U.S. CSI also provides detail design and execution for hygienic process systems in the food, dairy, beverage, pharmaceutical, biotechnology, and personal care industries. Specializing in process piping, system start-ups, and cleaning systems, CSI leverages technology, intellectual property, and industry expertise to deliver solutions to processing problems. More information can be found at www.csidesigns.com.