Hastelloy C-22 VS. C-22HS – Marine Engineering
Aug 04, 2026
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Foreword
As deep-sea oil and gas and seabed mining activities continue to operate in increasingly demanding environments, the requirements for structural materials in marine equipment are also rising. The insufficient strength of corrosion-resistant alloys, coupled with the susceptibility of high-strength steel to chloride stress corrosion, has long been a balancing act.
Hastelloy C-22, with its excellent corrosion resistance, is widely used in offshore operations. Its derivative, C-22HS, undergoes special heat treatment, resulting in significantly enhanced strength, providing a new solution for the selection of marine engineering materials.
This article outlines the compositional and performance differences between C-22 and C-22HS, aiming to provide support for the selection of marine engineering materials.
Article Key Points Index
1. The Industrial Dilemma of Marine Engineering(Harsh environments, where strength and corrosion resistance are mutually exclusive, and limited data)
2. Same lineage, same origin, performance optimization(In terms of chemical composition, Mechanical properties, corrosion resistance and heat treatment process)
3. Material selection(Typical application areas for both)
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The Industry Challenges of Marine Engineering
As is well known, the core challenge facing marine engineering is that the extreme environment of the deep sea places dual, demanding high-strength and corrosion resistance in materials, a requirement that traditional materials often fall short of.
Specifically, this can be summarized into the following interconnected dilemmas:
I. The Deep Sea Itself is a "Materials Killer"
With increasing depth, temperatures drop, dissolved oxygen decreases, and hydrostatic pressure rises sharply-fundamentally altering corrosion behavior. While uniform corrosion may be slowed, localized corrosion (pitting corrosion, crevice corrosion, stress corrosion) is significantly exacerbated. Worse still, sulfate-reducing bacteria (SRB) exist in the deep sea; their metabolic product, hydrogen sulfide (H₂S), acidifies the local environment and induces hydrogen embrittlement.
II. Insufficient Strength of Corrosion-Resistant Materials; Insufficient Corrosion Resistance of High-Strength Materials
A classic problem:
Corrosion-resistant alloys (e.g., C-22, titanium): possess excellent seawater corrosion resistance, but their yield strength is only 350-450 MPa, requiring thicker cross-sections under deep-sea pressure, leading to increased weight and cost.
High-strength steel: strength can exceed 800 MPa, but in H₂S + Cl⁻ environments, it is highly susceptible to sulfide stress corrosion cracking (SSC) and hydrogen-induced cracking. Data shows that in chloride-containing formation water, the annual failure rate of drill pipes is as high as 12%, and the loss from a single accident exceeds 10 million yen.
III. Severe Lack of Deep-Sea Corrosion Data
Existing standards and databases mainly rely on shallow water or laboratory tests. Deep-sea in-situ corrosion data is almost entirely absent, leading to a lack of scientific basis for material selection; designs often rely on experience or are overly conservative, severely restricting the development of deep-sea equipment.
Same lineage, same origin, performance optimization
C-22HS is not a completely new alloy independent of C-22; it is based on new research of C22, a common path for engineers to improve existing materials. Therefore, at the chemical composition level, C-22HS is entirely within the range of C-22-the contents of the main elements nickel, chromium, and molybdenum are essentially the same, and the control requirements for impurity elements are also the same. In the ASTM and ASME standards systems, C-22HS is explicitly classified as a heat-treated derivative of the C-22 alloy, rather than a separate parallel variety.
Comparison of the chemical components of the two
| Element | C-22 | C-22HS |
| Ni | 56 Blance | 61 Blance |
| Cr | 22 | 21 |
| Mo | 13 | 17 |
| Fe | 3 | 2 |
| W | 3 | 1 |
| C | max.0.01 | max.0.01 |
| Si | max.0.08 | max.0.08 |
| Mn | max.0.50 | max.0.80 |
| Co | max.2.50 | max.1.0 |
As can be seen from the table above, the two have essentially the same chemical composition, with only minor adjustments.
Same base material, different "formula"
The difference lies not in the "formula," but in the "process." Standard C-22 uses solution annealing, while C-22HS undergoes additional aging treatment. The result: yield strength jumps from 359 MPa to 1345 MPa, same chemical composition, different microstructure.
Consider graphite and diamond: same composition, but drastically different properties. C-22 and C-22HS work on the same principle, only their transformation occurs inside the furnace, not underground.
Because of the same chemical composition, C-22HS inherits all the corrosion-resistant "genes" of C-22. PREN values, crevice corrosion resistance, and weldability are essentially the same. Engineers can directly apply decades of corrosion data and design experience from C-22 to C-22HS-without starting from scratch.
So why add "HS"?--What are the differences between Hastelloy C22 and C22HS?
The meaning of "HS" is straightforward-it's an abbreviation for High Strength.
Literal meaning-high strength
This is the most intuitive understanding. The yield strength of C-22HS (≥1345MPa) is nearly four times that of standard C-22 (≥359MPa), and its tensile strength is also more than double. Adding "HS" clearly indicates in the grade designation: "I am the high-strength version in this family."
Deeper meaning: the high strength comes from heat treatment
"HS" is not just a performance indicator; it also implies the manufacturing process-High Strength originates from a special aging heat treatment. Standard C-22 is in a solution-annealed state, while C-22HS undergoes an additional aging process after solution treatment, precipitating nanoscale strengthening phases and further increasing its strength.
So, given that the main chemical composition remains unchanged, what can most intuitively demonstrate the difference?
Differences in mechanical properties(Bar/room temperature)
| Performance indicators | C-22 | C-22HS |
| Yield strength(MPa) | 359 | 1345 |
| Tensile strength(MPa) | 765 | 1382 |
| Elongation(％) | 70 | 18 |
| Hardness | 84 HRBW | 42 HRC |
Note: Due to the different measuring scales, hardness cannot be directly compared. For a rough reference, 84 HRBW is approximately less than 20 HRC.
The table shows that the yield strength of C22HS is approximately 4.5 times that of C22. Under the same design stress, using C22HS can significantly reduce the cross-sectional size, which is of great significance for space-constrained applications such as downhole tools. However, the increased strength comes at the cost of decreased plasticity; therefore, C22HS is not suitable for applications requiring extensive cold forming.
Resistance to Seawater Crevice Corrosion(aSTM G48)
| Performance indicators | C-22 | C-22HS(Time-limited state) | C-22HS(Annealed state) |
| Critical crevice corrosion temperature | 80°C | 75°C | 100°C |
| Critical pitting temperature | 120°C | 110°C | 120°C |
Therefore, it can be seen that the two are almost in the same class, and C22HS is better in the annealed state, with its strength doubling after aging, while its corrosion resistance is not significantly reduced. However, what we need to know is not "which is stronger", but that C-22HS still maintains the same level of corrosion resistance as C-22 in a high-strength state, which is where its value lies.
Differences in heat treatment processes
Hastelloy C-22
Achieving Corrosion Resistance in One Step
Heating to approximately 1080℃, holding at that temperature, and then rapidly cooling. The aim is to ensure all alloying elements dissolve uniformly in the matrix, resulting in optimal corrosion resistance and good plasticity.
Hastelloy C-22HS
Slow and meticulous work, pursuing high strength
First, the material is solution-treated according to the C-22 process. Then, two more "slow and meticulous" steps are added-first, it is heated to 705℃ and held for 16 hours, then furnace-cooled to 605℃ and held for 32 hours, and finally air-cooled. The entire process takes about 48 hours.
Application areas
| Application scenarios | C-22 | C-22HS |
| Chemical reactors and heat exchangers | Main force | |
| Flue gas desulfurization systems | Main force | |
| Seawater cooling systems | Main force | |
| Oil and gas well downhole tools/wellhead components | emphasis | |
| High-strength fasteners | emphasis | |
| Valves/pump components | Applicable | qualified |
| Nuclear fuel reprocessing | Applicable | qualified |
The difference between C-22 and C-22HS essentially reflects a classic path in the development of engineering materials: developing derivative varieties based on mature alloy systems through microstructural control. C-22 covers "breadth"-large-area corrosion-resistant components; C-22HS breaks through "depth"-high-stress load-bearing nodes.
Neither is inherently superior or inferior; rather, each occupies its own niche and leverages its strengths, continuing to play irreplaceable roles in its respective areas of expertise.
Disclaimer: The data in this article are typical values or reference ranges and are for reference only. Actual performance is subject to the material quality certificate and measured data. The material selection suggestions are general guidance; please consult the material supplier or a professional engineer for specific selection.
Lork Group
Marketing Operations Department
Email: layla@lorkgroup.com
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