Hastelloy C276 Corrosion Resistance: A Complete Guide to N10276 in Aggressive Environments

● Hastelloy C276 (UNS N10276) is widely regarded as the most versatile corrosion-resistant nickel alloy, resisting both oxidizing and reducing environments.

● Its corrosion resistance comes from a nickel-molybdenum-chromium-tungsten chemistry with about 16% molybdenum and an ultra-low carbon content (<= 0.010%).

● C276 is immune to chloride stress-corrosion cracking and resists pitting and crevice corrosion even in seawater, thanks to a pitting-resistance equivalent (PRE) near 68.

● It performs excellently in hydrochloric, sulfuric (especially contaminated/reducing), phosphoric, formic and acetic acids, and in wet chlorine and hypochlorite.

● The ultra-low carbon and silicon mean C276 does NOT sensitize in the weld heat-affected zone - it keeps full corrosion resistance in the as-welded condition, with no post-weld heat treatment needed for corrosion.

● Limitations: it is not ideal for hot concentrated nitric acid or strongly oxidizing conditions (where C22 leads), and it should not be held above about 550 deg C to avoid sigma-phase embrittlement.

Key Corrosion Specifications at a Glance

What Makes Hastelloy C276 So Corrosion Resistant?

Hastelloy C276 resists corrosion because its nickel-rich chemistry combines three complementary defenses - molybdenum and tungsten for reducing/chloride attack, chromium for oxidizing attack, and ultra-low carbon to keep the structure stable after welding. Together these make it the most versatile corrosion-resistant alloy in common use.

Think of C276 as a team of corrosion fighters. Nickel is the base that gives ductility and, critically, immunity to chloride stress-corrosion cracking. Molybdenum (about 16%) and tungsten (about 3.5%) are the heavy hitters against pitting, crevice corrosion and reducing acids such as hydrochloric and sulfuric. Chromium (about 15.5%) defends against oxidizing media such as ferric, cupric and wet chlorine. Finally, carbon is held to 0.010% maximum (and silicon to 0.08% maximum), which prevents harmful carbides and intermetallic phases from forming at grain boundaries during welding - the very problem that ruins the corrosion resistance of lesser alloys.

This balance is why C276 is called the "workhorse" for unpredictable or mixed chemical streams: whether the process fluid is oxidizing one day and reducing the next, C276 keeps performing. That is the single reason it has a 50-plus-year track record across chemical, pollution-control, oil-and-gas and marine service.

What Is the Chemical Composition Behind C276 Corrosion Resistance?

C276's corrosion resistance is engineered into its chemistry: roughly 57% nickel, 15-17% molybdenum, 14.5-16.5% chromium, 3-4.5% tungsten and iron 4-7%, with carbon capped at 0.010%. Each element plays a defined corrosion-fighting role.

 

A useful number for specifiers is the Pitting Resistance Equivalent (PRE), computed for nickel alloys as %Cr + 3.3 x %Mo. With about 15.5% Cr and 16% Mo, C276 reaches a PRE near 68 - dramatically higher than 316L (about 24-26) or even super duplex (about 40-42). That single figure explains why C276 shrugs off chloride pitting where stainless steels fail. The low carbon is equally important: by staying at or below 0.010%, C276 avoids the grain-boundary carbide precipitation that causes intergranular corrosion in welded structures.

Does Hastelloy C276 Resist Both Oxidizing and Reducing Acids?

Yes - C276 is unusual in resisting both oxidizing and reducing acids, which is precisely why it is called the most versatile corrosion-resistant alloy. Chromium handles the oxidizing side; molybdenum and tungsten handle the reducing side.

Most materials are good at one and weak at the other. Austenitic stainless steels resist oxidizing nitric acid but fail in reducing hydrochloric acid; pure molybdenum alloys resist reducing acids but oxidize easily. C276 straddles both because it carries enough chromium (about 15.5%) for oxidizing attack and enough molybdenum-tungsten (about 19-20% combined) for reducing attack.

In practice this means a single C276 vessel or pipe can handle a process stream whose chemistry swings between oxidizing and reducing without the engineer having to swap materials. The only notable weak spot is strongly oxidizing conditions (especially hot, concentrated nitric acid), where the relatively modest chromium content is the limiting factor - a role better filled by C22 or certain higher-chromium alloys.

How Does C276 Perform in Hydrochloric Acid?

C276 performs excellently in hydrochloric acid across a very wide range of concentrations and temperatures, making it one of the few alloys suitable for sustained HCl service where stainless steels would be destroyed.

Hydrochloric acid is a classic reducing acid, and reducing acids are exactly what molybdenum-rich C276 was built to defeat. C276 is widely used in HCl environments - including contaminated and hot streams - where 316L, 904L, Alloy 20 and even duplex stainless would corrode rapidly. This is also where C276 clearly outperforms Inconel 625, which is stronger at high temperature but less resistant to HCl. For the most aggressive HCl duties (very high temperature or concentration), corrosion rates still rise, so designers use isocorrosion data and sometimes step up to higher-molybdenum alloys - but for the great majority of HCl services, C276 is the standard workhorse. (For acid-specific design detail, see our Hastelloy C276 for Acid Service guide.)

How Does C276 Perform in Sulfuric Acid?

C276 has excellent resistance to sulfuric acid, especially in the contaminated, reducing or impure conditions common in real plants - which is where it earns its reputation far more than in pure acid tests.

Sulfuric acid behavior depends strongly on concentration, temperature and impurities. C276's isocorrosion charts show good resistance across broad sulfuric-acid ranges, and its performance improves markedly when the acid contains impurities or reducing species (the "contaminated mineral acid" case). This makes C276 a default for acid-recovery, pickling and waste-acid handling. It is worth noting that in some concentrated, hotter sulfuric conditions other alloys (such as certain high-silicon or higher-alloy grades) can compete, and that Alloy 20 is specifically famed for sulfuric service - but C276's broader versatility often wins when the stream is mixed or unpredictable. Acceptance in standardized testing is strict: in the ASTM G28 Method A ferric-sulfate/sulfuric acid test, C276 must show a corrosion rate no greater than 480 mpy (mils per year).

How Does C276 Perform in Phosphoric, Formic and Acetic Acids?

C276 shows excellent resistance to phosphoric, formic and acetic acids, covering the organic and fertilizer-acid duties that appear throughout chemical and pharmaceutical plants.

Phosphoric acid: C276 is rated excellent, with good resistance at all temperatures below boiling and at concentrations lower than about 65%; isocorrosion data extend its useful range well into the 100-150 deg C band depending on concentration. Formic and acetic acids (and acetic anhydride) are likewise handled excellently. These organic acids are common in pharmaceuticals and fine chemicals, where product purity and zero leakage matter - exactly where C276's clean, stable corrosion film is valued. As always, the controlling variables are temperature, concentration and impurities, so the project data sheet should be checked against the specific duty.

Does Hastelloy C276 Resist Pitting and Crevice Corrosion?

Yes. C276 resists pitting and crevice corrosion extremely well, even in aggressive chloride environments and seawater, because its roughly 16% molybdenum and 3.5% tungsten push its pitting-resistance equivalent to about 68.

Pitting and crevice corrosion are the two localized-attack modes that kill stainless steel in chloride service. Molybdenum is the key element that raises the threshold temperature at which these attacks start, and tungsten reinforces it. In the standard ASTM G48 ferric-chloride test, C276 demonstrates excellent pitting and crevice resistance - the reason it is specified for flue-gas-desulfurization (FGD) absorbers, pulp-bleach washers and seawater systems. Crucially, C276 also resists crevice attack under deposits and gasket surfaces, a geometry where many materials fail first. For comparison, a PRE near 68 means C276 sits far above the PREN ~40 "seawater threshold" used for super duplex, which is why it is chosen when duplex is not enough.

Is Hastelloy C276 Immune to Chloride Stress Corrosion Cracking?

Yes - C276 is effectively immune to chloride stress-corrosion cracking (SCC), a form of sudden failure that plagues austenitic stainless steels in hot chloride service. Its high nickel content is the reason.

Stress-corrosion cracking needs three things: a susceptible material, tensile stress and a corrosive environment (chlorides being the classic trigger for stainless steel). C276 removes the material susceptibility: its nickel content (about 57%+) makes it fundamentally resistant to chloride-induced SCC, a property confirmed by the boiling magnesium-chloride test of ASTM G36. This is a major differentiator versus 304/316 stainless and even versus some higher-alloys, and it is why C276 is trusted in critical, hard-to-inspect components such as heat-exchanger tubing, reactor internals and offshore hardware. C276 is also resistant to sulfide stress cracking in sour oilfield environments, broadening its appeal to oil & gas.

How Does C276 Handle Seawater and Brine?

C276 handles seawater and brine exceptionally well, including the crevice conditions under deposits and biofouling that rapidly attack ordinary stainless steels in marine service.

Seawater is a chloride-rich, often oxygenated, biologically active environment - a perfect storm for pitting and crevice corrosion in carbon and stainless steels. C276's high molybdenum-tungsten content and PRE near 68 let it resist both uniform and localized attack in seawater and brine, so it is used for seawater-cooled heat exchangers, desalination components, offshore platform piping and marine exhaust. While super duplex (such as F55/S32760) is often the economical first choice for seawater, C276 is selected when the duty also involves acidic contaminants, mixed process chemicals or a need to avoid any chloride pitting risk altogether. (See our Hastelloy C276 for FGD Systems and Common Applications guides for sector detail.)

Does Hastelloy C276 Corrode After Welding?

No - and this is C276's signature advantage. Because its carbon and silicon are held extremely low, C276 does not form harmful grain-boundary precipitates in the weld heat-affected zone, so it retains full corrosion resistance in the as-welded condition without post-weld heat treatment.

Older "C-type" nickel alloys suffered from sensitization: during welding, carbon would precipitate as carbides at grain boundaries, starving the adjacent metal of chromium and molybdenum and creating paths for intergranular corrosion. C276 was the first wrought nickel-chromium-molybdenum alloy designed to sidestep this, by driving carbon to 0.010% maximum and silicon to 0.08% maximum. The practical benefit is enormous - large vessels and pipe spools can be fabricated and welded, then put into corrosive service without a solution-anneal or stress-relief step for corrosion purposes. (Welding procedure still matters for mechanical integrity; see our Hastelloy C276 Welding Guide.) Filler metal is the matching ERNiCrMo-4 / ENiCrMo-4 (AWS classification).

What Are the Limitations of C276 Corrosion Resistance?

C276 is not universal: its main corrosion limitations are hot concentrated nitric and other strongly oxidizing acids (where higher-chromium alloys like C22 lead), and its metallurgical upper-temperature limit of about 550 deg C to avoid sigma-phase embrittlement. Cost is also higher than stainless alternatives.

● Strongly oxidizing acids: hot, concentrated nitric acid and similar strongly oxidizing media are the weak point, because C276's chromium (~15.5%) is lower than dedicated oxidizing-acid alloys. Hastelloy C22 (N06022) is generally preferred there.

● High-temperature exposure: C276 should not be held for long periods above about 550 deg C, where sigma and other intermetallic phases can embrittle it. Continuous oxidizing-service temperature is therefore capped well below its short-term high-temperature capability.

● Cost vs stainless: C276 carries a large price premium over 316L, 904L or duplex; justify it with the actual corrosion duty rather than by habit.

● Velocity/erosion: like all alloys, C276 can suffer erosion-corrosion at very high fluid velocities or with abrasive slurries - design and sizing still matter.

How Does C276 Compare with 316L, 904L, Alloy 20, Inconel 625 and C22?

C276 sits at the top of the corrosion-resistance ladder for mixed/reducing acid and chloride service: it far outperforms 316L and 904L, beats Alloy 20 in hydrochloric acid and versatility, trades the high-temperature lead to Inconel 625, and yields the strongly-oxidizing niche to C22.

 

The rule of thumb for specifiers: step up to C276 when 316L/904L/2205 have failed or are marginal, when the stream is mixed or reducing (especially with chlorides), or when chloride SCC is a risk. Choose C22 instead when the dominant hazard is strongly oxidizing. Choose 625 when high-temperature strength or oxidation dominates. Our comparison articles - Hastelloy C276 vs Inconel 625, vs Alloy 20, vs Stainless Steel 904L and vs Incoloy 825 - cover each trade-off in depth.

What Corrosion Tests Define C276 Quality?

C276 quality for corrosion service is verified by three standardized tests: ASTM G28 (Methods A and B) for intergranular/general corrosion in sulfuric-acid media, ASTM G48 for pitting and crevice resistance, and ASTM G36 for stress-corrosion cracking. Each has a defined acceptance limit.

These tests let a buyer confirm that a heat of C276 meets the corrosion bar before it goes into service - important for critical chemical and FGD equipment. Mill test certificates (EN 10204 3.1/3.2) report chemistry and mechanicals; corrosion test reports are supplied when the specification calls for them. (See our ASTM Standards for Hastelloy C276 guide for the product-form standards B575/B574/B622/B619/B626/B564/B366.)

Which Industries Rely on C276 for Corrosion Resistance?

C276 is specified wherever aggressive chemicals, chlorides or sour conditions meet critical equipment - most heavily in chemical processing, pollution control (FGD), pulp & paper, oil & gas, pharmaceuticals and waste treatment.

● Chemical processing: reactors, columns, heat exchangers, piping and storage for aggressive and mixed-acid streams.

● Pollution control / FGD: scrubbers, ducting and absorber components exposed to acidic flue-gas condensate.

● Pulp & paper: bleach washers and chemical-recovery equipment where chlorides and oxidants attack stainless steel.

● Oil & gas: sour-gas service, offshore topsides and subsea components resistant to sulfide and chloride attack.

● Pharmaceutical & fine chemicals: high-purity acid-resistant vessels and valves.

● Waste treatment & acid recovery: incineration and acid-recovery systems handling contaminated streams.

What Standards Cover Corrosion-Resistant C276 Products?

C276 corrosion-resistant products are covered by a complete family of ASTM/ASME standards that specify chemistry, mechanicals and corrosion-related quality for every product form - so a corrosion spec can be applied consistently across plate, pipe, bar, forgings and fittings.

 

How Should You Specify C276 for a Corrosive Service?

Specify C276 by UNS N10276 with the correct ASTM product-form standard and corrosion-test requirements, request an EN 10204 3.1 (or 3.2) certificate, and confirm the welding and heat-treatment route keeps the alloy in its optimum corrosion condition. A precise specification prevents substitution and gives a verifiable corrosion guarantee.

● Material: "UNS N10276 (Hastelloy C276), solution annealed, low-carbon, per ASTM B575/B622/etc."

● Corrosion proof: call out ASTM G28 (A and/or B) and G48 where the service is critical; state the acceptance rate.

● Certificate: EN 10204 3.1 minimum; 3.2 with third-party witness where required (SGS/TUV/DNV/Lloyd's).

● Welding: matching ERNiCrMo-4 / ENiCrMo-4 filler; qualified procedure; no PWHT needed for corrosion.

● Pipe selection: for line pipe and tubing, see our How to Choose Hastelloy C276 Pipes guide and the Hastelloy C276 product page.

Frequently Asked Questions

Q: What is Hastelloy C276 made of?

A: C276 is a nickel-molybdenum-chromium-tungsten superalloy (UNS N10276). Typical chemistry is about 57% nickel (balance), 15-17% molybdenum, 14.5-16.5% chromium, 3-4.5% tungsten, 4-7% iron, with carbon capped at 0.010% and silicon at 0.08%.

Q: Does Hastelloy C276 rust?

A: In the normal sense of iron rust (iron-oxide scaling), C276 does not rust because it contains almost no iron as a structural phase and forms a stable, protective passive film. It can still corrode under specific aggressive chemistry, but it is vastly more resistant than carbon or stainless steel.

Q: Is C276 better than 316L for corrosion?

A: Yes, dramatically. C276 has a pitting-resistance equivalent near 68 versus about 24-26 for 316L, resists hydrochloric and sulfuric acids that destroy 316L, and is immune to chloride stress-corrosion cracking that routinely fails 316L in hot chlorides.

Q: Can C276 be used in hydrochloric acid?

A: Yes. Hydrochloric acid is a reducing acid, and C276's high molybdenum-tungsten content makes it one of the few alloys suitable for sustained HCl service across wide concentration and temperature ranges - far better than 316L, 904L or Inconel 625.

Q: How does C276 perform in sulfuric acid?

A: Excellent, especially in contaminated, reducing or impure sulfuric acid typical of real plants. In the ASTM G28 Method A test it must show <= 480 mpy. It is a standard choice for acid recovery and pickling, though Alloy 20 is specifically famed for pure sulfuric service.

Q: Is Hastelloy C276 resistant to seawater?

A: Yes. With PRE near 68 and high Mo-W content, C276 resists uniform, pitting and crevice corrosion in seawater and brine - including under deposits and biofouling - making it suitable for desalination, offshore and marine components.

Q: Does C276 crack from chlorides (SCC)?

A: No. C276 is effectively immune to chloride stress-corrosion cracking because of its high nickel content, confirmed by the ASTM G36 boiling magnesium-chloride test. This is a key advantage over austenitic stainless steels.

Q: Does C276 need post-weld heat treatment for corrosion?

A: No. Its ultra-low carbon (<=0.010%) and silicon (<=0.08%) prevent sensitization in the weld heat-affected zone, so C276 retains full corrosion resistance in the as-welded condition without post-weld heat treatment for corrosion purposes.

Q: What is the PRE / pitting resistance of C276?

A: Using PRE = %Cr + 3.3 x %Mo, C276 reaches about 68 (with ~15.5% Cr and ~16% Mo). That is far above the PREN ~40 "seawater threshold" for super duplex and explains its outstanding chloride pitting resistance.

Q: What is the temperature limit for C276 corrosion service?

A: C276 is used from cryogenic temperatures up to about 400 deg C in many services and short-term to much higher. However, it should not be held long-term above about 550 deg C to avoid sigma-phase embrittlement, and strongly oxidizing hot acids are a weakness regardless of temperature.

Q: Is C276 better than Inconel 625 for corrosion?

A: For reducing acids (especially hydrochloric) and broad chloride/pitting resistance, yes - C276 is better. For high-temperature strength and oxidizing/oxidation resistance, Inconel 625 is better. The choice depends on which hazard dominates.

Q: Is C276 better than Alloy 20?

A: In versatility and especially hydrochloric/reducing acid service, yes. Alloy 20 is specifically excellent in sulfuric acid and can be more economical there, but C276 covers a wider range of aggressive chemicals and chlorides.

Q: What acids does C276 NOT resist well?

A: Its main weakness is strongly oxidizing acids - notably hot, concentrated nitric acid - where its modest chromium content is the limiting factor. Very high-temperature oxidizing conditions are also better served by C22 or higher-chromium alloys.

Q: What filler metal is used for C276?

A: The matching filler is ERNiCrMo-4 (solid wire) or ENiCrMo-4 (covered electrode) per AWS. These maintain the corrosion-resistant chemistry in the weld metal.

Q: What standards cover C276?

A: Product-form standards include ASTM B575 (plate), B574 (bar), B622 (seamless pipe/tube), B619 (welded pipe), B626 (welded tube), B564 (forgings/flanges) and B366 (fittings), all to UNS N10276, with ASME SB equivalents.

Q: How is C276 corrosion tested (G28/G48)?

A: ASTM G28 Methods A and B measure corrosion rate in sulfuric-acid media (limits ~480 mpy and ~300 mpy respectively); ASTM G48 evaluates pitting/crevice in ferric chloride; ASTM G36 checks SCC in boiling magnesium chloride.

Q: Is C276 good for FGD / flue gas?

A: Yes. Flue-gas-desulfurization systems expose equipment to acidic condensate and chlorides, exactly the pitting/crevice regime where C276 excels - it is widely used for scrubbers, ducts and absorber components.

Q: What is the density of C276?

A: Hastelloy C276 has a density of about 8.89 g/cm3, an elastic modulus near 205 GPa, and a melting range of roughly 1325-1370 deg C - useful for weight and stress calculations in design.