Hastelloy C276 for Hydrochloric Acid Service: Selection Guide

Hastelloy C276 (UNS N10276) is the most widely used nickel alloy for hydrochloric acid (HCl) service. It resists all HCl concentrations from dilute to the 37% azeotrope at temperatures up to about 60 deg C (140 deg F), with corrosion rates typically below 0.13 mm/y (5 mpy) - the industry threshold for acceptable loss in process equipment.

This guide gives you the concentration-temperature corrosion data, the alloy comparison, the ASTM product standards and the welding rules you need to specify C276 correctly on a purchase order. It sits inside the complete Hastelloy C276 hub and is the HCl-specific companion to the broader C276 acid-service performance-by-acid guide.

TL;DR - For pure HCl below 60 deg C, C276 is the best cost-performance choice of any nickel alloy. Three rules decide almost every selection: (1) keep the metal temperature at or below 60 deg C; (2) if the acid contains oxidizing species such as ferric, cupric or dissolved oxygen, upgrade to C22 or Alloy 59; (3) require solution annealing at 1121 deg C plus water quench for every welded component, because an as-welded heat affected zone corrodes 5 to 10 times faster in HCl.

What Is the Maximum Service Temperature for Hastelloy C276 in Hydrochloric Acid?

The conservative design limit for Hastelloy C276 in hydrochloric acid is 60 deg C (140 deg F) across all concentrations. Above that temperature the corrosion rate climbs past 0.13 mm/y (5 mpy) and then accelerates sharply, so boiling or near-boiling HCl needs C22, Alloy 59, zirconium or tantalum instead.

The 60 deg C figure is a design limit, not a cliff. Below it, C276 shows corrosion rates under 0.13 mm/y in every concentration from 1% to 37%, which is the rate industry practice treats as acceptable for long-life process equipment. Between 60 and 70 deg C the rate roughly doubles, and by the boiling point of the acid it is one to two orders of magnitude higher. That steepness is why the limit is quoted as a hard number rather than a trend.

Two practical consequences follow. First, wall-thickness corrosion allowances sized for 60 deg C cannot be stretched to cover a hot spot: a dead-leg flange or a pump casing that runs 20 deg C above design will fail first. Second, the limit is on METAL temperature, not bulk fluid temperature, so a heat exchanger outlet, a steam-traced line or a section downstream of a temperature excursion must all be checked against it. For the full thermal envelope including oxidation and code ceilings, see Hastelloy C276 temperature limits.

C276 corrosion rate in HCl by concentration and temperature (typical values, Haynes datasheet basis)

Interpretation: below 60 deg C the rate stays under 0.13 mm/y in all concentrations. Above 70 deg C it accelerates sharply. Note on the boiling column: the HCl-water azeotrope sits near 20.2% and boils at about 109 deg C, while stronger acid evolves hydrogen chloride gas well below its nominal boiling point - which is exactly why 37% acid is handled cold and vented. Boiling-point rates in the table are indicative ranges, not design allowables.

Why Does Hastelloy C276 Resist Hydrochloric Acid Better Than Stainless Steel?

C276 resists HCl because of its molybdenum and tungsten content - 15 to 17% Mo plus 3 to 4.5% W - not because of chromium. Hydrochloric acid is a non-oxidizing acid, so the chromium-oxide passive film that protects stainless steel cannot form, and the alloy has to survive on bulk resistance instead.

Stainless steels such as 304 and 316L resist acid through a passive chromium oxide film. That mechanism needs an oxidizing environment to maintain itself. Hydrochloric acid is strongly reducing, so it strips the film and then attacks the metal directly. Molybdenum and tungsten, by contrast, dissolve into the alloy matrix and raise the intrinsic resistance of the metal itself to reducing acids. C276 carries more molybdenum than any commercially common nickel alloy except Hastelloy B types, which is why it became the default HCl material in the 1970s and has stayed there.

The supporting cast matters too. Nickel at about 57% minimum provides ductility and broad acid resistance. Carbon is capped at 0.01% and silicon at 0.08%, which prevents carbide sensitization during welding and lets C276 be used in the as-welded condition in many services - though not in HCl, where the weld still needs annealing. Chromium at 14.5 to 16.5% is present mainly to handle oxidizing contaminants rather than the acid itself. Full detail is in C276 chemical composition.

Key specifications of Hastelloy C276 (UNS N10276) and why each matters for HCl

Source: ASTM B575, ASM Handbook Vol. 13B, and the Haynes International C-276 data sheet. PREN is a nominal mid-range figure - see the next section for how the band is derived.

What Does PREN Tell You About C276 in Hydrochloric Acid Service?

C276 carries a nominal PREN of about 69, which is why it survives chloride pitting and crevice attack. But PREN is a pitting-resistance index, not an acid-resistance index, so it explains only part of the HCl story - the molybdenum content is what actually resists the acid.

The pitting resistance equivalent number is calculated as PREN = %Cr + 3.3 x %Mo + 16 x %N. Using nominal mid-range chemistry for C276 (Cr 15.5, Mo 16, N not specified) gives 15.5 + 52.8 = about 68, which is where the quoted 69 comes from. Taking the specification upper limits (Cr 16.5, Mo 17) pushes it to about 73, so the honest statement is a band of roughly 68 to 73 rather than a single number.

The limitation is important. PREN was derived for chloride pitting in near-neutral, aerated solutions. Hydrochloric acid is neither near-neutral nor oxidizing, so a high PREN does not by itself predict HCl resistance - Hastelloy B3 has a far higher PREN than C276 yet is chosen for HCl on different grounds, and titanium has a high PREN while dissolving rapidly in non-oxidizing HCl. Use PREN to compare alloys for chloride service, and use measured corrosion-rate data to select for acid service.

How Do Oxidizing Contaminants Change the C276 Selection in HCl?

Pure HCl is C276's best case. Add oxidizing species - ferric ions, cupric ions, dissolved oxygen, nitric acid or free chlorine - and the corrosion rate can rise several-fold, at which point C22 or Alloy 59 becomes the correct choice.

Oxidizing contaminants change the corrosion mechanism. In clean HCl, C276 corrodes uniformly at a low, predictable rate. Ferric and cupric ions act as cathodic depolarizers: they accept electrons at the surface and sustain a much higher anodic dissolution rate. Dissolved oxygen does the same, though less aggressively, and a nitrogen sparge or blanket lowers the rate measurably. Nitric acid or hypochlorite contamination converts the environment into an oxidizing one, where chromium content governs - and that is C22's strength, not C276's.

The practical test is simple: if the acid comes from a pickling line, a metal-dissolving process, or any stream that has seen iron or copper, assume oxidizing contaminants are present. Recovered and recycled acid is the classic case - it is cheap, but it is ferric-rich, and it will punish a C276 selection that was sized on clean-acid data. Compare the options side by side in C22 vs C276: key differences and selection guide.

Which alloy wins as HCl gets contaminated - selection shift matrix

Which Nickel Alloys Compete With C276 for Hydrochloric Acid Service?

For clean HCl below 60 deg C, C276 is the most economical choice. C22 buys oxidizing-contaminant tolerance and a higher temperature ceiling; Alloy 59 buys both plus a wider margin; B3 buys the highest reducing-acid resistance; zirconium and tantalum buy boiling-acid capability at exotic cost.

The comparison that matters commercially is not raw corrosion performance - it is corrosion performance per dollar. C276 sits at a sweet spot: it is roughly 20% cheaper than C22 and about 40% cheaper than Alloy 59, while covering every concentration of clean HCl at moderate temperature. Once you need boiling acid or heavy oxidant loading, the cheaper alloys drop out and the step up is C22, then Alloy 59, then a reactive metal.

Nickel and exotic alloys for hydrochloric acid service - capability and cost comparison

Relative cost figures are indicative site-published ranges for plate and pipe, not quotations. For the seawater and chloride comparison rather than the acid comparison, see Inconel 625 vs C276 for seawater.

What Is the Composition Difference Between C276, C22, Alloy 59 and B3?

The four alloys separate mainly on chromium and molybdenum. C276 has 14.5 to 16.5% Cr and 15 to 17% Mo; C22 trades molybdenum for chromium; Alloy 59 maximizes both; B3 maximizes molybdenum and drops chromium almost to zero.

Chemical composition of C276 and its HCl-service alternatives (wt%)

Data note: the previous version of this page listed C22 molybdenum as 13 to 15%. The Haynes C-22 specification is 12.5 to 14.5%, so the table above corrects that cell. PREN values are nominal mid-range figures derived from %Cr + 3.3 x %Mo + 16 x %N; treat them as bands, not point values. Read the full breakdown in difference between Hastelloy C22 and C276.

Is Titanium or Zirconium Ever the Better Choice for Hydrochloric Acid?

Titanium is the wrong material for clean non-oxidizing HCl - it dissolves rapidly. Zirconium is the right material for boiling or concentrated HCl, but at four to six times the cost of C276 it is reserved for small critical components.

Titanium's passive film is titanium dioxide, and it is only stable in oxidizing environments. In hydrochloric acid there is nothing to re-form the film, so once a scratch or a weld discoloration breaks it, attack continues. Titanium does have a genuine role in mixed acid - for example an HCl plus nitric mixture, where the nitric keeps the film intact - and that is the only HCl-adjacent case where it should be considered.

Zirconium is the opposite case. It resists hydrochloric acid at all concentrations up to and beyond boiling, with rates under 0.13 mm/y, and it is the standard step up when the process genuinely needs boiling acid and the component is small. Tantalum performs even better but costs an order of magnitude more, so it appears only in the most severe small-bore applications. If your process needs boiling acid, size the duty against zirconium and check whether a C22 or Alloy 59 design with a lower wall temperature is cheaper overall.

What Are the ASTM Standards for C276 Hydrochloric Acid Components?

The controlling standards for C276 HCl components are ASTM B575 for plate and sheet, B619 for welded pipe, B622 for seamless pipe and tube, B366 for butt-weld fittings, B564 for forgings and flanges, and B574 for bar and rod - with the ASME SB- equivalents used for code-stamped equipment.

ASTM and ASME standards for C276 components in HCl service

Critical procurement point: always write solution-annealed on the purchase order. Some suppliers offer as-welded or as-rolled C276 at a lower price, and that material is unsuitable for HCl service. The mill test report must show the actual heat-treatment temperature and quench method, not just a statement that the material conforms. See the full standards map in ASTM standards for Hastelloy C276 and dimension data in ASTM B564 N10276 flange dimensions.

What Are the Mechanical Properties of Solution-Annealed C276?

Solution-annealed C276 delivers 283 MPa (41 ksi) minimum yield strength and 690 MPa (100 ksi) minimum tensile strength, with 40% minimum elongation. That is enough for all pressure-rated HCl service under ASME Section VIII, and the ductility makes it straightforward to form and machine.

Room-temperature mechanical properties of solution-annealed C276

Source: ASTM B575, ASM Handbook Vol. 2 and the Haynes C-276 data sheet. Yield strength is moderate compared with duplex stainless steels, so high-pressure HCl lines need either a heavier wall or a stronger jacket. Full detail in C276 mechanical properties.

Do Welded C276 Components Require Solution Annealing for HCl Service?

Yes. Every welded C276 component going into hydrochloric acid service must be solution-annealed at 1121 deg C (2050 deg F) and water-quenched. An as-welded heat-affected zone corrodes 5 to 10 times faster in HCl than the parent metal.

The mechanism is intergranular carbide precipitation. In the weld heat-affected zone the metal spends time in the 600 to 1150 deg C band, where molybdenum-rich and chromium-rich intermetallic phases - P-phase, mu-phase and sigma - precipitate. Those phases are molybdenum-rich and chromium-depleted relative to the matrix, which creates microscopic galvanic cells and accelerates HCl attack along the grain boundaries. Solution annealing at 1121 deg C re-dissolves the phases and restores uniform corrosion resistance; the water quench then has to be fast enough to stop them re-forming.

The quench matters as much as the soak. Air cooling risks re-precipitating mu phase, which is why the specification says water quench and why the mill test report must record the quench method. ASME Section VIII recommends post-weld heat treatment for C276 pressure vessels in corrosive service, and for HCl that recommendation should be treated as mandatory.

If a fabricated vessel is too large for a heat-treat furnace, the standard fallback is a C22 weld overlay on the heat-affected zone. It is expensive but it restores oxidizing-contaminant tolerance exactly where the sensitized metal sits. Get the overlay procedure qualified and inspected before committing to it.

What Filler Metals Should Be Used for Welding C276 in HCl Service?

Use matching filler: ERNiCrMo-4 for GTAW and GMAW, ENiCrMo-4 for SMAW, and a matching flux-coated wire for SAW. ERNiCrMo-22 (C22 filler) is also acceptable and sometimes preferred, but it changes the weld color and finish.

Filler metal selection and post-weld treatment for C276 in HCl service

Never use an unsaturated filler on C276 for HCl service, and never mix filler families in the same joint without qualifying the procedure. Full procedure detail, including heat input limits and interpass temperature, is in Hastelloy C276 welding guide.

What Is the Difference Between C276 and Hastelloy B3 for Reducing Acid Service?

B3 carries roughly twice the molybdenum of C276 (27 to 32% versus 15 to 17%) and almost no chromium, which makes it the stronger alloy in pure reducing acids - but it loses C276's tolerance for oxidizing contaminants, so the two are not interchangeable.

Where the acid is clean and strongly reducing, B3's molybdenum content buys a lower corrosion rate and a wider margin. Where the stream carries any oxidant - ferric, cupric, dissolved oxygen or chlorine - B3's near-zero chromium means there is nothing to sustain a passive film, and it can corrode faster than C276. In practice B3 is selected for very aggressive reducing duty such as concentrated hydrochloric or sulfuric acid with controlled chemistry, while C276 remains the general-purpose choice.

The two alloys also differ in availability and cost: B3 is produced in smaller volumes and is normally more expensive per kilogram than C276. Check current supply before committing a large HCl project to it. Product detail is at Hastelloy B3.

How Do You Specify C276 for Hydrochloric Acid Service on a Purchase Order?

Bottom line: A complete C276 HCl purchase order names the ASTM specification and product form, requires solution annealing at 1121 deg C with a water quench, demands a certified heat-treatment record, and states the corrosion-rate acceptance basis. Five steps cover it.

1. Define the duty envelope. Record acid concentration, maximum and normal metal temperature, pressure, flow velocity and any oxidants. Compare against the corrosion-rate table in this guide: if metal temperature exceeds 60 deg C or the acid is aerated or ferric-bearing, the selection moves to C22 or Alloy 59 before any purchase order is raised.

2. Choose the ASTM specification for each product form. Plate and sheet to ASTM B575, seamless pipe and tube to B622, welded pipe to B619, butt-weld fittings to B366, forgings and flanges to B564, bar and rod to B574. For ASME code-stamped equipment, call the SB- equivalent. See ASTM standards for Hastelloy C276 for the full map.

3. Write the heat-treatment requirement into the order. State that material shall be solution-annealed at 1121 deg C (2050 deg F) minimum and water-quenched, and that a certified heat-treatment record is required. As-rolled or as-welded material is unacceptable for HCl service and will fail in the heat-affected zone.

4. Qualify the welding procedure and the filler metal. Specify ERNiCrMo-4 for GTAW and GMAW, ENiCrMo-4 for SMAW, and a matching flux-coated wire for SAW. Require full-penetration welds with no crevices, and require post-weld solution annealing of the finished assembly. See the C276 welding guide.

5. Set the inspection and documentation package. Require mill test reports showing chemistry, mechanical properties, the actual anneal temperature and the quench method. For forgings, specify ultrasonic examination to ASTM E2375 or the standard invoked by the product specification, plus liquid penetrant examination to ASTM E165. For sour service, add the NACE MR0175 / ISO 15156 hardness requirement and verify it on the completed fabrication.

6. Plan the installation details that actually cause failures. Eliminate threaded connections and lap joints, isolate C276 from carbon steel and 316L with dielectric flanges or an area ratio that protects the couple, avoid dead legs and stagnant zones, and pickle the finished equipment per ASTM A380 or A967 before it enters service.

What Are the Five Rules That Prevent Premature Failure of C276 HCl Systems?

C276 fails early in HCl for five recurring reasons: material supplied as-rolled instead of solution-annealed, weld crevices and non-penetrating joints, missing post-weld annealing, galvanic coupling to less noble metals, and skipped pickling before service.

Rule 1: Specify solution-annealed material only

Purchase orders must state that material shall be solution-annealed at 1121 deg C (2050 deg F) and water-quenched, with a certified heat treatment record. Mill test reports must show the actual temperature and quench method, not just a conformity statement.

Rule 2: Make every weld full penetration and crevice-free

Hydrochloric acid is a crevice-corrosion accelerator. Any weld crevice, lap joint, threaded connection or stagnant zone will corrode preferentially. Use full-penetration welded joints and eliminate threaded connections in HCl service.

Rule 3: Solution-anneal every fabricated assembly

As-welded C276 has a sensitized heat-affected zone, and for HCl service the entire fabricated assembly must be re-solution-annealed. Where the assembly is too large for a furnace, use a C22 weld overlay on the heat-affected zone.

Rule 4: Prevent galvanic coupling with less noble materials

C276 sits at the noble end of most galvanic couples. If C276 must connect to 316L or carbon steel in an HCl system, either use a dielectric flange or ensure the C276 surface area is much larger than the less noble material so the couple is cathodically protected.

Rule 5: Pickle and passivate before service

Passivation for C276 means pickling in a nitric-hydrofluoric acid bath to remove embedded iron from cutting tools and forming. This step is recommended before putting C276 equipment into HCl service; ASTM A380 and A967 describe the procedure.

Does C276 Meet NACE MR0175 for Sour Hydrochloric Acid Service?

Bottom line: Yes. Hastelloy C276 is listed in NACE MR0175 / ISO 15156-3 for sour service, but only in the solution-annealed condition and within a hardness ceiling. Cold work beyond the standard's limit voids the listing.

Sour service matters for HCl because the two acids meet in oil-well acidizing: hydrochloric acid is pumped downhole to dissolve carbonate scale and open perforations, and in a sour reservoir the returning fluid carries hydrogen sulfide as well as residual acid. NACE MR0175 / ISO 15156-3 Table A.26 covers UNS N10276, and the requirements are that the material be solution-annealed and stay within the tabulated hardness ceiling.

Published hardness ceilings for C276 differ between sources and editions - some cite 35 HRC, others 40 HRC, and many owner specifications impose a tighter limit such as 200 HB. Annealed C276 normally lands at 85 to 95 HRB, comfortably inside all of them, so the real risk is not the base metal but cold work from forming, bending or machining, plus the weld heat-affected zone. Where a specification limits weld hardness it commonly does so at about 250 HV10. Confirm the governing edition and the owner's project specification before releasing the design. See also Incoloy 825 vs C276 for sour gas service.

What Does Hastelloy C276 Cost Compared With Other HCl-Resistant Alloys?

C276 is the most cost-effective nickel alloy for clean HCl below 60 deg C. It runs roughly 5 to 6 times the price of 316L, about 20% below C22 and about 40% below Alloy 59, which is why it is the default rather than the premium choice.

Indicative cost and lifecycle comparison for HCl-resistant alloys

The relative figures are indicative site-published ranges, not quotations, and they move with nickel and molybdenum prices. Lifecycle cost, not purchase price, is what decides the case: a C276 line that lasts fifteen years beats a 316L line that is replaced every eighteen months, even before downtime and maintenance labour are counted. For current plate and pipe pricing see Hastelloy C276 pipe price per kg 2026.

Which Product Forms of C276 Are Available for Hydrochloric Acid Service?

C276 is available as plate and sheet, seamless and welded pipe and tube, butt-weld fittings, forgings and flanges, bar and rod, and wire - each under its own ASTM specification, and each requiring the solution-annealed condition.

C276 product forms, ASTM specifications and typical HCl applications

When the duty is piping rather than vessels, the wall-thickness decision is separate from the alloy decision. Use how to choose Hastelloy C276 pipes for the selection sequence and ASME B36.19 pipe dimensions and wall thickness for the schedule tables.

How Does C276 Fit the Hastelloy C276 Content Cluster?

This page is the HCl-specific spoke of the Hastelloy C276 hub. The hub carries the overview, sibling spokes own composition, mechanical properties, corrosion resistance, temperature limits, welding and machining, and vertical spokes own chemical plants, FGD and pulp and paper - so this page stays inside its own lane.

The division of labour is deliberate. The hub page ultimate guide to Hastelloy C276 is the entry point and the only page that links every spoke. The property spokes - what is Hastelloy C276, chemical composition, mechanical properties, corrosion resistance and temperature limits - answer the material questions. The process spokes - chemical plants, FGD systems and pulp and paper - answer the industry questions. The comparison spokes - vs Alloy 20, vs 904L, vs Incoloy 825 and vs Inconel 625 - answer the head-to-head questions.

This page owns one thing only: hydrochloric acid. It should not restate the general acid-by-acid performance table, which lives at Hastelloy C276 for acid service: performance by acid, nor reproduce the welding procedure detail in the C276 welding guide. Where a reader needs the general case, the links point there; where they need the HCl case, it is here. The FAQ about Hastelloy C276 page collects the questions that span the whole cluster.

Where Can You Read More About C276 in Acid and Chemical Service?

The reading path for an HCl project runs: this page for the alloy decision, the welding and standards pages for the specification, the product pages for the forms, and the case studies for real shipments. Start at the hub if you are new to the alloy.

• The complete guide to Hastelloy C276 - the cluster hub and best starting point

• Hastelloy C276 for acid service: performance by acid - the general acid-by-acid comparison

• Hastelloy C22 vs C276: key differences and selection guide - when to step up for oxidants

• Difference between Hastelloy C22 and C276 - the quick chemistry comparison

• Hastelloy C276 welding guide - full procedure, heat input and inspection detail

• ASTM standards for Hastelloy C276 - the complete standards map by product form

• Hastelloy C276 machining tips - cutting parameters for bar and plate

• Hastelloy C276 applications - the cross-industry umbrella page

• Hastelloy C276 for chemical plants - CPI equipment and duty mapping

• Hastelloy C276 for FGD systems - flue-gas desulfurization duty

• FAQ about Hastelloy C276 - the cluster-wide question set

• Nickel alloy pipe for chemical plants: selection by acid type - the acid-type decision tree

Key Facts About Hastelloy C276 for Hydrochloric Acid Service

Frequently Asked Questions

What is the maximum temperature for Hastelloy C276 in hydrochloric acid?

The conservative design limit is 60 deg C (140 deg F) for all HCl concentrations. Above this temperature the corrosion rate rises above 0.13 mm/y (5 mpy) and then accelerates rapidly. For boiling HCl service, upgrade to Hastelloy C22, Alloy 59, zirconium or tantalum.

Is Hastelloy C276 better than titanium for HCl service?

No. Titanium has excellent resistance to oxidizing acids but dissolves rapidly in non-oxidizing hydrochloric acid. C276 is specifically designed for HCl and is the correct choice. Titanium should only be considered in HCl service if the acid contains a strong oxidizing agent such as nitric acid that keeps the titanium passive film stable.

Can I use welded C276 pipe for HCl without post-weld heat treatment?

Not recommended. Welded C276 pipe that has not been solution-annealed after welding has a sensitized heat-affected zone with 5 to 10 times higher corrosion rate in HCl. For any HCl service above 10% concentration or above 40 deg C, solution annealing at 1121 deg C with a water quench is mandatory.

What is the difference between Hastelloy C276 and C22 for HCl service?

C22 has higher chromium (20 to 22.5% versus 14.5 to 16.5% for C276) and slightly lower molybdenum (12.5 to 14.5% versus 15 to 17%). The result is that C22 is more resistant to oxidizing contaminants in HCl such as ferric, cupric and dissolved oxygen, and it has a higher temperature ceiling of about 80 deg C versus about 60 deg C for C276. C276 is more cost-effective for clean, pure HCl service.

Does Hastelloy C276 comply with NACE MR0175 for sour HCl service?

Yes, provided the material is in the solution-annealed condition and stays within the hardness ceiling tabulated for UNS N10276. C276 is explicitly listed in NACE MR0175 / ISO 15156-3 as acceptable for hydrogen sulfide service. This matters for oil-well acidizing, where hydrochloric acid is pumped into sour gas wells. Published hardness ceilings differ between editions, so confirm the governing edition.

What ASTM specifications should I specify for C276 HCl piping?

For welded C276 HCl piping, specify ASTM B619 with solution-annealed expressly stated. For seamless tubing used in heat exchangers, specify ASTM B622. For butt-weld fittings, specify ASTM B366. For plate, sheet and strip, specify ASTM B575. Always reference the ASME SB- equivalent if the equipment is ASME code-stamped.

How does the cost of C276 compare with other HCl-resistant alloys?

C276 typically costs 5 to 6 times the price of 316L stainless steel. It is about 20% cheaper than Hastelloy C22 and about 40% cheaper than Alloy 59. For clean HCl service at moderate temperatures, C276 offers the best cost-performance ratio of any nickel alloy. Zirconium and tantalum cost 4 to 10 times more and are reserved for boiling-acid duty.

What is the corrosion rate of C276 in 10% hydrochloric acid at room temperature?

Under 0.025 mm/y (1 mpy) at 25 deg C. That rate is low enough to allow thin-wall tubing and small corrosion allowances. At 50 deg C the rate is still under 0.025 mm/y, and it only crosses the 0.13 mm/y threshold between 60 and 70 deg C.

Why does C276 resist HCl when 316L stainless steel fails?

Because hydrochloric acid is a non-oxidizing acid. Stainless steels resist acid through a chromium oxide passive film that needs an oxidizing environment to maintain itself, and HCl strips that film away. C276 instead carries 15 to 17% molybdenum and 3 to 4.5% tungsten dissolved in the matrix, which gives the metal itself high resistance to reducing acids.

What is PREN and does a high PREN mean C276 is good for HCl?

PREN, the pitting resistance equivalent number, is calculated as percent chromium plus 3.3 times percent molybdenum plus 16 times percent nitrogen. C276 carries a nominal PREN of about 69. However, PREN was derived for chloride pitting in near-neutral aerated solutions, so it does not by itself predict acid resistance. Use PREN to compare alloys for chloride service and measured corrosion-rate data to select for acid service.

What happens if aerated or ferric-contaminated HCl contacts C276?

The corrosion rate can rise several-fold. Ferric and cupric ions act as cathodic depolarizers and sustain a much higher anodic dissolution rate, and dissolved oxygen does the same more mildly. Recovered and recycled pickling acid is the classic case. Where oxidants are present, step up to Hastelloy C22 or Alloy 59, or deaerate the stream with a nitrogen blanket.

Do I need to solution anneal the whole vessel or just the welds?

The whole fabricated assembly. Intermetallic phases precipitate throughout the weld heat-affected zone, and the only reliable way to redissolve them is a full solution anneal at 1121 deg C followed by a water quench. If the vessel is too large for a furnace, the standard fallback is a C22 weld overlay on the heat-affected zone.

What filler metal should I use to weld C276 for HCl service?

Use matching chemistry: ERNiCrMo-4 for GTAW and GMAW, ENiCrMo-4 for SMAW, and a matching flux-coated wire for SAW. ERNiCrMo-22, the C22 filler, is also acceptable and is sometimes preferred for improved heat-affected-zone resistance, but the weld will show a different color and finish.

Is Hastelloy B3 better than C276 for hydrochloric acid?

B3 carries 27 to 32% molybdenum against 15 to 17% for C276 and almost no chromium, which makes it stronger in clean, strongly reducing acid. But with almost no chromium it has no tolerance for oxidizing contaminants, so the two are not interchangeable. B3 is also produced in smaller volumes and normally costs more per kilogram.

Can C276 handle boiling hydrochloric acid?

No. At the boiling point the corrosion rate in C276 rises to 0.25 mm/y or more in dilute acid and to severe attack in concentrated acid. Boiling HCl requires zirconium 702, which resists all concentrations up to boiling, or tantalum for the most severe small-bore duty.

What hardness limit applies to C276 for sour HCl service?

NACE MR0175 / ISO 15156-3 Table A.26 covers solution-annealed UNS N10276 within a tabulated hardness ceiling. Published ceilings differ between editions and sources, with some citing 35 HRC and others 40 HRC, and owner specifications often impose tighter limits such as 200 HB. Annealed C276 normally lands at 85 to 95 HRB, so the practical risk is cold work and the weld heat-affected zone rather than the base metal.

Which is cheaper over the life of an HCl system: C276 or 316L?

C276, in almost every case. 316L costs about a fifth as much per kilogram but is not an acceptable material for hydrochloric acid service at any meaningful concentration. Lifecycle cost rather than purchase price decides the case, because a C276 line that reaches its design life avoids the replacement, downtime and maintenance labour that a 316L line would consume.

What causes premature C276 failure in HCl systems most often?

Five recurring causes: material supplied as-rolled rather than solution-annealed; weld crevices, lap joints and threaded connections that accelerate crevice corrosion; missing post-weld solution annealing; galvanic coupling to carbon steel or 316L without isolation; and skipping the pickling and passivation step before service.

Does C276 resist sulfuric acid as well as hydrochloric acid?

Not equally well. C276 performs well in sulfuric acid across a wide concentration and temperature range, but in hot, clean, concentrated sulfuric acid Alloy 20 is often the more economical choice, and in some reagent-grade sulfuric acid conditions Alloy 20 shows lower corrosion rates. See the comparison at Hastelloy C276 vs Alloy 20 for the full picture.

Where does the corrosion data in this guide come from?

The concentration and temperature rates are typical values drawn from the Haynes International C-276 data sheet and the ASM Handbook Vol. 13B corrosion tables, cross-checked against ASTM B575. They are indicative ranges for selection work, not design allowables. Any pressure-boundary or corrosion-allowance calculation must be verified against the governing code edition and the producer's current data sheet.

Need C276 plate, pipe, fittings or flanges for an HCl system? Send your duty conditions and specification to JN Alloy for a quotation including material certification, solution annealing and mill test reports.

Glossary