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Hastelloy C276 (UNS N10276) is the most widely used nickel alloy for hydrochloric acid (HCl) service across all concentrations at temperatures below 60°C, with corrosion rates typically under 0.13 mm/y (5 mpy).
C276 resists pure HCl extremely well, but if the acid contains oxidizing species (Fe³⁺, Cu²⁺, dissolved oxygen, nitric acid), upgrade to Hastelloy C22 or Alloy 59.
Welded C276 equipment for HCl service must be solution-annealed; the as-welded HAZ corrodes 5–10× faster in HCl.
This guide incoludes corrosion data, material comparison tables, welding rules, and ASTM specification references to support selection decisions.
Key Specifications at a Glance
Property | Hastelloy C276 (UNS N10276) | Why It Matters for HCl |
Nickel (balance) | 57% min | Nickel gives ductility and general acid resistance |
Molybdenum | 15–17% | Mo is THE key element for non-oxidizing acid (HCl) resistance |
Chromium | 14.5–16.5% | Provides resistance to oxidizing contaminants in HCl |
Tungsten | 3–4.5% | Tungsten supplements Mo, raising PREN to ~69 |
PREN | ~69 | Excellent resistance to pitting/crevice corrosion |
Max HCl concentration | All conc. (0–37%) | C276 is usable in all HCl concentrations at moderate temperature |
Max service temperature in HCl | ~60°C (140°F) | Above 60°C, corrosion rate rises sharply |
Typical corrosion rate, 10% HCl, 25°C | <0.025 mm/y (<1 mpy) | Essentially negligible — suitable for thin-wall tubing |
ASME Boiler & Pressure Vessel | Section VIII, Div 1 & 2 | Approved for pressure vessel construction |
NACE MR0175 / ISO 15156 | Compliant | Suitable for sour (H₂S) oil & gas service |
Source: ASTM B575, ASM Handbook Vol. 13B, Haynes International C276 datasheet
Hydrochloric acid (HCl) is among the most widely used industrial chemicals — and one of the most corrosive. It is the active agent in steel pickling, oil-well acidizing, chloride-based chemical synthesis, and metal surface treatment. Unlike nitric or sulfuric acid, HCl cannot be 'passivated' by chromium oxide films. It dissolves almost all common stainless steels.
The result: a typical chemical plant spends 15–30% of its maintenance budget on corrosion-related failures in HCl handling systems (NACE International, 2023). Selecting the wrong material does not just mean a leak — it can mean a total system shutdown, safety incident, or environmental violation.
Hastelloy C276 has been the industry workhorse for HCl service since the 1970s. This guide synthesizes corrosion data, material comparison tables, and engineering recommendations so you can make the best selection.
For pure hydrochloric acid at concentrations from 0% to 37% (azeotrope) and temperatures up to ~60°C (140°F), Hastelloy C276 delivers the best balance of corrosion resistance, weldability, and cost among all nickel alloys. Above 60°C or in aerated HCl, you must upgrade to C22, Alloy 59, or a zirconium/tantalum exotic.
Corrosion Rate Data
HCl Concentration | 25°C (77°F) | 50°C (122°F) | 70°C (158°F) | Boiling Point | Verdict |
1% HCl | <0.013 mm/y (<0.5 mpy) | <0.025 mm/y (<1 mpy) | <0.13 mm/y (<5 mpy) | 0.25–0.5 mm/y | Excellent up to 50°C |
5% HCl | <0.013 mm/y (<0.5 mpy) | <0.025 mm/y (<1 mpy) | <0.13 mm/y (<5 mpy) | 0.5–1.0 mm/y | Excellent up to 50°C |
10% HCl | <0.013 mm/y (<0.5 mpy) | <0.025 mm/y (<1 mpy) | 0.13–0.25 mm/y | 1.0–2.5 mm/y | Excellent up to 50°C |
20% HCl | <0.025 mm/y (<1 mpy) | 0.025–0.05 mm/y | 0.25–0.5 mm/y | >2.5 mm/y | Good up to 50°C |
37% HCl | <0.025 mm/y (<1 mpy) | 0.05–0.13 mm/y | 0.5–1.0 mm/y | Severe corrosion | Use below 60°C only |
Interpretation: Below 60°C (140°F), C276 has a corrosion rate under 0.13 mm/y (5 mpy) in all HCl concentrations — the industry threshold for 'acceptable' in process equipment (API 571). Above 70°C, corrosion accelerates sharply.
Hydrochloric acid is a non-oxidizing acid. It cannot be resisted by chromium oxide passive films. Instead, HCl resistance requires a high concentration of molybdenum and tungsten in the alloy matrix. C276 delivers both at a commercially viable price point.
C276's High Molybdenum Content (15–17%) Is the Fundamental Reason It Resists HCl
Chemical Composition of C276 vs. Other Ni-Alloys
Element (wt%) | C276 (N10276) | C22 (N06022) | Alloy 59 (N06059) | B3 (N10675) | Why It Matters |
Nickel | Balance | Balance | Balance | Balance | Nickel provides ductility and general acid resistance |
Molybdenum | 15–17 | 13–15 | 15–16.5 | 27–32 | Mo is THE key element for HCl resistance |
Chromium | 14.5–16.5 | 20–22.5 | 22–24 | 1.0–3.0 | Cr provides resistance to oxidizing contaminants |
Tungsten | 3–4.5 | 2.5–3.5 | 0–0.5 | ≤0.6 | W supplements Mo, raising PREN |
Iron | 4–7 | 2–6 | ≤1.5 | 1.0–3.0 | Fe is a low-cost filler; excess reduces corrosion resistance |
Carbon (max) | 0.01% | 0.015% | 0.010% | 0.01% | Ultra-low C prevents welding sensitization |
PREN* | ~69 | ~72 | ~76 | ~130 | PREN > 60 = excellent pitting resistance |
Why Molybdenum Matters for HCl (The 'Mo Effect')?
Molybdenum dissolves in the nickel matrix and forms a stable, low-solubility chloride film (MoCl₃-like species) that acts as a barrier to further HCl attack. The higher the Mo content, the stronger this barrier. This is why:
• 316L stainless steel (Mo ~2.5%): corrodes at >25 mm/y in 10% HCl at 25°C — essentially unusable.
• Alloy 400/Monel (Mo 0%): rapidly dissolves in HCl — not recommended at any concentration.
• Hastelloy B3 (Mo 27–32%): the 'gold standard' for pure HCl at all temperatures, but lacks Cr so it fails in oxidizing environments.
• C276 (Mo 15–17%): the practical compromise — enough Mo for HCl resistance, enough Cr for oxidizing contamination tolerance.
Welded C276 Equipment for HCl Service Must Be Solution-Annealed; Without It, the HAZ Corrodes 5–10× Faster
C276 is a 'solution-annealed-only' alloy. Its corrosion resistance depends entirely on a homogeneous, defect-free microstructure with all Mo and W in solid solution. Welding without post-weld heat treatment (PWHT) creates a Heat-Affected Zone (HAZ) that is highly susceptible to preferential corrosion in HCl — often 5 to 10 times the base-metal corrosion rate.
Why Solution Annealing Is Necessary for HCl Service
During welding, the HAZ is heated to 650–1100°C (1200–2000°F) and then cools rapidly. Within this temperature range, intermetallic phases (P-phase, mu-phase, and sigma) can precipitate. These phases are Mo-rich and Cr-depleted, creating microscopic galvanic cells that accelerate HCl attack.
Solution annealing (1121°C / 2050°F, water quench) re-dissolves these phases and restores uniform corrosion resistance. ASME BPVC Section VIII recommends PWHT for all C276 pressure vessels in corrosive service.
Welding Filler Metal Selection for HCl Service
Welding Process | Recommended Filler | Reason | Post-Weld Treatment |
SMAW (stick) | ENiCrMo-4 (C276) | Matching chemistry, proven in HCl service | Solution anneal 1121°C + water quench |
GTAW (TIG) | ERNiCrMo-4 | Cleaner, lower heat input, less dilution | Solution anneal 1121°C + water quench |
GMAW (MIG) | ERNiCrMo-4 | Higher deposition rate for thick sections | Solution anneal 1121°C + water quench |
SAW (submerged) | ENiCrMo-4 (flux-coated) | For very thick plates (>25 mm) | Solution anneal mandatory |
Note: Using ERNiCrMo-22 (C22 filler) on C276 base metal is acceptable and sometimes preferred for improved HAZ resistance, but the weld will have a slightly different color/finish.
ASTM B575, B619, B622, and B366 Are the Controlling Material Standards for C276 HCl Components
When procuring C276 for HCl service, the purchase order must reference the correct ASTM specification for the product form. Using the wrong specification can result in off-chemistry material that fails prematurely. Below is the complete standards matrix.
ASTM Standard | Product Form | Key Requirements | Applicable Equipment |
ASTM B575 | Plate, sheet, strip | Chemistry per UNS N10276; solution-annealed | Vessel shells, tube sheets, baffles |
ASTM B619 | Welded pipe | Welded + solution-annealed; hydrostatic test | HCl transfer lines, risers |
ASTM B622 | Seamless pipe & tube | Cold-drawn; solution-annealed | Heat exchanger tubes, instrument lines |
ASTM B366 | Butt-weld fittings | Chemistry + heat treatment verified | Elbows, tees, reducers for HCl piping |
ASTM B564 | Forgings | Solution-annealed; UT + PT/MT inspected | Flanges, valve bodies, nozzles |
ASTM B574 | Bar & rod | Solution-annealed; straightness spec | Shafts, bolts, valve stems |
ASME SB-XXX | All (ASME version) | Adds ASME stamping and pressure-design rules | All ASME-code pressure equipment |
Critical: Always specify 'solution-annealed' on the purchase order. Some suppliers offer 'as-welded' or 'as-rolled' C276 at a lower price — this material is unsuitable for HCl service.
C276 Delivers Yield Strength of 283 MPa (41 ksi) in the Solution-Annealed Condition — Sufficient for All HCl Pressure Service
C276 has moderate strength (lower than duplex stainless steel but higher than pure nickel) and excellent ductility. It is suitable for all pressure-rated HCl service under ASME BPVC Section VIII up to 427°C (800°F) design temperature. The key mechanical properties are tabulated below.
Room-Temperature Mechanical Properties (Solution-Annealed)
Property | ASTM Minimum | Typical Value | Test Standard | Implication for HCl Design |
Yield Strength (0.2% offset) | 283 MPa (41 ksi) | 320 MPa (46 ksi) | ASTM E8 | Thin-wall HCl piping is feasible — good strength-to-weight |
Tensile Strength | 690 MPa (100 ksi) | 760 MPa (110 ksi) | ASTM E8 | High UTS gives generous safety margin |
Elongation | 40% | 50% | ASTM E8 | Excellent formability for complex shapes |
Hardness (Brinell) | — | <200 HB | ASTM E10 | Soft enough to machine; work-hardening is moderate |
Impact Toughness (Charpy, -196°C) | >80 J | 120 J | ASTM E23 | Excellent low-temperature toughness — safe for cold HCl storage |
Source: ASTM B575, ASM Handbook Vol. 2, Haynes C-276 Datasheet
Even the best material (C276) will fail if the HCl handling system is poorly designed. The following 5 rules, derived from NACE MR0103 and chemical-process-industry best practices, prevent the most common failure modes.
Rule 1: Specify Solution-Annealed Material Only
Purchase orders must state: 'Material shall be solution-annealed at 1121°C (2050°F) and water-quenched. Certified heat treatment record required.' Mill test reports (MTRs) must show the heat treatment temperature and quench method.
Rule 2: Welds Must Be 100% Penetration, No Crevice
HCl is a crevice-corrosion accelerator. Any weld crevice, lap joint, or stagnant zone will corrode preferentially. Use full-penetration welded joints (no threaded connections in HCl service).
Rule 3: Post-Weld Solution Annealing Is Mandatory for HCl Service
As-welded C276 has a sensitized HAZ. For HCl service, the entire fabricated assembly must be re-solution-annealed. If the vessel is too large for a heat-treat furnace, use C22 weld overlay on the HAZ (expensive but effective).
Rule 4: Prevent Galvanic Coupling with More Noble Materials
C276 is the 'noble' end of most galvanic couples. If you must connect C276 to 316L or carbon steel in an HCl system, use a dielectric flange or ensure the C276 surface area is much larger than the less-noble material (cathodic protection effect).
Rule 5: Budget for Pickling/Passivation
'Passivation' for C276 means pickling in a nitric-hydrofluoric acid bath to remove surface contaminants (iron particles from cutting tools). This step is recommended before putting C276 equipment into HCl service. ASTM A380 / A967 describes the procedure.
Q1: What is the maximum temperature for Hastelloy C276 in hydrochloric acid?
A: The conservative design limit is 60°C (140°F) for all HCl concentrations. Above this temperature, the corrosion rate rises above 0.13 mm/y (5 mpy) and accelerates rapidly. For boiling HCl service, upgrade to C22, Alloy 59, or zirconium.
Q2: Is Hastelloy C276 better than titanium for HCl service?
A: No. Titanium has excellent resistance to oxidizing acids but rapidly dissolves in non-oxidizing HCl. C276 is specifically designed for HCl and is the correct choice. Titanium should only be used in HCl service if the acid contains a strong oxidizing agent (e.g., nitric acid / HCl mixed acid) that keeps the titanium passive film stable.
Q3: Can I use welded C276 pipe for HCl without post-weld heat treatment?
A: Not recommended. Welded C276 pipe that has not been solution-annealed after welding will have a sensitized HAZ with 5–10× higher corrosion rate in HCl. For any HCl service above 10% concentration or above 40°C, PWHT (solution anneal at 1121°C + water quench) is mandatory.
Q4: What is the difference between Hastelloy C276 and C22 for HCl service?
A: C22 has higher chromium (20–22.5% vs. 14.5–16.5% for C276) and slightly lower molybdenum (13–15% vs. 15–17%). The result: C22 is more resistant to oxidizing contaminants in HCl (Fe³⁺, Cu²⁺, O₂) and has a higher temperature limit (~80°C vs. ~60°C for C276). C276 is more cost-effective for pure HCl service.
Q5: Does Hastelloy C276 comply with NACE MR0175 for sour (H₂S) HCl service?
A: Yes, provided the material is in the solution-annealed condition and the hardness is ≤200 HB. C276 is explicitly listed in NACE MR0175 / ISO 15156 as acceptable for H₂S service. This is relevant for oil-well acidizing, where HCl is pumped into sour gas wells.
Q6: What ASTM specifications should I specify for C276 HCl piping?
A: For welded C276 HCl piping, specify ASTM B619 (welded pipe) with 'solution-annealed' expressly stated. For seamless tubing (heat exchanger applications), specify ASTM B622. For butt-weld fittings, specify ASTM B366. Always reference the ASME version (SB-XXX) if the equipment is ASME-code-stamped.
Q7: How does cost of C276 compare with other HCl-resistant alloys?
A: C276 typically costs 5–6× the price of 316L stainless steel ($35–45/lb vs. $6–8/lb as of 2026). It is ~20% cheaper than C22 and ~40% cheaper than Alloy 59. For pure HCl service at moderate temperatures, C276 offers the best cost-performance ratio of all nickel alloys.
