Hangbo Alloy Group
Shanghai · Est. 2012
Sulfuric acid is the most widely produced industrial chemical — and one of the hardest to contain. This guide shows engineers how concentration, temperature and impurities dictate the right nickel alloy, from Hastelloy B-3 and C-276 to Alloy 20 and Incoloy 825.
Sulfuric acid (H₂SO₄) is the single most consumed industrial chemical on earth — used in fertilizer, pigments, batteries, petroleum refining, metal pickling and countless other processes. Yet it is notoriously difficult to engineer for, because its corrosiveness is highly non-linear: a grade that survives dilute acid can be destroyed by concentrated acid, and vice versa. The wrong material choice means rapid general corrosion, pitting, leakage, unplanned shutdown and safety incidents.
This selection guide gives plant engineers and procurement teams a practical, data-driven framework for specifying nickel alloys for sulfuric acid service. As a direct nickel alloy manufacturer and supplier, Hangbo Alloy Group produces and stocks Hastelloy, Alloy 20, Incoloy 825 and related grades in all product forms, with mill test certificates and third-party inspection.
Three variables control corrosion in H₂SO₄ service, and all three must be defined before an alloy is chosen:
Golden rule: Define the environment first (acid type, concentration, temperature, contaminants), then consult isocorrosion data, then weigh lifetime cost against a larger corrosion allowance. Never pick a grade from a single data point.
The corrosion behavior of each alloy is a direct consequence of its chemistry. Molybdenum drives resistance to pure reducing sulfuric acid; chromium drives resistance to oxidizing species and chlorides; copper (in Alloy 20) aids resistance to intermediate sulfuric acid.
| Alloy (UNS) | Family | Ni % | Cr % | Mo % | Other key | Fe |
|---|---|---|---|---|---|---|
| 316L (S31603) | Austenitic SS | 10–14 | 16–18 | 2–3 | Low C | Balance |
| Alloy 20 (N08020) | Ni-Fe-Cr | 32–38 | 19–21 | 2–3 | 3–4 Cu | Balance |
| Incoloy 825 (N08825) | Ni-Fe-Cr | 38–46 | 19–23 | 2.5–3.5 | 1.5–3 Cu, Ti | Balance |
| Alloy 28 (N08028) | Fe-Ni-Cr-Mo | 30–34 | 26–28 | 3–4 | 0.6–1.4 Cu | Balance |
| Alloy 31 (N08031) | Fe-Ni-Cr-Mo | 30–32 | 26–28 | 6–7 | 1–1.4 Cu, N | Balance |
| Hastelloy C-276 (N10276) | Ni-Cr-Mo-W | Balance | 14.5–16.5 | 15–17 | 3–4.5 W, low C | 4–7 |
| Hastelloy C-22 (N06022) | Ni-Cr-Mo-W | Balance | 20–22.5 | 12.5–14.5 | 2.5–3.5 W | 2–6 |
| Hastelloy B-3 (N10675) | Ni-Mo | Balance | 1–3 | 27–32 | Ti, low C | 1–3 |
The contrast is stark: B-3 relies almost entirely on molybdenum and has almost no chromium, making it superb in clean reducing acid but vulnerable to oxidizing and chloride attack. The C-series balances chromium and molybdenum for universal resistance.
Typical room-temperature values (annealed, typical) help with pressure-part and structural sizing:
| Alloy | Density (g/cm³) | Tensile (MPa) | Yield (MPa) | Max Useful Temp* |
|---|---|---|---|---|
| 316L | 8.0 | 485–620 | 170–310 | ~200°C (acid) |
| Alloy 20 | 8.1 | 550–760 | 240–380 | ~65°C (acid) |
| Incoloy 825 | 8.1 | 550–760 | 240–380 | ~540°C (structural) |
| Alloy 31 | 8.1 | 650–820 | 300–450 | ~1000°C (oxidizing) |
| Hastelloy C-276 | 8.9 | 790–1000 | 355–480 | ~1040°C (oxidizing) |
| Hastelloy C-22 | 8.7 | 740–950 | 330–450 | ~1040°C (oxidizing) |
| Hastelloy B-3 | 9.2 | 760–950 | 360–450 | ~650°C (reducing acid) |
*“Max useful temp” for acid service is set by corrosion rate, not strength. The structural high-temperature limits of C-276 and 825 are far higher; in sulfuric acid the binding limit is corrosion, which tightens sharply with temperature.
The table below summarizes typical, defensible selection bands for pure sulfuric acid. Rates are illustrative of industry and manufacturer literature; confirm against isocorrosion curves for your exact conditions.
| H₂SO₄ Condition | Recommended Alloy | Notes |
|---|---|---|
| < ~10%, ambient, low chloride | 316L (limited), Alloy 20, 825 | 316L only very dilute/ambient; upgrade to Alloy 20 for reliability |
| ~5–70%, up to ~65°C | Alloy 20 (N08020) | The classic, cost-effective sulfuric-acid alloy |
| ~10–70%, hot or upset | Hastelloy C-276 / C-22 | Lower corrosion rate as temperature climbs |
| ~70–98%, pure, moderate temp | Hastelloy B-3 (N10675) | Lowest general-corrosion rate in clean concentrated acid |
| >93%, ambient storage (passive) | Carbon steel (tank) | B-3 or C-276 if heated/mixed/not pure |
| Any conc., with Fe³⁺/Cu²⁺/O₂/HNO₃ | C-276 / C-22 / C-2000 / G-30 | Oxidizing — chromium-bearing alloy required |
| Any conc., with chlorides | C-276 / C-22 | Avoid B-3 (pitting/SCC risk) |
Sulfuric acid alone is reducing, which favors high-molybdenum alloys (B-3). But few real streams are pure:
Nickel-molybdenum alloy engineered for pure, reducing sulfuric acid at essentially all concentrations. Its corrosion rate is nearly temperature-independent in clean acid — unique among nickel alloys. Replace B-2 in all new designs (better weldability and thermal stability, no post-weld sensitization). Avoid in oxidizing or chloride-containing service.
The versatile workhorse for dirty, hot, intermediate-concentration sulfuric acid, especially with oxidizing ions or chlorides. Excellent resistance to pitting, crevice corrosion and stress-corrosion cracking (PREN ~60). The safe default when the stream chemistry is uncertain or aggressive.
Higher-chromium upgrades of C-276 with even better resistance to oxidizing media, localized corrosion and mixed acids. C-2000 adds copper for broader reducing/oxidizing coverage. Choose when C-276 is marginal or the acid is heavily oxidized/mixed.
Nickel-iron-chromium with copper, developed specifically for sulfuric acid. The cost-effective workhorse for 5–70% H₂SO₄ up to about 65°C. Ideal for battery-acid, fertilizer, pickling and acid-cleaning equipment where a full Hastelloy is not justified.
Lower-cost alternative to Alloy 20 with good resistance to dilute-to-intermediate sulfuric acid and excellent chloride stress-corrosion-cracking resistance. Common in tanks, piping and heat-exchanger tubing for moderate acid duty.
High-chromium, high-molybdenum Fe-Ni-Cr grades. Alloy 31 (6Mo-class) is used in flue-gas-desulfurization and aggressive sulfuric/phosphoric environments where Alloy 20 is not enough but C-276 is cost-prohibitive.
| Your Service Condition | First Choice | Upgrade When… |
|---|---|---|
| Dilute H₂SO₄ (<10%), ambient | Alloy 20 / 825 | Chlorides or upset temp → C-276 |
| 5–70% H₂SO₄, ≤65°C, clean | Alloy 20 (N08020) | Temperature rises → C-276/C-22 |
| 10–70% H₂SO₄, hot / upset | Hastelloy C-276 | Oxidizers present → C-22/C-2000 |
| Pure >70% H₂SO₄, moderate T | Hastelloy B-3 | Any oxidizer/Cl⁻ → C-276 |
| H₂SO₄ + HNO₃ / oxidizers | C-22 / C-2000 / G-30 | Start here (B-3 fails) |
| H₂SO₄ + chlorides | C-276 / C-22 | Never B-3 |
| FGD / acid condensate | Alloy 31 / C-276 / 625 | Chloride + SO₂ → C-276 |
Sulfuric acid condensate in flue-gas-desulfurization (FGD) and waste-heat recovery combines sulfurous acid, chlorides and abrasion. Here a 6Mo alloy (Alloy 31) or Hastelloy C-276 / Inconel 625 is specified for absorbers, quenchers and reheater tubing. At true high temperature (structural, oxidizing) the C-series and 825 retain strength and oxidation resistance up to ~1000°C, while B-3 is limited to reducing-acid duty.
Hangbo Alloy Group manufactures and supplies sulfuric-acid-service alloys in a full range of forms, with mill test certificates and third-party inspection (SGS, TÜV) available:
| Alloy (UNS / W.Nr) | Plate | Rod/Bar | Pipe/Tube | Cast |
|---|---|---|---|---|
| Alloy 20 (N08020 / 2.4660) | ASTM B463 | ASTM B473 | ASTM B464/B468/B470 | A351 CN7M |
| Hastelloy B-3 (N10675 / 2.4600) | ASTM B333 | ASTM B335 | ASTM B622/B619/B626 | A494 |
| Hastelloy C-276 (N10276 / 2.4819) | ASTM B575 | ASTM B574 | ASTM B622/B619/B626 | A494 |
| Hastelloy C-22 (N06022) | ASTM B575 | ASTM B574 | ASTM B622/B619/B626 | A494 |
| Incoloy 825 (N08825 / 2.4858) | ASTM B424 | ASTM B425 | ASTM B423/B163 | A351 CN7M |
| Alloy 28 (N08028 / 1.4563) | ASTM B709 | ASTM B804 | ASTM B668/B619 | EN 1.4563 |
| Alloy 31 (N08031 / 1.4562) | ASTM B625 | ASTM B649 | ASTM B622/B619/B626 | EN 1.4562 |
All grades are also referenced by NACE MR0175/ISO 15156 (where applicable), AMS, EN and German W.Nr. designations, and are covered by ASME pressure-vessel codes.
Not sure whether your acid stream calls for Hastelloy B-3, C-276, Alloy 20 or Incoloy 825? Send us your concentration, temperature and impurity profile and our metallurgists will recommend the most cost-effective certified alloy. As a direct manufacturer and supplier, we offer competitive price quotes, full material certification and worldwide delivery.
Email: [email protected] | Phone / WhatsApp: +86-136-1165-6360
It depends on concentration, temperature and impurities. For pure sulfuric acid across most concentrations at moderate temperature, Hastelloy B-3 (UNS N10675) is the performance champion. When the acid contains oxidizing impurities (Fe³⁺, Cu²⁺, dissolved oxygen, HNO₃) or chlorides, Hastelloy C-276 (UNS N10276) or C-22 is mandatory. For dilute-to-intermediate acid (about 5–70%) up to roughly 65°C, the cost-effective workhorse is Alloy 20 (UNS N08020). For mixed sulfuric/nitric acid, Hastelloy C-22, C-2000 or G-30 are preferred.
Only very dilute, ambient-temperature acid. 316L tolerates up to about 10 wt% H₂SO₄ at room temperature and about 0.5–1% at 80°C; beyond that its passive film collapses and corrosion rates jump to 1–10 mm/year. In the 10–90% concentration window that covers most process streams, 316L is unsuitable and is one of the most common — and costly — material-specification errors in sulfuric acid service.
Hastelloy B-3 is a nickel-molybdenum alloy (Ni ~65%, Mo ~28.5%, Cr ~1.5%) optimized for pure, reducing sulfuric acid at all concentrations — it is effectively immune to general corrosion in clean H₂SO₄. Hastelloy C-276 is a nickel-chromium-molybdenum-tungsten alloy that sacrifices a little reducing-acid performance for broad resistance to oxidizing impurities and chlorides, which destroy B-3. Choose B-3 for pure acid; choose C-276/C-22 when the stream is dirty, oxygenated, or contains chlorides.
Alloy 20 (UNS N08020) was developed specifically for sulfuric acid. It gives reliable service from about 5% up to 98% H₂SO₄, with its best band at 10–70% and temperatures up to roughly 65°C (150°F). Above about 60–66°C in intermediate concentrations its corrosion rate climbs, and in hot, concentrated or heavily contaminated acid a Hastelloy is the safer specification.
Corrosion rate rises steeply with temperature. The nickel-molybdenum (B-series) alloys are unusual in that their rate is almost temperature-independent in pure acid, while Ni-Cr-Mo alloys (C-series) and Alloy 20 accelerate noticeably as temperature climbs. That is why a grade acceptable at 50°C can be unacceptable at 80–90°C — always size the alloy to the worst-case process upset temperature, not the design average.
Sulfuric acid alone is a reducing acid, which favors high-molybdenum alloys like B-3. But dissolved metal ions (Fe³⁺, Cu²⁺), free oxygen, or nitric acid make the environment oxidizing, and molybdenum-rich alloys lose protection and can pit. Chromium is the element that resists oxidizing attack, so any alloy with sufficient chromium — C-276, C-22, C-2000, Alloy 20, Incoloy 825 — is required once oxidizers are present.
No. Hastelloy B-3 has almost no chromium and is vulnerable to pitting and stress-corrosion cracking in chlorides. In sulfuric acid that also contains chlorides or seawater cooling, specify Hastelloy C-276 or C-22 instead. B-3 should be reserved for clean, chloride-free, reducing service.
Truly concentrated, pure H₂SO₄ (>~93%) forms a passive film on carbon steel, so mild steel tanks are widely used for ambient storage. For transfer, agitation, heating, or where even trace impurities or aeration exist, Hastelloy B-3 gives the lowest corrosion rate; Hastelloy C-276 is used when the concentrated acid is not pure. Alloy 20 is marginal in this concentration and generally not the first choice for hot concentrated acid.
Mixed sulfuric/nitric (oxidizing) acid shifts selection to high-chromium alloys: Hastelloy C-22, Hastelloy C-2000, Hastelloy G-30, and in some cases Alloy 59. These resist both the reducing and oxidizing components and the localized attack that low-chromium alloys would suffer.
Alloy 20 = UNS N08020 (W.Nr 2.4660), ASTM B463/B473/B464. Hastelloy B-3 = UNS N10675 (W.Nr 2.4600), ASTM B333/B335/B622. Hastelloy C-276 = UNS N10276 (W.Nr 2.4819), ASTM B575/B574/B622. Incoloy 825 = UNS N08825 (W.Nr 2.4858), ASTM B424/B425. Alloy 28 = UNS N08028 (W.Nr 1.4563); Alloy 31 = UNS N08031 (W.Nr 1.4562). Cast variants follow ASTM A351 CN7M (Alloy 20) and A494.
Yes. For large vessels, explosion-clad or weld-overlay construction (carbon steel + Alloy 20, 825, 625 or C-276 liner) gives the strength of carbon steel with corrosion-resistant alloy on the wetted surface at a fraction of the solid-alloy cost. Hangbo Alloy Group supplies both solid and clad forms with full material certification.
Yes. Hastelloy C-276 and C-22 are welded with matching C-276/C-22 filler; B-3 uses B-3 or ERNiMo-3 (Hastelloy W) consumables; Alloy 20 typically uses ERNiCrMo-3 (Inconel 625) or 20-type filler; Incoloy 825 uses ERNiCrMo-3 or 825 filler. Modern low-carbon grades are resistant to post-weld sensitization, but qualified procedures and proper purge are essential.
Send your acid concentration, temperature, any impurities (chlorides, oxidizers), pressure and required form to Hangbo Alloy Group at [email protected] or call/WhatsApp +86-136-1165-6360. As a direct manufacturer and supplier we provide competitive price quotes, mill test certificates, and worldwide delivery of bars, plates, tubes, forgings and welding consumables.
For help choosing between Hastelloy B-3, C-276, Alloy 20, Incoloy 825 or another grade for your sulfuric acid service — or for a quotation on bars, plates, tubes, forgings or welding consumables — contact Hangbo Alloy Group. We typically respond within 10 minutes and ship worldwide from our Shanghai facility.
Email: [email protected]
Phone: +86-136-1165-6360
WhatsApp: +86 13611656360
Send us your concentration, temperature and impurity profile and we will recommend the most cost-effective certified nickel alloy, with a competitive quote and full certification.