Excerpt:
Hastelloy G-30 (UNS N06030, W.Nr. 2.4603) technical guide from Shanghai Hangbo Alloy Group. High-chromium (28-31.5%) Ni-Cr-Fe-Mo-W-Cu alloy, the reference material for commercial (wet-process) phosphoric acid evaporators and nitric/mixed-acid service; ASTM B581/B582; as-welded use with ERNiCrMo-13 over-alloyed filler option.
Hastelloy G-30 (UNS N06030) Technical Guide: The High-Chromium Answer to Commercial Phosphoric Acid Service | Hangbo Alloy
Introduction
Commercial phosphoric acid is not the clear, reagent-grade liquid of the chemistry textbook. It is the product of digesting phosphate rock with sulfuric acid — wet-process acid — and it arrives at the evaporator carrying a corrosive cocktail of chlorides, fluorides, silica, sulfates, residual rock solids, and enough heat to defeat almost every conventional material. For decades, engineers fought this environment with successively tougher stainless steels, then with alloy 20, then with Hastelloy G-3, each upgrade buying a few more years of evaporator-tube life. Hastelloy G-30 (UNS N06030, W.Nr. 2.4603) was engineered to end that escalation for the most severe commercial phosphoric acid circuits by doing one thing decisively: raising chromium to approximately 30% — nearly double the level of the C-family workhorses and far above the 22% of G-3 — while retaining a balanced nickel-iron matrix with molybdenum, tungsten, and copper for reducing-acid and localized-corrosion defense.
That high chromium is not a number for its own sake. In wet-process phosphoric acid, and in the nitric- and mixed-acid environments of the chemical industry, chromium is the element that carries the oxidizing-acid load: it forms and repairs the protective passive film that keeps corrosion rates at fractions of a millimeter per year. G-30's ~30% chromium puts it in a performance class where it routinely outlasts G-3 by several times and alloy 625 by an even wider margin in aggressive phosphoric acid evaporator and heat-exchanger service. Shanghai Hangbo Alloy Group manufactures and supplies Hastelloy G-30 to ASTM B581 (rod, bar, and wire) and ASTM B582 (plate, sheet, and strip), with seamless and welded pipe and tube to the applicable ASTM product standards, and ships every heat with EN 10204 3.1 certification, PMI verification, and full traceability. This guide details the metallurgy, the corrosion data, and the application logic of G-30.
Chemical Composition
The composition limits below apply to G-30 mill products supplied to ASTM B581/B582. Nickel is the balance element.
| Element | Min % | Max % |
|---|---|---|
| Nickel (Ni) | Balance | — |
| Chromium (Cr) | 28.0 | 31.5 |
| Iron (Fe) | 13.0 | 17.0 |
| Molybdenum (Mo) | 4.0 | 6.0 |
| Tungsten (W) | 1.5 | 4.0 |
| Copper (Cu) | 1.0 | 2.4 |
| Niobium + Tantalum (Nb+Ta) | 0.3 | 1.5 |
| Cobalt (Co) | — | 5.0 |
| Manganese (Mn) | — | 1.5 |
| Silicon (Si) | — | 0.80 |
| Carbon (C) | — | 0.03 |
| Phosphorus (P) | — | 0.04 |
| Sulfur (S) | — | 0.03 |
Three design details deserve the specifier's attention. First, the chromium range of 28–31.5% with nickel still in the balance (~43–44% typical) keeps the alloy fully austenitic and fabricable while delivering its oxidizing-acid power. Second, molybdenum (4–6%), tungsten (1.5–4%), and copper (1–2.4%) are balanced to give resistance in the reducing regions and to chlorides — commercial phosphoric acid is never purely oxidizing or purely reducing, and G-30 must fight on both fronts simultaneously. Third, the niobium-plus-tantalum addition (0.3–1.5%) and the carbon ceiling of 0.03% ensure that welding does not degrade the alloy's corrosion resistance, a lesson inherited from the earlier G-family grades.
Why High Chromium Wins in Commercial Phosphoric Acid
The corrosion mechanism in wet-process phosphoric acid is complex because the acid is simultaneously hot, chloride-bearing, fluoride-bearing, and loaded with solids that create under-deposit crevice conditions in evaporators and exchangers. Laboratory testing and decades of plant experience agree on the hierarchy that chromium creates: as chromium rises from 20% to 30%, uniform corrosion rates in aggressive commercial acid fall steeply, and resistance to the pitting and crevice attack that occurs beneath scale and gypsum deposits rises correspondingly. The table below summarizes the qualitative performance ladder Hangbo Alloy uses when guiding fertilizer-industry customers, based on published comparative test programs in commercial and reagent phosphoric acid.
| Alloy | Chromium, typical | Relative resistance in aggressive wet-process H₃PO₄ | Typical role |
|---|---|---|---|
| 316L stainless | 17% | Baseline | Digestion and mild duty only |
| Alloy 20 / 904L | 20% | Moderate | Limited evaporator service |
| Hastelloy G-3 | 22% | Good | Older evaporator circuits, moderate acid |
| Alloy 625 | 21–22% | Moderate-good | Historically over-specified, now displaced |
| Hastelloy G-30 | 30% | Excellent | Severe evaporator and exchanger service |
| Hastelloy G-35 | 33% | Superior (high-Cl/F acid) | Most severe modern acid circuits |
The message of this ladder is practical: in hot evaporator acid containing several thousand ppm of chlorides plus fluorides, G-30 typically exhibits uniform corrosion rates on the order of a tenth of a millimeter per year or below in controlled tests, where lesser alloys are measured in whole millimeters per year. Where the acid's chloride and fluoride load is extreme, the ladder's top rung — G-35 — takes over, and Hangbo Alloy's G-35 guide covers that upgrade path.
Broader Corrosion Resistance
Because chromium at 30% makes the alloy genuinely comfortable in oxidizing media, G-30's envelope extends well beyond phosphoric acid:
| Environment | G-30 Performance |
|---|---|
| Wet-process phosphoric acid (commercial, high Cl/F) | Excellent — the design target |
| Reagent phosphoric acid, all concentrations | Excellent, to boiling |
| Nitric acid | Excellent — resistant across wide concentration range |
| Nitric + hydrochloric acid mixtures | Good — among the best Ni-Cr-Fe alloys |
| Nitric + hydrofluoric acid (pickling liquors) | Good — used for stainless pickling systems |
| Sulfuric acid | Good in middle and high concentrations at moderate temperature |
| Oxidizing chloride media (chlorine dioxide, hypochlorite) | Good |
| Reducing halide acids (pure hot HCl) | Limited — B-family alloys remain the reference |
This breadth makes G-30 a favorite in acid-recovery, pickling, and nuclear fuel-cycle services where nitric acid dominates, and in chemical processes where streams swing between oxidizing and reducing character. Its resistance to chloride stress-corrosion cracking, as a high-nickel fully austenitic alloy, is essentially total.
Physical and Mechanical Properties
Typical annealed values for G-30 are listed below; actual heat values are certified on the EN 10204 3.1 documents supplied by Hangbo Alloy.
| Property | Typical Value (Annealed) |
|---|---|
| Density | 8.22 g/cm³ |
| Melting range | ≈ 1,330 – 1,380 °C |
| Modulus of elasticity (RT) | ≈ 200 GPa |
| Mean coefficient of thermal expansion (RT – 100 °C) | ≈ 13.5 µm/m·°C |
| Tensile strength (RT, typical) | ≈ 650 – 720 MPa |
| 0.2% yield strength (RT, typical) | ≈ 310 – 370 MPa |
| Elongation in 50 mm | ≈ 45 – 60% |
| ASME Section VIII Div. 1 recognition | To approximately 400 °C |
G-30 is supplied solution annealed (typically in the range 1,120–1,180 °C with rapid water quenching) and is fully austenitic, ductile, and readily formed. For evaporator tubing — the classic G-30 application — the combination of thin-wall corrosion allowance and long-term structural integrity is what design engineers value, and the alloy's hot strength is adequate for the 90–130 °C operating range of phosphoric acid evaporators with generous margin.
Fabrication and Welding
G-30 welds readily by GTAW, GMAW, and SMAW using matching filler metals of G-30 chemistry (AWS ERNiCrMo-13-class bare wire is the common over-matching alternative where maximum weld corrosion margin is required). Because the carbon limit of 0.03% and the niobium-plus-tantalum stabilization prevent harmful grain-boundary carbide networks, G-30 is used in the as-welded condition for essentially all corrosive services without post-weld heat treatment. Standard nickel-alloy shop discipline applies: clean joint surfaces, argon shielding with backing gas, modest heat input, and interpass temperature control to limit distortion. Hot forming is performed with finishing above approximately 950 °C followed by full solution annealing; cold forming follows conventional practice with allowance for the alloy's higher strength relative to stainless steel, and a re-anneal is recommended after deformation exceeding roughly 7–10% strain in severe service.
Applications
- Wet-process phosphoric acid evaporators, heat exchangers, reboilers, agitators, and piping in fertilizer complexes.
- Phosphoric acid concentrators and acid-cooling systems handling merchant-grade acid with high chloride and fluoride loadings.
- Nitric acid recovery and concentration plants, including azeotropic acid service.
- Stainless steel and specialty-alloy pickling lines using nitric/hydrofluoric acid mixtures.
- Nuclear fuel-cycle equipment handling nitric-acid-based dissolver and recovery solutions.
- Chemical reactors and piping for mixed oxidizing/reducing acid streams in fine chemicals and agrochemicals.
- Flue-gas desulfurization absorber internals where chloride-rich, oxidizing condensates form.
G-30 versus the Field
Against G-3, G-30's ~30% chromium buys a large step-change in oxidizing-acid and commercial-phosphoric-acid performance, at a corresponding cost premium that is justified only where the acid is genuinely aggressive. Against alloy 625, which was historically used in phosphoric acid evaporators, G-30 is now the recognized superior: comparative tests in commercial acid routinely show G-30 at a fraction of 625's corrosion rate, and G-30 has displaced 625 across the fertilizer industry. Against C-276, G-30 offers better performance in oxidizing media and in phosphoric acid while C-276 retains the edge in strongly reducing, heavily chloride-laden hydrochloric systems. And against G-35 — the newest member of the family — G-30 remains the value choice for most phosphoric acid duty, while G-35's 33% chromium and higher molybdenum claim the top rung for the most severe wet-process acid. Hangbo Alloy supplies the full ladder and will map your acid analysis, temperature, and fabrication plan to the correct rung.
Hangbo Alloy Supply Program
| Product Form | Specification | Typical Size Range |
|---|---|---|
| Plate / Sheet / Strip | ASTM B582 / ASME SB582 | 1 – 60 mm thickness |
| Round Bar / Rod / Wire | ASTM B581 / ASME SB581 | 6 – 350 mm diameter |
| Seamless Pipe & Tube | ASTM B622 | 6 – 219 mm OD |
| Welded Pipe & Tube | ASTM B619 / B626 | 60 – 610 mm OD |
| Forgings & Flanges | ASTM B564 | Custom |
| Fittings | ASTM B366 | 1/2" – 24" |
Hangbo Alloy verifies chromium content by PMI on all delivered G-30 product and can supply ASTM G28 corrosion documentation and controlled test reports from commercial-acid testing programs where project specifications require independent evidence.
Technical FAQ
1. Why is Hastelloy G-30 so much better than G-3 in phosphoric acid?
The decisive variable is chromium. G-30 carries 28–31.5% chromium versus 21–23.5% for G-3. In hot, chloride- and fluoride-contaminated wet-process phosphoric acid, the higher chromium forms a far more protective passive film, cutting uniform corrosion rates dramatically and raising resistance to under-deposit pitting and crevice attack in evaporators.
2. What does "commercial phosphoric acid" mean, and why is it so corrosive?
Commercial (wet-process) phosphoric acid is made by digesting phosphate rock with sulfuric acid. Unlike pure reagent acid, it contains chlorides, fluorides, silica, sulfates, and suspended solids; when hot and concentrated it is one of the most corrosive industrial fluids, attacking both by general corrosion and by localized attack beneath scale and gypsum deposits.
3. Which standards cover G-30 plate and bar?
Plate, sheet, and strip are covered by ASTM B582 (ASME SB582); rod, bar, and wire by ASTM B581 (ASME SB581). Seamless and welded tubing are supplied to ASTM B622 and B619/B626 respectively, with fittings to B366 and forgings to B564.
4. Can G-30 handle nitric acid?
Yes. The high chromium content gives G-30 excellent resistance to nitric acid across a wide concentration range, including hot concentrated grades, and to mixed nitric/hydrochloric and nitric/hydrofluoric acid solutions. This makes it a leading candidate for pickling systems and nuclear fuel-cycle nitric acid service.
5. Is G-30 resistant to pitting and crevice corrosion?
Very much so. The combination of ~30% chromium, molybdenum, tungsten, and high nickel gives G-30 strong resistance to chloride-induced pitting and crevice attack, which is essential in phosphoric acid evaporators where scale deposits create aggressive crevice sites beneath them.
6. What filler metal is used to weld G-30?
Matching G-30 filler is preferred; AWS ERNiCrMo-13 filler (associated with alloy 59 chemistry) is the common over-alloyed alternative where maximum weld-metal corrosion margin is demanded in severe phosphoric acid service. Weld procedures should be qualified with corrosion testing for the actual acid.
7. Does G-30 need post-weld heat treatment?
No. With carbon capped at 0.03% and niobium-plus-tantalum stabilization, G-30 weldments retain their corrosion resistance in the as-welded condition, and PWHT is not required for corrosive service. This simplifies fabrication of large evaporator shells and exchanger bundles.
8. What is the maximum service temperature of G-30?
For corrosion service, G-30 is used to roughly 400 °C under ASME pressure-vessel rules. In phosphoric acid evaporators the practical operating range is far below that — typically 90–130 °C — where the alloy's corrosion resistance, not its temperature capability, is the design limit.
9. How does G-30 compare with alloy 625 in phosphoric acid?
In controlled tests in commercial wet-process phosphoric acid, G-30 exhibits corrosion rates that are typically a small fraction of alloy 625's, which is why G-30 has become the standard replacement for 625 in fertilizer evaporator and heat-exchanger service. The high chromium is the difference.
10. When should I move up from G-30 to G-35?
Choose G-35 (UNS N06035) when your phosphoric acid carries extreme chloride and fluoride loads, operates at the aggressive end of the evaporator envelope, or when G-30 corrosion rates in coupon testing exceed your design allowance. G-35's 33% chromium and ~8% molybdenum provide the next performance tier, and Hangbo Alloy supplies both grades for direct comparison testing.
This page is part of the technical guide series published by Hangbo Alloy (Shanghai Hangbo Alloy Group, nickel-alloy.com). Data presented are typical engineering values compiled from recognized industry and producer sources and are provided for material selection guidance; the governing documents for any purchase are the applicable ASTM/ASME/AMS specifications and the certified mill test report. Contact Hangbo Alloy for current stock, mill certificates, PMI verification, and application engineering support.
