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If you need an alloy that dramatically extends equipment life in fertilizer-grade phosphoric acid (P₂O₅) production, Hastelloy G-35 is your ideal answer. This high-alloy nickel-chromium-molybdenum material is purpose-built for the most demanding phosphoric acid evaporation, heat exchange, and chemical processing operations. Both field experience and laboratory tests confirm that G-35 consistently outperforms conventional stainless steels and standard nickel alloys in contaminated phosphoric acid media. As a result, it has become the global benchmark material for evaporator tube bundles and other critical equipment in the phosphate fertilizer industry.
Why Choose G-35?
G-35 solves your toughest corrosion challenges:
- Extends phosphoric acid service life – In fertilizer-grade acid, G-35 components significantly outlast traditional nickel alloys and stainless steels, directly reducing replacement frequency and maintenance costs.
- Resists under-deposit pitting and crevice corrosion – Chloride deposits inside evaporators are a common failure cause, but G-35 effectively withstands this localized attack.
- Eliminates chloride stress corrosion cracking worries – Its resistance to chloride SCC far exceeds that of conventional stainless steels and common nickel-chromium-iron alloys, giving you peace of mind in chloride-containing environments.
- Handles nitric acid and mixed acid systems – Thanks to its ultra-high chromium content, G-35 stays exceptionally corrosion-resistant in oxidizing acids such as nitric acid.
- Provides reliable reducing acid protection – A substantial molybdenum addition gives the alloy solid resistance to reducing acid environments.
- Unique advantage in hot hydrofluoric acid – Unlike other nickel-chromium-molybdenum alloys, G-35 resists dealloying corrosion in high-temperature HF service – a standout feature that sets it apart.
Grade Designations & Classification
- UNS Number: N06035
- Common Trade Name: Hastelloy G-35 Alloy
- Alloy Category: Ni-Cr-Mo corrosion-resistant superalloy
Chemical Composition – Precision-Engineered for Performance
G-35’s outstanding properties come from its tightly controlled chemistry. Every element in the UNS N06035 specification contributes to the alloy’s final corrosion resistance and mechanical strength.
| Element | Content Range (wt%) | Role |
|---|---|---|
| Nickel (Ni) | Balance | Provides the tough, ductile matrix and chloride SCC resistance |
| Chromium (Cr) | 32.25 – 34.25 | Delivers excellent resistance to oxidizing acids, nitric acid, and high-temperature oxidation |
| Molybdenum (Mo) | 7.60 – 9.00 | Enhances pitting/crevice corrosion resistance and reducing acid tolerance |
| Iron (Fe) | 2.0 – 6.0 | Helps control cost while maintaining structural stability |
| Tungsten (W) | ≤ 0.60 | Adds supplementary corrosion resistance |
| Copper (Cu) | ≤ 0.30 | Strictly controlled to preserve performance in oxidizing acid environments |
| Cobalt (Co) | ≤ 5.0 | Controlled impurity |
| Manganese (Mn) | ≤ 0.50 | Deoxidizer; improves hot workability |
| Silicon (Si) | ≤ 0.60 | Deoxidizer; strengthens high-temperature structural stability |
| Carbon (C) | ≤ 0.015 | Ultra-low carbon minimizes carbide precipitation during welding, preserving intergranular corrosion resistance |
| Phosphorus (P) | ≤ 0.030 | Controlled impurity |
| Sulfur (S) | ≤ 0.015 | Kept low to maintain toughness and corrosion resistance |
Physical Properties at a Glance
| Property | Typical Value |
|---|---|
| Density | 8.22 g/cm³ |
| Melting Range | 1325 – 1370 °C |
| Mean Coefficient of Linear Expansion (20–100°C) | 12.3 × 10⁻⁶ /°C |
| Thermal Conductivity (20°C) | 10.1 W/(m·K) |
| Specific Heat Capacity (20°C) | 450 J/(kg·K) |
| Electrical Resistivity (20°C) | 1.20 μΩ·m |
| Elastic Modulus (20°C) | 205 GPa |
| Magnetic Properties | Non-magnetic (fully austenitic) |
Mechanical Properties (Solution-Annealed Condition)
| Item | Minimum Requirement |
|---|---|
| Ultimate Tensile Strength | ≥ 700 MPa |
| 0.2% Yield Strength | ≥ 350 MPa |
| Elongation | ≥ 30 % |
| Brinell Hardness | ≤ 230 HBW |
The combination of high tensile strength and good ductility makes G-35 ideal for both pressure-containing components and complex forming operations.
G-35 vs. G-30 – What’s the Difference?
Many buyers compare Hastelloy G-30 and G-35 during material selection. Here is a straightforward comparison:
- G-30 is a cost-effective choice for moderate mixed-acid environments. It offers better ductility and easier machinability.
- G-35 is the upgraded solution for aggressive phosphoric acid service. With higher chromium and molybdenum and lower carbon, it delivers noticeably better performance in high-concentration, high-temperature wet-process phosphoric acid. You also get superior resistance to pitting, crevice corrosion, and chloride SCC.
If you are facing severe fertilizer-grade phosphoric acid evaporation, high impurity levels, and elevated temperatures, G-35 brings you longer trouble-free operation and a lower life-cycle cost.
Heat Treatment Practice
To restore full corrosion resistance after forming or welding, we recommend solution annealing all fabricated components. Use the following parameters:
- Temperature: 1120 – 1175 °C (2050 – 2150 °F), recommended 1122 °C (2050 °F)
- Holding Time: 1 – 2 hours (or 15 – 30 minutes per 25 mm of wall thickness)
- Cooling: Water quench or rapid spray cooling to avoid intergranular precipitation
Fabrication & Welding
Hot Working – G-35 can be hot forged, hot rolled, and hot extruded. However, it is more sensitive to strain and strain rate than austenitic stainless steels. Strict temperature control throughout the hot working window is essential.
Cold Forming – Bending and stamping are possible, but higher forming forces are needed due to the alloy’s strength. For large deformation processes, we recommend intermediate annealing.
Machining – Machinability is moderate. Because of its higher strength and work-hardening tendency, G-35 is more difficult to machine than G-30. Use sharp tools, appropriate feed rates, and ample cooling for best results.
Welding – You can weld G-35 with GMAW, GTAW, and SMAW processes using matching filler metals. Strict process control is necessary to prevent carbide precipitation and preserve weld joint corrosion resistance.
Typical Applications
- Fertilizer-grade phosphoric acid (P₂O₅) evaporator tube bundles and heating coils
- Wet-process phosphoric acid reactors, piping, and storage tanks
- Nitric acid and mixed acid process equipment and transfer lines
- High-temperature hydrofluoric acid process components
- Chemical heat exchangers, scrubbers, and pressure vessels
- Any severely corrosive environment where stainless steels and standard nickel alloys fail prematurely
Available Product Forms
To meet your project requirements, we supply a full range of semi-finished and finished products:
- Plate, sheet, strip, billet, bar, and wire
- Seamless pipe and tube
- Covered welding electrodes
- Custom-made pipe fittings (elbows, tees, reducers, caps) and flanges to your drawings
Frequently Asked Questions
Q: What is Hastelloy G-35 primarily used for?
A: It is mainly used for core equipment in fertilizer-grade phosphoric acid production — evaporator tubes, reactors, and piping — as well as in nitric acid and high-temperature hydrofluoric acid environments.
Q: What is the UNS number for G-35?
A: The UNS designation is N06035.
Q: How does G-35 differ from G-30?
A: G-35 has higher chromium and molybdenum and lower carbon, giving it better resistance to oxidizing acids, pitting, and chloride SCC. It excels in severe phosphoric acid applications. G-30 offers better ductility and cost performance for moderate mixed-acid services.
Q: What solution annealing temperature should I use?
A: Anneal at 1120 – 1175 °C, followed by rapid water quenching to maximize corrosion resistance.
Related resources: Browse our full range of nickel alloy pipe fittings & seamless tubes, or learn more about our manufacturing capabilities on the C&N YouTube channel for product testing and factory updates.
