Alloy 59 (UNS N06059) , Ultimate Corrosion‑Resistant Nickel Alloy

1. Basic Information

Alloy 59 (UNS N06059, W.Nr. 2.4605, Chinese standard NS3311, commercial name Hastelloy C-59) is a low‑carbon nickel‑chromium‑molybdenum corrosion‑resistant alloy with ultra‑low silicon and iron content. Its high chromium plus molybdenum design delivers exceptional resistance to oxidizing, reducing and mixed‑acid corrosive media. By eliminating tungsten, the alloy avoids brittle intermetallic phase precipitation, provides outstanding anti‑pitting, crevice corrosion and chloride stress corrosion cracking performance, and is fully suited to sour oil & gas, flue gas desulfurization and chemical processing equipment. It complies with ASME pressure vessel standards and NACE MR0175/ISO 15156 sour service specifications.

Alloy 59 pipes — Alloy 59 (UNS N06059) pipes

2. Standard Grade Cross Reference

Standard System	Grade Designation
UNS Number	N06059
Trade Name	Hastelloy C-59 / Alloy 59 / Nicrofer 5923 hMo
German DIN W.Nr.	2.4605 (NiCr23Mo16Al)
Chinese National Standard	NS3311
ASTM Plate & Strip	B575 / ASME SB575
ASTM Bar & Forging	B574
ASTM Seamless Tube	B622
ASTM Welded Tube	B619, B626
ASTM Fittings & Flanges	B366

3. Alloy 59 Chemical Composition (wt%, ASTM Standard Range)

Element	Content Range	Main Function
Ni	Balance (59.0–66.0%)	Austenite matrix, stable microstructure, foundation for stress‑corrosion resistance
Cr	22.0–24.0%	Forms dense chromium oxide film; resists oxidizing corrosion, pitting & crevice corrosion
Mo	15.0–16.5%	High molybdenum strengthens resistance to reducing media (HCl, H₂SO₄) and chloride brines
Al	0.10–0.40%	Deoxidizer, improves high‑temperature oxidation resistance
C	Max. 0.010%	Ultra‑low carbon prevents welding sensitization and intergranular corrosion
Si	Max. 0.10%	Ultra‑low silicon restricts precipitation of brittle intermetallic compounds
Fe	Max. 1.5%	Strict low‑iron control stabilizes corrosion resistance in severe corrosive environments
Mn	Max. 0.50%	Deoxidation, improves forming performance
P	Max. 0.015%	Impurity control to reduce hot cracking risk
S	Max. 0.010%	Low sulfur eliminates hot brittleness during thermal processing

4. Room‑Temperature Physical Properties (Solution Annealed Condition)

Density: 8.6 g/cm³
Melting Range: 1310 ℃ – 1360 ℃
Service Temperature Range: –196 ℃ – 450 ℃

5. Room‑Temperature Mechanical Properties (Minimum Guaranteed, Solution Annealed)

Property	Value
Ultimate Tensile Strength (Rm)	≥690 MPa
0.2% Offset Yield Strength (Rp0.2)	≥300 MPa
Elongation (A)	≥40%
Hardness	≤100 HRB

6. UNS N06059 Core Corrosion Advantages (vs Hastelloy C‑276 / C‑22)

Balanced oxidation & reduction resistance – Works stably in nitric/phosphoric acid (oxidizing) and hydrochloric/sulfuric mixed acid (reducing) environments.
High PREN value for chloride media – Superior resistance to seawater, concentrated brine and chloride‑induced stress corrosion cracking; certified for NACE sour gas service.
Excellent welding stability – Ultra‑low C & Si greatly reduce sensitization tendency; no post‑weld solution heat treatment is required to retain full corrosion resistance.
Low hot cracking susceptibility – Excellent hot and cold workability for rolling, forging and stamping.

7. Heat Treatment (Standard Supply State: Solution Annealing)

Solution annealing: Heat to 1120 ℃ – 1180 ℃, hold sufficiently, then rapid cool (air cooling or water quenching) to obtain uniform single‑phase austenite, maximizing ductility and corrosion resistance.
No age hardening treatment applicable.
Hot working finishing temperature shall not be lower than 900 ℃ to avoid brittle phase segregation.

8. Fabrication & Welding Characteristics

Formability: Great ductility in the solution‑annealed state, suitable for all cold and hot forming processes. Heavy cold forming requires re‑solution annealing to recover original corrosion resistance and mechanical properties.
Welding: Applicable processes include GTAW (TIG), GMAW (MIG), SMAW. Matching consumables: solid wire ERNiCrMo‑13, covered electrode ENiCrMo‑13. Same‑material welding and dissimilar welding with C‑276, C‑22, Alloy C‑2000 and other nickel alloys are possible. Post‑weld heat treatment is not mandatory for general anti‑corrosion service.
NDT: UT and PT inspections are commonly required to detect surface and internal defects.

9. Typical Applications (Pipe, Fitting & Pressure Vessel Focus)

Power & Waste Incineration: FGD scrubbers, heat exchangers, flue dampers, agitators, exhaust pipelines, marine exhaust desulfurization equipment.
Oil, Gas & Geothermal: Sour gas wellhead assemblies, downhole anti‑corrosion components, brine heat exchange pipes, high‑chloride pipelines (NACE compliant).
Chemical & Pharmaceutical: Chlorine‑containing catalytic reactors, hydrofluoric acid / acetic acid processing equipment, pickling tanks, mixed‑acid reaction vessels, hazardous chemical storage pressure vessels.
Pulp & Paper, Desalination: Bleaching equipment, seawater desalination heat exchangers, high‑chloride water pipeline systems.
General Corrosion‑Resistant Components: Anti‑corrosion pipes, flanges, elbows, tees, valves and special alloy forgings for severe acid‑chloride environments.

10. Comparison with Similar Nickel Corrosion Alloys

Alloy 59 vs Hastelloy C‑276 (UNS N10276): Alloy 59 removes tungsten, adopts ultra‑low silicon & carbon, making it less prone to brittle phase precipitation after long‑term high‑temperature exposure; it offers better resistance to mixed acids and post‑weld intergranular corrosion. C‑276 has higher molybdenum and tungsten, giving it better performance in strong reducing single‑acid media.
Alloy 59 vs Hastelloy C‑22 (UNS N06022): Alloy 59 has higher molybdenum content, providing superior anti‑pitting and anti‑crevice corrosion in high‑chloride environments. C‑22 has higher chromium and performs better in strong oxidizing nitric acid media.

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