Project Description
Alloy 59 (UNS N06059, W.Nr. 2.4605), commercially known as Nicrofer 5923 hMo, is a nickel-chromium-molybdenum alloy engineered with exceptionally low carbon (≤ 0.010%) and silicon (≤ 0.10%) content. Developed by VDM Metals and introduced in 1990 as an evolution beyond the Hastelloy C-4 and C-2000 platforms, it eliminates tungsten entirely while maximizing chromium and molybdenum to achieve a PREN of 74–78—the highest in the Ni-Cr-Mo family. This ultra-high PREN translates into best-in-class resistance to pitting and crevice corrosion in concentrated chlorides, coupled with exceptional stability in both oxidizing acids (nitric, chromic) and reducing acids (hydrochloric, sulfuric) across a wide concentration and temperature range. In the petroleum industry, Alloy 59 is the material of choice for flue gas desulfurization (FGD) scrubber piping, sour water stripper components, sulfuric acid coolers, AGR systems handling wet H₂S/CO₂, and chemical injection lines subjected to concentrated acid mixtures. It is fully certified under NACE MR0175 / ISO 15156 for sour service and maintains as-welded corrosion resistance without post-weld heat treatment due to its zero-sensitization metallurgy. SHUNFU METAL sources prime Alloy 59 from ISO-certified mills utilizing VIM+ESR double-melt processing to ensure ultra-low sulfur, phosphorus, and trace element levels. Every incoming billet is verified by optical emission spectrometry and inert gas fusion for full chemistry compliance before hot extrusion. SHUNFU METAL performs in-line ultrasonic testing per ASTM E213, eddy current inspection per ASTM E426, hydrostatic testing per ASTM A999, and positive material identification on 100% of finished pipe, delivering full EN 10204 3.1 / 3.2 documentation with every shipment.
Oil & Gas Applications of Alloy 59
Refinery and gas plant wet-scrubber absorbers, quench sections, and demister piping exposed to condensing H₂SO₄+HCl+HF mixtures at 50–80 °C.
Shell-and-tube and plate heat exchangers handling 93–98% H₂SO₄ at 80–110 °C in refinery alkylation and acid regeneration units. Resists velocity-accelerated corrosion at tube inlets.
Amine unit lean/rich solvent piping, regenerator reboilers, and overhead condensers in AGR trains removing H₂S and CO₂ from sour natural gas.
Stripper column trays, downcomers, overhead piping, and reboiler tubes handling NH₃-H₂S-HCN-H₂O mixtures with chloride carryover at 100–130 °C.
Hydrofluoric acid reactor tubes, acid rerun columns, and overhead condensers. Alloy 59 resists HF–H₂O azeotropic corrosion at concentrations up to 70% and 80 °C.
High-pressure quills and distribution piping for acidizing fluids (HCl/HF blends), corrosion inhibitors, and biocides on wellhead and subsea injection skids.
Gate valve internals, choke beans, and seat rings in extremely sour wellhead assemblies where elemental sulfur deposition creates pH below 1 at operating temperatures.
Production casing and tubing in high-enthalpy geothermal wells with acid gas (H₂S + CO₂) and hyper-saline brine at 150–250 °C.
Offshore platform seawater lift piping, brine concentrator tubes, and produced water treatment piping resistant to under-deposit crevice corrosion at chloride levels exceeding 200,000 ppm.
Chemical Composition of N06059 (ASTM B622 / B619)
The defining metallurgical feature of Alloy 59 is its combination of ultra-low carbon (≤ 0.010%), ultra-low silicon (≤ 0.10%), and the complete absence of tungsten. Carbon at ≤ 0.010% ensures that the time-temperature-sensitization curve is shifted so far right that grain-boundary chromium carbide precipitation is virtually impossible during welding and thermal cycling, rendering post-weld solution annealing unnecessary for most applications. Silicon at ≤ 0.10% suppresses the formation of intermetallic mu-phase (from 15–16.5% molybdenum) that would otherwise precipitate during hot working or long-term service at 600–900 °C. The deliberate aluminum addition of 0.10–0.40% serves as both a deoxidizer during melting and a stabilizing element that reinforces the passive Cr₂O₃ film at elevated temperatures. SHUNFU METAL employs VIM+ESR double-melt processing to achieve sulfur and phosphorus levels well below the ASTM maxima, and verifies full chemistry including trace elements by optical emission spectrometry and inert gas fusion analysis on every heat prior to release.
| Ni | Cr | Mo | Fe | C | Si | Mn | Al | Co | Cu | P | S |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Bal. | 22.0–24.0 | 15.0–16.5 | ≤ 1.50 | ≤ 0.010 | ≤ 0.10 | ≤ 0.50 | 0.10–0.40 | ≤ 0.30 | ≤ 0.50 | ≤ 0.015 | ≤ 0.010 |
PREN = %Cr + 3.3×%Mo ≥ 74. The tungsten-free formulation eliminates long-range-ordering embrittlement above 540 °C seen in W-bearing alloys. The Ni-Cr-Mo ternary synergy delivers universal acid resistance: high chromium defends against oxidizing attack (HNO₃), high molybdenum protects against reducing attack (HCl, H₂SO₄), and the nickel matrix provides immunity to chloride stress corrosion cracking. SHUNFU METAL reports nitrogen and oxygen residuals on every heat certificate.
Mechanical Properties — Alloy 59 (Solution Annealed)
Alloy 59 is supplied in the solution-annealed condition at 1,100–1,180 °C followed by rapid water quenching to suppress the formation of intermetallic phases. This high-temperature thermal cycle produces a fully recrystallized austenitic microstructure with uniform grain size, maximizing ductility, toughness, and corrosion resistance. Unlike tungsten-bearing nickel alloys, Alloy 59 does not develop long-range-ordered Ni₂(Cr,Mo) domains during cooling, allowing thicker sections to be quenched without centerline property degradation. SHUNFU METAL batch-anneals Alloy 59 pipe in computer-controlled furnaces with multi-point thermocouple logging and automatic overtemperature shutdown. Post-anneal grain size is verified per ASTM E112 (typical ASTM grain size 4–6). Tensile testing per ASTM E8, hardness per ASTM E18, and flattening/flaring tests per ASTM B829 are performed on each production lot, with full Charpy V-notch impact data available upon request.
| Property | Metric (min.) | Imperial (min.) | Typical Value |
|---|---|---|---|
| Tensile Strength, Rm | 690 MPa | 100 ksi | 750 MPa |
| Yield Strength, Rp0.2 | 310 MPa | 45 ksi | 340 MPa |
| Elongation (2″ or 4D) | 40% | 40% | 45% |
| Hardness | ≤ 200 HV | ≤ 90 HRB | 185 HV / 88 HRB |
| Modulus of Elasticity | 210 GPa | 30,500 ksi | — |
| Density | 8.60 g/cm³ | 0.311 lb/in³ | — |
| Melting Range | 1,310–1,420 °C (ASME B31.3 approved) | ||
Properties per ASTM B622 / ASME SB-622 in solution-annealed + water-quenched condition. The exceptionally high elongation (≥ 40%) enables severe cold-forming operations such as U-bending and tight-radius coiling without intermediate annealing. SHUNFU METAL certifies every pipe lot with a comprehensive EN 10204 3.1 mill test report covering tensile testing, hardness, flattening, flaring, intergranular corrosion susceptibility (ASTM A262 Practice C), and 100% hydrostatic pressure testing.