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Alloy 686 (UNS N06686) Nickel-Chromium-Molybdenum-Tungsten Butt Weld Fittings
Alloy 686 UNS N06686 Ni-Cr-Mo-W butt weld fittings to ASME SB-366 and B16.9. High-chromium superalloy for seawater, sour gas and HCl. NACE MR0175 / ISO 15156.
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Alloy 686 is a nickel-chromium-molybdenum-tungsten alloy developed for the most aggressive combination of wet chlorine, oxidising acids, seawater and sour service. It is the highest-chromium member of the family we stock, and for offshore, desalination and sour-gas buyers it has become the default answer where C-276 is close to its limit. The tungsten addition is what separates it from C-276: it raises resistance to reducing environments while the higher chromium retains the oxidising-side performance.
Product range
Butt weld fittings to ASME B16.9 — 45°, 90° and 180° elbows, equal and reducing tees, concentric and eccentric reducers, caps and lap-joint stub ends — supplied solution annealed with bevelled ends ready for welding. Socket weld and threaded forms to B16.11 are available to order. Forged flanges to SB-462 and ASME B16.47 in any of the pressure ratings you require are supplied from the same material heat.
Material specifications
| ASME spec | Product form | Notes |
|---|---|---|
| SB-366 / SB-366M | Wrought BW & SW fittings | Grade CRIN686 / WPIN686 |
| SB-462 | Forged flanges and forged fittings | UNS N06686 listed |
| SB-574 | Rod | UNS N06686 listed |
| SB-575 | Plate, sheet, strip | UNS N06686 listed |
| SB-564 | Forgings | UNS N06686 listed |
| SB-626 | Welded tube | UNS N06686 listed |
| SA-312 | Seamless pipe | TP686 listed |
Composition, ASME SB-575 Table 1 (% by weight)
| Element | Limit |
|---|---|
| Nickel | Remainder |
| Chromium | 19.0–23.0 |
| Molybdenum | 15.0–17.0 |
| Tungsten | 3.0–4.4 |
| Iron | 5.0 max |
| Carbon, max | 0.010 |
| Manganese, max | 0.75 |
| Silicon, max | 0.08 |
| Phosphorus, max | 0.04 |
| Sulfur, max | 0.02 |
| Titanium | 0.02–0.25 |
The titanium addition (0.02–0.25%) stabilises the alloy against sensitisation during welding and heat treatment. It is a controlled addition, not a residual — if your incoming certificate shows titanium absent, the heat may not be Alloy 686.
Mechanical properties, ASME SB-575 Table 2
| Property | Limit |
|---|---|
| Tensile strength, min | 100,000 psi (690 MPa) |
| Yield strength (0.2% offset), min | 45,000 psi (310 MPa) |
| Elongation in 2 in., min | 45% |
| Rockwell hardness, max | 100 HRB |
Solution annealing, ASME SB-366 Table 3
2150 °F [1177 °C], rapidly air- or water-quenched. No footnote applies to this row in SB-366 Table 3 — the cycle is a straight set point, so there is nothing to clarify beyond the temperature itself. (Note that C-22 and C-4 in the previous product do carry footnote D, “Minimum temperature”; Alloy 686 does not.)
Applications
Subsea and offshore piping, seawater lift and injection systems, desalination, oil and gas production with sour service exposure under NACE MR0175 / ISO 15156, hydrochloric and sulphuric acid plants, pulp and paper bleaching, chlor-alkali and hypochlorite handling, and pharmaceutical processing.
Inspection and certification
EN 10204 3.1 standard, 3.2 on request. PMI verification confirms the tungsten and titanium levels that distinguish this alloy from C-276. Tensile testing, hardness, ASTM A262 intergranular corrosion and ASTM G-48 ferric chloride pitting tests, plus third-party witness inspection, are all available.
Ordering information
Send grade confirmation (N06686), NPS size, wall thickness or schedule, quantity, end preparation, testing and certification requirements. For sour service, state the H2S partial pressure, temperature and chloride content so we can confirm NACE MR0175 / ISO 15156 qualification on the supplied certificate.
