ZYTC Inconel® 686 (UNS N06686) Nickel-Chromium-Molybdenum-Tungsten Alloy As an ISO 9001 and AS9120 certified supplier, ZYTC Alloy presents this technical guide for Inconel 686, designed for confident material evaluation. I. Product Information- Material Name: Inconel® 686 Nickel-Chromium-Molybdenum-Tungsten Alloy (UNS N06686)
- Material Definition: A nickel-chromium-molybdenum-tungsten alloy engineered for exceptional performance in the most severe corrosive environments, particularly mixed acids where it outperforms established alloys including the Hastelloy C family.
- Core Value Proposition: Outstanding resistance to localized attack (pitting and crevice corrosion) in hot acidic chlorides and oxidizing media, combined with exceptional uniform corrosion resistance in mixed acids and halogen-bearing environments.
- Key Metallurgical Advantages:
- High chromium, molybdenum, and tungsten create a robust, stable passive film
- One of the highest Pitting Resistance Equivalent Numbers (PREN ≈67) among commercial alloys
- Ultra-low carbon (0.010% max) minimizes carbide precipitation and maximizes corrosion resistance in as-welded conditions
- Effective against sulfuric acid, hydrochloric acid, and mixtures containing ferric and cupric chlorides
- Certification & Quality: ISO 9001 and AS9120 certified, ensuring full traceability and compliance.
- Product Forms Available:
- Bar & Square Bar | Plate & Sheet | Tube & Pipe (Seamless/Welded)
- Fasteners (Bolts, Nuts, Studs) | Wire | Custom Machined and Forged Components
II. Material Standards & SpecificationsSpecification | Applicable Standard | Description | ASTM B574 | Rod, Bar, Wire, Forgings | Low-carbon Ni-Cr-Mo-W alloys | ASTM B575 | Plate, Sheet, Strip | Low-carbon Ni-Cr-Mo-W alloys | ASTM B619 | Welded Pipe | Welded nickel alloy pipe | ISO 15156-3 (NACE MR0175) | Oil & Gas | Qualified for sour service (H₂S environments) |
III. Chemical Composition (wt%)Element | Ni | Cr | Mo | W | Fe | C | Mn | Si | S | P | Ti | Min | 59.0 | 19.0 | 15.0 | 3.0 | - | - | - | - | - | - | 0.020 | Max | - | 23.0 | 17.0 | 4.4 | 5.0 | 0.010 | 0.75 | 0.08 | 0.020 | 0.040 | 0.25 |
Note: Ultra-low carbon content is critical for maintaining corrosion resistance in welded conditions. IV. Service Conditions & Material Selection BoundariesSuitable Conditions (Why choose it?) - Mixed Acid Environments: Superior resistance to combinations of sulfuric, hydrochloric, nitric, and hydrofluoric acids with oxidizers.
- Hot Acidic Chlorides: Exceptional pitting and crevice corrosion resistance in wet chlorine, hypochlorite, and chlorine dioxide.
- Flue Gas Desulfurization (FGD) Systems: Ideal for components exposed to hot sulfurous gases and acidic condensates with chlorides.
- Oxidizing Media: Outstanding performance in ferric and cupric chlorides, nitric acid.
- Sour Gas Service: Qualified under NACE MR0175 for H₂S environments.
- Localized Corrosion-Prone Applications: Where pitting, crevice corrosion, or SCC are primary failure mechanisms.
Typical Applications: - FGD Systems: Absorber towers, outlet ducting, mist eliminators, spray nozzles
- Chemical Processing: Reactors, columns, heat exchangers for mixed acid and halogen catalyst service
- Pollution Control: Incineration scrubbing, waste acid recovery
- Pulp & Paper: Digesters, bleach plant equipment (chlorine dioxide stages)
- Offshore Oil & Gas: Seawater injection, sour brine production equipment
Material Selection Boundaries (When to consider alternatives?) - High-Temperature Service >500°C: Consider Inconel 601 or 602 CA
- Cost-Sensitive Applications: Consider 316L SS, Inconel 625, or Hastelloy C-276
- Strongly Reducing Environments: Consider zirconium or tantalum
- Fluoride-Containing Environments: Consider higher chromium alloys
V. Manufacturing Process & Heat TreatmentHeat Treatment Process Parameters: Process | Objective | Parameters | Critical Considerations | Solution Annealing | Dissolve secondary phases; maximize corrosion resistance | 1180-1200°C (2156-2192°F) | Must be followed by rapid water quench to prevent reprecipitation |
Fabrication Guidelines: - Hot Working: 1230-1090°C (2246-1994°F). Rapid cooling after hot working recommended.
- Cold Working: Work-hardens rapidly. Intermediate annealing may be required.
- Machining: Requires rigid machinery, sharp carbide tooling, high feed rates, moderate cutting speeds, and generous coolant use.
- Welding: Excellent weldability using GTAW/TIG, GMAW/MIG. Use matching filler metal ERNiCrMo-14. No pre-heat or post-weld heat treatment generally required.
VI. Mechanical Properties (Typical Values)Property | Metric | Imperial | Tensile Strength | 721 MPa (min) | 104,700 psi (min) | Yield Strength (0.2%) | 364 MPa (min) | 52,800 psi (min) | Elongation at Break | 71% (min) | 71% (min) | Hardness (Typical) | 85-95 HRB | 85-95 HRB |
Note: Exceptional elongation indicates outstanding ductility. Contact our team for certified test reports. VII. Material Comparison & Selection GuideDimension | Inconel 686 | vs. Inconel 625 | vs. Hastelloy C-276 | Primary Strength | Ultimate Corrosion Resistance | Strength + Wide Corrosion | Versatile Corrosion | Key Additions | Cr(19-23)+Mo(15-17)+W(3-4.4) | Cr(20-23)+Mo(8-10)+Nb | Cr(14.5-16.5)+Mo(15-17)+W | PREN Value | Highest (≈67) | High (≈52) | High (≈60) | Oxidizing Acid Resistance | Excellent | Good | Good | Reducing Acid Resistance | Excellent | Very Good | Excellent | Mixed Acid Resistance | Superior | Good | Very Good | Carbon Content (max) | 0.010% | 0.10% | 0.01% |
PREN Calculation: PREN = %Cr + 3.3(%Mo) + 16(%N). Inconel 686's PREN ≈67 makes it one of the most pitting-resistant commercial alloys. Procurement Recommendation: - Choose Inconel® 686 for the most aggressive mixed acid environments, hot acidic chlorides, or where other alloys have failed due to localized corrosion. Ideal for severe FGD outlet conditions and halogen catalyst processes.
- Choose Inconel® 625 for a versatile, cost-effective alloy combining strength with excellent corrosion resistance for marine, oil and gas, and general chemical service.
- Choose Hastelloy® C-276 as a workhorse general-purpose corrosion-resistant alloy for a wide range of chemical processing applications.
Request a Quote or Sample Today: If your processes demand the ultimate in corrosion resistance with alloy 686 for critical applications where failure is not an option, contact ZYTC Alloy today. We provide certified materials, technical expertise, and reliable global logistics. Contact us to request a free sample and a competitive quote. Our technical team is ready to assist with material selection and application support. Contact Us: Email:daisy@zytcsteel.com WhatsApp/WeChat: +86 17335753350 |
