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SS Hex Nut
QS Fastener: SS Hex Nut
Product: SS Hex Nut A194 8M
Size: 7/8 Inch
Production Standard: ANSI B 18.2.2
Material: A194 8M
Type: Heavy Hex
Thread: 9 UNC
Technical Requirement: NACE MR0175
Size: 7/8 Inch
Production Standard: ANSI B 18.2.2
Material: A194 8M
Type: Heavy Hex
Thread: 9 UNC
Technical Requirement: NACE MR0175
Quantity
SS Hex Nut strictly complies with the ANSI B18.2.2 standard, made from A194 8M alloy steel, and meets the NACE MR0175 requirements for resistance to hydrogen sulfide stress corrosion. Designed as a heavy hex nut (7/8"-9UNC thread), it delivers exceptional load-bearing capacity and anti-loosening performance, making it an ideal fastener for high-strength flange connections and high-pressure pipelines in demanding environments such as oil, gas, and chemical industries.
The surface treatment of SS Hex Nut significantly impacts its corrosion resistance, mechanical properties, and suitability for specific environments. Common surface treatments include passivation (ASTM A967) and electropolishing.
1. Passivation (ASTM A967)
Process Principle
Passivation of SS Hex Nut involves chemically forming a dense chromium oxide (Cr₂O₃) protective layer on its surface. The detailed steps are as follows:
1) Degreasing & Cleaning: Alkaline solutions remove surface oils from the SS Hex Nut.
2) Acid Pickling & Activation: Nitric acid eliminates free iron ions, ensuring uniform oxide film formation.
3) Passivation Reaction: Immersion in a 20%-50% nitric acid solution promotes chromium enrichment to create the passive layer.
4) Neutralization & Rinsing: Alkaline solutions neutralize residual acids to prevent corrosion risks.
Process Principle
Passivation of SS Hex Nut involves chemically forming a dense chromium oxide (Cr₂O₃) protective layer on its surface. The detailed steps are as follows:
1) Degreasing & Cleaning: Alkaline solutions remove surface oils from the SS Hex Nut.
2) Acid Pickling & Activation: Nitric acid eliminates free iron ions, ensuring uniform oxide film formation.
3) Passivation Reaction: Immersion in a 20%-50% nitric acid solution promotes chromium enrichment to create the passive layer.
4) Neutralization & Rinsing: Alkaline solutions neutralize residual acids to prevent corrosion risks.
Technical Advantages
- Passivated 316L SS Hex Nut withstands 96 hours in salt spray tests (ASTM B117), far exceeding untreated samples (typically rusting within 24 hours).
- Complies with ASTM A967, ideal for harsh environments.
- Modern passivation increasingly adopts chromium-free agents (e.g., molybdate, silicate), aligning with RoHS directives for eco-friendliness.
- Passivated 316L SS Hex Nut withstands 96 hours in salt spray tests (ASTM B117), far exceeding untreated samples (typically rusting within 24 hours).
- Complies with ASTM A967, ideal for harsh environments.
- Modern passivation increasingly adopts chromium-free agents (e.g., molybdate, silicate), aligning with RoHS directives for eco-friendliness.
Applications
- Marine Engineering: SS Hex Nut for ships (resistant to Cl⁻ corrosion).
- Chemical Equipment: Reactor flange SS Hex Nut.
- General Industry: Outdoor structures, transportation infrastructure (cost-effective corrosion protection).
- Marine Engineering: SS Hex Nut for ships (resistant to Cl⁻ corrosion).
- Chemical Equipment: Reactor flange SS Hex Nut.
- General Industry: Outdoor structures, transportation infrastructure (cost-effective corrosion protection).
2. Electropolishing
Process Principle
Electropolishing selectively removes microscopic surface peaks via electrochemical dissolution, achieving an ultra-smooth finish.
Process Principle
Electropolishing selectively removes microscopic surface peaks via electrochemical dissolution, achieving an ultra-smooth finish.
Key steps for SS Hex Nut:
1) Pretreatment: Mechanical polishing to deburr the SS Hex Nut.
1) Pretreatment: Mechanical polishing to deburr the SS Hex Nut.
2) Electrolytic Reaction: Immersion in a phosphoric-sulfuric acid electrolyte (50-80°C) under 5-20V DC. The anode (workpiece) undergoes metal ion dissolution, preferentially etching microscopic roughness.
3) Passivation Enhancement: Electropolishing naturally forms a more uniform passive layer (Cr₂O₃ content increases by >30%).
Technical Advantages for SS Hex Nut
- Surface Roughness (Ra) ≤0.2μm: Superior to mechanical polishing (Ra 0.8μm), reducing bacterial adhesion (critical for medical applications).
- Surface Roughness (Ra) ≤0.2μm: Superior to mechanical polishing (Ra 0.8μm), reducing bacterial adhesion (critical for medical applications).
- Corrosion Resistance Multiplied: Passive film thickness increases to 5-10nm (vs. 2-3nm for conventional passivation). 316L electropolished SS Hex Nut passes ASTM G48 ferric chloride tests (72 hours without pitting).
- Aesthetics & Functionality: Mirror finish (gloss ≥90%) for decorative use; reduced fluid resistance (food-grade pipelines).
Applications
- Medical Implants: SS Hex Nut compliant with ISO 13485.
- Food-Grade: FDA-certified SS Hex Nut.
- Semiconductor & Photovoltaics: Ultra-cleanroom equipment (minimizes particle contamination).
- Medical Implants: SS Hex Nut compliant with ISO 13485.
- Food-Grade: FDA-certified SS Hex Nut.
- Semiconductor & Photovoltaics: Ultra-cleanroom equipment (minimizes particle contamination).
Passivation vs. Electropolishing Comparison
| Feature | Passivation | Electropolishing |
| Cost | Low (~¥0.5-1/kg) | High (~¥8-15/kg) |
| Corrosion Resistance | 2-3x improvement | 5-10x improvement |
| Surface Roughness (Ra) | No significant change | ≤0.2μm |
| Applicable Materials | 304/316/416, etc. | Austenitic stainless only (304/316) |
Conclusion
- General Corrosion Protection: Choose passivated SS Hex Nut (ASTM A967 Class 3).
- Extreme Environments: Opt for electropolished SS Hex Nut with composite treatment.
Optimized surface treatments can extend the service life of SS Hex Nut by 3-10x.
- General Corrosion Protection: Choose passivated SS Hex Nut (ASTM A967 Class 3).
- Extreme Environments: Opt for electropolished SS Hex Nut with composite treatment.
Optimized surface treatments can extend the service life of SS Hex Nut by 3-10x.
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