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B8M Bolt
QS Fastener: B8M Bolt
Name: B8M Bolt
Material: ASTM A193 B8M, SS316
Size: 5/8 Inch
Length: 75mm
Type: Full Length Thread
Standard: ANSI B18.31.2
Feature: Corrosion Resistance Steel
Application: For Desalination Plants Construction
Material: ASTM A193 B8M, SS316
Size: 5/8 Inch
Length: 75mm
Type: Full Length Thread
Standard: ANSI B18.31.2
Feature: Corrosion Resistance Steel
Application: For Desalination Plants Construction
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Manufactured from ASTM A193 B8M (SS316) stainless steel, the B8M Bolt with a diameter of 5/8 inch and length of 75 mm complies with the ANSI B18.31.2 standard. Its exceptional resistance to chloride-induced corrosion ensures long-term stability and reliable performance in equipment. The full-thread design promotes even load distribution and facilitates installation, making the B8M Bolt an ideal fastening solution for marine structures, chemical equipment, and high-salinity environments.
B8M Bolt: Electrochemical Passivation Technology (Application in Desalination Plants)
1. Principle of Electrochemical Passivation
The B8M Bolt (material: ASTM A193 B8M/316 stainless steel) undergoes electrochemical passivation to enhance the formation of a chromium oxide (Cr₂O₃) layer and remove free iron ions (Fe²⁺/Fe³⁺). Under direct current (5–15 V), the B8M Bolt acts as the anode in an acidic electrolyte (e.g., 20–30% nitric or citric acid):
- Anodic reaction: Metal dissolution (Fe → Fe²⁺ + 2e⁻) and chromium oxidation (2Cr + 3H₂O → Cr₂O₃ + 6H⁺ + 6e⁻).
- Cathodic reaction: Hydrogen evolution (2H⁺ + 2e⁻ → H₂↑).
1. Principle of Electrochemical Passivation
The B8M Bolt (material: ASTM A193 B8M/316 stainless steel) undergoes electrochemical passivation to enhance the formation of a chromium oxide (Cr₂O₃) layer and remove free iron ions (Fe²⁺/Fe³⁺). Under direct current (5–15 V), the B8M Bolt acts as the anode in an acidic electrolyte (e.g., 20–30% nitric or citric acid):
- Anodic reaction: Metal dissolution (Fe → Fe²⁺ + 2e⁻) and chromium oxidation (2Cr + 3H₂O → Cr₂O₃ + 6H⁺ + 6e⁻).
- Cathodic reaction: Hydrogen evolution (2H⁺ + 2e⁻ → H₂↑).
This process selectively removes iron and forms a dense Cr₂O₃ layer (2–5 nm thick), significantly improving the B8M Bolt's corrosion resistance in high-chloride environments such as seawater desalination.
2. Passivation Process and Parameters for B8M Bolt
1. Pre-treatment:
- Degreasing: Alkaline solution (pH 10–12, 60–70°C) to remove contaminants.
- Pickling: 10–15% HNO₃ + 2–3% HF mixture, immersion for 5–10 minutes (oxide removal).
1. Pre-treatment:
- Degreasing: Alkaline solution (pH 10–12, 60–70°C) to remove contaminants.
- Pickling: 10–15% HNO₃ + 2–3% HF mixture, immersion for 5–10 minutes (oxide removal).
2. Electrochemical Passivation:
- Electrolyte: 25% nitric acid or 5–10% citric acid, temperature 40–50°C.
- Current density: 0.5–2 A/dm², duration 10–30 minutes (optimized for full-thread B8M Bolt).
- Cathode: Lead or 316 stainless steel plate, electrode spacing 10–15 cm.
- Electrolyte: 25% nitric acid or 5–10% citric acid, temperature 40–50°C.
- Current density: 0.5–2 A/dm², duration 10–30 minutes (optimized for full-thread B8M Bolt).
- Cathode: Lead or 316 stainless steel plate, electrode spacing 10–15 cm.
3. Post-treatment:
- Neutralization: Rinsing with Na₂CO₃ solution (5%, pH 9–10).
- Sealing: Deionized water rinse (conductivity <10 μS/cm), drying (80–100°C).
- Neutralization: Rinsing with Na₂CO₃ solution (5%, pH 9–10).
- Sealing: Deionized water rinse (conductivity <10 μS/cm), drying (80–100°C).
3. Key Performance Metrics of Passivated B8M Bolt
- Corrosion resistance: Salt spray testing (ASTM B117) shows the B8M Bolt's endurance extended from 96 hours to 1000+ hours, meeting desalination plant requirements.
- Surface composition: XPS analysis confirms Cr/Fe ratio increased from 1.5 to ≥2.5, with Cr₂O₃ content exceeding 70%.
- Iron removal: AAS testing indicates surface iron content reduced from 500–1000 ppm to <50 ppm (per ASTM A380).
- Corrosion resistance: Salt spray testing (ASTM B117) shows the B8M Bolt's endurance extended from 96 hours to 1000+ hours, meeting desalination plant requirements.
- Surface composition: XPS analysis confirms Cr/Fe ratio increased from 1.5 to ≥2.5, with Cr₂O₃ content exceeding 70%.
- Iron removal: AAS testing indicates surface iron content reduced from 500–1000 ppm to <50 ppm (per ASTM A380).
4. Factors Affecting B8M Bolt Passivation
- Electrolyte selection: Nitric acid is efficient, but citric acid is more eco-friendly (RoHS-compliant), suitable for food and marine applications.
- Temperature and time: Exceeding 60°C or 30 minutes may cause over-corrosion of the B8M Bolt.
- Current density: Optimal range is 0.3–3 A/dm² to avoid thread damage.
- Electrolyte selection: Nitric acid is efficient, but citric acid is more eco-friendly (RoHS-compliant), suitable for food and marine applications.
- Temperature and time: Exceeding 60°C or 30 minutes may cause over-corrosion of the B8M Bolt.
- Current density: Optimal range is 0.3–3 A/dm² to avoid thread damage.
5. Applications and Standards for B8M Bolt
Passivated B8M Bolt is widely used in:
- Marine engineering: Complies with ISO 9227, resistant to seawater Cl⁻.
- Chemical equipment: Meets ASTM A193 B8M mechanical requirements.
- High-salinity environments: FDA 21 CFR 178.3620 certified for long-term durability.
Passivated B8M Bolt is widely used in:
- Marine engineering: Complies with ISO 9227, resistant to seawater Cl⁻.
- Chemical equipment: Meets ASTM A193 B8M mechanical requirements.
- High-salinity environments: FDA 21 CFR 178.3620 certified for long-term durability.
6. Conclusion
Electrochemical passivation forms a chromium-rich oxide layer on the B8M Bolt, elevating its chloride corrosion resistance (CPT ≥25°C). This makes it an optimal fastening solution for desalination plants, offshore platforms, and other aggressive environments.
Electrochemical passivation forms a chromium-rich oxide layer on the B8M Bolt, elevating its chloride corrosion resistance (CPT ≥25°C). This makes it an optimal fastening solution for desalination plants, offshore platforms, and other aggressive environments.
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