Detailed Hydrogen Removal Methods

5. Stainless Steel Fasteners (A2/A4, ASTM F593) Risk: Less prone to embrittlement but still vulnerable after pickling. Removal Methods: Low-Temp Baking: 150–200°C (302–392°F) for 4–6 hrs (avoids sensitization). Passivation Alternatives: Nitric acid passivation (reduces hydrogen vs. electrolytic).

 

Author: Robby

Fastener-specific breakdown of hydrogen removal methods, including industry best practices for each type:

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1. High-Strength Structural Bolts (ASTM A325, A490, ISO 10.9/12.9)

Applications: Bridges, skyscrapers, heavy machinery.
Risk: Hydrogen embrittlement can cause catastrophic failure under load.
Removal Methods:

• Baking:

  • Temp: 200–230°C (392–446°F) for 8–24 hours (per ASTM F1941).

  • Critical Timing: Bake within 1 hour after plating to prevent deep hydrogen ingress.

• Alternative Coatings:

  • Zinc-flake (Dacromet/Geomet): No baking needed (hydrogen-free process).

  • Hot-Dip Galvanizing: Baking optional (hydrogen mostly escapes during dipping).
    Testing:

  • Sustained Load Test (ASTM F606) – Hold at 75% of yield strength for 200+ hrs.

  • Notched Tensile Test (ASTM F1624) – Measures ductility loss.

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2. Aerospace Fasteners (NAS, MS, AN Bolts)

Applications: Aircraft engines, landing gear, critical structures.
Standards: AMS 2759/9, MIL-STD-1312, NASA-STD-6012.
Removal Methods:

• Cadmium-Plated Bolts:

  • Bake at 190–220°C (374–428°F) for 18–24 hrs (per AMS-QQ-P-416).

• Electroplated Titanium Alloy Fasteners:

  • Bake at 175–200°C (347–392°F) for 10–12 hrs (prevents alpha-case formation).

• Non-Electroplated Solutions:

  • Ion Vapor Deposition (IVD) Aluminum: No hydrogen risk.
    Testing:

  • 200+ hr sustained load test (per ASTM F519).

  • Bend Testing (MIL-STD-1568) for titanium fasteners.

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3. Automotive Fasteners (Wheel Bolts, Engine Components)

Applications: Critical safety parts (e.g., brake systems, suspension).
Standards: SAE J2339, DIN 267-27, VW 01131.
Removal Methods:

• Baking (for Grade 10.9+):

  • 190–210°C (374–410°F) for 4–8 hrs (shorter due to mass production).

• Zinc-Nickel Plating:

  • Lower hydrogen absorption than pure zinc; may reduce baking time.
    Testing:

  • C-ring test (ISO 15330) – Fastener held under stress in corrosive environment.

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4. Anchor Bolts & Large-Diameter Fasteners

Challenge: Difficult to bake uniformly due to size.
Solutions:

• Localized Induction Heating: Focused baking on threaded regions.

• Room Temperature Aging: 7+ days (last resort for non-critical uses).

• Mechanical Galvanizing: No hydrogen risk (cold-bonded zinc).

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5. Stainless Steel Fasteners (A2/A4, ASTM F593)

Risk: Less prone to embrittlement but still vulnerable after pickling.
Removal Methods:

• Low-Temp Baking: 150–200°C (302–392°F) for 4–6 hrs (avoids sensitization).

• Passivation Alternatives: Nitric acid passivation (reduces hydrogen vs. electrolytic).

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6. Case Study: Hydrogen Embrittlement in Wind Turbine Bolts

Issue: M36 flange bolts (Grade 10.9) failed after galvanizing.
Solution:

• Baked at 220°C for 12 hrs + 100% ultrasonic inspection.

• Switched to Dacromet coating for future installations.

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Quick Reference: Baking Times by Fastener Type

Fastener Type	Baking Temp (°C)	Duration (hrs)	Key Standard
ASTM A490 Structural	200–230	8–24	ASTM F1941
Aerospace Cadmium-Plated	190–220	18–24	AMS 2759/9
Automotive 10.9 Wheel Bolts	190–210	4–8	SAE J2339
Stainless Steel A4	150–200	4–6	ASTM A967

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Final Recommendations

✅ For critical fasteners: Always bake within 1 hour of plating.
✅ For mass production: Use low-hydrogen processes (e.g., zinc-nickel, mechanical galvanizing).
✅ When in doubt: Test per ASTM F1624 or ISO 15330.