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Hydrogen Embrittlement Cause, Detection Method & Full Process Prevention Specification For Grade 10.9 & 12.9 High-strength Bolts
Hydrogen Embrittlement Cause, Detection Method & Full Process Prevention Specification For Grade 10.9 & 12.9 High-strength Bolts
Hydrogen Embrittlement Cause, Detection Method & Full Process Prevention Specification For Grade 10.9 & 12.9 High-strength bolts
Grade 10.9 & 12.9 high-strength bolts made of 42CrMo,35CrMo alloy have high hardness and dense lattice. Large amounts of hydrogen atoms penetrate steel during pickling and electroplating, accumulating at stress concentration positions and generating spontaneous cracks without impact load, known as delayed hydrogen embrittlement fracture, the most dangerous fastener hidden danger for energy storage containers and wind towers. Zhuhai Jiali Heavy Industry formulates standardized hydrogen prevention process based on years of production experience.
1. Hydrogen Embrittlement Risk & Process Parameter Comparison Of Three Anti-corrosion Coatings
| Coating Craft | Hydrogen Embrittlement Risk Level | Mandatory Dehydrogenation Baking Condition | Neutral Salt Spray Hours | Applicable For Grade12.9 Wind Bolts |
| Standard Electro Galvanized | Extremely High Risk | 220℃ hold 8h within 2h after plating | 500h no red rust | Short-term indoor inland energy storage only, forbidden for offshore wind power |
| Zinc-Nickel Alloy Plating | Medium Risk | 220℃ hold 6h within 3h after plating | 1500h no red rust | Universal first choice for onshore, coastal wind & energy storage projects |
| Dacromet Mechanical Coating | Ultra-low risk, barely no hydrogen absorption | No mandatory dehydrogenation, solidify at 180℃ only | 1000h no red rust | Suitable for long-term high temp boiler & heavy machinery working conditions |
2. Core Process Requirements For Full Hydrogen Embrittlement Prevention
1. Pickling pre-treatment control: Avoid long soaking in high-concentration hydrochloric acid, adopt weak phosphoric acid inhibited pickling within 5 minutes to reduce hydrogen absorption; 2. Two-stage electroplating: Low current pre-plating for 3 minutes to slow hydrogen evolution rate and prevent massive hydrogen penetration into metal lattice; 3. Dehydrogenation time limit: All plated high-strength bolts must enter oven within 3 hours after plating, delayed treatment leads hydrogen deep into lattice which cannot be fully removed by baking; 4. Storage isolation rule: Do not seal packaging before full cooling after baking to reserve channel for hydrogen volatilization; separate finished goods stacking to avoid compressive stress accelerating crack expansion.
3. Sampling Test Judgment & Failure Rectification Solutions
1. Delayed fracture sampling rule: Take 10 bolts per batch for 24h constant stress hydrogen test, zero crack & fracture means pass; one broken sample requires full batch re-baking; 2. Rectification for cracked bolts: Full batch scrapped with no repair allowed, cannot be delivered to wind & energy storage sites; 3. Long-term optimization plan: Offshore wind grade12.9 bolts prioritize Dacromet or thickened zinc-nickel coating with double dehydrogenation baking, keep baking temperature & time records for inspection.