Hydrogen Embrittlement Prevention for High‑Strength Bolts：Plating, Baking, Inspection & Overseas Project Acceptance

Hydrogen Embrittlement Prevention for High‑Strength Bolts：Plating, Baking, Inspection & Overseas Project Acceptance

Grade 10.9 and 12.9 high‑strength bolts are widely adopted in overseas construction machinery, energy‑storage support and railway projects. Carbon‑steel high‑strength parts absorb hydrogen during electro‑galvanizing. Without post‑plating baking treatment, hydrogen‑induced delayed fracture may occur days or months after installation, leading to extremely high repair cost at overseas site. Hydrogen risk control is critical for cross‑border fastener orders.

1. Hydrogen Embrittlement & High‑Risk Parts

Hydrogen penetrates steel during pickling and electroplating. Hydrogen accumulates at grain boundaries and triggers brittle fracture under sustained stress. Failure is delayed and cannot be easily found by ordinary outgoing sampling test.

High‑risk list:
① Carbon‑steel bolts & set screws of grade ≥10.9;
② High‑strength components finished with electro‑zinc / black‑zinc plating;
③ Spring retaining rings, spring washers and pins with hardness HRC≥32;
④ Non‑standard high‑strength stamping fasteners with thin wall and stress concentration.

A2‑70 / A4‑70 stainless‑steel normally have low hydrogen‑embrittlement risk, improper pickling may still introduce trace hydrogen for marine critical projects.

2. Standard Post‑Plating Baking Procedure

1. Baking timing: Start baking within 4 hours after electroplating. Delayed baking reduces degassing efficiency as hydrogen diffuses deep into steel matrix.
2. Baking parameter: 210‑230℃ holding temperature. Normal bolts keep 2‑4 hours; thicker cross‑section requires longer holding time.
3. Never bake before plating: subsequent plating re‑introduces hydrogen and invalidates baking.
4. Process suggestion: For critical high‑strength parts, mechanical galvanizing is preferred over electro‑plating to minimize hydrogen risk at source.

3. Technical Clauses Recommended for Cross‑Border PO & BOM

Many overseas quality disputes arise from missing baking requirements on purchasing document. Add below statement in BOM or Purchase Order for overseas projects:

“For electro‑plated carbon‑steel fasteners grade 10.9 /12.9, post‑plating baking shall be performed to mitigate hydrogen‑embrittlement risk. Supplier shall keep process record for audit.”

4. In‑Warehouse Receiving Inspection

• Check factory document confirming post‑plating baking execution;
• Visual check: no peeling, blister or burnt plating on high‑strength bolts;
• Constant‑load delayed‑fracture test is optional for high‑priority critical projects;
• Salt‑spray pass result cannot prove freedom from hydrogen‑embrittlement hazard.

5. On‑Site Assembly Guidance for Overseas Projects

1. Avoid on‑site re‑pickling or re‑electroplating for baked high‑strength bolts. Re‑plating requires full baking cycle again.

2. Tighten strictly per torque specification. Over‑torque raises stress level and increases fracture probability.

3. Avoid long‑term storage under hot‑humid environment. Re‑evaluate batches stored over 12 months.

6. fastener.hk Risk‑Control Service

For high‑strength fastener orders shipping to Hong‑Kong, Macau and Southeast‑Asia, we review BOM strength grade and finish requirement, monitor supplier baking procedure and provide process record together with shipment to end‑buyers. Third‑party hydrogen‑embrittlement test can be arranged upon special project requirement.