Hydrogen Embrittlement Failure
Hydrogen embrittlement (HE) is delayed brittle fracture caused by hydrogen in high-hardness steel. A bolt can be installed correctly and snap hours or days later under sustained tension.
Two kinds of HE
| Internal HE | Environmental HE | |
|---|---|---|
| Hydrogen from | Manufacturing: pickling, electroplating | Service: corrosion, cathodic protection |
| When it fails | Usually within hours or days of loading | After time in service |
| Controls | Bake promptly after plating; avoid electroplate on hard parts | Material and coating choice, lower hardness |
Risk and controls
| Risk threshold | Rises sharply above about HRC 39: Grade 8, 10.9, 12.9, A490, A574, F1554-105 |
|---|---|
| Relief bake | Typically about 190 - 220 C (375 - 430 F) for several hours, started promptly after plating per the governing spec |
| Testing | ASTM F1940 process control; ASTM F519; ISO 15330 sustained-load test |
| Fracture look | Bright, crystalline, intergranular, little or no stretch |
| On a failure | Quarantine the whole lot; pull bake and plating records; keep the pieces |
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Hydrogen embrittlement failure
What it is
FAILURE MODE
H
H
Hydrogen embrittlement (HE) is delayed brittle fracture caused by hydrogen in high-hardness steel. A
bolt can be installed correctly and snap hours or days later under sustained tension.
H
Hydrogen embrittlement: delayed brittle
fracture
Two kinds of HE
Internal HE
Environmental HE
Hydrogen from
Manufacturing: pickling, electroplating
Service: corrosion, cathodic protection
When it fails
Usually within hours or days of loading
After time in service
Controls
Bake promptly after plating; avoid electroplate on hard parts
Material and coating choice, lower hardness
Risk and controls
Risk threshold
Rises sharply above about HRC 39: Grade 8, 10.9, 12.9, A490, A574, F1554-105
Relief bake
Typically about 190 - 220 C (375 - 430 F) for several hours, started promptly after plating per the governing spec
Testing
ASTM F1940 process control; ASTM F519; ISO 15330 sustained-load test
Fracture look
Bright, crystalline, intergranular, little or no stretch
On a failure
Quarantine the whole lot; pull bake and plating records; keep the pieces
Key points
Do not re-install bolts from a lot with a delayed fracture until the lot is cleared.
Governing standards: ISO 4042:2022; ASTM F1941/F1941M-16(2025); ASTM F1940-07a(2024); ASTM F519; ISO 15330. Editions shown are the latest confirmed as of September
2026. The drawing and the governing standard always take precedence over this sheet.
torquing any fastener. Verify the current governing standard, project documents, OEM requirements, size, thread, coating and lot certification. To the fullest extent permitted by law, The Fastener App disclaims liability
arising from reliance on this reference.
Fastener Guide reference FG-F25AB7 · thefastenerapp.com/fastener-guide/failure-analysis/hydrogen-embrittlement-failure · © The Fastener App. Reference only — verify the current governing standard, drawing and manufacturer data before specifying or installing.
