Coating Failure Troubleshooting
Most coating complaints come down to the wrong finish for the environment, too little thickness, damage in handling, or a process fault. Hydrogen embrittlement is the one that breaks parts.
Symptom, likely cause, what to do
| Symptom | Likely cause | Action |
|---|---|---|
| White powder on zinc | Zinc corroding (normal early sign) | Heavier zinc, sealer or zinc-nickel |
| Early red rust | Thin coating, wrong finish, damage | Check thickness vs B633 service condition |
| Nuts will not start | Coating too thick (HDG) or no overtap | Use oversize-tapped nuts; check thread fit |
| Torque scatter | Inconsistent lubricant or finish | Specify a lubricated or controlled-friction finish |
| Flaking / blistering | Poor cleaning or adhesion | Reject lot; review plater process |
| Head pops off after hours or days | Hydrogen embrittlement | Quarantine lot; check bake records; see HE sheet |
These tables carry the same figures as the printed sheet below.
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Text version of this sheet
Coating failure troubleshooting
What it is
FIELD IDENTIFICATION
Most coating complaints come down to the wrong finish for the environment, too little thickness,
damage in handling, or a process fault. Hydrogen embrittlement is the one that breaks parts.
WHITE RUST
RED RUST
FLAKING
Common coating failure modes
Symptom, likely cause, what to do
Symptom
Likely cause
Action
White powder on zinc
Zinc corroding (normal early sign)
Heavier zinc, sealer or zinc-nickel
Early red rust
Thin coating, wrong finish, damage
Check thickness vs B633 service condition
Nuts will not start
Coating too thick (HDG) or no overtap
Use oversize-tapped nuts; check thread fit
Torque scatter
Inconsistent lubricant or finish
Specify a lubricated or controlled-friction finish
Flaking / blistering
Poor cleaning or adhesion
Reject lot; review plater process
Head pops off after hours or days
Hydrogen embrittlement
Quarantine lot; check bake records; see HE sheet
Key points
Any delayed fracture of a plated high-hardness bolt should be treated as hydrogen embrittlement until proved otherwise: quarantine the lot and keep the
pieces.
Governing standards: ASTM B633; ASTM F1941/F1941M-16(2025); ISO 4042:2022; ASTM F2329/F2329M-15(2023). 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-36A6E6 · thefastenerapp.com/fastener-guide/plating-coatings-finishes/coating-failure-troubleshooting · © The Fastener App. Reference only — verify the current governing standard, drawing and manufacturer data before specifying or installing.
