Introduction
You specified SS304.
You paid more for stainless.
Then one fine day during inspection, the client notices a faint brown stain around the bolt head.
Suddenly, it’s not about corrosion anymore.
It’s about credibility.
This happens more often than EPC teams admit:
SS304 fasteners showing rust at the edges.
And when it happens, everyone asks the same question:
“Is this even real stainless steel?”
Why SS304 Should NOT Rust
SS304 is an austenitic stainless steel with roughly:
- • 18–20% Chromium
• 8–10.5% Nickel
Chromium forms a protective oxide layer that stops oxidation.
That’s why SS304 is used in kitchens, hospitals, marine fittings, and solar rooftops.
When rust appears…
something is wrong.
Top Reasons SS304 Rusts in Solar Sites
1. Poor Material Grade
Some suppliers use:
• Low nickel alloy
• Mixed scrap steel
• Incorrect composition
It wears the label “304”
But behaves like mild steel.
2. No Passivation Treatment
After manufacturing, stainless must be chemically cleaned to remove free iron.
No passivation = surface contamination = early rust.
3. Edge Burning During Fabrication
Laser cutting and cold forming create micro cracks.
If these edges are not treated,
corrosion starts exactly there.
That’s why rust appears only on corners and heads.
4. Storage Contamination
SS fasteners stored next to:
• Carbon steel
• Dust
• Moist packaging
Absorb iron particles.
The stainless itself doesn’t rust.
The contamination does.
How Solar Teams PROTECT Themselves
Before installing any stainless fasteners:
✅ Demand Material Test Certificate (MTC)
✅ Check Nickel Content (should be ≥8%)
✅ Ask for passivated finish
✅ Verify batch traceability
✅ Conduct random salt spray test
✅ Inspect surface under bright light
✅ Reject discolored threads or edges
Recommended SS304 Specifications for Solar Projects
Use:
- • M8, M10, M12 SS304 bolts
• A2-70 grade minimum
• Passivated + waxed finish
• Full chemical and mechanical reports
• Clean, sealed packaging
Final Thought
Rust on stainless is not a fail.
Supplying fake stainless is.
Once your client doubts your steel,
they doubt everything else too.
Don’t let reputation rust before your fasteners do.