Why corrosion starts at joints first
Corrosion rarely starts in open steel surfaces.
It starts at:
- Cut edges
- Joints
- Fastener contact points
Because that’s where different metals and coatings meet.
What coating mismatch means
A painted structure with HDG fasteners creates:
- Different electrochemical potentials
- Localized corrosion cells
- Accelerated zinc or steel loss
This is bimetallic corrosion.
Common mismatch combinations
- HDG fasteners on epoxy painted steel
- Stainless bolts on carbon steel plates
- Zinc plated bolts on marine painted frames
All can accelerate corrosion if not designed correctly.
Why this keeps happening
1. Paint and fastener specified separately
2. No corrosion compatibility check
3. Supplier substitution
4. Ignoring environmental class
What happens if ignored
- Rust streaks at joints
- Paint blistering
- Coating undercutting
- Long-term section loss
How to prevent corrosion
Match coating systems
Use isolation washers if needed
Consider environment class
Avoid mixing metals
Consult coating compatibility tables
Final thought
Corrosion is a system problem.
You cannot fix it with one component.