Common Causes
Rust breakthrough can follow mechanical damage, edge corrosion, poor surface preparation, coating age, insufficient film thickness, missed stripe coats, contamination, or exposure that exceeds the coating design.
Locations around edges, welds, bolts, drainage points, and impact zones often show early signs.
What Inspection Should Establish
Inspection should determine whether corrosion is isolated or widespread, whether coating defects are active, and whether there is evidence of section loss or underfilm corrosion.
Where steel loss is suspected, ultrasonic thickness testing or a corrosion survey may be needed.
Repair Implications
Local repair may be appropriate for isolated defects, but widespread rust breakthrough often requires a broader maintenance strategy and review of coating performance.