Corrosion Protection – Minimum steel thickness when directly exposed to weather and not accessible for cleaning/repainting

Introduction / Context:
Atmospheric corrosion rate depends strongly on exposure and maintenance accessibility. Where members are exposed to weather and cannot be cleaned or repainted easily, a thicker section is mandated to provide corrosion allowance and preserve structural capacity over time. This question recalls the minimum thickness requirement for such inaccessible members.

Given Data / Assumptions:

• Structural steel member directly exposed to weather.
• Member is not accessible for routine maintenance.
• Design per traditional IS steel practice and detailing guidelines.

Concept / Approach:

Minimum plate/section thickness limits aim to ensure that expected corrosion loss during the service life does not reduce the net thickness below safe levels. When access is poor, the code stipulates a higher minimum thickness than for accessible members, commonly 8 mm, to provide durability without excessive reliance on maintenance.

Step-by-Step Solution:

Verification / Alternative check:

Accessible members (regularly maintainable) may be permitted at 6 mm, but this does not apply here. The 8 mm limit aligns with corrosion allowance needs in practical Indian conditions.

Why Other Options Are Wrong:

4 mm is too thin for outdoor exposure; 6–7 mm suit better-maintained situations; 8 mm is the accepted minimum for inaccessible, weather-exposed details.

Common Pitfalls:

Overlooking water traps, not sealing lap edges, or assuming paint alone will offset chronic inaccessibility.

Final Answer:

8 mm