Steel that performs perfectly in a dry inland climate can be visibly corroding in Mumbai within three years. The combination of high humidity, monsoon saturation and salt-laden coastal air makes protection specification part of the structural design, not an item to be decided when the paint contractor arrives.
Surface preparation decides the outcome
The single largest cause of coating failure is inadequate surface preparation. Mill scale left in place will take the coating off with it. Blast cleaning to the specified standard, with the surface coated before flash rusting begins, matters more than the price of the paint.
Match the system to the exposure
An internal member in a conditioned space and an exposed external canopy 400 metres from the sea do not need the same system. Zoning a project by exposure category and specifying accordingly gives better protection where it is needed and avoids overspending where it is not.
Galvanising where access will be difficult
For elements that will be genuinely hard to re-coat later — roof-level secondary steel, elevated walkway members, remote pipe supports — hot-dip galvanising is usually cheaper across the asset life than repeated access and repainting.
Detail out the water traps
Good coating cannot rescue bad detailing. Unsealed box sections, upward-facing angles that pond water, and connections that hold moisture at the faying surface will corrode regardless of the system applied. These get resolved at detailing stage, on the drawing.
Do the specification properly once and the structure needs inspection, not intervention. Get it wrong and you are budgeting for remedial access every few years.