If the steel surface can not be blast cleaned and surface can only be prepared to SP2/3, what would be the recommended coating system for corrosion protection? The existing coating is a 3-coat system with Zinc rich primer, epoxy intermediate coat, and polyurethane top coat.
The picture shows a 1/2" ASTM A36 steel plate from the mid-1970's. It is part of a tunnel with segmented steel liners. The tunnel is under groundwater so there has been leaking. I am puzzled what can cause a corrosion like this.