GB/T 30790.4-2014 "Paints and varnishes - Corrosion protection of steel structures by protective paint systems - Part 4: Surface types and surface preparation" specifies the requirements, methods, and evaluation criteria for the surface preparation of steel structures and metal-coated surfaces. The standard defines surface preparation grades and roughness requirements, recommends mechanical and chemical treatment methods, and requires the use of surface roughness comparators or roughness measuring instruments to inspect the treatment results. It also specifies surface preparation requirements for different corrosive environments, ensuring a strong bond between the coating system and the substrate, making it a critical preliminary step in corrosion protection.