Valve Painting & Coating Specifications Guide

The most common industrial valve painting system consists of: surface preparation to SSPC-SP10/Sa 2½ (near-white blast), inorganic zinc silicate primer at 75 μm DFT, epoxy MIO intermediate coat at 125 μm DFT, and polyurethane topcoat at 50 μm DFT — total minimum DFT of 250 μm. This system provides excellent corrosion protection for onshore industrial environments. For offshore or marine environments, NORSOK M-501 requires a higher total DFT (325+ μm) with Sa 3 surface preparation.

Generally, stainless steel valves (SS304, SS316, duplex, super duplex) are supplied unpainted with a natural mill finish. The chromium oxide passive layer provides inherent corrosion protection. However, some project specifications may require a color-coded topcoat for identification purposes, or a clear lacquer for cosmetic protection during storage and transit. In chloride-rich environments, some engineers specify a thin epoxy coating as additional protection against pitting.

NORSOK M-501 is the Norwegian offshore standard for surface preparation and protective coating of equipment and structures for offshore installations. It specifies coating systems based on corrosion category (C1-C5, CX for offshore atmospheric, Im1-Im4 for immersion). For valve external surfaces on offshore platforms, System 1 (atmospheric) or System 7 (splash zone) typically applies. Key requirements include Sa 3 surface preparation, qualified coating applicators, and documented DFT measurements at multiple points per component.