Classify a structure's atmospheric corrosivity category to select an appropriate protective coating system durability class

Steps

1. Use ISO 12944 (current multi-part edition; confirm latest part revisions on iso.org before citing a year, noting the series was substantially revised around 2017), specifically Part 2 for corrosivity category classification (C1 very low through CX extreme, plus separate immersion categories) and Part 5 for corresponding protective paint system examples
2. Classify the structure's environment based on actual exposure conditions (e.g., rural, urban, industrial, marine, offshore) using Part 2's category descriptions and, where available, site-specific corrosion-rate data rather than a generic regional assumption
3. Select a coating system durability range (low/medium/high/very high, per Part 5's durability ranges) appropriate to the desired maintenance interval, not just the corrosivity category alone — durability and corrosivity category are two separate axes in the standard
4. Cross-check the selected system against manufacturer technical data sheets to confirm the specific product combination has documented performance/testing appropriate to the target ISO 12944 corrosivity category and durability range
5. For immersion service (e.g., water tanks, submerged structures), apply ISO 12944's separate immersion categories (Im1-Im4) rather than the atmospheric C1-CX categories