ASTM A123

Covers — hot-dip galvanized zinc coatings on iron and steel products fabricated before galvanizing (structural members, plates, bars, pipe supports, gratings), specifying coating thickness by material category, finish, adherence, and inspection.

Does NOT cover (exclusions) — the following are governed elsewhere:

• Small hardware, bolts, nuts, fasteners (spun/centrifuged) → ASTM A153.
• Continuously (mill/sheet) galvanized products → ASTM A653.
• Paint systems (which may overcoat galvanizing) → ISO 12944.

A123 is for fabricated pieces galvanized after fabrication; A153 handles small threaded/centrifuged parts.

A123 sets minimum requirements for galvanizing:

• Coating Thickness — minimum average thickness by steel category (thicker steel gets thicker zinc).
• Finish & Adherence — smoothness, freedom from defects, and adhesion of the zinc.
• Inspection — thickness measurement, appearance, and sampling.
• Material Effects — steel chemistry (silicon/phosphorus) influencing coating growth.

ASTM A123 governs hot-dip galvanized zinc coatings on fabricated iron and steel — the standard behind galvanized pipe supports, structural steel, and gratings. Zinc protects both as a barrier and sacrificially: because it is anodic to steel, it keeps protecting even where the coating is cut or scratched.

Coating thickness is set by material-thickness category, and steel chemistry (silicon, phosphorus) affects how the coating grows. Small threaded hardware uses the companion A153, and painting over galvanizing follows ISO 12944 with proper surface preparation.

Engineering Note: Galvanizing is durable but the cut/weld areas made after galvanizing lose the coating — repair field cuts and welds with an approved zinc-rich coating to restore the sacrificial protection.