ASTM A653

ASTM A653/A653M, Standard Specification for Steel Sheet, Zinc-Coated (Galvanized) or Zinc-Iron Alloy-Coated (Galvannealed) by the Hot-Dip Process, is the main North American standard for galvanized steel sheet. It covers sheet in coils and cut lengths and can be ordered in inch-pound units (A653) or SI units (A653M). ASTM lists A653/A653M-25a as the active version.

What it covers

The specification defines:

• coating types: galvanized (pure zinc) and galvannealed (zinc-iron alloy produced by heat-treating the coating)
• coating mass designations, set out in tables in the standard. In inch-pound units, galvanized coatings are designated with a "G" followed by the total coating mass in hundredths of an ounce per square foot (for example G90). Metric designations use "Z" with grams per square metre.
• steel designations such as commercial, forming, drawing and structural steel grades
• testing, tolerances and ordering rules

Galvanized sheet is produced on continuous lines in which steel strip is cleaned and passed through molten zinc.

Use in roofing

Galvanized steel has long been used for corrugated and ribbed roofing, flashings, gutters and roof decks. Today most residential and commercial steel roofing in North America uses either A653 galvanized or ASTM A792 aluminum-zinc coated steel as the base, with a factory paint system on top. Heavier zinc coatings are chosen for harsher environments, such as coastal or agricultural exposures.

How zinc protects steel

Zinc corrodes in preference to steel (sacrificial or galvanic protection), so small scratches and cut edges are protected by the surrounding coating. The life of the coating is roughly proportional to its thickness and depends strongly on the environment.

Related standards

• In Europe, zinc-coated steel sheet is covered by EN 10346, with coatings designated Z (zinc), ZF (zinc-iron), ZA, ZM (zinc-magnesium), AZ and AS.
• Hot-dip galvanizing of fabricated steel (as opposed to sheet) is covered by other standards, such as ISO 1461.