title = "Hot-Dip Galvanizing and Zinc Coatings"

content = """
Hot-dip galvanizing is a corrosion protection process in which steel is immersed in a bath of molten zinc at approximately 845°F (450°C), forming a metallurgically bonded zinc-iron alloy coating on the steel surface. Galvanizing is used at Ridgecrest Metalworks and by its customers for structural steel, hardware, fasteners, sheet products, and fabrications requiring long-term corrosion protection in aggressive outdoor or industrial environments.

The hot-dip galvanizing process sequence: parts are first degreased (alkaline cleaning), pickled (in hydrochloric or sulfuric acid to remove mill scale and rust), rinsed, and fluxed (dipped in a zinc ammonium chloride flux bath that promotes wetting). The fluxed part is then immersed in the molten zinc bath; zinc reacts with the steel surface to form a layered structure of zinc-iron intermetallic phases (gamma, delta, zeta layers) topped by a pure zinc outer layer. The coating thickness depends on immersion time and steel composition/surface condition; typical structural steel galvanizing thickness is 3.0–5.0 mils (75–125 µm) per ASTM A123.

Reactive (silicon-killed) steels with silicon content above 0.3% or between 0.04–0.14% can produce very thick, brittle coatings (Sandelin effect) due to accelerated zinc-iron intermetallic growth—material selection and specification must account for this.

Galvanized coating life is proportional to coating thickness and environment. In moderately corrosive industrial atmospheres, 3 mil coating life is 40–80 years; in marine or severe industrial environments, shorter. Zinc provides both barrier protection and sacrificial (cathodic) protection—even where the coating is scratched or cut, the surrounding zinc corrodes preferentially, protecting the exposed steel.

Continuous hot-dip galvanizing of sheet steel (galvanneal, galvanized, or zinc-aluminum coated steel) is performed in-line at steel mills at very high speeds, producing thinner but highly uniform zinc coatings.

Inspection of galvanized coatings includes visual examination for bare spots, dross inclusions, and flux inclusions; coating thickness measurement by magnetic gauge per ASTM A123 or E376; and adhesion testing by knife or bend methods.
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