Technical Information

Specifications:

AMERICAN SOCIETY FOR TESTING AND MATERIALS (ASTM)

A123 Standard Specification for Zinc (Hot-Dip Galvanized) Coatings on Iron and Steel Products

A143 Standard Practice for Safeguarding Against Embrittlement of Hot-Dip Galvanized Structural Steel Products and Procedure for Detecting Embrittlement

A153 Standard Specification for Zinc Coating (Hot-Dip) on Iron and Steel Hardware

A767 Standard Specification for Zinc-Coated (Galvanized) Steel Bars for Concrete Reinforcement

A780 Standard Practice for Repair of Damaged and Uncoated Areas of Hot-Dip Galvanized Coatings

Galvanizing forms a metallurgical bond to the steel and the zinc itself. Different layers are formed each comprising of different ratios of steel to zinc. The outermost layer, called the Eta layer is purely zinc, next, the Zeta layer 94% zinc and 6% iron, then the Delta layer 90% zinc and 10% iron and finally the Gamma layer which is composed of 75% zinc and 25% iron.

Coating thickness and appearance are the two properties inspectors and customers are most concerned with. Several factors will affect the appearance and thickness of the steel being galvanized. Old steel being galvanized for the first time or steel getting re-galvanized will often have rough surfaces and as result the galvanized finish will reflect these abnormalities and create a thicker or rougher coating to the steel.

Withdraw time will also affect the thickness of the galvanized material. Removing steel quickly from the kettle will not allow all the zinc to run off the steel before it cools and as result you end up with a thick sometimes rippled appearance.