Difference between g60 and g90 galvanized steel

The continuous hot-dip coating process according to ASTM A653, Specification for Steel Sheet, Zinc-Coated (Galvanized) or Zinc-Iron Alloy-Coated (Galvannealed) by the Hot-Dip Process, is a widely used method to coat sheet products prior to fabrication. In this process, steel is passed as a continuous ribbon through production and into a bath of molten zinc at speeds up to 600 feet per minute. Once the product is removed from the bath, high-pressure air is used to remove any excess molten zinc to create a closely controlled coating thickness. Afterward, the steel is cooled and rolled into large coils for eventual fabrication. Today, the continuous sheet process is used to make seven different types of hot-dip coated products, including galvanized (zinc), galvannealed (90-92% zinc / 8-10% iron alloy), two alloys of zinc and aluminum (55% aluminum / 45% zinc alloy and 95% zinc / 5% aluminum alloy), two aluminum based alloys (100% aluminum, 89-95% aluminum / 5-11% silicon alloy), and the terne coating (85-97% lead / 3-15% tin alloy).

Both galvanized products provide barrier and cathodic protection, but have applications where they are best utilized. If you are simply trying to specify a hot-dip galvanized coating weight that is anywhere from 0.3 - 3.6 oz/ft2, this can be achieved using either process. However, if the steel is very thin (less than 7 gauge), warpage/distortion is a possibility with the batch process. Furthermore, if it is required to form the steel into various shapes after hot-dip galvanizing, then continuous galvanizing is preferred because it is very formable without cracking the galvanized coating. This is because the coating formed by the continuous process is made almost entirely of eta layer (free zinc) and has very little alloying unlike the hot-dip galvanized coatings produced using the batch process. This lack of alloying also means pre-galvanized sheet is less abrasion resistant than steel galvanized using the batch process.

G60 & G90 Galvanizing
The numbers included in G60 and G90 galvanizing signify the quantity of Zinc in the coating on the steel sheet. This means that G60 has a designated coating of 0.60 oz/square foot while G90 has a designated coating of 0.90 oz/square foot. This is the total weight of Zinc on both sides of the sheet. There are lighter and thicker coating as well, like G30 and G140, however, G60 and G90 tend to be the most commonly used.