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ASTM A123/A123M Requirements
Coating Thickness / Weight dependent upon material category and steel thickness
Finish continuous, smooth, uniform
Appearance free from uncoated areas, blisters, flux deposits and gross dross inclusions as well as having no heavy zinc deposits that interfere with intended use
Adherence the entire coating should have a strong adherence throughout the service life of galvanized steel
The hot-dip galvanized coating is intended for products fabricated into their final shape that will be exposed to corrosive environmental conditions. Once a product has been hot-dip galvanized, any further fabrication, which rarely occurs, may have negative effects on the corrosion protection of the coating. The coating grade is defined as the required thickness of the coating and is given in microns. All coating thickness requirements in specification ASTM A123/A123M, (Tables 1 and 2), are minimums; there are no maximum coating thickness requirements in the specification.
In atmospheric environments, the time to first maintenance of hot-dip galvanized steel is directly proportional to the thickness of the hot-dip galvanized coating. With all other variables held constant, the thicker the zinc coating, the longer the life of the coating. The aim of the finish and appearance requirements is to ensure no coatings have problem areas that are deficient of zinc or have surface defects that would interfere with the intended use of the product. In addition, the coating should have a strong adherence throughout the service of the hot-dip galvanized steel.
| Table 1: Minimum Average Coating Thickness Grade by Material Category | ||||||
|---|---|---|---|---|---|---|
| All Specimens Tested Steel Thickness Range (Measured) in. [mm] | ||||||
| Material Category | <1/16 [<1.6] | >1/16 to <1/8 [>1.6 to <3.2] |
>1/8 to 3/16 [>3.2 to < 4.8] |
>3/16 to <1/4 [>4.8 to <6.4] | >1/4 to <5/8 [>6.4 to <16.0] | >5/8 [>16.0] |
| Structural Shapes | 45 | 65 | 75 | 75 | 100 | 100 |
| Strip and Bar | 45 | 65 | 75 | 75 | 75 | 100 |
| Plate | 45 | 65 | 75 | 75 | 75 | 100 |
| Pipe & Tubing | 45 | 45 | 75 | 75 | 75 | 75 |
| Wire | 35 | 50 | 60 | 65 | 80 | 80 |
| Reinforcing Bar | -- | -- | -- | -- | 100 | 100 |
| Table 2: Coating Thickness GradeA | ||||
|---|---|---|---|---|
| Coating Grade | mils | oz/ft2 | µm | g/m2 |
| 35 | 1.4 | .8 | 35 | 245 |
| 45 | 1.8 | 1.0 | 45 | 320 |
| 50 | 2.0 | 1.2 | 50 | 355 |
| 55 | 2.2 | 1.3 | 55 | 390 |
| 60 | 2.4 | 1.4 | 60 | 425 |
| 65 | 2.6 | 1.5 | 65 | 460 |
| 75 | 3.0 | 1.7 | 75 | 530 |
| 80 | 3.1 | 1.9 | 80 | 656 |
| 85 | 3.3 | 2.0 | 85 | 600 |
| 100 | 3.9 | 2.3 | 100 | 705 |
|
A: The values in micrometers µm are based on Coating Grade. The other values are based on conversions using the following formulas: mils=µm x 0.0.937; oz/ft2= µm x 0.02316; g/m2 = µm x 7.067 |
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