Galvanized Steel Coil Coating Thickness
Use the following relationships to estimate the coating thickness from the coating weight [mass]:
1.00 oz/ft2 coating weight = 1.68 mils coating thickness,
7.14 g/m2 coating mass = 1.00 µm coating thickness.
Use the following relationship to convert coating weight to coating mass:
Weight [Mass] of Coating Thickness
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Minimum Requirement |
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Triple-Spot Test (TST) |
Single-Spot Test (SST) |
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Inch Pound Units |
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Type |
Coating Designation |
TST Total Both Sides, oz/ft2
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TST One Side, oz/ft2
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SST Total Both Sides, oz/ft2
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Zinc |
G30 G40 G60 G90 G100 G115 G140 G165 G185 G210 G235 G300 G360
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no minimum 0.30 0.40 0.60 0.90 1.00 1.15 1.40 1.65 1.85 2.10 2.35 3.00 3.60 |
no minimum 0.10 0.12 0.20 0.32 0.36 0.40 0.48 0.56 0.64 0.72 0.80 1.04 1.28 |
0.25 0.30 0.50 0.80 0.90 1.00 1.20 1.40 1.60 1.80 2.00 2.60 3.20
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SI Units |
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Zinc |
Z001 Z90 Z120 Z180 Z275 Z305 Z350 Z450 Z500 Z550 Z600 Z700 Z900 Z1100
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no minimum 90 120 180 275 305 350 450 500 550 600 700 900 1100 |
no minimum 30 36 60 94 110 120 154 170 190 204 238 316 390
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no minimum 75 90 150 235 275 300 385 425 475 510 595 790 975 |
NOTE –Values in SI and inch-pound units are not necessarily equivalent.
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Single Spot/Single Side Coating Mass
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SI Units
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Inch-Pound Units (information only)
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Type
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Coating Designation
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Minimum, g/m2
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Maximum, g/m2
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Minimum, oz/ft2 |
Maximum, oz/ft2
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Zinc
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20G 30G 40G 45G 50G 55G 60G 70G 90G 100GD |
20 30 40 45 50 55 60 70 90 100 |
70 80 90 95 100 105 110 120 160 200 |
0.07 0.10 0.12 0.15 0.16 0.18 0.20 0.23 0.30 0.32 |
0.23 0.26 0.29 0.31 0.33 0.34 0.36 0.40 0.62 0.65 |
The coating designation is the term by which the minimum triple spot, total both sides coating weight [mass] is specified. Because of the many variables and changing conditions that are characteristic of continuous hot-dip coating lines, the zinc or zinc-iron alloy coating is not always evenly divided between the two surfaces of a coated sheet; nor is it always evenly distributed from edge to edge. However, the minimum triple-spot average coating weight (mass) on any one side shall not be less than 40 % of the single-spot requirement.
As it is an established fact that the atmospheric corrosion resistance of zinc or zinc-iron alloy-coated sheet products is a direct function of coating thickness (weight (mass)), the selection of thinner (lighter) coating designations will result in almost linearly reduced corrosion performance of the coating. For example, heavier galvanized coatings perform adequately in bold atmospheric exposure whereas the lighter coatings are often further coated with paint or a similar barrier coating for increased corrosion resistance. Because of this relationship, products carrying the statement “meets ASTM A653/A653Mrequirements” should also specify the particular coating designation.
No minimum means that there are no established minimum requirements for triple- and single-spot tests.
Post time: Apr-09-2021