Galvanized and Galvannealed Steel Coils
Galvanized is produced from Cold Rolled (or Hot Rolled Pickled & Oiled) coil that has been passed continuously through a pot of molten zinc. The amount of coating applied to the surface is controlled by wiping, rollers and/or air jets. The coated product is then cooled and passes through leveling equipment. The zinc coating protects the steel substrate in two ways. First, it creates a barrier that retards the formation of rust. Second, zinc has a self-sacrificial character and will extend itself to cover nearby small uncoated areas (i.e., cut edges, scratches).
There is generally a direct correlation between the amount of zinc application and the steel's atmospheric corrosion resistance. The more the zinc, the more the corrosion resistance. The amount of zinc (referred to as coating weight) is represented in ounces per square foot (or sometimes grams per square meter) total both sides. Its designation, for example, may be G60 (or A60, in the case of Galvannealed), constituting .60 oz/ft2. As such, the material would have approximately one-third less protection than G90 (.90 oz/ft2).
Galvanized (and Galvannealed) are typically produced in accordance with ASTM A653 standards and tolerances.
| Zinc Coating Categories | |||
| Minimum Coating Wt. oz/ft2 Total Both Sides | |||
| Designation | Triple Spot Test | Single Spot Test | |
| Both Sides | One Side | ||
| G235 | 2.35 | .80 | 2.00 |
| G210 | 2.10 | .72 | 1.80 |
| G185 | 1.85 | .64 | 1.60 |
| G165 | 1.65 | .56 | 1.40 |
| G140 | 1.40 | .48 | 1.20 |
| G115 | 1.15 | .40 | 1.00 |
| G90 | .90 | .32 | .80 |
| G60 or A60 | .60 | .20 | .50 |
| G40 or A40 | .40 | .12 | .30 |
| G30 or A30 | .30 | .10 | .25 |
| A25 | .25 | .08 | .20 |
Coating Weights
Coating weights are sometimes denoted in metric standards (SI units), grams per square meter each side. For example, category 60G/60G stipulates that each side has a minimum single spot coating weight of 60 grams per square meter (g/m2).
Essex Trading Company normally furnishes coating weight descriptions using single-spot testing per ASTM A90 standards.
US and metric conversion factors are:
1 oz/ft2 = 305.15 g/m2 · 1 g/m2 = 0.00328 oz/ft2
In terms of coating thickness, 1 oz/ft2 = 1.7 mils.
| Coating Conversion Formula | ||
| Convert From | Convert To | Multiply By |
| ounces/square foot (oz/ft2) | grams/square meter (g/m2) | 305.15 |
| grams/square meter (g/m2) | ounces/square foot (oz/ft2) | 0.00328 |
| Coating Comparisons (Approx.) | ||
| Grams per Sq. Meter Per Side | Grams per Sq. Meter Both Sides | Ozs. Per Sq. Ft. Both Sides (approx. equiv.) |
| 98G/98G | 196 | G64 |
| 90G/90G | 180 | G59 |
| 70G/70G | 140 | G46 |
| 60G/60G | 120 | G39 |
| 50G/50G | 100 | G33 |
| 40G/40G | 80 | G26 |
| 20G/20G | 40 | G13 |
| 10G/10G | 20 | G07 |
| 5G/5G | 10 | G03 |
Finishes
As the zinc solidifies during the coating process, snowflake or flower-like patterns ("spangle") emerge. Neither spangle appearance nor its size determines corrosion resistance.
Regular Spangle: Moderate-large (approx. 1/2" diameter) and usually bright/shiny
Minimum Spangle: Small (approx. 1/8" - 1/4" diameter) and usually bright/shiny
Zero Spangle (aka extra smooth): No visible spangle; generally duller than Regular or Minimum Spangle; usually intended for painted applications
Galvannealed: A form of hot-dipped galvanized consisting of an iron-zinc alloy coating on both sides. When the coil exits the zinc bath, the molten zinc coating is subjected to an in-line annealing (thus the name "Galvannealed") process that creates the zinc-iron alloy layer. The coating is denoted by an "A" designation (i.e., A60). It has a uniform light-medium gray color and a semi-porous finish that is easily paintable. Compared to regular hot-dipped Galvanized, it has similar corrosion resistance and a harder coating that is more resistant to scratching. Galvannealed tends to have somewhat less ductility and the coating sometimes powders (especially in heavier coating weight, i.e., A60) under severe forming.
Bonderized: A form of hot-dipped galvanized which has been phosphatized to promote paintability. Appearance is typically dark-grey and sometimes the underlying spangle pattern may be visible. Has same corrosion protection as regular galvanized, usually available in G60 and G90 coating weights. Bonderized's popularity has declined since the 1980s, having been replaced by Galvannealed for many applications.
Galvanized Base Metal Classifications
Commercial Steel (CS Types A,B,C), Forming Steel (FS), Deep Drawing Steel (DDS), Extra Deep Drawing Steel, Structural Steel (SS), High Strength Low Alloy (HSLA), Full Hard
| Mechanical Properties | ||||
| Classification | Yield Str. psi | Tensile Str. psi | Elong. % / 2" | Rock. B typical |
| Commercial Steel (Type B) | 40000 typ. | -- | >20 typ. | 48 |
| Forming Steel | 35000 typ. | -- | >26 typ. | 38 |
| Deep Drawing Steel | 28000 typ. | 48000 typ. | >32 typ. | 34 |
| Extra Deep Drawing Steel | 20000 typ. | -- | >40 typ. | 30 |
| Struct. Steel - Grade 33 | 33000 min. | 45000 min. | 20 min. | 58 |
| Struct. Steel - Grade 40 | 40000 min. | 55000 min. | 16 min. | 65 |
| Struct. Steel - Grade 50 Cl. 1 | 50000 min. | 65000 min. | 12 min. | 75 |
| Struct. Steel - Grade 80 | 80000 min. | 82000 min. | -- | 85 |
| Full Hard | 70000 typ. | 90000 typ. | -- | 90 |
| HSLA Grade 45 Cl. 1 | 45000 min. | 60000 min. | 25 min. | 65 |
| HSLA Grade 50 Cl. 1 | 50000 min. | 65000 min. | 22 min. | 70 |
| HSLA Grade 55 Cl. 1 | 55000 min. | 70000 min. | 20 min. | 75 |
| HSLA Grade 60 Cl. 1 | 60000 min. | 75000 min. | 18 min. | 80 |
| Structural Steel - Bending Properties 90° long. bend · t = steel thickness | |
| Classification | Min. Inside Diameter |
| Grade 33 | 1½-t |
| Grade 40 | 2-t |
| Grade 50 Cl. 1 | not applicable |
| Grade 50 Cl. 2 | not applicable |
| Grade 80 | not applicable |
| Coating Bend Test Requirements (ratio of inside bend diameter to thickness) | ||||||||
| CS, FS, DDS, EDDS | Grd. 33 | Grd. 37 | Grd. 40 | Grd. 50 | Grd. 80 | |||
| Sheet Thickness | ||||||||
| Coat. Wt. | .010"-.039" | .040"-.079" | .080"-.160" | |||||
| G235 | 2 | 3 | 3 | 3 | 3 | 3 | n/a | n/a |
| G210 | 2 | 2 | 2 | 2 | 2 | 2½ | n/a | n/a |
| G185 | 2 | 2 | 2 | 2 | 2 | 2½ | n/a | n/a |
| G165 | 2 | 2 | 2 | 2 | 2 | 2½ | n/a | n/a |
| G140 | 1 | 1 | 2 | 2 | 2 | 2½ | n/a | n/a |
| G115 | 0 | 0 | 1 | 1½ | 2 | 2½ | n/a | n/a |
| G90 | 0 | 0 | 1 | 1½ | 2 | 2½ | n/a | n/a |
| G60 | 0 | 0 | 0 | 1½ | 2 | 2½ | n/a | n/a |
| G40 | 0 | 0 | 0 | 1½ | 2 | 2½ | n/a | n/a |
| G30 | 0 | 0 | 0 | 1½ | 2 | 2½ | n/a | n/a |
Special Essex Features/Offerings
For especially-discounted pricing, we offer several products that are well suited for many building products (i.e., studs, framing components) and other noncritical appearance applications:
Mixed Coils: Having galvanized (bright) and galvannealed (dull) coatings. Little or no loss in corrosion resistance.
Pup Coils: Coils smaller than about 200 piw. Our savings often far outweigh any related increase in processing/production time.
Full Hard: For applications that are flat, require higher strength and/or little bending or forming.