Galvanising

1.0 Scope

This specification defines the quality levels, coating requirements, and visual inspection criteria for hot-dip galvanised steel parts.

2.0 Environment class

This section defines galvanising service levels (Level A-B). Unless otherwise specified we would require parts to be suitable for Fractory service level C (or C3 Environment).

4.0 Viewing Conditions

For all viewing situations a minimum of 1.0 metre shall apply provided that further distance be allowed commensurate with the use of the product and its in-situ viewing distances. Inspection shall be conducted using the unaided eye under 500 Lux lighting conditions.

4.1 Lux

A measurement of luminous intensity from a light source. The following table represents the illumination from common sources:

Illuminance Example

50 lux Family living room80 lux

320–500 lux Office lighting

400 lux Sunrise or sunset on a clear day.

1,000 lux Overcast day; typical TV studio lighting

10,000–25,000 lux Full daylight (not direct sun)

32,000–130,000 lux Direct sunlight

5.0 Galvanising defects

This section defines common galvanizing defects to align expectations. Understandably the manufacturing partner, who provides coating, does not perform metalworking processes such as laser cutting, bending or machining - however, it remains the manufacturing partner's responsibility to notify Fractory if the parts received are in a condition that prevents a defect-free result. 

5.1 Bare Spots (Uncoated Surfaces) 

Bare spots are localized areas on a steel part where the molten zinc failed to react with the substrate, leaving the base steel completely exposed. These spots are often dark or "black" in appearance immediately after galvanizing. Because these areas lack the sacrificial protection of zinc, they are highly susceptible to immediate corrosion (red rust) once exposed to the environment. 

5.2 Zinc Runs and Sags 

Runs and sags are localized areas of excessive zinc build-up that occur when molten zinc fails to drain completely from the surface of a part. As the part is withdrawn from the kettle, the liquid zinc "runs" toward the lowest point due to gravity; if it solidifies before it can drip off, it leaves behind thickened ridges, frozen droplets, or spikes. Zinc build-up is not allowed as can interfere with the fit of mating parts!

5.3 White Rust (Wet Storage Stain) 

White rust is a white, powdery or bulky deposit that forms on the surface of freshly galvanized steel. It is composed of zinc hydroxide and zinc carbonates. Unlike the stable, protective "zinc patina" that forms naturally in open air, white rust occurs when the zinc is exposed to moisture (rain, dew, or condensation) while the parts are closely stacked or poorly ventilated, preventing a normal chemical reaction with the atmosphere 

5.4 Flaking of the Galvanised Coating

This is usually a sign of a mechanical bond failure or an excessively thick, brittle coating. Flaking refers to the detachment of the protective zinc coating from the steel substrate in the form of thin scales or chips. Unlike "peeling," which often involves the entire coating lifting off, flaking is typically characterized by smaller, brittle pieces breaking away, often leaving the dark grey inter-metallic alloy layers or the bare steel exposed. Flaking defect is not allowed!

5.5 Surface unevenness

Surface unevenness refers to a non-uniform distribution of the zinc coating, resulting in a finish that is not smooth to the touch. This can manifest as thick ridges (runs), localized mounds (lumps) or a general "orange peel" texture. While often an aesthetic concern, extreme unevenness can interfere with the fit of mating parts or create sharp edges. Surface unevenness is usually caused by process error and therefor is not allowed!  

5.6 Bad material surface 

Bad material surface refers to physical defects or contaminants present on the steel substrate prior to galvanizing that negatively affect the coating’s appearance, adherence, or thickness. Because the zinc-iron reaction is sensitive to the texture and cleanliness of the steel, irregularities like scratches, burrs, and heavy rust often lead to a non-uniform or defective finish.