Design, Specification & Inspection of Galvanized Products

 

Consultation between design engineers, specifiers, fabricators and the galvanizer is essential to ensure the safe, efficient and cost-effective production of high quality galvanized products.

 

Most ferrous metals can be galvanized. Mild and low alloy steels and iron and steel castings are all successfully galvanized. Steel fabrications with stainless steel fittings are also readily galvanized.

 

The steel's composition will determine the nature of the appearance of the galvanized coating. Steels with high silicon and/or high phosphorous content tend to produce a thicker galvanized coating which has a duller grey finish compared to usual bright, lustrous spangled appearance of galvanized steel.

 

Items ranging from small threaded fasteners up to massive structural members can be galvanized. Large structures can be galvanized by designing them in modular sections for later assembly by bolting or welding.

 

Mill scale on rolled steel is removed in our acid tanks as part of the preparation process prior to hot dip galvanizing. When ordering, all steel should be specified as 'unpainted' unless a palmer coat or similar water-based protective coating has been applied. As with mill scale, these coatings are easily removed in the de-greasing process prior to hot dip galvanizing.

 

Arc welding slags must be mechanically removed before delivery to the galvanizer. Welding suppliers are producing weld electrodes with fluxes that make the slags virtually self-detaching and their use is recommended.

 

Consideration must be given to the design of any fabrication intended for hot dip galvanizing as any residual liquids from the degreasing, acid pickling, rinsing and pre-fluxing tanks trapped in internal spaces will be rapidly converted to superheated steam during hot-dipping, with the potential to cause an explosion. It's essential that these pre-dipping solutions are able to freely enter and drain from fabrications, while the molten zinc must be able to drain and the air be able to vent freely during the hot dipping process itself.

 

Detailed specifications for the design, hanging, safe venting and drainage including hole dimensions and positioning are outlined in our comprehensive Hot Dip Galvanizing CD-ROM manual.

 

The simplest means for quality assessment is by visual inspection. Galvanized coatings are virtually 'self-inspecting' and a key characteristic is that if the surface coating is continuous and has a satisfactory appearance, it will be predictably sound and adherent. Due to the sacrificial cathodic protection characteristics of galvanizing, small areas of coating irregularity are permissible. Refer to AS/NZS 4680 for further details.

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