Galvanizing of tubular members

Certain special requirements for galvanizing tubular sections are noted below:

Table 12.1 Suitable sizes of vent holes in tubular member

Size of tubular section Minimum diameter of hole

25-50 12

50-100 16

100-150 20

>150 25

Filling, venting and draining should be provided in tubular members. Holes not less than 10 mm diameter must be provided in sealed tubular sections to allow access for molten zinc, venting of hot gases and the subsequent draining of zinc. Sealed tubes which are to be galvanized will require vent holes to allow the escape of hot air during the hot-dipping process. Table 12.1 indicates suitable hole sizes.

Generally, tubular sections should not be welded after galvanizing due to the possibility of poor welding due to porosity caused by the gases given off from the zinc coating. Sections are generally welded before galvanizing and components bolted together after galvanizing.

Owing to the smooth surface created by galvanizing, a special etching primer or 'T' wash or light 'sweep' blasting will be required before painting, before the final two coats are applied on site.

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