These products frequently have higher than normal levels of silicon or phosphorous, which in turn affects the reactivity of the steel and the rate of alloy growth at galvanizing.
Coating weight of 2 to 3 times the standard may result which although providing proportionally greater life results from alloy growth affecting the metallic shine and in some cases surface texture.
The brightness variation is transitory in nature and will moderate to a neutral appearance over time. The surface roughness will therefore be more visible in the early life of the coating but will be less apparent with ageing over 6-12 months.
The composition of Australian steel is a well controlled constant in terms of the elements referred to but their presence has an effect over which the galvanizer has no control.
The current wave of steel imports arriving in Australia has resulted in the frequent occurrence of these conditions.
In general, in a time frame dependent on the severity of the exposure, the entire surface will take on a neutral uniform appearance and will provide longer than the specified service life.
Normally the cost of the extra zinc used has to be borne by the galvanizer, as there is no easy way to anticipate the steel composition variations in advance.
Source: Galvanizers Association of Australia
For more information on this source please visit Galvanizers Association of Australia