Galvanizing How To

Bolting Galvanized Steel


Galvanized steel's superior corrosion resistance properties have made it the accepted standard for exposed steel around the world. With the wide use of steel in exposed industrial structures, bridges, power transmission and communication towers, often in remote areas, the need for low maintenance corrosion protection is essential.


Bolting has become the most widely used method for making field connections as it has several key advantages over welding like its speed and economy or erection, reliability, easy inspection, and the absence of coating damage and cracking as a result of welding.


In bolted structures, the bolts and nuts are critical items on which an entire structure's integrity depends. Where the steel members are galvanized, fasteners used should also be galvanized to maintain uniform corrosion protection.


Various grades of nut and bolt assemblies are produced for the structural steel industry with a range of tensile strengths designed for specific bolted joint applications.


Welding Galvanized Steel


There is something of a misconception that welding galvanized steel can be difficult. In fact, galvanized steels are routinely and successfully welded with ease using all the commonly practiced methods including gas metal arc, carbon arc, gas tungsten arc, manual arc and oxyacetylene welding.


Extensive industry testing has shown that sound gas metal arc welds and manual metal arc welds in galvanized steel are equivalent to those of sound welds in uncoated steel. Industry tests have also proved that the presence of zinc at the levels occurring in the weld metal does not affect tensile, bend or impact properties. The fatigue strength of arc welds in galvanized steel is equivalent to welds in uncoated steel.


Depending on coating thickness, porosity will occur in certain joint designs in galvanized steel due to volatilisation of the zinc coating and entrapment of gas in the weld. This has no effect on joint properties except in loss of fatigue strength. When joints are subject to fatigue loading, welds in galvanized steel should be made oversize to reduce the influence of any porosity in the weld metal.


Procedures for controlling the welding conditions of galvanized steels are also well established. Zinc vaporizes near the arc and oxidizes in the air as a non-toxic fine white zinc oxide powder. So, as with all welding, adequate ventilation and fume extraction should be in accordance with normal industrial practice. When welding in confined spaces, operators should wear suitable respirators.


Welding can damage the protective galvanized coating. Small exposed areas usually have little adverse effect due to the sacrificial cathodic properties of the surrounding galvanized coating. Larger damaged areas may require repair by the removal of welding slag with a chipping hammer, followed by wire brushing and the application of a protective coating. With manual metal arc welding and oxyacetylene welding of galvanized steel, the weld metal itself will corrode in most environments, so the application of a protective coating is essential. An organic zinc-rich paint is the most convenient and rapid method of repair. In some cases, zinc metal spraying may be used for coating repairs.


Welding galvanized steel is now a commonplace practice. Galvanized steel welds are proven to perform equally with those of uncoated steel welds. Fabricators can have all the flexibility of traditional welding techniques with the added advantage of superior corrosion protection that only galvanizing offers.

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