Weld Seepage Staining

Staining and discolouration sometimes takes place at or adjacent to welds as a result of weld seepage.

This occurs as a result of pretreatment solutions used to clean the steel prior to hot dip galvanizing becoming trapped in weld pin holes. The heat of the galvanizing process drives off any moisture leaving behind a residue in the pin holes. However, when externally exposed, moisture is drawn into the pin hole by capillary action and the residue dissolves and then seeps out to give a reddish/brown discolouration.

Where an article for galvanizing contains an overlapping surface that are stitch-welded together, pretreatment solution may become trapped between the overlapping surfaces. Moisture is driven off during the galvanizing process leaving a residue which may subsequently dissolve in moisture drawn in between the overlapping surfaces. Such moisture may then seep out giving a reddish/brown stain similar to weld seepage.

Whilst unsightly, it is not detrimental to the protection that the galvanized surface will provide. In both cases such staining may be removed by wire brushing and provided all the residue has seeped out, staining should not occur. This can also be covered up by brush applying a good quality zinc rich paint and if required for aesthetic reasons, a finish coat of aerosol spray may be applied.