Letter 32001

The effect of rough white spots on galvanized steel electric masts on durability [Qatar]  

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One contractor has delivered to the site (which is sea port site) a number of 30 m electric masts made of galvanized steel. These were stored near the sea raised on wooden platforms by half a meter. white rust has appeared. Some spots of the white rust areas are rough in texture whereas the other parts of the white rust areas are smooth like the rest of the galvanized steel areas. Measurement of the thickness of galvanization on all spots gave higher results than required . The thickness at the rough spots seems to be more than the rest of the white rust spots. I am concerned about the rough spots .The contractor as well as the material supplier and factory engineers suggest applying a rich zinc paint after cleaning with special chemicals . Please advise of the effectiveness of the proposed treatment.

Dr. Jamal Omari
Ministry of Municipal Affairs & Agric. - Doha, Qatar

This white rust is probably also what is known as "wet storage stain" and results from damp parts not getting enough fresh air to form corrosion-resistant corrosion products. While I can't say if these parts are satisfactory or not, I can note that wet storage stain usually isn't as serious as it looks because the corrosion products are so voluminous compared to the amount of zinc that was actually consumed to generate them.

If you search this site or galvanizeit.org for "wet storage stain" you'll find some further input.

Ted Mooney, P.E.  finishing.com Brick, New Jersey

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