Galvanized Steel

Galvanized steel piping is widely used to handle water, particularly fresh waters.  It relies for its corrosion resistance on the formation of protective films of zinc and calcium carbonate.  This means that medium and hard waters, with a total alkalinity>100mg/L (as CaCO3) and a positive Langelier Index will form protective scales.  However, soft and particularly soft, acidic waters will not be able to form scale and they will corrode more rapidly.  However, the low conductivity and low dissolved solids content of such waters means that the corrosion rate is usually low enough to be acceptable (<0.1mm/y).

In seawater galvanized steel offers no advantages over bare carbon steel.  The reason for this is that, despite the total alkalinity of seawater exceeding 100mg/L, the high chloride content means that zinc corrosion products are soluble at normal seawater pH (8.2).  Hence, the zinc layer dissolves rapidly and then the pipe corrodes just like carbon steel.

Posted on: 21st Feb 2017

< NewerArchiveOlder >

Image (top left) by Agnieszka