Corrosion Control in Water Transmission Systems

Water is pumped from temporary storage tanks or from the treatment facilities through large-diameter transmission water pipes. The transmission water piping system contains large valves where the water amounts are measured using water meters. The materials of construction of transmission pipe are cast iron, ductile iron, prestressed concrete, asbestos concrete, PVC and welded steel piping. All of these materials except PVC contain ferrous metal components, which need corrosion protection. The different materials used in transmission are as shown in Table 4.31. 

Ductile iron pipe is used extensively for drinking water and wastewater systems. The pipes are made from the manufactured sections of pipe, with a bell-and-spigot connection sealed with O-rings. 

The most common failure modes of these pipes are uniform corrosion (both external and internal), graphitization, and pitting under unprotected corrosion scales. Loose tubercles may cause blockage of pipes. The corrosion control of loose particles is by the addition of corrosion inhibitors, which protect the inside pipe walls or internal lining of the pipe. Other protective linings are specialty cement mortars, epoxies, polyethylene, and polyurethane. 

In some cases, coal tar has been used, but these pose health hazards and oily organic residues given off by coal tar coatings limit their use. Steel pipes are used for about 4% of the US transmission water lines. The most common corrosion control methods for external corrosion of steel pipes are coatings or coatings and CP. 

1 Effect of Reduced Pipe Wall Thickness Significant problems occur in older transmission pipes made from cast iron and ductile iron, as the wall thickness is reduced by corrosion until a leak occurs. Problems in newer iron pipes are similar to those found in older iron pipes, but occur after shorter time periods because of decreased wall thickness. Therefore, an effective corrosion control method is the selection of thicker wall pipe to provide a larger corrosion tolerance to wall thinning. Expensive thicker wall pipe will be cost-effective because of its long life and low need for maintenance. 

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