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Erosion Corrosion of Copper Water Piping System

ENVIRONMENT:

Potable Water for Office Building

EQUIPMENT:

Water Supply System

SERVICE TIME:

11 Years

FAILURE:

Erosion Corrosion
 
Water pipes for an office building started leaking after seven years of service. The leaks were primarily on the fifth floor where a booster pump pumps the water to the upper floors. The water pressure to the inlet of the pump was very low or negative. As the pump took suction on the city water feed, it lowered the pressure even more, removing air (oxygen) from the water. Small bubbles of air then entered the water stream on the discharge side of the pump at high pressure where they were carried along throughout the remainder of the water system until they were re-dissolved in the water. While they were being carried along and before they were re-dissolved, the air bubbles scrubbed off the soft but protective film of copper oxide allowing corrosion as well as erosion to locally attack the pipe system, Figures 1 and 2. In this system, it was particularly noticeable in the hot water sub-system (where the corrosion rate is higher), in the top portions of horizontal pipes and in high velocity turbulent locations of other piping where air can accumulate and be swept along at relatively high velocities.
 
Figure 1. Section of copper hot water pipe; notice the erosion marks Figure 2. Air bubbles eroded the brass pump impeller

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