Stray Current Corrosion of Copper Water Pipe

A section of corroded copper water pipe was submitted for examination and failure analysis. An overall view of the subject copper water pipe is shown below in Photograph A.

Photograph A  Overall view of corroded
 copper water pipe submitted for failure
 analysis.

The subject pipe was examined visually and using the stereomicroscope. No visual evidence of pipe perforation was observed. External corrosion and roughening of the outside pipe surface was clearly evident. A close-up view of the corroded surface of the subject copper water pipe is shown below in Photograph B.

Photograph B  Close-up view showing
 corrosion/pitting of external surface of
 subject copper pipe.

The subject copper pipe section was pressure tested with a soap bubble solution and by water submersion while pressurized and still no perforations of the copper pipe wall could be detected. The soap bubble solution and submersion tests are shown in Photographs C and D, respectively.

Photograph C  Subject copper water pipe
 being pressure tested (soap bubble test) to
 locate pipe wall perforations.

Photograph D  Subject copper water pipe
 being pressure tested (submersion test with
pipe pressurized) to locate pipe wall perforations.

No pipe wall perforation was noted visually or with the stereomicroscope. Soap bubble and submersion pressure testing also failed to reveal any pipe wall perforations. The highly pitted, striated external surface is characteristic of corrosion resulting from electrical activity. This form of corrosion is commonly referred to as stray current corrosion. The source of this electrical activity was unknown and undetermined.