Metallurgical failure analysis was requested of a corroded residential copper water pipe following a water leak in a private residence. Two small sections of copper tubing, one approximately 5/8 x 4 and 0.40-inch wall and the other approximately 7/8 x 8 1/2 x .52-inch wall were submitted for visual examination and metallurgical failure evaluation. Three water faucet stream diffusers and an attachment ring were also submitted. Due to the limited extent of the residential damage, no destructive testing, metallographic, x-ray diffraction, spectroscopy, or chemical analysis was authorized. No water chemistry was available.
The smaller 5/8-inch diameter section was visually examined. The section of water pipe had a small, elliptical shaped through-the-pipe-wall hole, 0.100 x 0.120-inches, as shown in Photograph A below.
Photograph A Smaller water pipe with the pipe wall hole denoted by a white arrow.
The larger section of water pipe shown below in Photograph B did not contain a through-the-wall perforation, however, the outside surface exhibited green external corrosion as well as non-uniform areas of darker oxide.
Photograph B Larger section of water pipe with green external pipe corrosion.
Photograph C Clogged water diffusers/strainers.
The smaller 5/8-inch diameter section of water pipe was cut longitudinally to facilitate the inspection of the water pipe's inside surface. The resulting longitudinal sectioned copper pipe is shown in Photograph D.
Photograph D Split, smaller section of water pipe.
The inside pipe surface shown in Photograph D contained light to dark green friable or fragile corrosion products. The darker green deposits were often in the form of tubercles, which once easily dislodged, revealed a corrosion pit filled with corrosion product. These corrosion filled pits are illustrated in Photograph E below.
Photograph E Inside surface of water pipe showing corrosion/corrosion pits.
In Photograph E above, the corrosion deposit in the area in the center of the tube located just above the 3-inch marker is loosely held. This corrosion product was lifted and turned over. Photograph F shows the same area after lifting and turning over the corrosion deposit.
Photograph F Area in which corrosion deposit was lifted and removed, revealing interior wall pitting corrosion.
The light green deposit within the copper area is corrosion product and is the result of pitting corrosion. The pits extend into the copper tube. Had this corrosion been allowed to proceed, a through-the-wall perforation of the water pipe would have resulted. A stereo microscopic (magnification 70x) view of the through-the-wall perforation is shown below in Photograph G.
Photograph G Close-up view of through-the-wall perforation of copper water pipe.
Clearly, there is less evidence of the dark green tubercle corrosion product on the larger section of tubing. However, removal of the light green corrosion product did reveal some minor pitting and pipe wall surface attack.
Photograph H Limited internal corrosion within larger tubing piece of copper water pipe.
Cold water pitting is well recognized since the research of H.S. Campbell. It is characterized by friable or fragile nodules (tubercles) with underlying corrosion pits on the waterside of copper tubing.
Metallurgical failure analysis showed clearly that the copper tubing wall was initially compromised by pitting corrosion resulting from the water chemistry being delivered to the residence.