Pinhole Leaks in Copper HW Piping

Hi All,

I am sure this has been covered in the past, but i think i have a fairly interesting situation on my hands. The situation is this, pinhole leaks are a wide spread issue in the domestic hot water and heating hot water lines at a small apartment building in the Northeast. The pinhole leak issue is expansive and pinholes can be found approximately every 2 feet on the above mentioned hot water lines. All water lines in the building are copper. It was noted that the city water main (galvanized steel) inside the building is piped directly to the copper water lines of the property, also no dielectric unions appear to be installed on the hot water leaving the natural gas boiler. In addition it appears pipe hangers are another source of corrosion on the hot water lines, as they appear to be lacking a rubber or plastic seat. What is confusing about all of this is that the domestic cold water lines are not experiencing the same pinhole leak issue. All of the corrosion is taking place on the DHW and HW piping.

My first assumption is that we have galvanized corrosion happening due to the lack of dielectric unions. But since we have two dissimilar metals in contact and corroding at the entrance of the city water into the building, i would assume the cold water lines would also be affected.

Does anyone have any bright ideas as to what is going on here? If pictures will help, i can get some uploaded. Thanks for the help.

In time, copper pipe starts to erode based on pH level and/or Chlorine in the water.
I believe heat accelerates this problem.

EDIT: I don't believe the copper erosion is the result of the connection to the galvanized steel pipe. It is rarely the copper tube that fails because of galvanic corrosion.

I have multiple rental properties (row homes) in one development that was built in the late 60s and early 70s. They used copper for both the supplies and for the waste (3 inch copper that transitions to 4 inch cast iron in the basement). In any case, I have seen the same thing in these houses, multiple times, on the supply pipes. Typically, when a tenant would call and tells me about a leak, when I opened the wall or ceiling, I would find that the pipe has a green stain at the point of the leak, and the leak is usually a pinhole. The simple solution while a tenant is living at the property, is to cut out the bad section of pipe, and re-install a piece of pex and two shark bite couplings, and repair the wall or ceiling. When the tenant moves, I will typically remove all of the old copper (supply and waste) and replace all of it with pex (supplies), and schedule 40 pvc(waste). Once I have done that. I have not had any problems. I have 2 properties left to do, once the tenants move. I then take the old copper to a metal recycling place, and usually get enough money from the copper to more that pay for the materials needed for the re-piping.

I have seen that type of deterioration in copper tube as well on both hot and cold piping. Had a house that only the H & C horizontal runs in ceiling to kitchen seemed to be effected.
No galv piping.
I think it has something to do with PH of water also but not really sure.
Sorry I’m not much help on the cause

This is pretty interesting

It is pinhole corrosion, caused by small particles of something on the inside of the line acting as a locus for electrical currents. Wikipedia has a good explanation in the “copper tubing “ articles corrosion section. The solution is proper bonding.