I noticed while working in my crawlspace that a lot of the copper pipes have a patina on them. One cold water supply line seems to be so badly corroded that drops of water are forming along the bottom:



It isn't presently very humid in the crawlspace, and all of the other pipes are dry to the touch. However, during the rainy season (winter) it gets very damp and there is standing ground water in this crawlspace. I do need to find out why, and address the root cause.

I will replace this pipe soon. I'm posting here to better understand what's happening:

1. How long would you expect this pipe to last before catastrophic failure (spraying at least a small jet of water)?

2. Is it likely that the ambient moisture is causing the corrosion, or is this worse than what you'd expect in a wet environment?

3. I see that this pipe may be in contact with steel conduit. I also noticed that ~20 feet away (outside on the deck) it is supported by steel pipe tape. Is it possible that galvanic action is causing corrosion far away from where the dissimilar metals are touching, or is the problem more likely to be localized?

That is truly a horror picture straight from the depths of hell.

Notched / weakened structural joists.

Copper tube supporting metallic 'tube' of some sort.

Uninsulated water piping in a crawl space.

Improperly supported piping.

Galvanic action may, or may not, be an issue.

If it is 'M' tube it needs replacement ASAP.

It may, or may not, be corrosion from the inside - out.

It may, or may not, be simple condensation depending on the 'dew point' of the air and the temperature of the running cold water.



LICENSED BONDED INSURED Plumber required

AND

a skilled framing carpenter.

Not condensation IMO. The weather isn't humid and none of the other nearby pipes have any sort of moisture on them.

I'm going to replace it but I want to better understand what caused the damage in the first place. If it is galvanic or electrical, then that will eat the new pipe until I find the source.

I have another length of brand new copper, installed last year by a plumber, which has a patina on a ~6in segment in the middle. It's not touching anything. I want to fix whatever is wrecking my pipes, rather than playing whack-a-mole with it.

Is it 'L' or 'M' tube?

You do NOT want to install 'M' tube (albeit minimally code compliant) due to its thinner wall thickness.

You will need to insulate the tube from other metallic contact.

You will need to insulate the tube to prevent condensation.


A 70 degree crawl space with 70% humidity will condense onto a 60 degree uninsulated cold water pipe. The CW pipe will become the temperature of the water when running.

see: [www.truetex.com]





also: Cu tube does not, repeat not, like acidic water - it likes sliiggghty alkaline


what is the pH of your water ?



Edited 1 times.

I doubt there is galvanic corrosion going on between the steel conduit and the copper pipe.

First of all for galvanic corrosion to happen there needs to be constant moisture between the two metal. It doesn't appear to be that way.

Second, copper is a more noble metal than steel or galvanized steel, so if galvanic corrosion happens the steel conduit would be the one corroding badly and it looks fine.

If you are worried about galvanic corrosion or movement between the pipes rubbing against each other, one temp solution is to insert a piece of tar paper or roofing felt in between.

I looked again from another angle and the copper+steel pipes aren't touching. Also, the copper was dry the second time so perhaps it isn't rotted through.

This is located underneath a laundry room and near a questionable-looking dryer vent duct. I'm wondering if the drips were caused by moist air escaping from the dryer vent (more likely) or by leaks from the washer drain (less likely, because I didn't see leaked water elsewhere). I'll head down there again with the dryer running to scope it out.



Edited 1 times.

>Not condensation IMO. The weather isn't humid and none of the other nearby pipes have any sort of moisture on them.

Condensation occurs as a function of the temperature of each pipe, the temperature of the air, and the humidity. It often occurs on cold water pipes that drop below the Dew Point that Bern mentioned.

The water drops on the pipe are likely caused by corrosion, especially if the copper is touching steel. When different metals touch, it can cause corrosion to happen faster.

Since there are water drops, the pipe might not last long before it starts leaking. It’s best to replace it soon.

The damp air in the crawlspace is probably making the corrosion worse, but the contact with steel is speeding it up.

Corrosion usually happens where the metals are touching, like the steel conduit or pipe tape, so the issue is likely close to where they’re in contact.

Replacing the pipe and making sure it doesn’t touch steel should fix the problem. You can check @#$%& for replacement parts if needed.