What can cause a never-frozen indoor copper drain pipe to crack?

Question

The 1-1/2" copper waste pipe than runs from our kitchen just up and cracked two days ago along its length, and for no apparent reason.

The crack is in a section of pipe that runs vertically through the kitchen floor down into the basement, where it connects to an angled length of pipe (two 45-degree elbows) and then a section of pipe that connects to cast iron sewer pipe (lead and oakum seal).

I would venture to say that this cracked pipe is from the 1970s (when former owners remodeled the kitchen) and that the section of copper pipe (which didn't crack) going into the cast iron hub dates from around 1948-49, when the house was built.

Could the crack have been the result of twisting forces when the pipe connection was made to the garbage disposal beneath the sink? Or does copper waste pipe just eventually give out, perhaps because of corrosion over a period of 50 years?

Answer 1

I would inspect the entire property for more such pipe and replace any that was found. That's almost certainly a manufacturing defect and likely to be pending failure wherever that batch of pipe was used.

That is not a natural crack, nor a corrosion crack, it's too straight and uniform.

Typical "natural" cracks look like:

   

Possible ways it could have formed:

• There was a defect/contamination in the extrusion die for that batch of pipe, propagating weakness down the length of pipe as it was extruded.
• The pipe was rolled rather than extruded and then poorly joined (trying to make it look seamless).
• Something/someone else uniformly scored the length of the pipe before it was installed.

Then after some years of thermal cycles and possibly mild corrosion, a crack formed and rapidly propagated along the rest of the weak line.

Answer 2

Copper does erode over time through mechanical wear and chemical corrosion. My guess is that it simply got thin enough that thermal stresses popped the weld (or the extrusion resulted in a thin side, causing a very straight crack).

I'd put in plastic and be happy.

Answer 3

Back in the 1970's the company that I worked for ran into a slew of copper tubing sizes through 3" that was manufactured with a defect that weakened the whole length of the copper. Since the copper was new the supplier replaced all the tubing (pipe) that was installed. This could be a similar problem. As "Isherwood" said, just replace it with plastic. I have to add this one comment; it turned out that the copper tubing was foreign made in a newer factory using a questionable process. That is what we were told at a later date.

Answer 4

Having worked with brass chrome, my personal bet is it just got old. I wanted to teach my son how to use a wrench and when he went to crank off the old nut, the pipe shattered like an eggshell. Yours looks like a a small crack just gave way, which doesn't surprise me at all. These older pipes are not terribly thick either (the cast iron drains look to be just fine).

Cut off the old pipe and use a compression coupler (like a Fernco) to make the transition to PVC.

Answer 5

It looks like it was thinned by corrosion until any stress opened it. Ammonia and it's compounds are notorious for attacking copper alloys ; Ammonia cracks brass not copper, but corrodes copper quickly. Maybe a previous owner liked to use ammonia for cleaning in the sink. That is why brass flex-tubes are not permitted for gas service, ammonia cleaners are common in kitchens and utility rooms and they will stress corrosion crack brasses rapidly. The answer is still replace with plastic.

Answer 6

I'll just throw one more thing into the mix. You say it was connected to a garbage disposal so I'm thinking that vibration, over time, might have either caused the problem or made an existing defect in the pipe worse.

In the end, though, the advice to replace it with plastic and move on is good.

Answer 7

Being made of copper caused it. Copper is a completely unsuitable material for a pipe which will be handling waste water, which will contain all sorts of substances that will chemically (corrosion) and physically wear away at it.

Answer 8

The environment and any known history are clearly clues, however I tend to think of the copper refining process, a "manufacturing defect" someone mentioned. Impurities quite possibly. Is it similarly split in other places in the house of similar or different ambient environment. If isolated, replace and watch. Not to tough a job for someone with plumbing skills I would think. Tougher for me, I deal with wood. Not too much call for a carpenter in the plumbing trade.

Answer 9

My vote is a defect in the forming die caused a stress concentration. Stress corrosion cracking appeared here from residual built-in forming stresses. A corrosive environment and the residual forming stress propagated the crack along said stress concentration.

Was there evidence that the crack had been growing for a long time (mold or similar at/around the failed location)? The fact that two different pipe sections (likely cut from the same "mother" pipe) failed in similar fashions would, in my opinion, point to something not really dependent on the part's stress environment (other than the built in forming stress), since that external load would cause different stresses at different locations in the pipe.

Answer 10

Looks to me like water hammer! Over the months have you heard "bang bang bang...", for instance when the water that's been travelling along the pipe has had to come to a sudden stop?