Corrosion of copper water line?

[ACtrafficengr]

A village water department suffered a failure of a water service line installed under one of our highway projects roughly 8 years ago. It's a 1" lateral that serves a local diner.

The copper line was heavily pitted and perforated from the inside out. The copper on the inside looks almost silver, as if it was plated with some other metal.

It was backfilled with course sand meeting (or supposedly meeting) NYSDOT specs for select granular fill.

Based on this article, I suppose the first steps might be to test for sulfates, chlorides, stray electric currents, etc.

If anyone has any additional suggestions, I'd really appreciate it. This is, as you might expect from my handle, a bit out of my area of expertise.

Maybe the tyranny of Murphy is the penalty for hubris. -

http://xkcd.com/319/

 

[ACtrafficengr]

PS: I did find this thread:

http://www.eng-tips.com/viewthread.cfm?qid=104480

Maybe the tyranny of Murphy is the penalty for hubris. -

http://xkcd.com/319/

 

[bimr]

Hard to say without seeing the tubing.

A couple of observations:

The 1-Inch pipe size is too small for a restaurant. Would expect that a high water velocity would be contributing to the corrosion problem.

The location of the tubing under the road would indicate that the tubing is exposed to road salt. Is the pitting on the exterior or interior? Other metallic piping systems that are located near roads have also experience corrosion due to road salts.

Have other water services experienced corrosion? If not, there is lttle reason to expect that the water quality is the problem.

 

[ACtrafficengr]

Thanks for the reply.

Looking at the pipe again, it could well be erosion from velocity and turbulence, not corrosion:

[ul]
[li] I was wrong - the pipe i.d. is ~0.7, not 1". Even though it's a tiny diner, but they'd still use a lot more water than a residence.
[li] the inlet end was cut square, with a burr on the inside, not smoothed or reamed in any way.
[li] The pitting is from the inside out, with only a bit of oxidation on the copper.
[/ul]

I've attached a photo. For scale, that's 1/4 graph paper.

We'll have to check the plans, and see if it was a mistake by the designer or the contractor.



Maybe the tyranny of Murphy is the penalty for hubris. -

http://xkcd.com/319/

 

[ACtrafficengr]

Oops. Here's the pic:

Maybe the tyranny of Murphy is the penalty for hubris. -

http://xkcd.com/319/

 

[ACtrafficengr]

Hmm. try again?

Maybe the tyranny of Murphy is the penalty for hubris. -

http://xkcd.com/319/

 

[ACtrafficengr]

One more once, w/o the url in my sig?

http://files.engineering.com/getfil...803a-455d-a4c7-28be5a71cc4e&file=DSC00832.JPG

 

[bimr]

You appear to have the typical erosion/corrosion of turbulence and velocity. See the attachment.

 

[ACtrafficengr]

bimr, it looks like you've had the same attachment issues I did. I ended up pasting the URL directly into the message text box, rather than using the "step 3" box.

 

[bimr]

Attachment

 

[rconner]

Am curious what is coupling or fitting partly out of view? Any chance "silver" area that looks like plating of other metal IS other metal (solder)? [As to "erosion" silver interior surface appearance, as well as fluid velocity limitations I notied in the linked douments, for copper pipes are interesting. While copper pipe is much harder than most of the plastics, e.g. as can be observed in Figure 8 of the site at

http://www.calce.umd.edu/TSFA/Hardness_ad_.htm

and other references, it is much softer than e.g. steel or ductile iron etc.]

 

[ACtrafficengr]

It's a compression fitting coming off the T in the main.

 

[dicksewerrat]

I think it is a combination of velocity and a sligthly acid water . A compression fitting should NEVER be buried. Use flared fittings. My guess would be that the diner needs at least a 1" tap and 1 1/4" line. May have to talk to the local water authority now that there is some consumption history for the proper size.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[hydrae]

Does the restaurant have flush-o-matics? (tank-less toilet and urinals) even if you have low overall consumption, a flush-o-matic pulls 20 to 30 gpm for the first second or two of the flush.
Minimum size for just one flush-o-matic is 1.25". Add in a commercial 90 second cycle time dishwasher and you have some very high velocities.

If you replaced the line like for like, then require the restaurant to install a large hydro pneumatic tank to reduce the surge velocities or replace the flush-o-matics with tank type toilets.

Hydrae

 

[rmw]

The black indication on the surface says sulphur to me.

rmw

 

[ACtrafficengr]

Apparently, the same thing happened on a residential line, also.

 

[hydrae]

Have you put an clamp-on amp meter around the copper service line?
If one location has a bad ground with a damaged element in the electric hot water heater, it will corrode service lines for hundreds of feet in the area.

You may have to wait until the hot water heater cycles on to see the stray current.

Other cases show up as the electric service uses the water line as the neutral due to bad earth ground and lacking an adequate service line neutral. The current will follow the water line to the neighbors earth grounds and neutrals to close the circuit.

Hydrae

 

[bimr]

Don't believe that stray current has anything to do with your corrosion problem.

The electrical code has required for some time that if the electrical service is grounded to a water pipe, an additional earth ground is required. In addition, metallic hot water pipes and cold water pipes are required to be bonded together at the water heater.

Your picture shows corrosion on the interior of the tubing. Note that stray current corrosion will occur on the outside of the tubing, not the inside. That is because the current actually travels on the outer surface of the wire (or tube) not on the inside of the wire.

Here is an additional reference for erosion corrosion:

"As has been emphasized, copper water tube is highly dependent upon the formation and maintenance of a protective film on the inside to provide a long trouble free service life. The film is not hard and abrasion resistant, but rather soft and easily damaged."

"An even more conservative recommendation limiting water velocity to a maximum of 4 fps has been published by the National Association of Corrosion Engineers (NACE)."

http://www.wssc.dst.md.us/copperpipe/copperpipewp.cfm

 

[rconner]

When you say the "same thing happened" also on a (one would think more normal flow) residential service, do you mean a similar perforation in roughly or exactly the same location/goose-neck? area immediately off the main? This brings me to a couple other questions in additions to those already asked, has anyone looked at the external or internal condition (or measured wall thicknesses et.) at other locations of the services in question? [I ask these questions, of course, in that it might be argued (with regard to at least the internal erosion and/or corrosion theories) that roughly the same conditions might arguably exist to some extent/be contacting the inside of all areas as well]. What kind of main and specific type of corporation? connection to same is involved?

I once read that some Roman copper water pipe was found intact after 5,000 years of burial -- while I agree it is hard to tell much just from the picture, it would certainly appear however you had at least something going on here the Romans didn't have!

 

[rconner]

[Oops, in retrospect I don't think Rome as such, or even Romulus and Remus, were around that far back! -- very early and old copper pipes were probably in Egypt)