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Water Pipe Pitting

02/24/2011 4:26 PM

Recent events have revealed instances of what I describe as "pitting corrosion" from the inside of water pipes. The pipe material is hard drawn copper, it is evident in three different pipe diameters in the same community, but seems to be focused on a particular facility. (A retirement village).

The pitting is very localized (see picture) and seems to originate from the pipe interior. It is not isolated to only the bottom or top of pipe as installed.

The contents of the pipe is potable water from a municipal supply. The water source is stream extraction with Chlorine and Allum treatment. There is pH adjustment before the water is released into the network and the affected property is close to the midpoint of the distribution network.

There have been no complaints from the whole community (not just the affected property) relating to taste, odour or cloudiness of the water.

I'm wondering if anyone has experienced similar issues or has some insight into possible cause.

Locally we have ruled out the following for identified reasons.

"Bad batch of pipe":- Ruled out since three diameters of pipe are affected in the same facility.

"Galvanic" issue:- Ruled out due to internal and very localized failures.

Mechanical damage:- The failures seem to start inside the pipe, there is no evidence on the outside of pipes of damage.

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#1

Re: Water Pipe Pitting

02/24/2011 5:36 PM

Engage a qualified electrician to do a detailed survey and test of the facilities. One possibility is that neutral and earth have been crossed over, and the water pipe is partly connected to the neutral. If so, then it is a safety-critical electrical fault that requires immediate correction, and once corrected the piping problem will probably stop.

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#2
In reply to #1

Re: Water Pipe Pitting

02/24/2011 7:48 PM

Agreed, sounds like you have some electrical "magic" happening. Floating ground, bad ground, etc. Seek an Electrician.

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#3
In reply to #1

Re: Water Pipe Pitting

02/24/2011 9:29 PM

Thanks for the prompt feedback.

I had thought this might be a possibility, but the failures are "inside" the building and the earth connection is within 300mm of ground level in the gardens outside. Thus I'm reasonable confident that the pipes wold not be in any earth/neutral imbalance circuit.

We will definatley check that out, but in Aus, we don't run centre tapped electrical systems, so "earth" and "Neutral" are bonded in the meter/supply box and this place has "current ballance" detection in the electrical cabinet (Active and neutral through same device to verify current balance). A stray current to ground would trip that (Usual disclaimers for threshold levels and such.) system.

Our initial suspicion related to a batch of thin walled pipe that arrived in Aus around 10 years ago, but this pipe has the expected wall section. We also had a spate of copper electrical conduit being used by some plumbers, but this also is not the case in this instance.

My research is tending towards "Type 1" pitting, but there is currently insufficient evidence. The pipe samples arrived from a customer 70km away with no documentation or information on orientation as laid, whether from hot water or cold water lines and the plumber involved hasn't been specific as to which building was affected. If we knew that, then we might be able to determine if there was stagnant water when the house was first occupied (Time lag between plumbing inspection and first water use).

It's currently a mystery that I would like to solve/understand so that we can predict whether all the pipes in the community are at risk (including our underground portions) or whether a single building has some specific issues.

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#4

Re: Water Pipe Pitting

02/25/2011 8:29 AM

Root in this search tree.

Copper pipe pitting

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#5

Re: Water Pipe Pitting

02/25/2011 8:33 AM

Chlorine is corrosive. Are these pipes closer to the water supply than others in the community?

Maybe an enclosed poly/plastic storage tank upstream from these pipes to allow chlorine to become neutralized. Or switch to pvc piping for residential water use.

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#6

Re: Water Pipe Pitting

02/25/2011 8:58 AM

Chlorine and alum? If No Reverse Osmosis water used for a blend, and its the cold water lines. Look to electric faults in grounding. Puzzles like this can drive you crazy but copious ways to pit copper. Good luck.

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#7
In reply to #6

Re: Water Pipe Pitting

02/25/2011 9:01 AM

Yes and what tests have been done for the chlorine/alum system. What is the ph ''balanced'' to?

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#8

Re: Water Pipe Pitting

02/25/2011 10:33 AM

Retirement community?

Is the frequency of the pipes noted less than any of the others in the complex?

Are you sure that there is a backflow preventer installed?

And possible contamination from pharmaceuticals.

The pharms may have no taste or odor.

I have seen the destruction of flushing pharms in drain pipes and it was rapid.

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#9

Re: Water Pipe Pitting

02/25/2011 11:04 AM

I have had a similar situation arise in a retirement complex using municipal water. One of the problems we found in the complex was a lack of real water flow. It seems older people use much less water than younger people and families. What that meant was as the chlorine residual was lost, bacteria (HPC) was gaining a foothold on the interior of the copper plumbing. Most of the plumbing was 2 inch if I remember correct with smaller lines serving each apartment. We did find that in certain apartments, when the taps were first turned on, a slug of high turbidity water was discharged. The turbidity slug was not noted in all apartments and only occurred after the water was sitting idle in the piping overnight. We spent a little time taking plumbing apart to do a visual inspection and were able to detect the slight slime formation on the inside of the plumbing. Once we started sampling first flush water we were able to detect significant levels of HPC (>500 cfu/ml). After the water ran for a few minutes these levels dropped. The biofilm formed was not specified as to the types of bacteria present but indicator groups related to health were absent.

The water problem seemed isolated at the retirement home. The municipal water as distributed met all regulatory quality objectives.

We had thought there may be a problem with the main out in the street and checked it and determined it was fine. We even super disinfected the street main as a precaution. One thing we did note was that the FAC (free available chlorine) was very low and difficult to increase at this point. It was near the end of the municipal distribution system but was looped.

Biofouling can create niches within the plumbing where galvanic cell can set up and cause pinhole leaks. Our objective then became developing methods of controlling the problem. After flushing and superchlorinating the plumbing in the complex we set up controls. There was no recirculation pump installed when the complex was built and it would be very difficult to retrofit. What we did was install a second chlorine (hypochlorination) metering pump and rechlorinated all the water entering the building. We also instructed the custodians to flush water at key locations on a regular (weekly basis). This action helped to obtain FAC throughout the system.

Regards

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#11
In reply to #9

Re: Water Pipe Pitting

02/25/2011 11:58 AM

That's a great answer!

I have a follow up question, just out of curiosity.

Considering that the entire system is closed, and the water from the municipal water supply to the apartments is chlorinated, how was the bacteria introduced?

I think I may have figured it out myself.........chlorine doesn't kill 100% of bacteria. Whatever bacteria survives starts reproducing while standing in the copper pipes at the retirement home.

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#12
In reply to #11

Re: Water Pipe Pitting

02/25/2011 12:53 PM

You are correct - not all bacterias are eliminated in the regular disinfection process! In the disinfection process of the municipal water, surviving bacterias and other chemical byproducts of chlorine reactions, biofilms are produced and clings to the walls of the pipes. It is similar to the accumulation of plaques in our arteries which later on destroys the wall as well as the proper blood flow! To minimize or eliminate biofilm accumulations that are created during the use of free chlorine as a disinfection agent, it should be regularly flushed using another disinfection agent such as a combination of chlorine+ammonia. Low water usages resulting to lower flow further aggravates the situation since bacteria thrives and multiplies faster in such situations!

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#13
In reply to #12

Re: Water Pipe Pitting

02/25/2011 3:21 PM

Kramarat and vsar

Vsar is correct. There are always microbes that are very resistant to chlorine. Once they form colonies and have attached to pipes, there is a new consortium of bacteria that take over. Some of these bacteria actually can go dormant when environmental conditions for their survival are adverse. These guys are tricky and have been around a long time. The underlying side of a biofilm can become very reduced (chemically) and then you have ideal conditions for pitting. What we used in wells that were severely biofouled (biofouled = biofilms that are advanced enough to affect quality or quantity) was a strong dosage of hydrogen peroxide at about 900 mg/L and a contact of 2 hours. The peroxide would penetrate the biofilm and the oxygen evolved would scrub the area. The biofilm could then be flushed.There are many forms of bacteria in the consortium and isolating speices is expensive and not very good at giving good information. You get everything from molds, yeasts, bacillus types, etc. HPC evaluation only measure the density of bacteria found under aerobic conditions. To evaluate anaerobic HPC would be again very expensive, time consuming, and not provide goodinformation. It does not take very much food like TOC, P, etc to drive these biofilms.

The site I mentioned was actually done about 10 or 12 years ago and the biofouling issues have disappeared as well as the pitting of plumbing. We targeted Free Chlorine and did not use ammonia in the process. Introducing Ammonia with chlorine is called chloramination and may actually create taste and odour issues. Also it is not as powerful a disinfectant as free chlorine. Many municipalities practice chloramination to control chlorine/organic byproduct formation like trihalomethanes and haloacetic acids. It is OK if you have a problem with THM or if you are trying to get persistent residuals out into a distribution system. I never measured the THM at the retirement home but the municipality did by regulation and do so near the retirement home....no problems. Prior to our company evaluating/installing the remedy, the plumbing had been one of those head scratchers for the municipal staff.

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#10

Re: Water Pipe Pitting

02/25/2011 11:30 AM

Usually after a piping job is finished the system is flushed and chlorinated water is injected into the system. This is usually circulated to disinfect the installation. If this water, which has considerably higher chlorine contents than the drinking water we get, is not flushed out and is allowed to remain in the pipes it can adversely affect the life of the copper tubing and cause premature failure.

If this is the cause than the problem could be building specific, if it was accidental or universal if that was the modus operadi of the plumbers.

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#14

Re: Water Pipe Pitting

02/25/2011 10:10 PM

Besides Ph, there is 'hardness' in water, which can affect plumbing. Locally we have a hotel with this problem. Someone told me the water there was 'agressive'. It's a big problem, the pipes go everywhere.

Also, I have seen stainless steel pitted by 'oxygen deprivation'.

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#15

Re: Water Pipe Pitting

02/26/2011 8:00 PM

The Washington Suburban Sanitary Commission (WSSC) in metro Washington, DC, had a similarly puzzling problem with pitting in copper potable water pipe. They conducted extensive testing and their findings might be of use to you, particularly with respect to the role of chlorine, aluminum and organic material. Start here:

http://www.wsscwater.com/home/jsp/content/pinholescroll.faces?pgurl=/EngAndConst/recent-phl-research.html

Good luck!

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#16
In reply to #15

Re: Water Pipe Pitting

02/26/2011 8:51 PM

Interesting article, and it makes me wonder what the MTRs and/or chemistries of the pipe in question would show. I doubt that strict quality control is adhered to in the tube mills.

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#17

Re: Water Pipe Pitting

02/27/2011 3:52 PM

Thanks all for the wonderful replies and links.

A very special thanks to post 9 and the insight there.

I had already trawled the entries for "copper pipe pitting" and such and the Washington documentation and while many explained the chemistry behind the three different types of pitting but were general in their description of the instances that had brought about the investigations.

We can check for microbial content, and that may confirm the presence of that cause.

I will try to have the buildings checked for the rounting of the plumbing and where specifically within those lines the concerns are noted. There will be "dead end" lines in each property that will have lower flow than others providing opportunity for significant "stagnation" for the microbes.

Again, thanks all for your help.

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Anonymous Poster (1); aurizon (1); honur (1); Just an Engineer (2); Karl Hungus (1); kevinm (2); kramarat (2); mike k (1); PWSlack (1); qaqcpipeman (2); RVZ717 (1); THE RPR (1); vsar (1)

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