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Pinhole leaks copper piping

Mark Eatherton
Mark Eatherton Member Posts: 5,853
All of these suggestions are valid and excellent. If in fact it is Hydraulic Erosion Corrosion, when the pipe is split length wise, there will be U shaped tracks associated with HEC. There may also be a corrosion tubercle. In some cases, if aluminum is present, wherever it displaces a few ions of aluminum into the copper, it will cause localized electrolytic corrosion cells. These look like a miniature mounds on the inside of the pipe.

As as been pointed out, no DHW circ return system should be without flow control, time of day operation and return temperature operation. I prefer to use GRAVITY circ returns whenever possible. Erosion corrosion is virtually eliminated. The only side consequence is that if the plumber ran the cold, hot and circ return in the same floor joist bays, you will NEVER get a drink of cold water from the tap so long as you may live in that house :-) Keep a pitcher of water in the refrigerator for cold water.

As a former plumber, I too was guilty of violating that rule. If I were to do it again, I'd run the circ return and hot water lines with at least on joist bay of separation betwixt it and the cold...

The fact that the leaks are occurring immediately after the elbows could indicate HEC, or as Glenn S pointed out, it cold be flux corrosion.

The CDA went back and re-reviewed many of its HEC diagnosis' and determined that it was actually FLUX corrosion that was causing pitting and consequent failure.

Aluminum pitting generally occurs more in cold water lines that it does hot water lines, but has been seen in both.

I personally suspect that PEX lines are also subject to HEC, it's just that they have a thicker material wall to burn through before they present themselves as a leak. I suspect that in situations with higher concentrations of chlorine, this failure rate will be accelerated.

I have witnessed the HEC equivalent in Poly Butylene plumbing lines with excessively large pumps.

Only time will tell....


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  • Ron S_2
    Ron S_2 Member Posts: 7
    pinhole leaks copper piping

    Help. I've had 4 pinhole leaks in my basement copper piping in 3 months. The copper tubing is only 4 years old. All the leaks have been in the hot water circulator return line, and within 6 feet of both the 4 year old W-M indirect hot water heater and the Taco circulator pump.

    The home is well grounded according to the electrician. Water is supplied by Long Island's Suffolk County Water Authority.

    How do I diagnose and fix the problem? How do I determine which pipes are so damaged that they need to be replaced?

    Neither the electrician, plumber, or water authority have any suggestions.

    Ron S.

  • Brad White_203
    Brad White_203 Member Posts: 506
    Water Velocity and Quality

    Where on the piping does this occur? At the elbows for example where velocity pressure makes a turn? Or on straight runs? Is it at a solder joint or through the wall itself?

    Do you have a sense of the velocity in the piping? Water pressure, is that excessive (over 80 PSI)?

    Is the area known for water quality issues? I have no idea what LI Suffolk has for water quality.

    As one example, north of us there is Cambridge, MA, where they have their own water system separate from nearly every surrounding town. I suppose in general, that is a good thing, for there is something in their water besides minerals.... :)

    Anyway, they have high mineral content, magnesium I believe among other things; a white powder precipitate comes out of solution especially in ultrasonic humidifiers. But that water is notable for eating copper. Just a thought.

    What issues if any do your neighbors have?
  • Paul Fredricks_9
    Paul Fredricks_9 Member Posts: 315

    It seems to me that a domestic water pipe would have more of an issue than a heating pipe if water quality is an issue.

    If it's all in the same pipe, or all in the same diameter pipe, maybe it was a bad pipe. I've seen it before, but usually with soft drawn copper.
  • Paul LeGron
    Paul LeGron Member Posts: 11
    Pin hole leaks in copper

    It sounds like to me that you are experiencing erosion from the inside out do to turbulence caused from the piping not being reamed properly. I have found this in the past.

  • Home Depot Employee
    Home Depot Employee Member Posts: 329

    Also remember improper electric isolation or grounding methods with copper piping contribute to pin-hole leaks also.
  • MikeyB
    MikeyB Member Posts: 696

    It might be a bad section of tubing, if it's "M" tubing try replacing it with "L' or "K" tubing, Long Island water is pretty hard from what i hear. I have seen this happen on domestic use in Manhattan, 3/4" type L on a domestic hot water line, 2 pinholes in one month, only a few feet away from each other on the same length of tubing. The holes were right on the tubing itself not near the fittings.
  • Ron S_2
    Ron S_2 Member Posts: 7
    Water Velocity and Quality

    Hi Brad --
    Two of the leaks occured on the elbows, right at the turn on the side. One occured about 2" from the elbow. All were through the walls, not the solder joint.

    Don't know the velocity, but the nearby circulator pump is a Taco-006 at 3250rpm. Water pressure tends to be on the low side.

    Regarding water quality, the water authority insists it is good, but we have lime-like sediments in the main shower.

    Haven't heard of the neighbors having any issues, but both homes are vacant at the moment.

    Thanks again,
  • As an aside...

    in Manchester, CT they add lime to neutralize the water as it is acidic to start with and will leach the lead out of the old pipes that still have lead solder in them. It also produces a white powdery film when used in cold spray humidifiers. Played hell with the pricey cigars in a walkin humidor I know of. This may be the same thing going on with the white residue mentioned back a few posts.
  • tim smith
    tim smith Member Posts: 2,774
    It sounds like to me that maybe a combination of things,

    sounds like the recirc pump is larger than you need, causing too high velocity. Also very possible that the copper tube was not reamed and will do exactly what you are talking about. Good luck
    EBEBRATT-Ed Member Posts: 15,840

    I have never seen this in a heating system.

    On a domestic water job (my boss's house) we had recurring leaks in the cold water but the hot was ok. We did some reasearch and the most reasonable conclusion was to much flux of the corrosive varity. The hot water would flush it out and the cold water would not. Thats why I use "NOKRODE Flux"

  • I've seen it

    on heating pipes and hot water . And it's usually just one piece of pipe .

    My best guess ? The copper pipe itself was made with a defect . Why not ? Alot of the other parts we work with aren't made with quality in mind anymore .
  • Derheatmeister
    Derheatmeister Member Posts: 1,572
    Like someone used an Drill

    I've seen it on both Heating/ domestic waterlines!

    A piece of Iron shavings from some one working on the lines was flushed into the piping...

    The two different metals react.. and the Copper is the one that losses this battle...

    The worst one that i've seen was in Germany were the water was spraying from the ceiling onto the piano..

    It looked like someone drilled an hole into the pipe..

  • Doug_7
    Doug_7 Member Posts: 247
    Velocity-Assisted Corrosion

    What you have is velocity-assisted corrosion. This will occur in copper DHW recirculation systems with too high a water flow velocity. The result is pinhole leaks.

    The pinhole leaks typically occur at points of high water turbulence, such as at burrs on the unreamed pipe ends, at elbows or even at imperfections in the straight pipe.

    Copper water piping is protected from corrosion by a copper oxide film inside the pipe. The water would corrode pure copper, but the copper oxide film protects it. Localized turbulence at one spot - like a burr, scrubs away the protective film, the copper corrodes and eventually you get a pinhole leak.

    This will continue to occur until you reduce the flow velocity. Velocities up to 8 feet per second are OK for cold water pipe and 4 – 5 feet per second are OK for hot water piping. For Domestic Hot Water recirculation systems the velocity needs to be kept below 2 – 3 feet per second. Remember that it is scrubbing away the protective film 24 / 7 / 365.

    The main causes are too big a pump, too small a pipe diameter and no flow-control.

    There are several things you can do. First – check your pump curve and figure out the flow velocity. I will bet it is over 10 feet per second.

    The simplest cure is to install a throttling valve on the discharge of the recirculation pump and throttle the flow way-back. Judge if you have enough flow by the recirculation return water temperature. Strap a temperature sensor on it. Shoot for 10* F to 15* F below the supply temperature.

    I have a UP 15-10 B5 Pump with a 3/4” globe valve that is only 1/2 to 3/4 of one-turn open. That is plenty of flow to maintain a warm return with insulated DHW piping in a 45,000 sq ft building.

    It really helps if the DHW supply and return piping is insulated. That will reduce the flow required to maintain a warm return to about 1/4 to 1/3 of the flow required for un-insulated pipe. Saves energy too. Timers that shut off the recirculation flow when not needed, also help.

    Piping design is important. On supply piping - we start with a large line then reduce the line size when lines branch off. When we design recirculation returns - we should increase the line size when different return flows combine. Never use less than 3/4” piping in DHW recirculation systems.

    It is all about reducing the water flow velocity to minimum.

  • Doug_7
    Doug_7 Member Posts: 247
    Velocity Assisted Corrosion - 2

    The attached Information Sheet from the Canadian Copper & Brass Development Association explains Velocity Assisted Corrosion (Erosion Corrosion) quite well - with diagrams.

    The 2 - 3 feet / second I referred to is from other sources.

    The lower the flow velocity the better.

  • Jamie Hall
    Jamie Hall Member Posts: 23,657
    check your pH

    it is, most likely, a velocity problem -- but low pH won't help a bit, and it is possible that you have a pH problem as well...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592

    While all the comments above may be valid, another contributing factor may be from the flux used to solder the joints.

    If the piping laid dormant for an excessive amount of time (2-4 months) after the joints were soldered, without being flushed/filled with water, small pin-holes can develop in the copper from what I believe is amonium-hydroxide crystals - a chemical component of the flux.

    This was determined from a joint panel about 30 years ago looking into leaks that occurred during/after the trac building boom in the late 60's and 70's. The panel consisted of a representative of the copper institute, Utility chemical, Embassy industries, and 2 trac plumbing contractors, myself (representing a wholesaler), and a couple of other industry people.

    Besides this conclusion, the instructions on a can of flux (from Utility Chemical) were changed on the side of the can from "apply liberally", to "apply a small amount" .

    My $.02

  • Ron S_2
    Ron S_2 Member Posts: 7
    Velocity-Assisted Corrosion

    I thank all of you for your input on this. An update: I had the water tested today -- results will take some time, but the Water Authority did test for grounding and current, and everything was in order: grounding was fine, no current flow anywhere near the indirect heater, circulator, or thermostat.

    Some whitish scale is evident in the damaged tubing. Again, it could be all the lime that the water company dumps into the well station down the street.

    To answer Doug's question, I do not know what the flow velocity is off the Taco 006. I can trim down the flow as there is a valve between the Taco and the indirect heater.

    The tubing is 1/2" (interior diameter) type L (I have no idea what quality the elbows are). Each successive leak, incidentally, has been further away from the circulator.

    To answer Glenn's suggestion, it's been a few years, but the home was under construction for some time so it might not be far-fetched that the pipes remained empty.

    Questions at this point:
    1. Assuming velocity is at least part of the problem, should I switch in a smaller pump?

    2. Do I need to re-pipe?!! I can only assume that all the tubing in the vicinity has the same problems? If so, should I up the ID to 3/4" as Doug suggested?

    3. Should I consider pex as an alternative?

    Thanks again for all your kind input.

    Ron S.

  • Doug_7
    Doug_7 Member Posts: 247
    Suggested Actions

    The #1 thing to do is to install a good flow-throttling valve and cut the recirculation flow way-back. You probably need to cut the flow to 1/10 of what you currently have.

    Just pinching an existing ball valve may not do it. I prefer a dedicated throttling valve - I am using a rising stem hand wheel type valve with a rubber washer type seat. Pretty easy to set to 1/2 turn open, or 3/4 turn open. Installed between pump and discharge block valve which is a ball valve. The seat of this low-cost valve may wire-draw in a few years and I will need a better quality throttling valve.

    Fasten a digital temperature sensor on the return water line and cut the flow until you get a 10 or 15 degree lower return than the supply.

    The Taco pump sounds way too big at 10 GPM. The 25 watt Grundfos I am using in a 45,000 sq ft building is only 5 GPM and I am using 3/4" pipes.

    It is more important to get good flow control and some local temperature measurement. Putting in a smaller pump would be a step in the right direction, but without proper flow control and temperature measurement you may still have a velocity problem.

    Turbulence goes up with the square of the flow. Double the flow and you get four times the turbulence. Ten times the flow gives you one-hundred times the turbulence. Turbulence causes velocity erosion-corrosion.

    If you can get the velocity down low enough you may save the rest of the piping from failure. If you have to replace large sections of pipe I suggest you use 3/4" copper or Pex.

    Pex is a good alternative. I am still using copper but my flow velocity is way down low - about 2 feet / second. I also replaced the 90 elbows with two 45 elbows to further reduce turbulence. Makes a nice long-radius elbow.

    Good luck.

  • Larry Weingarten
    Larry Weingarten Member Posts: 3,389
    a suggestion

    Cut out one of the bad elbows and slice it lengthwise. If you see thinning of the pipe and/or fitting, you'll know it's erosion corrosion. Less run time and slower water flow will help a lot. Ph matters too. PEX holds up to this "erosion" much better than copper.

    Yours, Larry
  • Bill Clinton_5
    Bill Clinton_5 Member Posts: 38
    probably not velocity

    Out of curiosity, I looked up the pump curve for an 006 Taco. That's a real small pump. Since I understand this to be a recirc line, I guessed it to be at least 40' long and got out my B&G System Syzer calculator wheel and plotted a rough pressure drop curve over the pump curve. The 006 runs intersects the pressure drop curve at about 3.5 gpm and 5.5 feet of head. The velocity of water in a 1/2" pipe at 3.5 gpm is about 4.6 feet per second according to the B&G.
  • Ron S_2
    Ron S_2 Member Posts: 7
    a suggestion

    Hi Larry --
    What would be the best method to slice the elbow so that the corrosion and any scaling deposits would not be dislodged?


  • Weezbo
    Weezbo Member Posts: 6,232
    this is sorta a wag

    erosion corrosion is velocity and failure to ream pipe.

    outside that look for pieces of shiney Calvy pipe...it doesn't really belong in heating systems and many munis have continued to weed the stuff out everywhere that they can within the potable water system....
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,389
    cutting pipe

    Hi Ron: I'm pretty low tech. I'd cut out the leaky elbow and replace it with a longer sweep one. Then I've simply used a fine tooth hand powered hacksaw to slice the old elbow lengthwise. Another way to cut it is with a coping saw. These can have very fine teeth. If erosion is present, you'll see a pinkish color to the metal and thinning down to nothing at the pinhole.

    Although cutting will break off deposits at the cut, it will leave the pipe intact elsewhere so it's obvious what happened. I carry a chunk of old recirc line with erosion damage in a "box of stories" I use to explain plumbing troubles. Nothing beats the physical item for teaching.

    Yours, Larry
  • bruce_21
    bruce_21 Member Posts: 241

    I had this happen to me many years ago. We roughed in a job and then there was a long delay of about 4-5 months before the finish and an opportunity to turn on the water and flush the system. The holes were on the bottom of the pipe near joints where the flux had sat. As I remember we got lucky and only had to remove a small amount of the tile floor.
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