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Hot Water Recirculation pipe erosion

DanDan Member Posts: 15
I have a commercial customer who is experiencing major pipe erosion on the return line feeding the recirculation circulator for the hot water . I have attached a photograph for you review. I will try to give you an abbreviated description of the installation and history of the job. The return pipe is 1" copper with the exception of approximately 20' of PEX  we used to repair the leaking sections. The circulator is a Grundfos stainless steel UPC-15-42SF which is good for 16GPM at a 0 head. I don't know how much equivalent pipe there is but I will estimate about 250'. The internal pipe erosion seems more prevalent closer to the inlet side of the circulator rather the supply side. The circulator runs 24/7. The water temperature is around 128 degrees.The last repair lasted around 6 months before another leak developed. The complex thought it may be the hard water. They installed a large water softener system. It seems to prolong the leaking intervals but did not stop it. We isolated the pipe in some instances where it lying against galvanized duct work. We added a ground wire and bonded the pipe back to the electrical service ground. I don't think it is a velocity problem in the pipe because I added a balancing valve on the outlet side of the circulator trying to restrict the flow. Has anyone else seen or experience this condition. Thanks in advance for your help.  Dan


  • TomTom Member Posts: 458

    Have you had the water tested for ph or minerals?
    Montpelier Vt
  • RJRJ Member Posts: 484

    Looks like the pipe was not reamed, are there any leaks at the solder joints
  • Paul48Paul48 Member Posts: 4,253
    edited April 2013

    If it was a velocity issue, it would fail at any elbows first. It is considered an "Open" system model. What is the application? From the manufacturer.....For Open Systems- 140*F (60*C) is the maximum recommended fluid temperature to avoid precipitation of calcium in water.

  • heatpro02920heatpro02920 Member Posts: 991
    Looks like Type M tubing to me

    the red markings lead me to believe its thin walled pipe, try using L {blue} copper..  I have seen M last less than 3 months on a domestic supply for a commercial dishwasher in a medium sized restaurant, and that was 3/4" I would imagine 1" will errode faster...  I would switch it all to either the correct pipe for potable water or go with 1" wirsbo pex...  Also I don't know what the function is beyong a recirc system, but as far as size goes, it looks poorly designed, why have a recirc run 24/7 with all that water in 1" M {that piping is going to lose energy faster}, and run such a fast pump..  When I do recircs, even for commercial systems, they get the smallest return line I can run with a slow pump, set on an aquastat {normally a 009 will do it, but I have done a few with SS alphas for the ecm motor, turned all the way down}..... 
  • hot rodhot rod Member Posts: 7,059
    a few factors

    combined possibly, ph, velocity, un reamed tube. has excellent info on copper tube, failure causes and prevention. Go to the tech section.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • paulpaul Member Posts: 91
    pipe erosion

    we had the same type of problems on the re circulation lines on some of our buildings. pipes leaking and the whole repair and replace. we ended up putting on circuit setters on the lines and also put on strap on aqua stats to shut the pumps down when they hit 120 degrees on the return. the strap on stats are johnson model number A19DAC-1

    you don' need to pump a lot of gpm all you need is is a few gallons a min. the pipes started to have erosion problems after about 12 years.
  • DanDan Member Posts: 15
    Pipe erosion

    My customer had Culligan install a Water Softener system. I don't know if the PH was checked.  Thanks for the reply.
  • DanDan Member Posts: 15
    Pipe erosion

    My customer had Culligan install a Water Softener system. I don't know if the PH was checked.  Thanks for the reply.
  • DanDan Member Posts: 15
    Pipe erosion

    Thanks for all of your feed backs.... Dan
  • icesailoricesailor Member Posts: 7,265
    Water Softners:

    Adding a water softener can make the problem worse. The conductivity of the water is as important as the Total Dissolved Solids (TDS). In water treatment, you usually try to correct one problem and create another. If the PH is low (less than 7.0) and the TDS is high with high sodium and chloride levels in the water, the potable water systems become storage batteries. Especially in the potable hot side. The spinning impellers a can add static electricity. Dissolved solids stick to the inside of the pipe and the solids will give a path to the copper tube. The pitting is in such a place.

    IMO, many large buildings, especially ones that have multiple additions, have undiagnosed grounding and neutral issues. Especially if 3 phase is involved. Many electricians I meet haven't a clue about unbalanced 3 phase loads and what can happen.
  • HenryHenry Member Posts: 720
    Water velocity

    We have had several customers that experienced pin holes in the hot water and not recirculation outlets. Most are caused by using thin wall M over L and high velocity, IE too MUCH pump! Adding softeners that are not properly adjusted will increase salt in the water and increase corrosion. You just need a few gpm for recirculation and try to get rid of the softener on the hot water side.
  • Steve WhitbeckSteve Whitbeck Member Posts: 669

    It is caused by velocity erosion. The erosion will be on the inside of the downstream side of every elbow. Thicker pipe will not stop the erosion it will just delay the repair. ( L versus M copper )

    You need to slow the water down a LOT. 1 GPM would be great. 2 story houses usually don't need a pump at all. ( I unplugged mine.)
  • SWEISWEI Member Posts: 7,356
    recirc flow

    In a properly designed and insulated system, "a couple of GPM" will suffice for a hotel with 30 or more rooms.
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