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Velocity

Zman
Zman Member Posts: 7,493
edited March 2019 in Pipe Deterioration
I have been working with a building owner that has been told by contractors that their pipe failures on domestic recirc lines are due to harsh water. I have started bisecting the failed components to prove otherwise.
"If you can't explain it simply, you don't understand it well enough"
Albert Einstein

Comments

  • STEVEusaPA
    STEVEusaPA Member Posts: 6,373
    I think you mean dissecting...lol
    What conclusion are you drawing based on the second pic? Can't really tell what I'm looking at.
    steve
  • Zman
    Zman Member Posts: 7,493
    The water is coming into the valve from the left. The erosion on the left is very consistent and laminar. The is noticeable thinning of the pipe with some deeper spots just after the joint where there are solder boogers.
    The interesting part is the valve and beyond. The ball in the valve is eroded to the point that it wont operate. The section of pipe after the valve has a nice patina, indicating normal wear and some deep gouges where the turbulence ate the pipe wall.
    The building is 22 years old and the recirc pump was replaced a couple years ago. At first glance, the new pump is oversized. The original pump must have been way oversized.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • hot_rod
    hot_rod Member Posts: 20,725
    It can be, and usually is a combination of things, velocity as shown, un-reamed tube, high mineral content water, and elevated hot water temperatures.

    An ECM delta P circulator and thermal balance valves like ThermoSetters can fix a lot of those chocked down conditions.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Intplm.
  • Lance
    Lance Member Posts: 257
    This has been studied extensively. There can be different causes.
    If water velocity is too high, two things can occur, 1) a biofilm that could coat the pipes can't form and leaves them unprotected. We do not need to recirc fast flow if constant recirc is operating.
    2) with fast flow, small imperfections, a dimple can be easily eroded away with laminar flow causing a pinhole. We frequently find in commercial apartment complex pumps that are way too big and keep being replaced by the same because no one wants or knows how to fix it.
    Also chemically, with copper usually, certain fluxes not cleaned from pipe, inside or out have shown to corrode pipes. Another is electrolysis from dissimilar metals and anode / cathode reaction to stray currents in grounding of pipes with electrical wires.
    We have job security when no one wants to fix it right.
    Oh and some stuff built with does not meet code and is just junk. But who checks product quality from overseas and who even knows anymore after the first couple of years go by. I personally have had to reject thousands of feet of substandard pipe and found many products would not pass government standards.
    No one can track all the proliferation out there. One USA mfg spent many years suing against cast iron pipe coming in from overseas that failed to pass inspection.
    One could also recognize the changes in municipal systems as they raised water pressures to meet over building demand.
    Zmanburn_your_money
  • Gordy
    Gordy Member Posts: 9,537
    Water is the most universal natural solvent Mother Nature has in her arsenal. It made the Grand Canyon :)
    Zman