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Green rust on water heater discharge pipe, what causes it? The tank is pretty old, almost 20 years.

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Brian Z
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1 Answers1

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Copper oxides = Green "rust"

Water causes that, can be aggravated by failure to clean acid flux from soldered fittings, but since yours starts right up by the threads I'd guess you have some "weeping" out the valve and the threads are none too watertight (sloppy workmanship - "just a drain, no need for it to hold water, never going to be used anyway...")

Weeping can be caused by a failing valve, or by a lack of expansion tank combined with a check valve or thing that acts like a check valve (such as a pressure reducing valve or PRV) causing the pressure to rise when the tank is full of cold water, no water is used, and the cold water in the tank is heated and expands.

At 20 years old, have you changed the anode and flushed the bottom regularly, or just let it sit? You might be reaching end of life, if you have not maintained it. The oxides on the drain line don't indicate one way or the other on that, really, but it's worth thinking about anyway.

Ecnerwal
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  • I'd probably say condensation. Metal tends to have condensation first so periods of high humidity coupled with the flux serving to allow the water to stay in that area of longer periods. – Fresh Codemonger Oct 18 '20 at 20:16
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    It's attached to **a tank full of *hot* water**, and in my experience tends to be warm since it's a hunk of copper thermally and mechanically attached to a tank full of hot water, so condensation is *very unlikely on this particular pipe,* IME. – Ecnerwal Oct 18 '20 at 20:19
  • Even if you've maintained it, 20 years is a long time +1 – JACK Oct 18 '20 at 20:41
  • @Ecnerwal I changed the pressure release valve 1.5 years ago. What should I do now? Check the pressure valve whether works. I didn't change the anode (not sure whether the last homeowner changed it or not), should I change it and drain the tank to continue using it? Recently hearing the rumbling in the tank also. – Brian Z Oct 18 '20 at 23:45
  • Will the old water heater tank turn into a bomb some time? Wow – Brian Z Oct 18 '20 at 23:50
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    Normally they just start leaking. The whole point of pressure/temperature relief valves is NOT turning into "a bomb." Beware falling for stupid internet/TV videos where all the safety mechanisms have been bypassed to make dramatic footage... – Ecnerwal Oct 19 '20 at 00:34
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    Over many years ,I have had 3 hot water tanks leak, all were pinhole corrosion drips in weld seams. – blacksmith37 Oct 19 '20 at 02:15
  • Flood insurance is void if your tank is over 10 years. I have a water leak solonoid on my 25 year old tank so if it goes the water suppy to the tank is shutoff. The iron particules from your hot water tank are likely running through your water supply system and will cause pin hole leaks in horizontal runs of copper. https://www.youtube.com/watch?v=nD5lMITzx_Y&t=3m17s – Fresh Codemonger Oct 19 '20 at 16:13
  • @Ecnerwal can I consider the weeping water from PRV is normal? (I don't have the expansion bank) Or, should I take any action to avoid it? Thanks – Brian Z Oct 25 '20 at 14:29