What is the crud that builds up in old galvanized pipe?

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Old 08-01-13, 07:46 PM
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What is the crud that builds up in old galvanized pipe?

I was dissembling some sections of 32-year-old 3/4" galvanized piping from my solar water heater in the back yard and to help loosen the joints, along with using PB Blaster (evil-smelling stuff), I whacked them with a piece of pipe on the outside and noticed that pieces of the encrusted gunk on the inner surface actually got dislodged and fell out of the pipes. I kept at it and managed to remove quite a bit of the buildup. I hope to re-use the pipes (I was just moving the heater to a different location and will hook it back up--still works well after 32 years on the job).

Where the encrustation fell away, the inner surface of the pipe actually looked pretty good. Smooth, intact, and not eaten away by rusting. So--what the heck IS all that rusty-looking gunk that builds up in old galvanized pipe if it is mostly NOT rusted metal from the pipe itself? I am in Berkeley, CA, and we do not have hard water.

I'm tempted to whack my encrusted and impeded-flow hot-water pipes in my 1930s house, but it'd prob. lead to a massive blockage somewhere in there. Still, is this a technique that is ever used? Thanks.
 
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Old 08-02-13, 04:56 AM
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I've seen this in both of my homes (city water and on well water).
regardless of the water source, you'll probably pick up minerals alone the way (if not already desolved in the water). Over time, some will settle and stick to the pipe.

Was the crud thick that came off the pipe walls?
How to remove or clean out this stuff is a good question. I have been meaning to talk with our piping group (work for an engineering firm) to see how we deal with it in industry.
In my case, I found that letting the pipe dry while working on a repair did dislodge a lot of it. Caught it all in the filter.
 
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Old 08-02-13, 06:27 AM
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Yes, it was very thick; in some places almost filling the pipe, and more at joints than elsewhere. I wondered about the drying too, because this section of pipe had been dry for a few weeks. Maybe drying makes the crud more brittle.
 
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Old 08-02-13, 06:48 AM
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Originally Posted by DaveLS
What is the crud that builds up in old galvanized pipe?
Bacteria and reduced sulpher or other dissolved minerals.

Technical term is "biofilm".



Microbially influenced corrosion of galvanized steel pipes in aerobic water systems.

Pioneer colonizer microorganisms in biofilm formation on galvanized steel in a simulated recirculating cooling-water system.

No matter how hostile the location, if there's water, there will be something growing...
Isolation and identification of bacteria from spent nuclear fuel pools | Isabel Sarró - Academia.edu
 
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Old 08-02-13, 07:15 AM
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Yes, it was very thick; in some places almost filling the pipe, and more at joints than elsewhere. I wondered about the drying too, because this section of pipe had been dry for a few weeks. Maybe drying makes the crud more brittle.
You could run a thin snake (use a new one if domestic water) down the pipe to scratch it up.
I know in my case, I was soldering the pipe, so around where the heat was, the stuff broke away from the pipe walls with a couple taps.
If you use a snake, be very aware about how far you are pushing it, and if you have a point where the crud can exit instead of going through your appliances, this would be a good idea. I've been able to use my water filters to collect the crap.
 
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Old 08-02-13, 07:38 AM
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Thanks; I had no idea this was bio-anything. Galvanized pipe as petri dish. Reminds me of dental plaque.
 
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Old 08-02-13, 07:43 AM
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No filters here; I'd have to snake the pipes upstream so the loosened crud could get washed out where the snake goes in. Thanks.
 
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