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  • Galv. chips in air line

    A while back someone, possibly Bob D. offered several explanations for galvanize chipping in air lines. I didn't need the information then, but now I do. Does anyone remember that discussion?
    Thanks,
    Dan

  • #2
    Re: Galv. chips in air line

    Basically, it's not a very good idea to use galvanized pipe for air lines because of the fact that the galvanized coating could possibly flake off and clog the outlets. Black pipe and/or copper tubing are the best materials to use IMO but in a pinch you could just use air hose, which would probably be the least expensive way to go. DO NOT use PVC pipe and fittings!
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    • #3
      Re: Galv. chips in air line

      Originally posted by BadgerDave View Post
      Basically, it's not a very good idea to use galvanized pipe for air lines because of the fact that the galvanized coating could possibly flake off and clog the outlets. Black pipe and/or copper tubing are the best materials to use IMO but in a pinch you could just use air hose, which would probably be the least expensive way to go. DO NOT use PVC pipe and fittings!
      What Dave said is all good but I would prefer welded SS over black pipe, threaded SS second, followed by copper. All three are expensive and financially don't make sense in a small shop. Copper would be the way to go but the price of copper now a days its tough to justify for a home shop.

      Yes, the big concern is flaking of the galvanize coating. The most likely place for this to occur is where the pipe has been cut by any method (pipe cutter, portaband, hacksaw, etc), some being worse than others. Under sized pipe with high flow rates can erode the inside of fittings where the air (which will always have some measure of grit in it) will impinge on the pipe of fitting wall and over time can even wear a hole through the pipe. I have seen and replaced pipe where this has happened.

      So maybe 1/2" will meet your demand needs at some pressure, but stepping up to 3/4" will reduce the velocity of the air in the pipe considerably, and leave room for future expansion without a complete repipe. Same applies for larger bore pipe. Black pipe WILL scale even with filtered, dry air, you'll never keep it all out or from forming in the pipe downstream of your dryer and/or filters. So you will always have a problem with black pipe, it just depends on your application if it will be a problem for your equipment or not.

      DO NOT use hard plastics like PVC or CPVC, they are not designed to be used for pneumatic systems, it is very dangerous to use them for air lines no matter how attractive the installation cost savings might appear to be.

      So long story short use black pipe for the normal air use in a small or home shop unless you have some special need for higher purity air. Upsize at least one pipe size from what you calculate you will need and run your pipe properly to help mitigate problems with rust or scale being carried through to your tools/equipment. Use filters and moisture seperators initially right off your compressor (to help keep the pipe clean) and also at the point of use (end of line) to catch any junk you picked up along the way. Install a couple full size blow downs on you lines using full port ball valves if you can so you get maximum flow, and blow down regularly to clean out any junk. Minimize the oil used when threading pipe and be sure to clean out any oil from the pipe before installation or you will be fighting that oil fo rthe next 4 years.
      Last edited by Bob D.; 07-28-2012, 11:21 AM.
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      • #4
        Re: Galv. chips in air line

        Over my more than 35 years in the heavy compressor industry, "galvanized" pipe for air lines has been forbidden as a rule. Recommendations (at least for industrial use) as been for black pipe and in some applications thickwall copper for lower pressure runs (I can't remember the rating for the copper, sorry).

        The general thought against "galvanized" pipe for air line use, is that it could possibly flake and the zinc plating thus find it's way downstream in the airline where, unfiltered it would severely damage air tools and contaminate any process use.

        With black pipe, there is always the concern for corrosion of course and therefore air lines must be constructed in a fashion that recognizes the fact that there is the probability of condensation build-up in the air line system. Hence, air piping must be constructed so that it slants away from the compressor outlet (so water does not drain back into the compressor... water does NOT compress and a "slug", as we called it, would be highly destructive), and that "drain legs" must be installed at any point where an air connection for a tool was to be established. (See image below.)

        I hope this helps,

        CWS

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        • #5
          Re: Galv. chips in air line

          I would lay that tee on its back and use 2 90s to turn downward. That keeps and water from
          being pushed down and helps stop rust and scale from getting into the branch lines.

          At the end of the main have a 90 looking down with a full port ball valve for a blowdown.
          ---------------
          Light is faster than sound. That's why some people seem really bright until you hear them speak.
          ---------------
          “If I had my life to live over again, I'd be a plumber.” - Albert Einstein
          ---------
          "Its a table saw.... Do you know where your fingers are?"
          ---------
          sigpic http://www.helmetstohardhats.com/

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          • #6
            Re: Galv. chips in air line

            drip legs at ever out let should catch most of the chips, and like said they should exit out the top of the main line and then elbow over




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            • #7
              Re: Galv. chips in air line

              Thanks to all of you for your input. You've been a huge help to me.

              Dan

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              • #8
                Re: Galv. chips in air line

                I agree, providing there is an eventual drain to take the moisture out of the main line. This was just a quicky for a small home system (and possibly the only outlet).

                I do recall when I first worked at "the Rand" and had the maintenance dept tap into the main airline so that I could use my airbrush. That line was so full of moisture and rust it made a he!! of mess out of my office when they first "cracked" open the new drain leg. Splattered everywhere!

                Thanks again, I'll change my sketch.

                CWS

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