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  • can someone tell me what caused this pipe corrosion?

    I went to see a job on Friday where the person put in a new cast iron boiler about 3 years ago. There are a few fittings that are coroding and there is leakage. please see photos. There is a 6" black nipple coming out of top of boiler which goes into a steam tee then another nipple which screws into a taco pump. you could see the green color in photo _001. Out of the tee is screwed in a line voltage mcdonald miller low water cut off. I was hoping someone could tell me why the pipes are coroding. looks to me like there are metals interacting but its all iron to iron. I thing the low water cut off has brass in it on the probe, but that isn't suppossed to touch the wall of pipe. I don't want to replace the bad fittings and for it to just happen again.
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  • #2
    Re: can someone tell me what caused this pipe corrosion?

    What you have there is a very small leak and a system filled with anti freeze. Anti-freeze will find the smallest hole imaginable and because it is not effected by oxygen it will not rust closed like it probably would have if the system was filled with water. Repair the leak, check the anti freeze and put a can of stop leak in the system.
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    • #3
      Re: can someone tell me what caused this pipe corrosion?

      I agree with the leak. If it was dissimilar metals, the corrosion would be concentrated at the joints, and not affect the whole fitting exterior. Appears to be more of a chemical/oxygen attack aggravated by the anti-freeze. Because the corrosion rate doubles for every ten degree rise over 140 degrees F., it would be quite rapid in that location. The area affected is probably not larger due to the electrolyte (leakage) evaporating before it travels much further.

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      Practicing at practical wood working

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      • #4
        Re: can someone tell me what caused this pipe corrosion?

        Thanks for your response. I was told by customer there is only water in system. The house is in queens, nyc. usually its only water in this area.

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        • #5
          Re: can someone tell me what caused this pipe corrosion?

          Originally posted by joefarrock View Post
          Thanks for your response. I was told by customer there is only water in system. The house is in queens, nyc. usually its only water in this area.


          Do they get snow? I pretty sure they do.......I would check to see if there is Antifreeze like NH said.....Chances are you will find that there is some AND to much at that...

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          • #6
            Re: can someone tell me what caused this pipe corrosion?

            Water only will cause the same result, as well as will mean accelerated corrosion throughout the inside of the system. The corrosion will level off after all the free oxygen is used up from the water, but every time new water is added, it starts all over again. Even if anti-freeze is not used, a corrosion inhibitor will greatly add to the system's life.

            Of course that means you will get less repair calls! In reality, even if an inhibitor is added, the levels need to be checked and and adjusted as more water is added. As for the correct inhibitor, it depends on if the water is high oxygen content or high solids (highly conductive), or both. Usually, antifreeze will take care of both problems if the system is made leak free, and it's use does not cause a bunch of environmental permit issues.

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            Last edited by Gofor; 08-10-2009, 10:41 PM.
            Practicing at practical wood working

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            • #7
              Re: can someone tell me what caused this pipe corrosion?

              I saw a flow switch, I think, in the system, did you check for residual voltage on the water piping, ie a short, this could easily cause this.

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              • #8
                Re: can someone tell me what caused this pipe corrosion?

                I would say that most of the problem exists because of the use of black iron. Black iron has no protection from water or corrosion and especially if glycol is added, would make the water even more corrosive to the black iron.
                ANYONE CAN TAKE THE HELM WHEN THE SEA IS CALM.

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                • #9
                  Re: can someone tell me what caused this pipe corrosion?

                  The simplest anwer is usually the correct one. Slow leak (ooze) onto black fittings on steam system. We see them around here all the time. No antifreeze in our steam systems.
                  I see the same type of corrosion on black pipe that was improperly installed on water lines and a slow leak develops that corrodes the outside while the water flow corrodes the inside.

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                  • #10
                    Re: can someone tell me what caused this pipe corrosion?

                    Originally posted by mtnman1100 View Post
                    I would say that most of the problem exists because of the use of black iron. Black iron has no protection from water or corrosion and especially if glycol is added, would make the water even more corrosive to the black iron.
                    Black iron is commonly used in forced hot water and steam systems with no corrosion problems provided there are no leaks and the system remains sealed and under pressure. The appearance of the green color however indicates one of two things. Either anti-freeze is in the system, or there is a leak that causes the auto fill to keep adding water to the system and that water is either alkaline or acidic or finally there is a mess of old flux that dripped down onto the fittings. Again, clean it off, and fix the leak.
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