Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit

Frequent replacement of black pipe nipples and other fittings.

galileogalileo Member Posts: 6
In the past few years, I've had to replace several nipples and fittings in my low-pressure steam heating system. An old timer in my area has told me that it's because of the cheap steel that comes from China that may contain many impurities. As well, I have recently been told that using pipe dope on threaded fittings will decrease the life of the fittings since the pipe dope reacts with the hot steam and the chemical reactions caused by the process will "eat away" the black nipples and tees etc. especially the threads. I have had to replace several black pipe fittings in the past few years. Some lasting only one or two years.
Any thoughts on whether the pipe dope could be contributing to the premature replacement of black pipe fittings?
The pipe dope I use now is grey in color.



  • nicholas bonham-carternicholas bonham-carter Member Posts: 7,641
    How are the nipples failing?
    Are the failing nipples below or above the waterline?
    I doubt that any pipe dope able to eat through steel would remain on the market for long.
    Is your water pure and clear in the sight glass?—NBC
  • Shane_2Shane_2 Member Posts: 122
    Does your steam boiler have an auto fill? If you are adding more makeup water than before, it will eat steel pretty quickly. I would check all connections, even packing on radiator valves (which can evaporate before you see them)
  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 4,755
    It's not the pipe dope. excessive mu water will do it. I would take a water sample and have it tested. You could use schedule 80 nipples much thicker
  • galileogalileo Member Posts: 6
    Hi Ed, I have considered schedule 80 nipples and pipes. Now that I know it's not the pipe dope I will order more schedule 80. I will have the water tested as well.
    appreciate your input
    Thank you kindly
  • MilanDMilanD Member Posts: 1,107
    I am assuming this is in the wet side of things, yes? I had a similar issue on my pumped boiler feed line, in the 2" equalized side, capped dead-end nipple off the bottom of the equalizer return. The only thing I could surmise was that the seam inside the nipple in combination with pumped flow and muck caused water turbulence and this particular pipe erosion. I caught it before it leaked as I removed the nipple to wand the boiler. But, wow... So, schedule 80 it was as a replacement, and I throttled down the feed via a valve, which it previously wasn't done. Will see how long this lasts.
  • galileogalileo Member Posts: 6
    Milan, yes, it's on the wet side of the system. We have very hard water in my area and even though the boiler is fed via the hotwater tanks, thus reducing the hardness to some extent, I have to clean out all pipes and controls every few years on account of the constant hardwater residue in the system.

  • nicholas bonham-carternicholas bonham-carter Member Posts: 7,641
    edited May 2018
    Is the hot water softened?
    We have unsoftened water, and it seems that the whole hot water distribution system including taps, gets limed up more than the cold side.
    Depending on the size of your boiler, only a few gallons of makeup water should be needed for each season. Do you know how much water you have to add?
    Oxygen in fresh water is the real danger to cast iron.—NBC
  • MilanDMilanD Member Posts: 1,107
    edited May 2018
    Where in the system is the failing nipple and fittings located? If this is on the side after the pump for feeding the boiler, try throttling down the flow with a valve. Those pumps should be throttled down anyway, to avoid stem collapse while the boiler is making steam by introducing makeup water at a slower rate. This will also slow the flow and possible eroding effect of turbulence. Worth the shot.
  • Jamie HallJamie Hall Member Posts: 9,417
    I'm very concerned about your comment on makeup water. As several have said, excessive -- which I would count for the average residential system as anything over a gallon a week (perhaps a little more in really cold weather) -- makeup is just lethal on the wet side of the system. Find and fix any steam leaks! Or vents which leak, or...

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • galileogalileo Member Posts: 6
    Hi Jamie,
    I have a 600 thousand BTU Weil McLean boiler which I flush down on a weekly basis. I open the 4 valves on the boiler starting from the top down and I would say that I definitely flush out more than a gallon each week. I don't have a water softening system for my building but feed the boiler via two hot water tanks, thus hot water feeds my boiler. I was told many years ago that I should flush the controls on the boiler on a weekly basis. I have also throttled down the water feeder line from the pump to the boiler in order to reduce turbulence.
    Every heating season I have several leaks in the water lines in my system. Like I said, the black pipe available lately is not as good as it was years ago. Too many impurities are introduced through the use of recycled metal in the smelting process is what I was told.

    Thanks for your input.
  • nicholas bonham-carternicholas bonham-carter Member Posts: 7,641
    What valves are you opening here? The weekly flush of the LWCO should suffice: (open drain valve until running clear).
    You could do a monthly flush of the boiler drains to remove any accumulated sediment.
    Opening all the valves once a week might introduce 4 or 5 gallons of fresh oxygenated water into a system which may not fire for a few hours, thus exposing those thinner pipes to corrosion.—NBC
  • GBartGBart Member Posts: 678
    You should have some way of metering your fresh water intake as well, Hydrolevel makes one or on large systems people use a standard water meter, we usually put them on cooling towers as well, you could be taking in a lot of fresh water.
  • You may have some stray electricity causing electrolysis, I've never seen a nipple wear out in two or three years, and I buy them from all different places, something else is going on here. Is there an automatic feed for the boiler? How many sq feet is the building?

    Thanks, Bob Gagnon
    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • RomanPRomanP Member Posts: 101
    Well, according to chief here @Dan Holohan minerals in hot water are more aggressive than in cold. I always feed my boilers using cold water. Now if you have leaks in the system, bad water, which is constantly getting added to the system at high temperature, with fresh oxygen... that could do some damage.

    I’ve never encountered such an issue, with nipples rotting out

    Good Luck
  • GBartGBart Member Posts: 678
    This is an interesting article, not sure if it's related because I've only seen velocity erosion in high pressure steam systems but...
  • MilanDMilanD Member Posts: 1,107
    edited May 2018
    > @GBart said:
    > This is an interesting article, not sure if it's related because I've only seen velocity erosion in high pressure steam systems but...

    Most interesting! I was supposing that excess pumped flow turbulence plus make-up water flashing as it's introduced to the boiler, and steam collapsing, all in combination, could have something to do with our nipple failure. It looks like this article confirms it. Comes back to reading instructions: condensate pumps need to have a throttling valve installed to slow down the makeup water flow rate. This also allows for the steaming inside the boiler to continue without collapsing due to too much colder water being introduced too quickly.
  • RomanPRomanP Member Posts: 101
    edited May 2018
    Any different metals within the system? Any chance for galvanic corrosion?
    Btw, in my first plumbing company, we installed and serviced a whole bunch of Fulton high-pressure steam boilers. The feed pumps were pretty big ( had to overcome 100 psi inside the boiler). Yet we never had a leak and none of these nipples ever fell apart. The only schedule 80 nipple we used, was he first one coming out of the boiler, all the rest was done with schedule 40 nipples and Black Maleable fittings.

    I’d recommend testing your water
  • rbeckrbeck Member Posts: 56
    TEst water for Chlorides and PH. I would also be concerned with stray electric or acids produced by boiling water and not enough venting. This usually shows up in wet returns.
    I have a piping diagram using hot water to feed steam boilers fo for steaming crabs. They usually waste all condensate. When converting to hot water from a water heater the life of the boler was extended a few years.
  • galileogalileo Member Posts: 6
    I would like to thank all who have contributed to my concerns regarding frequent replacement of black pipe fittings. There are so many factors to consider in resolving the problems and causes. I will be doing some changes to my piping system as well as following the suggestions that you experts have put forth. I very much appreciate everyone's comments and input.

    Thank you kindly
  • JackmartinJackmartin Member Posts: 128
    You have a case of classic carbonic acid groove corrosion. Read Dans book he clearly states: you have groove corrosion in the bottom of your condensate pipes and the corrosion will appear as a groove in the bottom of the pipe. Schedule 80 will slow it down, because it is twice as thick , ,but it does not address the root problem :air venting of your system. The major problem of not venting a steam system is allowing co2 and oxygen to remain in the system .You have to get rid of these gases as quickly as you can and that is using good properly sized air vents. Groove corrosion is caused by mixng water with co2 in the system it then becomes by chemical process; carbonic acid ,which is very corrosive to steel. Cotrect you venting , limit ftesh water as much as possible, and make sure the condensate moves as quickly as possible out of the returns.Look on page 191 of Dans book ,The Lost Art of Team Heating Revisited, Dan explains it well. All the best and good luck Jack
Sign In or Register to comment.


It looks like you're new here. If you want to get involved, click one of these buttons!