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derect bury of low pressure steam piping

We have a customer that has an old existing low pressure steem single pipe system. In one section of the building there are eight rooms on the first floor with a radiator in each room all on one loop. the loop is buried in soil grading back to the boiler. About 10 years ago the piping started leaking in several areas and we went in and patched the loop two times and about 4 years ago it started leaking again so we excavated the whole loop and found all the black steel piping was rotten, even the new repairs, we replaced the whole loop installing the new black pipe in a bed of sand buried 18" to 36" deep making sure the piping was grading back to the boiler. Now 4 years later I am getting a call from the owner telling me the floors are getting hot, to hot to stand on. Q why is the piping deteriorating so fast . Q is there a different materal that can be buried.


  • Roger Litman
    Roger Litman Member Posts: 64
    Use Schedule 80

    When we have to do piping that is going to be buried, we use schedule 80 pipe, you could use stainless steel, but the price is very high and you will need to use special dies to thread the pipe. Check the bad pipe and be sure that it is corroding from the inside. You can tell that by looking at the pits on the pipe with a microscope and they will be cone shapped with the large part of the cone at the side where the corrosion is coming from.You may want to check the input water and find out if it unusual from the water department or a testing lab.

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  • Tony Conner
    Tony Conner Member Posts: 549
    Direct Buried Low Pressure Steam Piping...

    ... is just the right temperature when it's hot to give a nice kick-start to corrosion with any moisture present around the outside of the line. Cold in the ground all summer is pretty much as bad.

    What kind of insulation are you using? For underground service, it should be Foamglas. They make 2 kinds, one for cold service, like refrigeration, and one for hot. It costs more than fiberglass, or calcium silica, but water will not affect it. Nasty, brittle stuff, abrasive to handle, and stinks like sulphur when you cut it. But it works. We just wrapped ours in heavy roofing paper to keep the dirt out of the joints. This is not water tight though, but most of our lines were high pressure, and kept hot all year. You can give it an outer jacket of pitwrap, but it's akward to deal with. If it folds over on itself, you will NOT get it apart without an unbelievable struggle. Toss it, and get another piece. It will be pretty much water tight, however.
  • Dale
    Dale Member Posts: 1,317
    Check out thin film epoxy

    I'm not sure of the temp range, the piping wholesaler would know, best thing for exterior corrosion. The joints are covered with a 2 part epoxy from tape coat Co. You do need to sandblast the joints first. Put sand arround the pipe and if you are serious attach a few mag annodes.
  • Tony Conner
    Tony Conner Member Posts: 549
    My Experience...

    ...with coatings on steam stuff is not good. Expansion & contraction, over and over, as things heat up and cool down tends to crack them, and allow corrosion to start between the coating and the metal. There could be something new on the market though.

    I've seen people try to use yellow-jacket gas piping for buried steam lines. The steel pipe takes it no problem. The jacket, however, lasts for about 5 minutes once the steam comes on, then turns into a long, sticky puddle along the bottom of the now bare line :)
  • JimGPE_3
    JimGPE_3 Member Posts: 240
    In our neck of the woods

    (the rust belt) people used to bury piping in slag because it was cheap backfill. Problem is it makes a pretty good acid when it gets wet, and eats the pipe.

    If the corrosion is coming from the outside, check the nature of the backfill.
  • Tony Conner
    Tony Conner Member Posts: 549
    It'll Corrode...

    ...even in sand. There were a LOT of material selections that turned out to be something less than ideal. The material you mention was one of them. Local conditions play a HUGE role in this kind of problem. What makes perfect sense in one place is just a recipe for disaster someplace else.

    The one common factor I've found (and this is from people in the district heating business from all over North America) is that low pressure steam pipe, and condensate lines are the biggest corrosion & maintenance problems. High pressure/temperature lines aren't a fraction of the trouble. Any ground moisture that gets near them just steams-off before it actually contacts the pipe. The low pressure and condensate lines are just hot enough to act as a catalyst for corrosion. I've never seen a leaking underground steam line that didn't fail from the outside in, unless somebody hit it with a backhoe bucket.

    Any buried steam or condensate line that gets shut down for the summer just corrodes at warp speed.
  • Bob Morrison_2
    Bob Morrison_2 Member Posts: 10
    How much money do you have to spend...

    A premium commercial product is MultTherm-500, or equal

    A lower grade, but very good product is the ESCON-A.

    A schedule 40 steam carrier pipe is fine; sch 80 for condensate.

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