Steam system -- pipe replacement


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Old 10-11-06, 05:48 AM
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Steam system -- pipe replacement

I am planning to replace a small section of corroded pipe (just a nipple near the boiler, actually) on a steam system. From what I can tell, the process is similar to working with gas pipe (except of course for the size, which is 1 1/2"). Not having done this before, I have a couple of questions. First, presumably one uses pipe dope on the threads, correct? If so, does it matter whether one uses regular vs. teflon-impregnated compound? Does the nipple need to be black iron? (The system appears to use a combination of galvanized and black iron, but it's not exactly new, so I could be wrong.) In addition, the nipple is so corroded that there is a small hole in it. One end of it was attached to what appears to be a brass tee. The tee is a straight-through run, with the center portion capped off with a cleanout plug). Could the mating of the iron pipe nipple to the brass tee have caused the corrosion? If so, how do I prevent a recurrence? Finally, any tips for easing the process of removing the corrpoded portion (i.e., use a torch or Blaster PB spray?) Thanks.
 
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Old 10-11-06, 02:32 PM
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Replacing Nipple

The nipple should be black. If you can find one made domesticly, I much prefer them to the stuff that comes from across the water. I seems to be better steel. I've so much trouble with the imported stuff, I pay twice the price for domestic. It's far cheaper than having to take apart a piping system to replace one fitting or piece of pipe. Off my soap box now & back to your questions.
For steam, I prefer a pipe joint compound called "Blue Block".
I wouldn't think the brass would cause a problem but maybe. Normally brass is used when joining copper to steel to prevent such problems.
As to disassembly: I think I would stick to the torch, lest any PB Blaster find it's way into the system especially working that close to the boiler.
 
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Old 10-11-06, 07:13 PM
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Grady is correct on all points. Whatever sealer you use, keep it back at least one full thread so it cannot get into the system either. If you do any cutting and threading of pipes, ream everything and avoid leaving cutting oil inside the pipe. Don't be surprised if the system acts up for a few days after all the banging on pipes loosens up years of crud inside the them.

Ken
 
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Old 10-13-06, 05:44 AM
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Thanks for the tips. I learned that the section of piping I'll be working on was disassmbled around 5 years ago, so I may not need to wield the torch or the the 36" wrench. You're right about the fittings -- the quality difference between the Chinese stuff sold by HD and the stuff offered by my local supply house is obvious. One other question -- I've seen more than once in this forum the comment that adding fresh water to a system is one of the worst things you can do to it. Why is that?
 
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Old 10-13-06, 10:11 AM
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Fresh water contains entrained oxygen and oxygen=oxidation. There is plenty of steel and cast iron to give up some of its thickness to neutralize the oxygen but why cause a problem if it can be avoided. There are oxygen destroyers and corrosion inhibitors on the market but you have to be careful not to throw the ph out of balance either. If you drain on etime and repair the pipe, don't worry too much about it but when you are finished, run the boiler and make steam for at least 15 minutes to drive the oxygen out of the water. Then if it sits for a week it won't corrode the boiler and piping unnecessarily.

Ken
 
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Old 10-13-06, 06:22 PM
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A steam system is a completely different animal from a hot-water system when it comes to adding water.

A hot-water system may go for years without needing any "make-up" water if all the piping is tight and once the air has been bled from the system. A steam system will lose a bit of water every time it cycles from cold. It is acceptable (yet rarely done) to run a hot-water system with the make-up water valve closed but you never want to do this with a steam system unless the automatic water feeder has failed in the open position, and then only until the feeder is repaired.

Because a steam system loses water (and "new" water has to be added on a regular basis) the boiler water will concentrate any minerals and "junk" that is present in the make-up water. These minerals (mostly calcium) will tend to "scale up" the inside of the boiler and will "insulate" the boiler from the heat of the fire. This will lower the overall efficiency of the boiler and also cause the metal where the scale has formed to run hotter. Eventually this can cause boiler failure.

Depending on just how much water is added, how often and the quality of the make-up water a steam boiler needs to be periodically "blown down", that is, a small amount of water needs to be drained from the bottom of the boiler when the burner is not running. If you use a minimal amount of water this blow down may only be necessary once a heating season.

With a closed hot-water system that does not leak (and thereby does not take on "new" water) it is NOT a good idea to blow down for the reasons expressed by Grady and KField.
 
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Old 10-13-06, 08:09 PM
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Furd

That was as well put as I have ever seen it. You might want to hang on to that speel so you can post it whenever the subect comes up, as it does from time to time.
 
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Old 10-16-06, 05:34 AM
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Thanks again for all the help. The project went okay, but we did have one new joint that has a very slow leak. In that regard, I assume the pipes should all be quite tight. But what do you do when, for example, an pipe elbow has to be in a certain position, and when you get to that spot, it not yet nice and tight, but is close enough that there's not enough left to turn it one more full revolution? Also, I assume that if you discover that you can't make it one more turn, you cannot then back it off back to the right spot because the pipe will then leak. Is that right?
 
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Old 10-16-06, 04:30 PM
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Pipes

You elbow question is a good one. That is one of those things that come with experience. Another thing that comes with said experience is to buy good pipe & fittings. By that, I mean domestic, not imported. They will cost at least twice the price but worth every penny 'cause you don't have near as many leaks. You should not back off fittings once "tight" but you can take them apart, add an extra wrap or two of teflon & a healthy coat of dope.
 
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Old 10-17-06, 06:22 AM
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I did not use teflon tape, only pipe dope. So here's the next (adn hopefully last) sophomoric question: how many turns of tape (again, I'm dealing with 1 1/2 and 2" pipe)? And can yellow gas line tape be substituted for the standard white tape? And if so, how many turns of that? The reason I ask about yellow tape is that when I replaced my water heater, I had a leak where the nipple screws into the heater even though I used teflon tape. Someone suggested trying the yellow tape, and it worked like a charm.
 
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Old 10-17-06, 03:07 PM
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Yellow Teflon

I honestly don't know anything about the yellow teflon tape other than if the gas pipe inspector around here sees it on any gas piping, somebody is going to be taking some gas piping apart. There is also pink teflon & again no idea why. Anything more than one overlapping layer is likely just to slip & come off.
 
 

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