Wood boiler project - a few questions

[Rdubs]

I am making a wood boiler using a 1/2" wall ~400 gal tank for the fire box, and a 4 1/2' x 14" pipe for the water tank. I welded 8 pieces of 2" pipe in the water tank top to bottom, as fire tubes to increase surface area / heat transfer.

My inlet / outlets for the water are 2" threaded, because after I put the tank in the firebox I won't be able to get inside to weld them and check for leaks. I want to use a high temp epoxy to seal the threads because I feel like pipe dope will crack over time.

Any thoughts on a good high temp epoxy 2000+ degrees f ?

Any experience with this ?
https://www.amazon.com/dp/B002UJ1EF4/?tag=hearthamazon-20

See attached pics

 

[lotawood]

If you are counting on a water seal with threaded pipe, pipe dope is good.

Structure holding water not going to get to 2,000 degrees safely. Counting on epoxy to hold something instead of pipe dope probably not built for the long term.

In other words, if you can't count on pipe dope, it better be welded. I build some homemade stuff myself, but glorified glue is not to be trusted with a pressure vessel or long term use of high heat.

 

[Rdubs]

Basically I am looking for something to smear on the threads before putting them together, is there some type of hi temp pipe dope?

Are you saying welding it is the only way to ensure a good seal (that is if my welds are good)?

Pressure in the tank will be low, 15 psi +/- But temperature range will be drastic.

 

[Rdubs]

Also I was thinking about a cast iron sectional boiler. When they put the sections together they are not welded. Do they use some goop?

 

[lotawood]

I'm not a boiler maker. So for what it is worth, I would avoid a threaded connection inside of a burn chamber.

I can't tell what exactly you have going on in your build. I guess this is low pressure hot water and not steam?

Maybe lookup sealant acceptable for steam, which provides a little overkill for hot water. I also suggest you pressure check before use, otherwise things can and do go wrong.

Hopefully somebody with more experience with reply.

 

[Rdubs]

Thanks for the responses.

I have changed the design so the threaded fittings will be outside the firebox.

I think it will also lower my overall labor by a few hours

 

[warno]

For what it's worth, the taper on pipe threads is what does the sealing. The dope or thread tape is simply a lubricant to make sure you get the threads to the sealing point in the joint.

 

[mike van]

Also I was thinking about a cast iron sectional boiler. When they put the sections together they are not welded. Do they use some goop?

There are gaskets between the sections, a few years back I watched a team of plumbers take apart the large boiler at the school here. Hot water, not steam.

 

[HoosierHillJack]

Teflon tape and soft set pipe dope are what I use on steam lines everyday. I'm a union pipefitter.

 

[velvetfoot]

Both at the same time?

 

[HoosierHillJack]

Both at the same time?

Yes we do 3 wraps around the pipe with the tape and then put the pipe dope on the first few threads. It doesn't hurt to go with more tape a lot of foreign manufactured fitting will be out of spec. A rule of thumb we use is 3 spins before its tight, 3 spins to tighten and 3 threads showing outside of the fitting. It doesn't always happen that way though haha.

 

[HoosierHillJack]

Thanks for the responses.

I have changed the design so the threaded fittings will be outside the firebox.

I think it will also lower my overall labor by a few hours

when you are finished welding cap and plug everything and put together a test rig consisting of a pressure gage, ball vavle, and a air chuck and fill it with double of what your operating pressure will be(or a random number like 50 psig) and let it sit overnight to see if you have any pressure drop. A psi or two is normal from the compressed air equalizing temperature. If you have leaks a spray bottle full of dish soap and water will show you a nice Santa Claus beard at the source. Grind weld and repeat. Also add a thread o let for a sacrificial anode from a water heater to prevent rapid rust out.

 

[coaly]

Both at the same time?

Yes, the thread tape should be wrapped around the male threads dry and lubricated on the outside. (liquid teflon paste is the best) When used dry it can stick to the outer threads and not turn into the joint. You want the tape to grab to the male threads and slip against the female without tearing.

 

[velvetfoot]

I've had some bunching up of the tape in the past with tape alone.

 

[coaly]

That's why, it's not to be used dry.

 

[HoosierHillJack]

Also make sure to put in on in the direction the fitting spins on or it will push it off the threads.