Hot Section Thread Sealant

[TomG]

I hate to show my ignorance, but I'm at a dead-end. I'm just about ready to finish a new exhaust system (including MMI's new SS Tartan Standpipe!), but I can't figure out if the threads in the joints should be sealed with something (tape or PTFE). The only thing I can find on the forum is one of Don's tips to just seal the joints with "never-seize". Seems like the hot section would get too hot for most sealers I've found.

What have you folks done?

Thanks,

[hanleyclifford]

Tom - I never use any sealant in this situation. Just hand tighten the pieces and corrosion and carbon from the inside will finish the job. Small leaks disappear quickly.

[Mo]

Hi Tom,
Exhausts are always troublesome when trying to get them apart after years of use. I really don't know if it will make a difference.

I replaced the exhaust manifold when I bought the boat in 2007 and put nothing on the bolts or studs assembling it. Sept 2010 I pulled on my hot exhaust and broke it while under the cockpit.

Removed the hot exhaust and the manifold as one piece. The manifold bolts came out easily, no problem. I used heat to remove the nuts and later the studs from the manifold at the flange joint.

I sort of look at it like working on old cars. I have never had any luck removing studs, without heat, while replacing an old "donut" gasket on a 350 chev. I approached the A4 the same way.

[hanleyclifford]

If you use black iron threaded pipe to assemble a hot section (galvanized should never be used) it should be considered expendable with a service life about 5 years. As Maurice said the manifold and hot section are best handled as a unit and on a bench there should be no problem getting nuts off a stud even if this means destroying them. In the picture that follows all the parts painted silver will be replaced at once except the flange and the output threaded nipple which is bronze. A pair of pipe wrenches will back it out nicely. At the flange the first 1 1/2"NPT close nipple will be destroyed and the threads chased for a new one. No attempt will be made to separate any other components. The extra expenditure for a new manifold gasket is a small price for the gain in working convenience on this assembly.

[JOHN COOKSON]

Something like MollyCoat might work. I have not investigated this myself. It probably would be super expensive and not worth the added expense and trouble. Just an idea.

TRUE GRIT

[msmith10]

Agree that no sealant should be necessary. However, I have entertained the idea of using automotive exhaust system sealer on the threads of the pipes, to act like a high-temp pipe joint compound. Didn't do it, though. The above responders are right- when you have to replace the system, you'll cut off and scrap the whole thing.

[TomG]

Thanks for the input. The old hot section is out (it came out cleanly) and the new is ready. I just wanted to make sure the new joints didn't need to be sealed. As I, too, consider the hot section to be "consumable", I do like Don's suggestion regarding "never-seize" on the flange and the coupling to the standpipe.

Pictures of the new system to follow.

Thanks for the help.

New standpipe being dry-fit:

[ArtJ]

If you use black iron threaded pipe to assemble a hot section (galvanized should never be used) it should be considered expendable with a service life about 5 years. As Maurice said the manifold and hot section are best handled as a unit and on a bench there should be no problem getting nuts off a stud even if this means destroying them. In the picture that follows all the parts painted silver will be replaced at once except the flange and the output threaded nipple which is bronze. A pair of pipe wrenches will back it out nicely. At the flange the first 1 1/2"NPT close nipple will be destroyed and the threads chased for a new one. No attempt will be made to separate any other components. The extra expenditure for a new manifold gasket is a small price for the gain in working convenience on this assembly.

I am surprised to hear about the 5 year service life of the black iron. I rebuilt the standpipe
(original bronze from Tartan) in 2000 and planned on it lasting 20 years.
The original was still in place from 1970 with no leaks. I am pretty sure
that it was original because of the asbestos plaster surrounding it.
Does it depend on engine hours, and also the fact that the standpipe
maybe sits dry most of the time?

Regards

Art

[TomG]

Also, as long as I've interrupted, what's the convetional wisdom on painting the hot section Iron pipe? Seems like it might help a little with corrosion, but I would think you would need pretty high-temp paint to have a chance of it not burning off.

I do plan on wrapping the hot section with MMI's exhaust wrap tape. Perhaps that is enough.

"To paint, or not to paint, that is the question."

[ndutton]

My opinion is it rusts from the inside out. I think painting would be an exercise in futility.

But I don't see any harm either as long as it's non-toxic.

[Mo]

Hi Tom,
I agree with Neil. It is exposed to hot and cold temperatures regularly as well as the salt water. I don't think paint will help at all.

Best

[hanleyclifford]

I like the paint because it reduces the rust and flaking mess in the engine room. Neil is right in that most of the damage is from the inside. The build up near the injection point is another reason to disassemble regularly.

[ArtJ]

Hanley

I am surprised to hear about the 5 year service life of the black iron. I rebuilt the standpipe
(original bronze from Tartan) in 2000 and planned on it lasting 20 years.
The original was still in place from 1970 with no leaks. I am pretty sure
that it was original because of the asbestos plaster surrounding it.
Does it depend on engine hours, and also the fact that the standpipe
maybe sits dry most of the time?

Regards

Art

Copied the above here

[sastanley]

After some discussion with some sailors outside this group, when I assembled mine a couple of years back, I used Permatex #2..this is the thicker stuff...kinda like toothpaste. Like Hanley, I'll probably never take the assembly apart again...the black iron pieces cost about as much as the gasket!

[msauntry]

What's wrong with galvanized pipe? Why only black iron?