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Thread locking inside boilers

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John Billard 124/01/2022 13:02:37
108 forum posts

What is the best sealant to use these days for screwed joints within a 5" gauge boiler when subsequent access might be "difficult".

Best wishes

John B

Former Member24/01/2022 13:22:14
1085 forum posts

[This posting has been removed]

Former Member24/01/2022 13:22:14
1085 forum posts

[This posting has been removed]

Former Member24/01/2022 13:22:15
1085 forum posts

[This posting has been removed]

KWIL24/01/2022 15:03:51
3549 forum posts
70 photos


It must be something you do, does not happen to me!

Grindstone Cowboy24/01/2022 15:58:49
854 forum posts
64 photos

Not saying it's the cause of multiple posts, but I sometimes double-click where I should single-click.

And to (partly) answer John B's original question, I'm afraid I've never built a boiler. However, I have had success with this for other sealing requirements, and I'm sure I read somewhere that it's suitable for steam. Doubt whether it has any thread-locking capabilities, though.


Links to

John Rutzen25/01/2022 08:42:48
348 forum posts
19 photos

Hi, I think Loctite is ok with steam for say screwing a thread into a boiler to hold on a support bracket but it does lose it's strength as I found out. I had screwed my regulator rod into the cam it used to operate the device and sealed it with loctite. I steamed up and wondered why the loco wouldn't move - the thread had unlocked itself! So I don't know of any thread sealant which will do anything other than seal inside a boiler.

John Billard 125/01/2022 11:50:26
108 forum posts

Thanks for the replies. I am just interested in sealing threads at the moment e.g.main steam pipe in to the regulator and oil pipes etc into unions/bushes.

Farmer para 287 uses Boss White but this was 1964.

John B

Paul Lousick25/01/2022 12:16:14
2009 forum posts
711 photos

I used graphite sealant on the studs that screw into the barrel on my boiler. Graphite based compound is the traditional sealant for threaded and flanged connections on steam engines.

old mart25/01/2022 12:21:30
3717 forum posts
233 photos

Google Loctite thread sealants to get the exact specifications.         



Edited By old mart on 25/01/2022 12:24:09

John Purdy25/01/2022 18:14:29
337 forum posts
198 photos

I have used Loctite PST high temperature  thread sealant #567 on my boiler fittings (internal and external), for many years and have never had a problem. Its a white paste in a tube, Loctite part #56747. It doesn't set hard so fittings can be easily removed in the future. According to the spec sheet its strength reduces to 55% of initial strength after 1000 hours exposure at 250C (482F). That's equivalent to a boiler pressure of about 550 PSI.



Edited By John Purdy on 25/01/2022 18:20:19

Edited By John Purdy on 25/01/2022 18:51:58

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