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Old 26-04-2013, 12:58   #1
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Sealant for NPT fittings?

Whats the best sealant for bronze fittings below the water line. I've got bronze street elbows and barbed hose fittings that I need to install in bronze seacocks. I was thinking either 3M 4200 or perhaps a plumbers thread sealant like Rectorseal.
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Old 26-04-2013, 13:29   #2
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Re: Sealant for NPT fittings?

Fast drying 4200. This is what I see the pros at the yard where I haul out using for exactly that...bronze NPT below the waterline. I quit using Teflon tape and plumbers putty many moons ago.
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Old 26-04-2013, 14:45   #3
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Re: Sealant for NPT fittings?

Well, I'm *back* to teflon tape. I use a regular mil spec T27730A tape with 100% success for *water* below and above waterline on NPT threads.

For linear thread I use either Permatex #1 or #2. #1 is permanent (brown colored) and #2 (black colored) can be disassembled IIRC. These need time to dry.

For diesel: I have used Permatex High Temperature Thread Sealant. It's expensive and rated for hydraulics and 100% for diesel. The end of sweating connections.
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Old 26-04-2013, 14:57   #4
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Re: Sealant for NPT fittings?

I use PST. I think it's made by Loctite, (EDIT- it is, it's Loctite 567) Many years of 100% success in many many different types of applications on pipe threads.
I tried cheap stuff, it's not the same.
Works for water, oil, air, hydraulic, ATF, you name it.
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Old 26-04-2013, 19:55   #5
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Re: Sealant for NPT fittings?

For NPT, as Jedi said, a good Teflon tape is all you need. The teflon tape like pipe dope, mainly acts as a lubricant so the tapered threads slightly deform and seal metal to metal when tighten. Done right, which is pretty easy after all, its all you need. Generally for NPT connections sealants are not needed. For NPS sealants are required as there is no metal deforming with straight threads.
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Old 26-04-2013, 20:08   #6
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Re: Sealant for NPT fittings?

Another vote for Loctite PST. I have used it with steam at 500psi, fittings are always easy to disassemble later.
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Old 26-04-2013, 22:41   #7
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Re: Sealant for NPT fittings?

My favorite thread sealant is Leak Lock because it works on just about everything.
You can use it on metal or plastic fittings carrying water, gasoline, diesel, propane, natural gas, refrigerants, and oil. Don't use it if you're building a still, it doesn't like alcohol.
Highside Chemicals Inc. manufacturers Leak Lock and Leak Lock Gold.

Leak Lock by Highside INC.
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Old 27-04-2013, 05:17   #8
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Re: Sealant for NPT fittings?

I like telfon tape, someday you may want to take it back apart
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Old 27-04-2013, 06:42   #9
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Re: Sealant for NPT fittings?

See also:
"Thread Sealing 101"
by Robert Valitsky, Technical Communications Manager Henkel Corporation (Locktite)
http://www.useloctite.com/filephotos...ch_article.pdf
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Old 27-04-2013, 07:07   #10
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You had the right answer included in the question. Use Tru Blue Rectorseal. Like the ad says "I put that **** on everything". Tape is a PITA.
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Old 28-04-2013, 06:15   #11
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Re: Sealant for NPT fittings?

This is from a professional plumber who works on boats and the US Arctic station:

Mil spec Teflon tape first, Blue Monster pipe sealer over the tape.

Myself have used this system on all types of thread applications for years with 100% success.
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Old 28-04-2013, 07:33   #12
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Re: Sealant for NPT fittings?

Quote:
Originally Posted by silverp40 View Post
This is from a professional plumber who works on boats and the US Arctic station:

Mil spec Teflon tape first, Blue Monster pipe sealer over the tape.

Myself have used this system on all types of thread applications for years with 100% success.
+1

Many years ago, shortly after getting out of college, I was a manufacturers rep in the Hydronics and HVAC industry. One of my lines was Hercules Chemical Company makers of Teflon tape and some of the best pipe dopes money can buy. I spent countless hours in commercial, industrial and pharmaceutical installations and the pipe fitters very often used both tape and dope. I began using it too.

My pipe dope of choice (the one I use most) is Hercules Real-Tuff. In a boat you don't really need tape and dope, at 2-3 PSI, but I have seen Real-Tuff and Hercules Mega-Loc at thousands of pounds per sq in not leak.. (I also sold high pressure steam boilers for industrial applications rated at hundreds of horse power)..

Neither of these dopes ever harden and the fittings come apart years later without issue. I also use them in threaded exhaust fittings & fuel fittings (but no Teflon tape with fuel) and they survive perfectly.

Real-Tuff is available at most Home Depot's now days. It used to be a trade only product but since joining with Oatey they have begun selling these products through retail chains. Today there are a number of good dopes out there but I still prefer Real-Tuff or Megaloc..

One bottle will probably last the average DIY about 20 years.....

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Old 29-04-2013, 15:14   #13
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Re: Sealant for NPT fittings?

Thanks for the responses. Looks like the consensus is tape and sealant. I like the idea of purpose made pipe thread sealant as if something like 4200 is used, if you ever had to get the joint apart, you'd have all that cured 4200 gumming up the threads. It'd be a mess to clean the threads out.
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Old 29-04-2013, 15:24   #14
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Re: Sealant for NPT fittings?

Go to the plumbing supply store or home center and get a tube or can of pipe dope. Read and follow the instructions. Don't think a marine sealant is better, it is not.

Pipe dope insures electrical contact between the objects to be joined and this is important for bonding. Teflon tape may (or may not) interrupt the electrical continuity between the parts. The only way to tell is with a meter after you have completed the joint.

Not really part of the question, but never use Teflon tape on fuel system piping. Small bits of tape can break off and get into your fuel system.
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Old 29-04-2013, 18:10   #15
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Re: Sealant for NPT fittings?

Quote:
Originally Posted by HopCar View Post
My favorite thread sealant is Leak Lock because it works on just about everything.
You can use it on metal or plastic fittings carrying water, gasoline, diesel, propane, natural gas, refrigerants, and oil. Don't use it if you're building a still, it doesn't like alcohol.
Highside Chemicals Inc. manufacturers Leak Lock and Leak Lock Gold.

Leak Lock by Highside INC.
Wow that looks like great stuff. When I installed my autopilot I used teflon tape to seal the hydraulic fittings. It developed minor leaks and I had a hell of a time burping it. I eventually found that using Permatex High temperature thread sealant worked to seal the joints properly. I like the look of the leak lock seems like they don't pay as much in marketing because the price is reasonable.
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