High Temperature Stainless Steel Thread Sealant 1

[AMatthews]

I am looking for a good high temperature thread sealant for use on stainless steel NPT threads over 250C to 650C, and on pressures up to 1500 psig in hydrocarbon service. Does anyone have any experience with a product that performs well under these conditions? Masters Metallic has been disallowed at our company due to its lead content.

 

[btrueblood]

I've used a product similar to this, but with a copper flake added. It worked okay, but as an anti-gall compound it was worthless.

From McMaster-Carr online catalog, their p/n 1965K1:

High-Temperature/Pressure Pipe Thread Sealant

Use in high-temperature applications for close-fitting threaded joints on 2" diameter and smaller carbon steel and stainless steel pipe. Sealant is made of graphite with a petroleum-based carrier. It's heat and corrosion resistant and can also be used as a bolt lubricant. Not recommended for use on oxygen lines. Max. temp. is 1200° F. Max. pressure is 7500 psi (air). Meets General Electric NEDC-31735P App. A and D50YP12 (Rev.2) specifications. Comes in a 125-gram (4 oz.) tube. Color is dark gray. Each $34.20

 

[btrueblood]

Sorry, two more things came to mind just after I hit "submit" (I hate that):
1 - I used a similar product at high temps, but fairly low pressure (a few psi to 15 psi) (think exhaust manifolds). We never tried to measure leakage very accurately, just looked to see if any parts near the seal were catching fire...

2 - I think there is also an issue with graphite and steam at high pressures and temperatures (you essentially are creating a coking oven, and convert the graphite to methane, destroying your seal over time).

 

[unclesyd]

You might want to checkout Grafoil Thread Sealant Tape.

 

[dcasto]

Try this

http://www.gasoila.com/index.php?pa...tm&PHPSESSID=de9a0d492166fdcfe8ace2f205cb7527

 

[moltenmetal]

At temperatures up to 650 C, you shouldn't be using threaded (NPT) joints except where you absolutely CANNOT avoid it!

Admittedly, there are a few places where you cannot avoid it!

In our experience, the graphite flakes in oil products (UCAR's product for instance) are only useable for close tolerance machined pipe threads with excellent surface finish- i.e. on Swagelok fittings etc. Don't bother even trying that crap on threads cut into piping using conventional threading equipment. Once the grease is gone, the joints will leak.

You can get expanded graphite ("gra-foil") tape with an adhesive backing. Properly burnished into the pipe threads before assembly, it works well- unless you're carrying air above 300-400 C, or exposed to air at temperatures ~ 600 C or higher- the grafoil will eventually burn out of the joints in these services. That's not speculation- we've been there and done that and seen the material literally disappear.

There IS one sealant of last resort: X-Pando. It's a graphite-bearing cementitious material. No good for acids or bases, but fine for hydrocarbons, gases, vapours etc. You make it up as a paste with water to a thick oily consistency and paint it on the male threads, then screw them together BY HAND with a little final nipping force with a wrench. Screw the joint together like you would with Teflon tape and the joint almost certainly will leak- you need to leave enough material in the joint to expand and form the seal. The good news is, joints sealed with X-Pando seldom leak. The bad news is, joints sealed with X-Pando are VERY difficult to disassemble...