Hot Oil Piping, method or sealant.

[haze10]

Got a problem with a two roll lab mill using Paratherm NF, like a mineral oil, at a temperature of 380F. Piping is 1"npt carbon steel. We can't stop the leaks at the threads. We reworked all the piping using the factory recommended Permatex High Temp Pipe Dope, but it didn't work. What is the best method for piping, ie should I be using flared tubing or compression fittings, and what is the best pipe sealant for convential NPT steel pipe. Also, and idea how to seal a pipe union, or should I just replace with flanges.

 

[TBP]

Are the fitters cutting the threads properly? Threading pipe is increasingly becoming a lost art. A great many guys cut the threads too deep, which increases the spiral clearance and makes it harder for Teflon tape or dope to seal it. They should be get 3 - 4 turns to hand tight on clean dry threads, if the dies are set properly.

I've never used Permatex - is there a cure-time? If all else fails, have you considered X-Pando? It's typically got a 24 hour cure-time which doesn't usually lend itself to maintenance work. Production people always want the line back in service about 15 minutes ago, and aren't interested in cure-times.

 

[haze10]

We are using experienced pipethreaders and yes they are getting about 3 to 4 turns before the threads tighten up. I think we are just suffering from thermal expansion problems. The permatex can directions are being followed, but there is only a 5 minute cure time. In this case the machine was left for 48hours to cure, but we still had leaks when started.

 

[pmover]

seems like a good situation to weld the joints (socket weld), especially if temps are that high and there are thermal cycles to consider as well. may need to consider expansion loops or joints for long pipe lengths.

not much help, but . . .

good luck!
-pmover

 

[Ashereng]

You may consider to try 600# RTJ flanging.

Welding works well.

 

[moltenmetal]

As has already been recommended, use X-pando. It's a cementitious expanding pipe thread sealant, very effective for hot oil. If there's a trick to using it successfully, it's this: don't over-tighten the assembly. Leave enough sealant in the joint so that it has a chance to expand and seal.

Get rid of threaded unions and replace with pairs of flanges. If there isn't enough room for flanges, replace with a union which has a brass seating ring. Ordinary steel to steel or MI to MI unions are notoriously leakage-prone.

Threaded piping gets a bad name because people don't know how to do it properly, use it in inappropriate services, and use incorrect sealants. Properly done, threading is a very efficient and flexible method of joining pipe below 2" NPS, and can be used for far more than air and water.

 

[stanier]

In my experience hydraulic piping and fittings to SAE standards provides for a better system