Pipe dope on hydraulic line connection?

[Texasmark]

Pipe dope of any kind is not meant to seal but rather to act as a lubricant so you don't gall the threads when tightening. Proper threads that haven't been overtightened will generally seal with any pipe dope used. One containing copper or/and graphite will work well for hydraulic systems.

Pipe dope will sometimes help seal a bad thread by allowing additional tightening. A turned thread from overtightening usually needs to be replaced to stop it from leaking.

Gotta differ with you on this one. If you are talking about a tapered pipe joint, NPT, read up on the specs and they are a sloppy fit. I don't remember the circumstance, but when I was working I did and after that research I always used dope. Included was when to and not to use teflon tape which obviously is a lube besides a filler.

 

[Gary Fowler]

Gotta differ with you on this one. If you are talking about a tapered pipe joint, NPT, read up on the specs and they are a sloppy fit. I don't remember the circumstance, but when I was working I did and after that research I always used dope. Included was when to and not to use teflon tape which obviously is a lube besides a filler.

And yes I am talking about NPT joints only. Just what are you disagreeing with? That the threads do/do not do the sealing? Thread dope is a lubricant? What? And I did say pipe dope is not "meant" as a sealant although a lot of it is used that way with mostly unacceptable results. Properly cut NPT joints are not a sloppy fit. The first threads only are cut a bit deeper for started threads but the rest are tightly fitted so that pressure between the threads holds the pressure. Thread dope is only used for a lube so the joint can be properly tightened without galling the threads.

Not many professional pipefitters really know how to thread and tighten NPT threads. 99.999% of leaks in industrial construction are from improperly threaded and tightened NPT threads. Mostly the leaks are from overtightening rather than under-tightening. A properly tightened joint will have 1-3 threads showing. If no threads are showing it has been overtightened OR improperly threaded (threads cut too deep). For this reason, I always recommended to our engineers to just delete threaded pipe from the specs and go with socket weld only for any thing smaller than 1.5" nominal pipe size.

 

[RickB]

Blah, Blah, Blah. People don't cut their own threads on NPT hydraulic fittings. The mating threads probably weren't cut on the same continent, much less with the same brand of tooling.

Use of a dope style or tape style sealant is mandatory for leak free connections where one of these engineers insisted on not using a better ORB or JIC connection. We aren't professional pipefitters or ME's and we are not working in industrial construction. This is the real world, and all this crap about not needing anything on NPT threaded connections is simply that. I've been around too long to be convinced otherwise.

 

[whitepine2]

Retorseal #5 best stuff of any pipe dope have used it for years on hydraulic fittings on fishing boats and
other machinery with good results. It is a soft set and good for gas and other chemicals.

 

[PILOON]

ust do as the chicoms do. LOL.
Use epoxy paste which will set up hard and seal any treads.
Only heat will cut that joint loose.

 

[ultrarunner]

Since a few posts have expanded this topic I hope it is ok to add some early experience.

My earliest helper-job was for a semi-retired plumber from a long line of plumbers... my Dad worked for his Dad one summer years before.

Threaded joints were sealed with hemp or jute and my job was to pull out just the right amount of hemp and orient the strands as needed for the pipe size for the water and gas pipe.

Cast iron bell joints were all Oakum and Molten lead although sometimes for repairs we used Lead Wool and a curved punch to pound in the lead into the joint after the oakum went in...

Still come across this on very old houses and farm machines...

I was introduced to Loctite when I started restoring my Model A Ford... it did wonders in keeping screws and nuts from backing off and have used it every since...

Over the years I have frequently found problems traced to improperly applied Teflon Tape... either contaminated the fluid obstructing passages and screens or the worst was when a neighbor came home after just picking up his car from Chrysler/Plymouth for service... he pulled in his driveway and odor of gas was strong... the Dealer used Teflon Tape to seal the threads of the carburetor to fuel line and the tape was wound the wrong way and large piece was inside the float chamber and kept the fuel float stuck open... lucky the car didn't end up a fireball!!!

 

[RickB]

Since a few posts have expanded this topic I hope it is ok to add some early experience.

My earliest helper-job was for a semi-retired plumber from a long line of plumbers... my Dad worked for his Dad one summer years before.

Threaded joints were sealed with hemp or jute and my job was to pull out just the right amount of hemp and orient the strands as needed for the pipe size for the water and gas pipe.

Cast iron bell joints were all Oakum and Molten lead although sometimes for repairs we used Lead Wool and a curved punch to pound in the lead into the joint after the oakum went in...

Still come across this on very old houses and farm machines...

I was introduced to Loctite when I started restoring my Model A Ford... it did wonders in keeping screws and nuts from backing off and have used it every since...

Over the years I have frequently found problems traced to improperly applied Teflon Tape... either contaminated the fluid obstructing passages and screens or the worst was when a neighbor came home after just picking up his car from Chrysler/Plymouth for service... he pulled in his driveway and odor of gas was strong... the Dealer used Teflon Tape to seal the threads of the carburetor to fuel line and the tape was wound the wrong way and large piece was inside the float chamber and kept the fuel float stuck open... lucky the car didn't end up a fireball!!!

Unfortunately improper use will usually lead to problems.

 

[Texasmark]

Since a few posts have expanded this topic I hope it is ok to add some early experience.

My earliest helper-job was for a semi-retired plumber from a long line of plumbers... my Dad worked for his Dad one summer years before.

Threaded joints were sealed with hemp or jute and my job was to pull out just the right amount of hemp and orient the strands as needed for the pipe size for the water and gas pipe.

Cast iron bell joints were all Oakum and Molten lead although sometimes for repairs we used Lead Wool and a curved punch to pound in the lead into the joint after the oakum went in...

Still come across this on very old houses and farm machines...

I was introduced to Loctite when I started restoring my Model A Ford... it did wonders in keeping screws and nuts from backing off and have used it every since...

Over the years I have frequently found problems traced to improperly applied Teflon Tape... either contaminated the fluid obstructing passages and screens or the worst was when a neighbor came home after just picking up his car from Chrysler/Plymouth for service... he pulled in his driveway and odor of gas was strong... the Dealer used Teflon Tape to seal the threads of the carburetor to fuel line and the tape was wound the wrong way and large piece was inside the float chamber and kept the fuel float stuck open... lucky the car didn't end up a fireball!!!

I used Lead and Oakum when I added my 3rd bathroom to a house in town (late '60's) using code cast iron sewer pipe.

 

[ultrarunner]

Should last a lifetime as long as no one uses acid drain cleaner... seen cast iron turn to Swiss Cheese!

 

[tkevan]

Loctite 569. Made specifically for this purpose.