Teflon is 99.9% inert to my knowledge and perfectly suited for use on threaded joints on hydrocarbon services. I've used it on fuel oils, natural gas, Acetylene, ethylene, LPG, Butane, Propane, etc. with no problems as far as the Teflon reacting or being attacked by the fluids.
However, in today's technology, I would not use Teflon tape or screwed fittings. I've already proved numerous times at the operating plant level that it is far more cost effective and safer to weld 100% and come back later with a bandsaw, if necessary, to do pipe internal access or modifications in the future. I can apply Teflon tape without any potential problems; however, I will not trust any pipefitters today to correctly apply the stuff without causing strips and pieces to enter the fluid spaces and flows. This is because of the extra-ordinary pressures being put on maintenance crews with respect to time, training, tools, supervision, and adequate resources. Today, more often than not, the damn Teflon tape winds up being trapped in downstream screens, filters, valves, drains, and other process equipment - causing process upsets, shutdowns, and other deviations. I don't think its worth the pain and the risks. With class A pipe welders and electric bandsaws, its easy, quick, safe, and dependable to simply weld all the pipe - especially the 3/4" to 2" sizes with socket weld couplings.
Montemayor is correct in all that he says, I would add.
We hate threads, buggy things.
Small tubes and sensors are threaded, up to about 1/2".
We also use grooved fittings, mechanical joints, etc.
Very nice when people know how to use them, much faster than welding in situations where they are suitable.
If you have no choice but to use the tape, then heed well what Art Montemayer has said. Many a problem has been found to be teflon tape in some small orifice, or other small passage. I would select the paste over the tape for the problems stated, and the time element. Even Bubba can put on a little paste without messing it up real bad.
Agreed with Montemayor, tape doesn't get put on properly and teflon threads do wind up downstream - especially problematic in a lube oil reservoir, that stuff works its way into a bearing race and you're looking at an overhaul. I'd stick with teflon paste.
In rough-and-ready gas-field operations, most jobs don't have access to welders--there just isn't enough time in the job schedule for isolation-for-hot-work or for x-ray. Typically 2-inch and often 3-inch pipe on lower-pressure wellsites (below about 500 psig) is threaded. Some companies are just fine with threading 4-inch, but I've had a hard time finding the gorillia's who can tighten that stuff successfully by the end of a day.
If threading in field operations is here to stay, then the best way I've found to keep chunks of tape out of downstream equipment is to tape the joint and follow the tape job with teflon paste. I've found this to effectively capture the tape and provide better results than either by itself.
rmw - you must not be familiar with the "technique" of swabbing a brush-load of pipe dope INTO the female threads of fittings
The fundamental problem with screwed joints is that few people know properly thread pipe anymore. Combine this basic problem with improper selection of thread sealant, and let the leaks begin. Many don't realize that there are pipe size limitations on all kinds of dopes & tapes, as well as factors like temperature. A lot of dopes are only rated to 300*F, many more to 400*F. It's important to read the label on the container.
all these supporting postings and not one star for art!?
u got one art.
although not explicitedly mentioned, but integrity of piping systems is essential to overall plant performance and life. a threaded joint is a weak joint and a risk assessment ought to be accomplished/considered for the fluid/piping system.
Hey, TBP, guilty as charged. You notice that I left myself a little wiggle room by saying 'real bad'. That allowed Bubba the leeway to do it the wrong way and swab the female threads.
Plus, I assumed by the question asked, that it was within the temperature range of teflon, or the question would have not been asked. If we go higher than that, then we are going to have to talk about some really high pedigree pipe dopes.
I see threads in 5000 psi, 900F service all the time.
rmw - it was only the first part of my post that referred to your original. The second part was just a general comment. Sorry for the confusion.
We do thousands of threaded joints on industrial steam systems every year, and the leakers can be counted on the fingers of one hand. I don't recall a problem with strings of Teflon tape from our installations being found anywhere in the downstream piping. But I also realize that we're often the exception to the rule - around here, anyway.
Then, go give someone in your system some kudoo's. They are doing a fine job, or the nature of your system is such that there are not a lot of small diameter connection points to the system, which I doubt. I am referring to flow orifice taps, instrument taps, sample taps, etc.
Lots of teflon tape has ended up in these locations, or the instruments attached to them. On the other hand, if done right, it never has to happen, which seems to be your situation.
Tapped internal pipe threads will always have a line where the tap stopped and is reversed. Our experience is there is no good way to seal liquid tight at high pressure or temperature with tapered pipe thread. Thread sealants will help solve this problem, but vibration, changes in pressure and temperature make the joint move enough that the sealant or tape will fail over time.
If you need a fluid tight threaded connection use straight threads and a sealing surface, o-ring, or gasket.
tfe tapes are not recommended for greater than 600 psi class service. It has to do with worn threads.
On new threads tape has been used succesfully in most pressure classes that permit npt connections. when the threads are worn there is a habit of just wrapping more tape to make the joint secure. a number of failures have occured where tfe tape has been used and the joint failed.
I've never actually seen the term "worn" used to describe pipe threads before, and I'm not sure that it applies. I very often see threads that have been re-taped for re-assembly, without removing the old tape. The first thing that the occurs to me is that someone has been doing "steamfitting" that shouldn't have been. If they didn't get the old tape of the male pipe threads, then it's highly unlikely that they brushed the female threads on the fitting to get the bits of tape off those.
The single main "problem" with screwed piping in most general industrial applications isn't the joint, or thread sealant (if it's been selected properly) - it's that screwed piping is typically looked at as something for the millwrights to use as fill-in work, between production machine repair work orders.
Worn pipe treads according to measurement. there was a near fatal incident in a UK hydrotest facility in the 90's. The fitting was a threaded thermowell and had seen various degrees of corrosion and material loss over the years. the threads were bulit up with teflon tap to obtain a pressure tight condition but it could not hold the pressure (>3500 psig or so). believe there is still a web site with the Health and Safety Executive in the UK that documents the incident - viewer warnings are present. the thermowell had the impact of a shotgun blast as you might expect. Fortunately the employee survived.
It's certainly too bad that someone got hurt, but the accident sounds much more related to sloppy practices in general than a particular fault with the selection of a threaded connection and/or the use of tape as a sealant. In situations where systems contain pressures anything like 3,500 PSIG, somebody (everybody!) needs to be paying close attention to things like worn, corroded/eroded components. In applications where there is constant disassembly-reassembly, I'd like to think that there would be some scheduled replacement of the fittings involved. When the components hit the time interval and/or number of cycles, they get scrapped and replaced with new.
