Watching the Trades

The answer that I have in a book called Plumbing a House is four wraps. I have seen this rule applied in real life by real people and their work has not leaked. So all is cool right?

Well, the issue is more complicated than that. Some people argue that for the bigger diameter pipes you need to wrap them more times around. If this is true, how many wraps should correspond to what diameter of threaded pipe?

While doing research on this very question I came across information calling into question the four wrap rule. In fact, the most common recommendation on the web seems to be 2 wraps. This comment from a forum is typical……

Many years ago a study was made on a large irrigation system that had numerous leaks. It was found the more leaks were caused by excessive teflon tape, than anything else. Two wraps was deemed adequate. Any more and the fittings were stressed.

Now I was not able to find that study on the net so I have no idea of how accurately this guy is reporting the findings. Nor do I know how rigorous the study was. But many people on the net seem to share his opinion that anything more then two wraps is excessive.

I even came across people who seem to cite the same study that he cited. But nobody seems to want to give the study its proper name. They always just refer to it as a study of an irrigation system. How aggravating.

One of the reasons that I want to see the actual study is that it is my understanding that a lot of agricultural irrigation systems use threaded plastic pipe. It seems to me that the rules for threaded plastic pipe and threaded steel pipe might be considerably different. I can easily see how four wraps of Teflon tape might stress a plastic fitting. I am little more iffy on the concept that four wraps of Teflon is going to stress a 2″ steel fitting designed to handle high pressure steam.

So, should you vary the amount of Teflon you use by the type of joint you are working on? I know one tradesman who argues that you should. Well, maybe argues is too strong of word. He just says that it is something that he does just “to be safe.” He uses the four wrap rule on the smaller diameters but on the bigger diameters he use up to 8 wraps (depending on the size).

But I know better than to go by someone’s “just to be safe” rule. A lot of tradesmen don’t really understand how the materials they are using work, so they just default to the rule that more is better.

Sometimes this rule of thumb works all right. If you are not sure how big your braces should be, err on the side of making them too big. But sometimes more of something can be harmful. So if you don’t know how or why your material works, you don’t really know if more is helpful or harmful.

The problem is that there is some dispute over how and why Teflon tape works. I always thought that Teflon tape worked by sealing up all the little irregularities that are in the pipe threads. But some people argue that Teflon’s primary function is to act as lubricant so that you can apply more torque without breaking things. As this commenter on a maintenance forum says….

When a study was conducted on PVC joints that failed, it was found that it was because too much tape had been used and it cracked the fittings. Obviously that will not happen with metal pipe and fittings, but, normally no more than two layers are needed. However the important thing to remember is that the tape, or any other thread compound’s, prime purpose is to reduce friction, so that the mating threads will make full contact. Filling any voids is a secondary function, so if the threads are old and rusty, there may be nothing that will prevent them from leaking.

But on the same thread another guy replies and says that this guy does not know what he is talking about…

Wrong!! Pipe threads on regular iron pipe will almost never seal 100% without a filler of some kind. male and female threads will not match exactly and something must flow or distort to fill in the gaps. If the pipe could be torqued enough to make the steel distort and fill in the gap it would seal, however regular iron pipe will usualy burst the female thread before reaching that much torque. Brass pipe and fittings coated with grease, can frequently be torqued enough to make a seal. This is just because the brass material is softer. High strength steel fittings made for extreme pressures, can usualy be torqued enough to make at least a low pressure seal without tape or dope.

Just on the basis of my own non-existent knowledge, I would tend to think that the second guy was right. But I recently received a mini -lecture from a former navy man who has gone through nuke school and has been working threaded pipe for almost as long as I have been alive. He claims that the first guy is right. Circumstances did not permit me to cross examine him, but I am awful leery of trying to contradict someone with that kind of résumé.

It may seem like it is splitting hairs to argue about whether the primary function of Teflon tape is to act as a lubricant or as a filler. If its primary function is to act as lubricant then you have to be careful about not putting down too much as it will just gum things up and make it harder to apply the proper torque. On the other hand, if its primary function was to act as a filler, it is possible that there would be times that you would need to apply more wraps as there would be times that you would need more filler.

As an example, let us say that you had old corroding pipe fitting that you took apart to fix a different problem. Let us say that you needed to get the fitting back together again without it leaking and you did not have the parts on hand to replace it. If you thought that the purpose of Teflon was to provide filler, it seems to me that you might want put a little extra on to take care of the extra gaps caused by the corrosion. On the other hand, if you thought that the purpose of Teflon was to provide lubrication you would only want to put two wraps on the pipe because you would not want anything to interfere with your ability to apply enough torque to get a good seal.

I was working with another fellow recently when we ran into this very problem. We could not stop this fitting from leaking in the short amount of time we had available to us. As it happens, the ex-navy man that I previously mentioned was the one who fixed this particularly fitting after we had left. When I asked him how he did it, I got the “primary purpose of Teflon is to lubricate” lecture for the first time in my life. And that is what occasioned this blog post.

Of course, one data point does not prove anything. But I sure would like to find some reliable test data on how and when you should use Teflon.

The scary thing is that people who do plumbing where it really counts do not use Teflon at all. According to this guy….

The teflon tape goes into the piping system and plugs things up. That is why Navy Shipyards will fire any mechanic the find with a roll of teflon tape in their tool box.

This blogger gives a slightly longer explanation on why they don’t use Teflon in refineries…..

I wrapped up an FAT (Factory Acceptance Test) yesterday and learned something new during the inspection: the use of PTFE ‘Teflon’ tape on instrumentation joints is generally banned in oil refineries because the tape can tear off inside a pipe and accumulate at a valve, increasing the chances for equipment failure.

For those who haven’t done much plumbing, PTFE tape is an inexpensive, white, plastic tape that is commonly wound around pipe threads to enhance the sealing of a joint. It also acts as a lubricant of sorts, which can be a big help when disassembling a pipe joint at a later date. Teflon tape has become a staple of the plumping industry and can be found at any respectable home improvement store. Heck, as a general rule of thumb, I always put Teflon tape on a metal pipe joint just because there wasn’t really harm in doing so in the household — it didn’t harm the pipe, and it ensured a more secure seal.

Unfortunately, Teflon tape has a tendency to break off in little particles. As a pipe joint is tightened, the threads ‘bite’ into the Teflon tape and sometimes cut off entire portions of the tape. These liberated pieces are generally found on the internal edge of the threads and get carried away by the fluid that flows through the pipe. For household plumbing, joints are disassembled and reassembled often enough that Teflon tape doesn’t get a chance to accumulate (ex., a garden hose), but, in a refinery, where entire process lines may operate continuously for years, the accumulation of particles in a pipeline is a very real danger. These particles can build up over time and block the operation of critical shutoff valves.

I am not entirely reassured by his statement that this is not a problem in household plumbing. According to p.86 of Plumbing a House (the same book that tells you to use four layers of Teflon)…

When you have finished assembling a gas or water piping system, especially a threaded piping system, you should purge the lines before putting it to use. In the case of a water line, small fragments of metal threads, bits of Teflon tape and excess pipe-joint compound will ride down the inside of the pipe and lodge in your faucets and other valves.
….

Gas lines are less prone to blockage from thread chips because the gas line pressures are only a fraction of water-line pressures and the heavy chips will not migrate so easily, but dust, dirt and small cuttings of Teflon tape will go down the pipe and lodge in sensitive regulators and diaphragms.

I can see how purging the lines would work on new construction. But how can you effectively purge a line when you are doing repair work and much of the line is valved off?

Maybe the title of this blog post should be “should you use Teflon tape?”