HOME  |  NEWS  |  BLOGS  |  MESSAGES  |  FEATURES  |  VIDEOS  |  WEBINARS  |  INDUSTRIES  |  FOCUS ON FUNDAMENTALS
  |  REGISTER  |  LOGIN  |  HELP
Blogs
Sherlock Ohms

The Pipe Sealant Was Not Compatible With Jet Fuel

Jim Gammon
12/17/2013  
21 comments
NO RATINGS
View Comments: Threaded|Newest First|Oldest First
bob from maine
User Rank
Platinum
Use of thread sealant on fuel lines
bob from maine   12/17/2013 11:25:33 AM
NO RATINGS
Jim: Enjoy your use of the visual aid to verify a vacuum leak. I've done fuel systems that could hold 15" of vacuum for days and others that leak down over minutes or hours. Chasing vacuum leaks is the bane of installing fuel systems. I've had marine systems that work perfectly for years until the filter got a little plugged and the fuel pump tried to pull 5 or so inches of vacuum. Then air began entering the fuel line through a tiny leak somewhere and the engine started exhibiting some really unique behavior. Easy answer: Change the filter. Hard answer: Before or after we are driven onto the rocks.

WKTaylor
User Rank
Iron
Re: Use of thread sealant on fuel lines
WKTaylor   1/17/2014 9:58:17 AM
NO RATINGS
I suspect that the real problem here is the nature of aviation "jet fuels".... commercial [Jet-A, -B, etc] and military [JP-5, -8]... in that they consist of refined hydrocarbons loosely called "kerosene" AND various additives to control physical properties. Also, all-too-often, various levels of contaminates including moisture, microbes/fungus, particulates, etc become part of the fuel mix.

Ask any fuel formulator to explain "fuel", and You will quickly understand that "pure fuel" consists of dozens of fundamental hydrocarbon molecule chains [chemistries], from very light to very heavy, mixed in various % levels, to make the fuel, IE: gasoline, diesel, kerosene, etc. The whole discussion will make You light-headed/dizzy.

I suspect that jet-fuel additives are most likely the big culprit in this scenario; especially when combined with the lightest fuel hydrocarbons and trace moisture. The additives enhance or control lubricity, static electricity, microbes and fungus, ice formation, free metal ions, coking tendencies, etc/etc. Trace moisture/contaminates can effect changes in the fuel and affect how the additives perform. Throw-in even minor changes in jet fuel "kerosene" [IE Jet B] formulations can force significant alterations in the nature of fuel. Unfortunately, some of these additives and contaminates, even in small quantities... especially in hotter climates... have aggressive effects all-too-similar to paint stripper.

This problem with jet-fuel is one of the reasons that specially formulated rubber seals, and precisely threaded metal-metal pipe connections, are used on aircraft in-lieu-of relying on thread sealants. The other reason thread sealant/tape should be avoided in aviation fuel systems [including in-ground, above-ground and tanker systems] is that the particles released as these materials disintegrate WILL flow into/through-out the aircraft fuel system as particulate contaminates that MUST be captured in the filters to avoid pump and engine fuel control problems.

Combine this with the scenario described where "air" appeared to be in the system and You have aircraft engineer nightmares of particulates, moisture and bio/fungus build-up. Obviously, moisture is a critical element in ice formation in winter operations; and allows fungus/mold build up at the water/fuel interface in warmer climates. Contamination from all sources [many of which I have not mentioned in an effort to KIS this discussion] make for  aircraft operator nightmares. When fuel filters become clogged-up, pumps and engines tend to fail, fuel level sensors become erratic, etc. Take my word for it, BAD things happen when an aircraft fuel system is contaminated! It can be a horribly painful, expensive, time-consuming situation to rectify. However, being ignorant of it... or ignoring it [IE: just changing filters more often]... risks possible catastrophe.  

William K.
User Rank
Platinum
Re: Use of thread sealant on fuel lines
William K.   1/23/2014 6:17:25 PM
NO RATINGS
@WKT, absolutely correct, especially about the severity of problems. There is just no place in the sky to stop and fix an engine. Even worse on some of those jets, which glide like a rock. Problems that would be an irritation in a car can be fatal in a plane.

naperlou
User Rank
Blogger
teflon tape for everything
naperlou   12/17/2013 1:11:11 PM
NO RATINGS
I like the use of teflon tape as a sealant.  I find I use it a lot, mostly in plumbing repairs, but sometimes in pressurized systems.  It is wonderfully easy to work with and easy to "clean".  I like the idea of the Vaseline to protect the tape.  Great job.

gtpjimgammon
User Rank
Iron
Re: teflon tape for everything
gtpjimgammon   12/17/2013 2:07:15 PM
NO RATINGS
We have found an interesting trick with small straight thread connections that have flats. We twist tape into a rope, wrap it around the base of the thread and tighten the pieces together. The teflon flows into the area of the flats and makes a gasket of sorts. It takes the right kind of flats and the right amount of tape, You should not count on any particular application to work without testing, that is my CYA message. We have not used this on high pressure - Jim

redrok
User Rank
Iron
Teflon Tape? Not so fast here!
redrok   12/18/2013 9:53:58 AM
NO RATINGS
Teflon tape can, sometimes, have problems too.

Teflon tape by its nature is kind of stringy. Sometimes the tread can cut a bit off which can get lodged in solenoid valves causing them to leak.

I recall that NASA once had found the root cause of some leaky valves to be tiny Teflon "threads" in the system. They had banned Teflon tape in favor of Teflon dopes or other dopes.

If Teflon tape was required they had to be able to visually inspected the inside of each connection. Obviously, very difficult or impossible to do.

Dopes are essentially, a sealing powder with a flowable liquid binder. If the powder somehow "escapes" it doesn't cause problems like the thin hairs of Teflon tape. Of course, all the components of the dope must be compatible with your application.

I now always use Teflon dope. Makes sense to me.

redrok

William K.
User Rank
Platinum
Re: Teflon Tape? Not so fast here!
William K.   12/18/2013 12:36:36 PM
NO RATINGS
Over the years we have had quite a few customers who forbid the use of teflon tape as a sealer just because of those little strings. They are quite real and they will certainly cause valves to leak, and they are incredibly difficult to completely remove feom a system. The recommended sealer has been teflon paste, applied per a fairly detaled specification. But one would need to use a teflon paste compatible with the particular fluid. Probably any rated for gasoline service would also work for jet fuel.

gtpjimgammon
User Rank
Iron
Re: Teflon Tape? Not so fast here!
gtpjimgammon   12/18/2013 3:47:42 PM
NO RATINGS
The correct way to apply teflon tape is to not apply it to the first thread and not to apply it too thickly. On good threads, 1.5 wraps is enough, for pipe sizes under 1". We use more on larger pipe. This prevents "strings" from forming, they are the excess tape before the first thread.

This doesn't work is you are trying to prevent galling of, for example aluminum threads on aluminum threads.

 It also must be applied under tension, to deform it into the threads. If just piled on, it will strip off. 

William K.
User Rank
Platinum
Re: Teflon Tape? Not so fast here!
William K.   12/18/2013 4:24:21 PM
NO RATINGS
gtp, of course it is possible for a skilled person to apply tape so that no shreds of teflon are created during assembly. During dis-assembly there would be shreds that could get into the system. In addition, the procedure that you describe would require a bit of skill and remembering to do the job just right. So while it could be done that way, the potential for problems is not woth the savings produced by using the teflon paste sealer. That was the decision by at least one of the large automakers.

gtpjimgammon
User Rank
Iron
Re: Teflon Tape? Not so fast here!
gtpjimgammon   12/18/2013 4:30:33 PM
NO RATINGS
I'll agree that it is a sealant not to be used by unskilled people, but the sealing dope that is the subject of the article was a teflon  dope, brushed on from a can It would seem that the liquid carrier was soluble in the fuel. I was not told the brand, but I was told it listed avaitation fuels as compatible.

We have enough trouble hiring people who can read 5/8" on a ruler! and don't have to be told "rightie tightie"

Either way, our little tester is a simple way to detect leaks in suction pipe if there is a verticle lift.

William K.
User Rank
Platinum
Re: Teflon Tape? Not so fast here!
William K.   12/18/2013 4:35:42 PM
NO RATINGS
OK, I did not get that the sealant was teflon filled, from the article. There are a lot of types and chemistries of pipe sealers around, and many of them are both low performance and quite cheap, and not nearly as good. I have had good luck using the more reliable brand of the TFE filed sealer, but I am aware that poor quality products are always available and often sold for less.

Amclaussen
User Rank
Platinum
Re: Teflon Tape? Not so fast here! Which is worst: Tape or Paste?
Amclaussen   12/26/2013 2:16:24 PM
I've had my own batch of problems with either.

Teflon threads in pressure regulators, and "good quality, famous brand" paste drying and disintegrating, clogging small passages too.

And I refer to that famous brand that used to sell its "STT" product (called in spanish: "Sella Tuberias con Teflon" (pipe sealant with Teflon)... no less than "LOCTITE" (!!!).

Now sold as Henkel LOCTITE® 567™ PST®, that stuff appeared to be a great product, until I saw several failures, where the allegedly superior product dried and disintegrated into a powdery residue, which is undesirable too.

In the end, I found that applying the tape myself, carefully applying it, avoiding the first few exposed threads was the less problematic of the two approaches. And using a minimum quantity of lubrication helps (I use what won't cause additional problems, if I can find it, like silicone grease or PAG Synth oil, but only where it definitely won't contaminate the system).

William K.
User Rank
Platinum
Re: Teflon Tape? Not so fast here! Which is worst: Tape or Paste?
William K.   12/26/2013 9:40:07 PM
The challenge withteflon tape is that the correct application requires both operator skill and good judgement, which is whyISO9000 would forbid it's use. Yes, used correctly it does do a great job, no question. Used incorrectly it can leadto problems. And ISO 9000 does not allow for user judgement,which is required to use it correctly.

WireGuy1950
User Rank
Iron
Caution on the use of Vaseline
WireGuy1950   12/18/2013 10:12:36 AM
NO RATINGS
While the Vaseline trick may be effective in most situation do NOT use on Oxegen fittings!

notarboca
User Rank
Gold
Re: Caution on the use of Vaseline
notarboca   12/30/2013 3:57:45 PM
NO RATINGS
Petroleum + pure O2= BOOM!  Glad you mentioned this Wireguy1950.

OLD_CURMUDGEON
User Rank
Platinum
And, what about ......
OLD_CURMUDGEON   12/20/2013 8:08:21 AM
NO RATINGS
About a thousand years ago, during my college days, I worked as a plumber's helper summer job.  At that time it paid about 25 cents/hr.  Good pay back then! 

At any rate, we used ONLY two products for sealing threaded pipes, be they steel, galvanized, black iron, or brass.  IF the piping circuit was for gas or petroleum products, we ONLY used PERMATEX, the shellac-based GOO that stuck to your fingers & tools better than SUPER GLUE.  And, for water, steam & drainage, we used this gray glop, called PRO-DOPE.  Even though the printing on the can said it was OK for gas, we NEVER used it there.

So, I guess my question now is, "Why can't PERMATEX be used for this critical application?"

Even now in my adult life, I avoid teflon tape, both professionally when building pneumatic/hydraulic computer-controlled machines, OR personally, when dealing with plumbing problems at home.  The "Stringiness" is one problem area that I've had to overcome.  There are others.....

GlennA
User Rank
Gold
read the applicable code
GlennA   12/25/2013 12:46:07 PM
NO RATINGS
Then there is the old story of a refinery that was assembled with teflon tape, but the contractor had failed to read the code requiring the use of pipe dope.  An expensive re-fit.

Flyby
User Rank
Silver
Pipe Sealing
Flyby   1/27/2014 7:36:48 PM
NO RATINGS
An experienced plumber just installed some water pipes for me and used teflon tape as the lubricant and pipe dope as the sealant. Both the tape and the dope were not put on the fist thread.

Our oil company installed new oil tanks and used only a green colored paste for all of the oil lines, no tape. A short search will find the product.

Ye Ole Professor
User Rank
Iron
I know the feeling too well
Ye Ole Professor   2/4/2014 5:41:23 PM
NO RATINGS
We use a type of soap to clean our filters of oily residue. A couple years ago the system was updated and the old steel pipes were replaced with Sch 80 PVC as a lower priced alternative to the  stainless steel I and another recommended. What the cost cutters didn't look at was the composition of the soap. Basically Formula 409 on steroids. It contained a caustic compound and various methyl-ethyl solvents that were nearly identical to the solvents used in the pipe glue.

Hmmm... Could we have some compatability issues here??


After about 3 months of operation soap was squirting out of most all of the glued joints. A ferensic examination of the failed joints showed that the glue had been completely dissolved.

The piping was then replaced with 216 SS.


Gotta love it: I told you so!!!

 

Ye Ole Professor
User Rank
Iron
A Side Note:
Ye Ole Professor   2/4/2014 6:05:42 PM
NO RATINGS
I would NEVER ride in a plane that received its fuel from a storage system I knew was assembled with Teflon tape.

NHRA and other racing sanctioning bodies won't let your car off the trailer if they find any trace of Teflon tape anywhere on the fuel system during inspection. 30 years ago I helped extinguish multiple engine fires and pushed numerous disabled race cars off the tracks due to bits of that stuff stuck in the fuel system orifices and controls.


NEVER NEVER NEVER use that stuff on a fuel system or fuel strorage system.

Dig that pipe back up and go get the recommended sealant on those threads.


Or I'll recommend this article for the Made By Monkeys post.

Cabe Atwell
User Rank
Blogger
Re: A Side Note:
Cabe Atwell   3/26/2014 4:45:46 PM
NO RATINGS
This post just reinforced my fear of flying.

 

Partner Zone
More Blogs from Sherlock Ohms
Sherlock Ohms highlights stories told by engineers who have used their deductive reasoning and technical prowess to troubleshoot and solve the most perplexing engineering mysteries.
Sherlock Ohms highlights stories told by engineers who have used their deductive reasoning and technical prowess to troubleshoot and solve the most perplexing engineering mysteries.
Sherlock Ohms highlights stories told by engineers who have used their deductive reasoning and technical prowess to troubleshoot and solve the most perplexing engineering mysteries.
Sherlock Ohms highlights stories told by engineers who have used their deductive reasoning and technical prowess to troubleshoot and solve the most perplexing engineering mysteries.
Sherlock Ohms highlights stories told by engineers who have used their deductive reasoning and technical prowess to troubleshoot and solve the most perplexing engineering mysteries.
Design News Webinar Series
9/10/2014 11:00 a.m. California / 2:00 p.m. New York
7/23/2014 11:00 a.m. California / 2:00 p.m. New York
7/17/2014 11:00 a.m. California / 2:00 p.m. New York
9/25/2014 11:00 a.m. California / 2:00 p.m. New York
Quick Poll
The Continuing Education Center offers engineers an entirely new way to get the education they need to formulate next-generation solutions.
Sep 22 - 26, MCU Software Development – A Step-by-Step Guide (Using a Real Eval Board)
SEMESTERS: 1  |  2  |  3  |  4  |  5  |  6


Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.
Next Class: September 30 - October 2
Sponsored by Altera
Learn More   |   Login   |   Archived Classes
Twitter Feed
Design News Twitter Feed
Like Us on Facebook

Sponsored Content

Technology Marketplace

Copyright © 2014 UBM Canon, A UBM company, All rights reserved. Privacy Policy | Terms of Service