Gas pipe / Hemp as a sealing compound 4

[topgun67]

We install a great deal of threaded gas pipe, and use hemp and boss white as a sealing compound on all threaded joints.
Recently I have been made aware that this practise is frowned upon. Is this the case and if so why? What compounds would you recomend?
Many thanks

 

[BobPE]

topgun67:

What part of the world are you in?

BobPE

 

[topgun67]

We are based in the UK

 

[moltenmetal]

What the heck is "boss white"? That's a regional term I've never heard before...

The practice of using "plumber's putty" (principally limestone powder in linseed oil) sometimes combined with jute or hemp twine, went out of style about 50+ years ago here. It's a tough sealant but not very forgiving- it has near zero elasticity, low lubricity to prevent galling, and you need a torch to get the parts disassembled (even after they start leaking). In my experience it's poor sealant choice and fitting practice which is responsible for much of the bad reputation that threaded piping has in industry.

For low pressure utility gas lines, there are a number of approved sealants in North America but the most popular is full-density (i.e. unstretched, s.g. ~1.3-1.5) teflon tape, often dyed yellow to distinguish it as being suitable for gasfitting.

 

[topgun67]

Hi moltenmetal.
Thanks for your reply. Do you know if the tape you describe has a trade name?
Many thanks

 

[TBP]

Gas and other codes can vary quite a bit, between jurisdictions. Things like Teflon tape (and other materials) for gas service are permitted in some places, but not others. There are a whole variety of Teflon tapes, pipe dopes, etc for pipe threads, and they'll have what services they're good for, the range of pipe sizes, etc on the can or package. They'll also list any approvals by regulatory bodies that they may have. Some dopes are only rated up to 1-1/2" pipe, many others to 2". Always important to know what's approved by code in your jurisdiction & to read the label and/or instruction sheet for the particular product.

 

[Montemayor]

topgun67:

What moltenmetal is advising is what I would also recommend. However, my experience with Teflon tape goes back for over 40 years and I don't have any problems with it - as long as I install it personally. I would not trust someone else doing it when I'm not looking. The reason is that many, many persons just don't apply the tape correctly and it winds up getting shredded and torn inside the piping itself, winding up under some flow obstacle - like a valve, regulator, or other instrument. This effect plays havoc with the expected operation and gas flows and is an expensive task to locate and remove.

For the above reason, Teflon Paste, a very efficient and effective sealant was developed. I would recommend you try this out if you are going to delegate the thread sealing to others that you can't supervise personally.

I hope this experience helps.


Art Montemayor
Spring, TX

 

[unclesyd]

Boss white is or was white lead. This is from my little red maintenance handbook circa 1950. The present formulation is probably has different ingredients.

Lead oxide in triple boiled linseed oil or linseed oil and tallow is very good pipe dope. At one time this was the universal pipe dope. It was used in all services.

We used hemp or jute packing saturated with some oil ?? and beeswax/tallow on water pumps.

I’ve seen variation of various fibers combined with lead and it’s oxides combined under various trade names, the one I remember is “ALL PACK” for valves.

 

[moltenmetal]

There are definitely jurisdictional and regional codes and standards that apply for gasfitting- too many to mention. Make sure you follow them, as insurance companies love to deny claims from people who break the local rules.

As to brand names of teflon tape, there are many, but the ones I'm familiar with here in North America are likely not available for sale in the UK. Just make sure that if you use teflon tape, it's the full- or near-full density material. In our experience, we get good performance with tapes of s.g. 1.0 and higher- 1.5 s.g. is not completely necessary. Some teflon tapes have been expanded or stretched to a specific gravity as low as 0.25, though the nominal thickness of the tape can be the same as for the denser tapes. The stretched materials are often sold in hardware stores for general-purpose plumbing and are often either brilliant white or dyed a peach/orange colour. These tapes are seldom approved for use in gasfitting.

If you're using teflon tape only, care in installation and proper threading practice is key to a good joint. Poorly installed tape is useless and can clog downstream equipment, and in some jurisdictions tape is banned from a certain point in the line onward (for fear it jams a gas shutoff valve in the open position at some time in future).

Modern anaerobic paste pipthread sealants (aka "pipe dopes") are far superior to the previous generation of lead-and limestone- based sealants, though plenty of those can still be had. Some of the modern pastes contain particles of teflon, and some don't- in our experience the teflon particles are superfluous and other, cheaper fillers work just as effectively.

Our general-purpose solution for threaded piping is a Henkel Loktite brand anaerobic paste on top of teflon tape. With this combination, leaks are a rarety even when using cheap Chinese 150# threaded fittings. Some services require either tape alone (generally for purity reasons or where the acrylate resins in the paste are attacked), or paste alone (ie. for instrument air between a filter and a sensitive device like an I/P converter).

 

[topgun67]

Guys

Many thanks for your advice. Am now in the process of trying to source the above mentioned materials. If I have any problems I may ask for further help

Thank you