Globe Valve PTFE Gland Packing Failure

[sahsanb]

Dear All,

We are using plug globe valves as isolating valves on our ammonia circulation pumps. Temperature of service varies between zero degree C to ambient temperature of 25 degree C. We have recently been observing leakages from these valves glands. The valves were installed about 30 years ago and progressively there service life has reduced from 4-5 years in service to 2-3 years now. As recommended by OEM 30 years ago we are still using chevron style Plain PTFE material packing rings on the valve. During every refurbishment we observe the packing rings to be very hard. PTFE obviously gets hard while in service and I am trying to get to the bottom of why these packing rings get hard even though we are operating in standard operating range for PTFE.

Is it because PTFE material is inherently a bad conductor and hence friction induced heat does not dissipate easily and hardens the packing? If so feedback from experts here would be greatly appreciated to improve my understanding of the situation and actual phenomena that is occuring.

If the experts here feel there may be another reason for this kindly share your feedback as well.

We are also cognizant of the fact PTFE with fillers are now available in the market now that are there precisely to cover for plain PTFE's deficiencies. Graphite or Graphite filled PTFE packing rings is expected to provide improved result?

Regards,

 

[3DDave]

Leakage is more likely because the metal parts have developed abrasions and the abrasions are cutting the PTFE allowing it to leak.

Polish the metal interfaces and see if that helps.

All I can think of for hardness is that some material is being absorbed into the PTFE. The PTFE molecules are extraordinarily tough; the Fluorine atoms are well bonded to the carbon core. All I see for hardening is high density x-ray exposure.

Alternatively, one aspect of specifying PTFE is the %crystal content. It's possible that this has changed, though I don't see how that would cause a hardness change over time with the temperatures you are using.

Most fillers are to increase the hardness of PTFE, which is normally extremely low. A person's fingernail can damage a PTFE surface.

 

[LittleInch]

What are" plug globe valves"?

A glove valve moves up and down, a plug valve rotates a plug within the valve.

If your shaft is only rotating then that is one issue but vertical up and down is another. Which is it?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[gerhardl]

Looking at the chemistry PTFE or PCTFE (Polytetrafluorethylen and the somewaht mechanical stronger Polychlortrifluorethylen) are the best sealing material for ammonium based fluids.

It could (but not very likely) happen that the materials you now buy differ slightly in production process and composition from the original and therefore will give a shorter lifetime.

I believe the reason to be other, and also believe that other material compositions/additions will not improve the standing time.

The most common causes for increased sealing leakage over time is dirt, corrosion, wear giving unprecise movement or all in combination. This kind of leakages will not be stopped by renewing sealings, the imprecision in movement, hairline scratches rougher surfaces causing leakage will still be there.

(This is often case in spite of properly maintained and 'cleaned' production pipes.)

Earlier hardening of sealings (presumed material composition exactly equal as original) might well come from earlier starting leakages giving gas exposure to larger areas of the now more roughened up sealing material.

Good luck, it will be interesting to hear your further conclusions!

 

[ninjasam17]

A bit confused in regards to the plug globe valve as well. Need additional clarification before I can provide my input.

 

[HitokiriAoshi]

Your old packing will tell you the answer you seek. However, i will say 3 years is definitely acceptable life for them.

a couple hint, look to see differences between top and bottom rings. can email me if need additional help.

chevron ptfe style packing have one of the lowest torques and widest compatibility, and works perfect for rotating stems.

Luke | Valve Hax |

https://valvehax.com/