What type of valve would work in solid depositions?

[sebjunioreng]

I have reviewed a few threads on this topic including thread 408-146612 but have not quite found the answer I am looking for.
I have a low pressure gaseous service where scale, corrosion products, and other solids tend to develop and drop out in the piping. In an effort to clean this system, I will require some isolation valves to be installed on the piping in the horizontal pipe runs.
What type of valve would work best to ensure that I get positive isolation (does not have to be tight shutoff) if I have solids deposition on the pipe bottom and valve seat? These valves would be operated quite infrequently (let's say once/year) and are generally inaccessible and therefore must be able to close when needed (i.e. I cannot close and open these valves frequently to break up the scaling on a regular frequency).

I would prefer something of lower cost (obviously) and a valve with a small face-to-face dimension.
A few other tidbits:
6" or 8" lines, 150# rating carbon steel
Low pressure = 0-1kPag (this is vent gases from atmospheric tanks)
Lines are glycol traced for freeze protection

Any ideas?

 

[JimCasey]

This sounds like a textbook case of why partial stroke testing has become a hot topic. Safety shutdown valves need to be cycled frequently enough so that there is confidence that the WILL close when the system NEEDS them to be closed. Valves that get fouled with process debris are a safety hazard if they won't close when necessary.

Looking at the materials and the mechanical needs of the system you described, I am thinking that a fluorocarbon-lined valve might be appropriate. Nothing is slicker then fluorocarbons, so any deposits that accumulate on the valve's internals will flake off when the valve cycles and the sealing surfaces flex. Durco offers a butterfly valve called the BTV with a TFE liner and PFA-coated disc. I think that would do the trick for what you describe.

 

[Ashereng]

What type of valve would work best to ensure that I get positive isolation (does not have to be tight shutoff)

I am a bit confused. How do you mean positive isolation, but not tight shutoff?

Small face to face at 6" to 8" leads me to butterfly valves. Perhaps a triple offset from Tyco?





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[JimCasey]

Ashereng,
The Tyco Vanessa triple-offset >might< work. It's claim to fame is that it seats without rubbing. So if the gunk that accumulates is hard, the valve will just trap the crust and not completely close. That's why I suggested the lined valve. The closure member flexes the seals and wipes as it closes so it >should< crack the deposits and flake them off. I mentioned the Durco BTV. The comparable Tyco offering is marketed as Neotecha.

 

[NGiLuzzu]

sebjunioreng,
if you choose to install triple-offset butterfly valves in your horizontal pipe runs, please remember that they should be installed with the valve stem in horyzontal position, so that the bush bearings in the two hubs remain free from solid deposition.

In addition, being the valve seat conical, you should pay attention to set the more inclined side of the seat on the top and the less inclined at the bottom, as per the following scheme:

/ ___
/

YES NO

___ \
\


In this way, it should be easier for the disc to "sweep away" the solid deposition...



Ashereng,
the triple-offset from Tyco is VANESSA Series 30,000, take a look at:

http://www.tycovalves-eu.com/brands_results.asp?Selection=Vanessa

May be they can supply valves according to the above requirements (also with full metal, one-piece seal rings, that "should" be capable of cracking entrapped solids), but I don't think they will be much "economic"... but, of course, it depends on which are the alternative options ;-)

For a list of other Manufacturers of the same type of valves, please refer to thread408-126483 and thread408-139775 within this Forum.


For other technical considerations about the same, take a look (for example) at thread408-141966 and thread408-154748...




Hope this helps, 'NGL