Propylene Glycol and Failing Sanitary Ball Valves

[Spike2000]

Guys
I have a sanitary ball valve where the Teflon seats are failing. product is propylene glycol running at 250 f and 100 psi
other products run at these temps and pressure with no issues
we are new to propylene glycol, but what I can find Teflon should be fine with this chemical
are there any ideas out there....

thank you

 

[jari001]

Please describe the mode of failure in detail. What else is in your propylene glycol? Have you ruled out mechanical causes for failure?

 

[georgeverghese]

It may be what you're using this valve for - a ball valve with Teflon seats in pressure throttling service isnt going to last long, for instance. Though Teflon has good chemical resistance, it doesnt do well in high velocity - high shear conditions.

 

[Spike2000]

thank you for the responses
ok a little more details, it seems like the Teflon is deforming and cannot close
looks like it is getting forced out (think squeezing playdoh)just not that extreme
as the pressure/temperature is within spec, I am thinking a chemical reaction, I don't know what else
is being used besides the propylene glycol, but will find out
thanx again

 

[mk3223]

Is it a single incident on a ball valve?
Is it possible the valve defect from the vendor?

 

[EdStainless]

What is the teflon? I am guessing that it isn't a solid seal but one built of layers.


= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[Spike2000]

Thanx Edstainless
not a plastics expert here, not sure how the Teflon seats are constructed
but I do have new info.
the failing valves are exposed to a cycling of the temperature from 40 degrees f to 265 degrees f
in the same process line same valves with a consistent temp are not failing...
its great how you get piece meal information....looks like we found the smoking gun

 

[jari001]

I am tangentially aware that certain Teflon formulations are not as good as other formulations w.r.t. temperature cycling, so the temperature cycling condition is a good lead.

 

[bcd]

Ball valve....PTFE seats extruding into the flow port.....happens on valves with temperature increase. You have a cavity relief issue. Liquid is trapped between the seats when the valve is open or closed and wants to expand when heated (i.e., thermal expansion). Volume of the fluid cavity between the seats is fixed so the pressure in the liquid rises and pushes the seats into the flow port. Get a ball valve that has cavity reliving seats or drill a hole though the side of the ball so the trapped fluid has a direct path out of this cavity and back into the pipe.

 

[StoneCold]

We have had problems with teflon seats in some similar services.
We switched to either PEEK seats or a 50% teflon 50% stainless seat.
Both last multiple years in tough services.

Regards
StoneCold