Butterfly valve leaks over time 4

[DavidScott1]

I have a problem with some 3 inch butterfly valves. The body is made from polypropylene, with a butterfly made of HDPE. It contains a circumferential nitrile seal.

The system pumps wine up to a dynamic pressure of 80kPa. The valve is tested to 100kPa and passes. However, after approx 12 months some of them start to leak and fail to provide a tight shut off.

We are struggling to get to the root cause and suspect it is more than one. We do not have much valve experience in the company and the suppliers are not helpful. We are investigating sharp particles but I read about a potential issue with hydrocarbons. Can you point us in the right direction as to what we should investigate ? Many Thanks.

 

[zdas04]

It sounds like you have a materials incompatibility. It sounds like the polypropylene might be drying out and losing resiliency. The valve manufacturer should be able to provide a different seat material that is resistant to changing in your service.

David

 

[Ashereng]

I don't have any experience with plastic valves (I'm in oil and gas).

Just out of curiosity - how much is your 3" butterfly valve?

Would it be more cost effective to perhaps go to an all metal valve?

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[zdas04]

Ashereng,
An "all metal valve" would still have a rubber seat. The only thing he would be "gaining" is a metal disk instead of the plastic disk.

David

 

[Sircrashalot]

He might also gain if he went to a double offset or tripple offset valve. Tripple might be a bit of overkill, but I doubt the plastic valve he has has any offsets at all.

You also might want to look at a ball valve for the application too if space is available. If you are not using the valve for throttling service and can take the extra space and weight, ball valves may be a better option.

Andy

 

[NGiLuzzu]

DavidScott1,
I would suggest to consult a "Chemical Resistance Guide" to check the compatibility of the polymers you mention with wine (or a mix of etilic alcohol, acetic acid, polyphenols, etc. etc.).

Using the one by DuPont-Dow, for instance, I found that Chlorinated Polyethylene, Polyacrylate, Polysulfide, Propylene and Epichlorohydrin may be dangerous with wines or whiskey (while Nitrile should be OK; see

http://www.dupontelastomers.com/Tech_Info/chemical.asp)...

but a more specific investigation will probably give more accurate results.


Even on double or tripple off-set metallic valves, I feel that PTFE would be applicable for soft parts (... in any case, I would look for FDA-approved materials!).


Regarding ball valves, see for example

http://www.4gghidini.it/catalogo.php?liv_id=1_7

and browse into details manual level or actuator, type of connection, etc...), down to the model you're interested in.
I know for sure that this Italian Company is supplying the Wine Industry since a couple of decades (at least): they'll probably be able to assist you selecting the materials that best suit your application.


Hope this helps, 'NGL

 

[gerhardl]

Lifetime before leakage of any butterfly valve will depend on suitable materials not only to fluid, but also to number of operations, temperature, concentration of cehemicals in fluid and purity of fluid. Any coarse particles or dried residuents (for instance sugar) may give abration in addition to material problems. CIP process with steam or high temperature would not be suitable to NBR. CIP chemicals?

Solution is to upgrade the valve. EPDM sealings might give a longer lifetime in your case than NBR. As best for price/lifetime I suggest(check with suppliers): centric butterfly, allowed for food industry, highly polished stainless steel disc, PTFE liner with soft backing. Also check to suitability with yuor CIP process

 

[NGiLuzzu]

Good post, Gerhardl!

May I ask what do you mean whit "CIP"? Perhaps Clean-In-Place?

Thanks and Regards, 'NGL

 

[gerhardl]

Yes, CIP = clean in place, which again for food industry may be sterilization with steam at 100deg C plus at certain intervals.

NBR is usually (may vary according to producer and quality) allowed up to about 70-80 deg C, EPDM up to 120 deg C. Plastic and palstic composites according to respective manufacturers specs.

CIP would else normally be done by various chemical solutions, at various concentrations and temperatures,again to be checked against all materials, including sealing materials. Please also remember to check stem sealing materials!

 

[JimCasey]

Wine is usually very fussy about what materials contact it. Materials normally considered "resistant" may still alter the flavor. So I am looking skeptically at the suggestions for double-or triple offset valves. THose expose the metal of the disc and body to the wine, AND they also expose the bearing (crevice) to the wine. A rubber-lined butterfly valve seals because of interference between the hub of the disc and the liner. So it is sanitary. Many rubber-lined valves have no stem packing at all.

I checked here:

http://www.marcorubber.com/compatibility.htm

and it appears that food-grade EPDM would be resistant and able to tolerate a steam-out. EPDM is not compatible with hydrocarbons, biut I cannot think of a hydrocarbon in wine. Ethanol is not a hydrocarbon. As the National Safety Council slogan said(about 40 years ago), "Gasoline and Alcohol do not mix". Dean Martin (famous drunken entertainer) replied: "They mix, but it tastes AWFUL!"

If you are worried about polypropylene, you could always use a metallic valve with a Fluorocarbon jacketed disc...or even a TFE liner. If you find that 316 stainless steel does not change the flavor of the wine, then a 316 polished one-piece disc in a food-grade EPDM liner would be a nice resolution to the problem.

If you are experiencing abrasive wear, you would see scratches on the edge of the polypro disc. Polypro is not goos for high temperatures, so you could just be altering the disc if tyou steam out the valve. CIP with a different sterilizing agent may be the only change you need consider.

 

[Ashereng]

zdas04,

Hi David. Check out this manufacturer:

http://www.scorevalves.com/

They make an "all metal" butterfly, with metal seals.

Jim,

With regards to metal altering the flavour of wine, I am out of my element. I guess if the metal will change the taste of wine, then a metal valve would not work.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[DavidScott1]

Thanks to all for your help.

I am trying to understand the cause of the failure rather than just change to another type of valve/liner etc (due to the 12month period before I know if the change has been successful).

Therefore some more info.
The flowrate is 800-1000 litres/min
SG's range from 0.89 to 1.4
and temp range is 4degC to 60degC
Immediately attached to the valve is an elbow made from HDPE with two nitrile o-rings.

To focus in on the root cause what should I check ?
Jim has stated scratches on the disc. What else ?
What can I check on the installation of the liner ?
How far away from the valve should the elbow be ?
The valve should be fully open or closed but I do not know if the operators use it for throttling - how would this show up ?
etc etc

Thanks again.

 

[NGiLuzzu]

60°C???

I hope this temperature is reached during the clean-in-place process only (what about chemicals for cleaning?)... otherwise you're producing vin brûlée*!! ;-)

Bye, 'NGL



* = hot wine with cinnamon, apple pieces (and other ingredients), typical of the Northern regions of Italy, good to warm you up during the out-door exchanges of Christmas greetings or other winter social occasions...!

 

[gerhardl]

SG under 1 will indicate a certain content of alcohol and pure wine, as high as 1,4 indicates high sugar content and / or not filtered wine with grape rests(?) The 1,4 gives possible abration from harder particels or dried, crystallised sugar(?)if the system is not properly cleaned before being allowed to dry up.

The flow amount given gives an average speed of about 2,5 to 3,5 m/s, which is normal. Cavitation damage would only occur if the valve is throtteled in such a way that the P2 pressure (after the valve)is 'considerably'lower than P1 for 'longer' time, and this is probably unlikely given pressure and amount and application. The bend described would give turbulence, but would most probably not affect an (unthrotteled) suitable valve. Normal required distance before bend 2 to 5 times diameter, but often not done in practice at low velocities.

The damage could be difficult to pinpoint to any one of these causes, and could easily be caused by combinations.

To check:
Visual check for damage, scratches, especially if centered around special parts of disc or lining. Type of scratches: abrasion sandpapered, cavitation pinpointed over area.

Any miscoluoring or difference in material, any encrusting, any other visual damage or hardening of soft surfaces.

With handle: operate valve to closing. Compare necessary torque with new valve. Compare angle of disc when closed with new valve. Compare thightness and movement of spindle. If higher torque or less degree before closing than new: materials have changed properties and valve and materials are not suitable. Check with handheld lamp if valve closes (any light openings), try with unpressuried water (valve held horizontally) if the valve keeps thigt. Observe for several valves if type and places for damage gives a pattern.

Next is to decide if you can live with the cost of a change of existing valves each year, or if you should upgrade.

Note that temperature (60deg C) could be a problem even if allowed temperature is noted as higher for PP and HDPE. Plastics are more suspectible to material changes at higher temperatures, and more suspectible to swelling and hardening. Properties may vary according to quality from producer to producer, and your 60 degrees could be an avarage with higher temperatures locally. Allowed operating temperatures for both PP and HDP has a wide range from about 40 deg C to well above 100 deg C.

 

[JimCasey]

I checked polyproylene compatibility here:

http://www.upchurch.com/TechInfo/chemMatList.asp

note the PP is rated compatible with ethanol at room temp only. They did not mention if it swells, but that is a common effect for a polymer suffering chemical attack.

Wine has literally hundreds of chemicals in it. Looking up the ones we know in a corrosion table may not tell us the way the combinations of chemicals would affect the material.

 

[wsuengineer]

I AM IN SEARCH OF A COMPATIBILITY CHART FOR PROPYLENE GLYCOL (DOWFROST HD) WHEN SELECTING SEAT MATERIALS FOR BUTTERFLY VALVES. SPECIFICALLY: EPDM, NBR, PTFE

 

[HEC]

Another check for changes to the seat would be the material hardness or resiliance. a simple thumbnail impression comparison between old and new may show some difference. SS disc and EPDM seal is a popular butterfly valve trim combination for food beverage and wine industry.

Mark Hutton

 

[JimCasey]

wsuengineer: It would have been appropriate to start a new thread. This one was about valve materials compatible with wine.

In any case, your info about PG is at:

http://www.upchurch.com/TechInfo/chemMatList.asp?vChem=Propylene Glycol

 

[ALEXANDRAHARPER]

Hi
One question, Does the valve as tested per API 598?
or could you let me know which is the standar that you use to test the valve hydrostatically?
If your valve was tested per API 598 maybe has a leakage allowed, please verify it with this standard.

Also you should verify the leackage class, IV V ETC