Rubber lined butterfly valve failures 6

[monaco8774]

We are experiencing a large number of failures of the seats on some rubber lined (carbon steel bodied) butterfly valves we have installed in a sulphate reducing package (sea water filtered to 5 microns with occasional acid and alkali washes).These valves have to seal against 20 bar(g) and are only 150# valves. We sent the first batch of failures off to the vendor who recommended changing the rubber spec, we installed these and they also failed, we sent these off and the vendor recommended changing to super duplex bodied high performance butterfly valves ( as they say we have solids in the system), we are purchasing some but they are very long deliveries and expensive. We have some existing hard seated triple offset stainless butterflys in the system that are also passing. As an alternative we can source some composite plastic valves which certainly should be resistant to any corrosion problems but we have never used any before.

Is there someone out there with some practical recomendations or who have some valves that work fine in another sulphate reducing package ? Im struggling here

 

[JimCasey]

20 bar is an awful lot for lined rubber butterfly valves. The highest-rated butterfly I know has the liner bonded to the body, and it is rated to 250 psi ( 17 bar).

20 bar is out of the ANSI 150 limitations by a hair, so you should technically use ANSI 300. The High-performance butterfly valve sounds like a better choice. Super duplex may not be necessary-my corrosion chart shows lots of reasonably common materials choices good for up to 20%wt NaCl solution at up to 212F, and Monel, Hast-C, and several others good for ANY concentration of salt in water.

 

[NGiLuzzu]

monaco8774,
could you please provide some more information about the "existing hard seated triple offset stainless butterflys in the system that are also passing..."?

Many thanks, 'NGL

 

[stanier]

Have you checked your system for pressure transients. The problem may be negative pressures creating conditions where the seal fials. If this is the problem and you solve that the existing valves may work.

Selecting butterfly valves is the cheap option in the first place and you ask for problems. You perhaps should have used ball valves.

 

[monaco8774]

Anegri

the existing hard seated triple offset valves are by Zwick they are the TRI-CON type, at the moment we think it might be just case of insufficient torque on the gearbox for these valves as we cant understand why they are failing - as I understand it these need torque to seal

Stanier
We have not checked for transients yet, I agree ball valves give us less problem but these were supplied by the packager and we didnt specify, now its too late without changing the piping

 

[ZwickTriCon]

monaco8774,

Stainless is not the best solution in this sevice, it will work fine only the general lifetime is shorter than ofSuperduplex (which we have on stock, so no long delivery times).
Regarding the "valve-failure": first of all this is a class 300 application and the gear is probably rated on class 150 only. In any case, you should loosen the bolts of the gear as this valve is a torque seated valve, could be that the output of the gear is sufficient.If not you need a bigger gear.Any further question, just call the company.

Best regards,

Marcel Zwick

 

[monaco8774]

Thanks for the advise, we have been in touch with Zwick and we do have a gearbox torque issue, as yet unfortunately we havent had the required shutdown time to get the valves out and see if the seat is corroded but we will now in about five weeks time at our next shutdown, likely will change seat material anyway

Cheers

Jeremy

 

[alrose]

monaco8774, we are looking for some large buttterfly valves (32" / 800 mm. class 300 or PN25) for isolation valves for a hydrostation (i.e cold fresh water). I was wondering if I could get away with using non-offset rubber lined/rubber seated valves? Can you recomend suppliers for suitable valves?

 

[monaco8774]

Alrose

We by rubber lined butterfly valves from Bray, I think you should be OK as long as you dont have solids in the system. Check with the supplier what pressure the valves will seal against as well as flange rating as they often only seal against lower pressures.

 

[stanier]

Alrose

You could try Ebro Germany, Fortress India (Boving rebadge them), Keystone (Tyco Australia). They allmake suitable valves.

Geoffrey D Stone FIMechE C.Eng;FIEust CP Eng

http://www.waterhammer.bigblog.com.au

 

[mrctchlr]

You could also try Wouter Witzel Eurovalve, they have a double eccentric hp valve called Dynaxe.

http://www.wweurovalve.nl/

 

[ytse]

monaco8774,

The problem with your valve seem to be a problem of the valve design, not material. (I am not sure whether the material is suitable because I don't know what is the service fluid and what is the effect of it on the lining and valve material).

Your are using a 150# rubber lined butterfly valve for an operating pressure of 20 bar (300 psig). Most of these type of butterfly valves are NOT designed to handle that kind of pressure. They are not even ANSI Class 150 pressure rated (285 psi). Many are just designed to 150 psig. The Bray butterfly valve that you are using is one of them (design pressure for Bray valve is 175 psi for sizes up to 12" and 150 psig for sizes 14" to 20"). You are using this valve way above their design capacity.

As for the hard seated tripple-offset valve in your system that is passing, it all depends on what type of shut-off that valve is capable of. Mant metal (hard) seated butterfly valves are not designed to be leak free. Many vendors will sell a butterfly valve with ANSI Class V or Class VI shut-off and yet claiming it to be "bubble tight". However, the ANSI/FCI 70-2 standard where this Classes comes from is for control valve, no shut-off valves. An 8" Class VI valve (Class VI only covers up to 8") has a permissible leakage rate of 6.75 ml per minute (tested at 50 psig when new). So for an operating pressure of 300 psig, the leakage rate could be 5 - 6 times that or even more because there is no requirement for leakage rate at rated pressure, so no test is required. A Class V valve is even worse.

So, aside from the material problem that you may or may not have, the valve that you are using may not even have the proper design to handle the job.

For a good shut-off valve, you should specify one tested per API 598, which required the valve be tested at 110% of pressure rating of the valve with no detectable leakage for resilient seated valve, or 2 drops/inch diameter/minute for metal seated valves (1 ml = 16 drops).

 

[ytse]

For your operating pressure, you should look at getting a ANSI Class 300 high performance butterfly valve with resilient (rubber, teflon, etc) seat.

 

[NGiLuzzu]

ytse,
why do you say that Class VI only covers up to 8"?

Please check FCI-70-2-2003 (Table 2 on page 3) and/or IEC 60534-4 (Note 5 to Table 2 on page 29): sizes up to ND 16" (DN 400) are covered, but a rule which may be easily extended to larger sizes is also given...


In addition, I'm afraid I can't agree with you about the capability of triple-offset metal-seated design to be "bubble-tight" in on-off services or else to reach "zero leakage", whatever the hell this really means.
About this latest matter, please take a look at thread408-150132 within this Forum (for example).


Hope this helps, 'NGL

 

[ytse]

Anegri,

I made a mistake when I say than Class VI only covers up to 8". I wrote that comment based on my memory of the old FCI 70-2 standard.

As to my other comment on the triple offset metal seated valve, I am merely pointing out to monaco8774 that many valve vendors will call their valve "bubble tight" (to sell you the idea that the valve will seal with no leakage) when the valve is actually designed to a Class VI Class V, or even Class IV leakage rates.

I agree with you that the terms "bubble tight" or "zero leakage" does not mean anything without specifying a standard test procedure and leakage criteria. For example, the following is from a brand name high performance double-offset butterfly valve brochure "XXX provide bi-directional,
drop-tight closure in vacuum and throughout all pressure ranges, as well as at full rated differential pressure." Yet at the end of that brochure, under the standards section, it stated "XXX polymer, elastomer and fire-safe seats provide ANSI Class VI shutoff. XXX metal seats provide ANSI Class IV shutoff."

That's whay I suggested that he should specify a valve to the API 598 standard. That way he will at least know what kind of leakage to expect in the valve at the rated pressure.

 

[NGiLuzzu]

ytse,
thanks for your valuable reply!

I would like to add just a couple of things: for some Customers the same "tight shut-off" requirement means Class VI if the valve is intended for a control application and API 598 if the valve is intended for a on-off service. This is probably a more correct approach...

In addition, I would recall the differences (in terms of reachable performances)between "high performance double-offset" and "triple-offset" designs.

Regards, 'NGL