Modifying lug type butterfly valve to wafer 1

[mthakur]

Dear all,
We have a 16" x 1500# butterlfy lug type valve, in lug type design, individual studs are fastened through both flanges to the valve body which has tapped screwed holes.

Removal of valve from line requires removal of nuts and all studs from valve body and result in delays, one of the options is to change tapped holes on valve body to through hole by drilling, this will require replacing all studs with longer studs which wil pass through the drilled holes. This will eliminate the need of removing studs from valve body as studs can be removed after loosening the nuts.

Can anybody help in assesing whether this modification will require a design check and revisit on studs design? Though here is no change in the design parameters, but length of studs may or may not have effect on its tightness or torqueing.
kind regards

 

[davsy]

What sort of indutry are you in, if your standards allow, why not use hexagon Headed Setscrews (or even Bolts if the thread length is OK)of the correct grade.

This removes the need to take out the studs each time but also leaves you with the ability to keep the tapped lugs so that the valve stays in place allowing you to remove one side of the piping (the main advantage of the tapped lug valve).

 

[gerhardl]

Technically you could probably do it, and everything could probaly work well.

In my opinion there is, however, two important counterpoints to be considered.

a) From a QA point you would make a mechanical change in an already fabricated (factory guaranteed, construction checked), and tested (body pressure, seat leakage) mechanical component. You or the factory would then be juridical responsible for all possible internal or external damage resulting from this change. This would be, I belive, a general and worldwide rule, covered by local laws.

b) There is a theorethical possibillity that full borings will alter torque, position and give uneven flange sealing tightening. What type of flange sealing and service do you have? Borings could also uncover or cause otherwise hidden/not present defects in the material structure.

Check that you are covered or comfortable for a and b, or else (as I personally would have done) change to new valve or pipeline (with dismantling joint?) construction.

 

[JimCasey]

You will assume all liability for the valve from the moment the first chip hits the floor.

The idea of using bolts was a good one. torque it into place on one flange, slide the other one up, and torque the other side.

If you want to modify it, contact the vendor of the valve to see if they will take it back on a repair PO to ream out the holes. Have them put in new seals and bearings, too, while it is in their shop, so in effect it will be completely refurbished. In the unlikely event that the boring discloses a defect, they will be in a position to be able to repair it or to replace the body with another "true" wafer body.

 

[JLSeagull]

Avoid a wafer valve installation if in hydrocarbon service. Cap screws or some other means to keep the valve secure with the flange could be permitted. In the event of fire the expanding through bolts open a gap that could feed the fire, thus would not pass muster in a proper process hazard analysis for flammable or toxic service.

 

[mthakur]

Thanks for your replies,
1. vendor response has not been very clear, the answer was you can do it at your risk!!
2. The process media is synthesis gas which is mixutre of hydrogen and nitrogen at 170 bar.
3. The flages are RTJ type, I assume the chance of leakage are same irrespective of valve type, whether it is wafer or lug type, as there are many high pressure valves with wafer design.
4. I agree that drilling would expose any hidden material defect.
5. with full boring, torque on the studs could be an issue, but as for as centering of the flanges are concered I dont see this could be a problem.
6. can I get studs design philosohpy for butterfly valves where these can be compared.
regards,

 

[unclesyd]

Reading from old notes and recalling from an older mind the use of wafer type valves in high temperature service was actively discouraged, but not prohibited. Your mention of RTJ gaskets would lead one to think some high temperature so I would definately get a nod by the valve manufacturer.

In our large valves up to 36" in high temperature service all are of the double flange type. We use through flange, both, bolting except where the valve might need to act a open end line stop. According to my notes the longer studs take some of the forces applied by the piping off the valve.

Our valve manufacturer doesn't offer a wafer valve in their high temperature valve line.

Does your valve manufacturer offer a wafer type valve in the same series as your valve?

What temperature is you mixture?

 

[rzrbk]

I agree with unclesyd that a wafer valve in high pressure/temp service seems like a step backwards. It may be beneficial to look at why this valve is having to be removed so much.
The existing lugged design should allow removal of a pipe spool on either side without total removal of the valve.

 

[Hench]

I would suggest you DO NOT drill out the upper and lower tapped holes on the lug style valve. Doing so could compromise the integrity of the valve. These areas are where the stem or shaft extends through the body. Even wafer a wafer style (non lug type) valve has these tapped holes.

Good Luck!

 

[wafflestiger]

You could try The Leeds Valve CO. This company do any mods you may need, give them a call. leedsvalve@aol.com.