Lug Type Butterfly Valves

Good Day Everyone,

My current project i'm working on only specify that stud bolt to be used for all flange connection.
No machine bolt or cap screw is allowed.
Now for the case of lug type butterfly valves, as per API 609, the default design is the lug shall be tapped hole (unless specified otherwise by the purchaser).

My understanding is, since the project only allowed stud bolt to be used, the lug holes shall be through hole in order to suit the purpose of having stud bolt.
I mean stud bolt is more appropriate to be used at through hole rather than tapped hole.
The flange connection will be controlled by the strength of the stud bolt if used at through hole compared to if stud bolt is used at threaded tapped hole, where the connection is controlled by the threads of the bolt and threaded tapped hole.

Can i say that even though it is possible to use stud bolt at tapped hole, but as a good engineering practice, stud bolt shall be used at through hole.

Can anyone please verify or confirm on my understanding.

Thank you.

Dear Jop,

Thanks for the link you have provided.
For the case that i have mentioned previously, it is used at Cooling Water service and as per the Project Piping Material Specification, lug type butterfly valve is specified for that line class.

Let's narrow down the issue on applying stud bolt at tapped hole rather than through hole for the hole of the valve lugs.
I found it is odd to apply stud bolt with tapped hole and it is not a good practice.
Stud bolt shall be best used at through hole with 2 hex nuts.

Correct me if i'm wrong.

Thank you.

Good afternoon

I have a few constructability thoughts regarding butterfly valves:

-When selecting tapped or through holes, you should consider how the system will be installed and maintained. Consider if the valve will be a maintenance/or construction isolation boundary. A valve with through holes will require flanges on both faces of the butterfly valve to hold it in place, and this may not be possible during maintenance activities if piping needs to be removed. Compare to a tapped lug style where the valve can be secured to one flange and used as isolation boundary, while the down stream flange and piping can be removed and maintained (if needed)

-Consider butterfly valve operational clearances: Had a peer that had a contractor install a branch line with butterfly valve isolation during a system shutdown. Contractor put a reducing flange on the downstream side (blocking the swing of the disc). Contractor then proceeded to "test" valve and smashed disc into reducing flange and discovered valve was blocked from opening...So remove the flange and replace? Nope they used a wafer-style butterfly valve and there was no way to remove the flange and hold the valve and isolation boundary in place. Ended up taking the system down again....

Just my thoughts...been burned before

Jeff

Ajak,

The butterfly valve you're referring to can be a lug type with a through hole. This is common practice. However, also consider that the tapped hold provides some added stability for a simple valve like the butterfly, and the flanges surrounding the butterfly valve will address the pipeline integrity challenges, so long as the proper flange classes (and corresponding stud bolts) are properly selected for the pipeline medium and pressure. In case it is useful, I've attached a reference bolt chart for common flange sizes.