Bolting for Cast Iron Lug Style Butterfly Valves

[GBTorpenhow]

Service: 50/50 water/propylene glycol, design 150 psig @ -20 to 150F, oper. 30-80 psig 80-120F
Valve: Class 125 lug style concentric butterfly, API 609 Cat. A, cast iron body with integral EPDM seat/gasket
Mating flanges: B16.5 Class 150 A105 RF

Curious what others prefer for bolting for this type of valve.

The incumbent solution is to use the same A193 B7/A194 2H stud/nut combo as the rest of the piping. My concerns with this are:
A) high strength B7 bolting isn't close to being required based on the valve vendor's torque spec to seal the EPDM seat/gasket of these valves
B) the valve thicknesses in the range of sizes that we are dealing with (up to 12" NPS or so) are such that it isn't going to be possible to fully engage a high strength bolt in a cast iron body (by fully engaged I mean that the bolt is threaded enough that the bolt shank will yield before the internal thread does). Functionally, if the field contractor mistakenly uses the 'default' torque spec meant to seat a regular nitrile sheet gasket they can easily damage the valve.
C) I prefer a headed bolt, ideally a hex cap screw, here vs studs whenever feasible for a tapped hole because I trust the engineer (myself) to specify the right bolt length more than I trust someone in the field to correctly install a stud with one nut into a tapped hole with the correct engagement length.

 

[TugboatEng]

Bolting is ASME B18.2.1

ASTM A307 cap screws are recommended.

https://www.milwaukeevalve.com/wp-content/uploads/technical-service-information/FlangeBolting.pdf

 

[MJCronin]

Tugboat ...

Thank you for your reference

Why do you prefer two cap screws in lieu of a single through bolt/stud ?

I can see advanatges and disadvantages with each bolting style ....

Whay does the valve vendor say about the prefered bolting method ?

MJCronin
Sr. Process Engineer

 

[TugboatEng]

The cap screws method requires less space to remove a flange.

Withdrawing long studs from valves that have been installed can be a long and difficult process if they are corroded or fouled with paint.

 

[GBTorpenhow]

Using one set of hardware per side (cap screw or short stud + 1 nut) also allows one side to be removed if needed. Some valve of this type are rated for dead end service.

I don't have a specific valve vendor because the spec is intended to be generic. Poking through vendor IOMs, most seem to just give the lengths for the different options and leave it up to the user. I assume nobody wants the liability of providing bolting recommendations blind (no pun intended).

 

[Krausen]

I prefer to maintain the same studs & nuts as the rest of my piping system (B7s & 2Hs). I'd specify B7 stud bolts with two 2H nuts (per stud) in lieu of one-off cap screws. Show the minimum thread engagement of stud bolt to tapped valve body holes on drawing. Two nuts per stud allow for one nut to be used for controlled torque (at lower torque values than typical B7 studs) & the second nut to act as a "jam nut". This is a more robust bolting arrangement compared to using cap screws in my experience. Some could argue it's overkill, but I prefer.