TAPPED HOLE STUD V/S THOUGH HOLE WITH BOTH SIDE NUT IN PIPELINE FLANGES 5

[skengg]

hey all,
let me first give detail of my query, i am designing a flange end valve fitting, it's DN 40 size CL-300 pressure rating. for body & bonnet round flange connection i have choice to either use tapped hole in flange with other side stud holded by nut or through hole in flanges with both side of stud holded by nuts.
so my question what's the difference between of both these flange bolting in perspective of bolting strength, pressure holding capability, stud as well as flanged fitting life cycle?
which one is suitable for which case?
can i use tapped hole for high pressure classes like cl-300 which have around 700psig working pressure?
thanks in advance.

 

[GBTorpenhow]

I'll offer the observation that valve body bolting seems to be almost universally tapped holes with a stud and one nut, even up to Class 1500/2500. At the size you are considering bonnets are also often tapped holes with a cap screw for common API 602 Class 800 type valves.

Assuming proper thread engagement the strength of the joint should be pretty equivalent, the main difference to me would be the extra fastener live length afforded by a stud and two nuts, this may or may not influence your decision.

 

[MJCronin]

Suggest that you repost in the "Valve Engineering" forum ...

MJCronin
Sr. Process Engineer

 

[LittleInch]

skengg,

Can you add a drawing or sketch so we know which flange exactly.

If your casting is basically a flange so that you could use a stud and a bolt, why would you not do that?

The other options incur more cost for the manufacturer to tap the hole and then install the stud correctly to the right depth. Every now and then one stud goes wrong and then you end up discarding the casting?

So long as the thickness of the hole is the same as a nut and the same strength then there is no practical difference. For a stud which is removed only occasionally then a tapped hole would normally reduce the casting size.

Tapped studs are commonplace in all sorts of components of pressure ratings.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[skengg]

Littleinch, here's general demonstration sketch of flange bolting conditions.

 

[skengg]

thanks,GBTorpenhow
for information.

 

[skengg]

yea,MJCronin i also thought to post in "valve engineering" forum but i think it was question of flange and bolting only of valve flanged fittings that's why i posted here.

 

[r6155]

How do you make sure the stud doesn't rotate during installation and tensioning?

Regards

 

[bcd]

Technically having threads for the studs in the opposite flange is ok provided you have enough length of engagement. This is done on some valves with short face-to-face lengths. However, it is generally considered undesirable practice. For one, as mentioned above, if the threads in the flange ever get damaged (cross-threaded, corrosion, etc.), then the item may be unusable. Also, it is more difficult to remove the item with the threaded flange holes from the system.

 

[LittleInch]

skengg,

What I meant was which flange are you talking about. The body flanges within the valve or the end connection flanges?

Tapped studs are usually inserted with some sort of sealing compound and often use studs with an end hex hole in order to screw it into the correct depth.

Studs direct into end flanges are generally frowned upon as they can be difficult to install correctly, risk of cross threading or not getting the right depth of the stud and can start to move when tightening / removing.

Some really high pressure valves like chokes and christmas trees do have studs as they can machine the whole thing from a block of steel...



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[skengg]

yea littleinch,
the flanges are within the valve, and yea i understand its after effect, thanks for providing information

 

[skengg]

thanks all,
i got the general idea of using tapped studs in which kind of conditions.