? Flanged or threaded ends

Hi people,
I suppose that valves with flanged ends load higher pressure than valves with threaded ends.
Is it true?
Which factors are important and how they affect on selection of flanged or threaded ends (for example ball valves).
May you tell me something about valves with full and reduced ports.

Thankfull forever,
student

 

[Hush]

Normally (but not always) threaded connections are less expensive but have pressure limitations and to a lesser degree temperature limitations. Threaded connections are also (in general) more susceptible to corrosion and stress corrosion cracking.

Full port valves are exactly what they sound like. A 2" full port will have a 2" bore, a 2" reduced port will have less than a 2" bore.

 

Thank you Hush again!!
If valve-designer need decide between full and regular port, what are his main considerations?

 

[pkhenry]

There are other more complex issues between the differences in threaded and flanged valves. Typically flanged valves are used for high pressure and temperature due to better sealing. There are too many unknowns with threaded valves, when I spec a SS valve I do not allow threads due to galling, I use only flanged or butt weld valves on hazardous fluids.
The pressure and temp rating of threaded and flanged valves are different. A threaded valve is rated on a different bases then flanged valves. A threded valve may have a rating of 2000psig WOG this means it is good to 2000 psi at 100deg F, the ratings for threaded valves are 800, 1450, 1000, 1500, 2000 and 4000 psig. I should also indicate that the WOG stands for Water Oil Gas service valves and is a standard relating to testing. Now as for flanged valves they follow the ASME B16.34 pressure temperture ratings for pipe flanges i.e. a class 150 A105 flange has a rating of 285 psi at 100 deg F (I think). To make the whole thing more complicated the ratings given for the valve body thickness or end connection ratings are usually based on ASME A16.34 and actually matbe misleading. At higher temperatures it is the seat and gasket material which will dictate the pressure temperture rating, as a rule of thumb if the temp is over 450F you best check the seat material rating. One last difference between the valve end types is the selection of the material of construction which may also vary for a given manufacture based on size. They may only sell a WCB body in the threaded model and only handle up to 2", but have a wide range of flanged valve materials in all sizes. This maybe an issue in selecting your vendor.
As for porting a full port valve has basically the same pressure drop as sch 40 pipe, a reduced port valve can have 5-7 times the pressure drop.

 

[TD2K]

I'm a visitor,

Well, as a process engineer, I typically don't really care if you pick a reduced port or full port valve. The pressure drop across either, which is what I'm usually concerned with, is relatively small compared to all the piping I'm putting in. This isn't always the case, sometimes if dP is a problem, I will specify a full port valve but for regular piping, this is pretty rare.

Some exceptions:

Inlet valves and outlet valves on PSVs are typically specified as full port due to concerns with pressure drop.

Pipeline valves are typically specified as full port valves to allow pigs to go through them.

Other than those, the most common use for full port valves is if you are hot tapping through them. You want the biggest port you can since the tool you are using to cut through the pipe has to fit through the valve.

 

[Hush]

A lot depends on your application. There are more specs than B16.34. In our industry we may spec 1/2" NPT threaded valves up to 10,000 psi cwp. We normally use full port only when we require through bore access for running tools.