orifice flange connection

[pipe15]

ok, I see that std orifice flange tap is 1/2 npt, which is easily changed to socket if desired. what if you want 3/4 socket? I see that on many P&ID's, but it looks like it will violate min weld size near the flange facing edge. how do you get around this requirement for weld size?

last, what are the downsides, if any, to just using a male by tubing adapter and coming off the orifice flange with the instrument tubing, eliminating all hard pipe off the orifice flange?

thanks in advance,
mark

 

[jsummerfield]

The standard orifice flange tap is 1/2-inch NPT. One issue related to 3/4-inch socket is the flow measurement. The center to center for orifice flanges including plate and gaskets is one-inch. The 1/2-inch connections also eliminate Class 150 flanges.

Normally we want piping specification a.k.a. line class valves as the first block between the process and the instrument. The issue regarding socket weld fittings is related in that many piping standards require a weld-end valve instead of threaded connection for the first block. At that point you can direct connect the manifold valve, or close couple the instrument using tubing. Compliance with ASME process piping standards could be an issue with eliminating the first block valve.


John

 

[pipe15]

thanks for both replies. Regarding this post, I do not want to eliminate the block valve, I am just looking for info on the weld qualification when a 3/4" tap is specified with 3/4-160 (with a socket weld) going out to a 3/4 inch socket welded valve. it looks like the weld dim would be 5/32" (assuming a 1/4" RF) and the thickness of the pipe would be .218.

thanks again
Mark

 

[legs]

I would highly recommend you go to the manufacturer and see what they offer. I think you will find the answer to your questions there. Also, don't be afraid to call the manufacturer's sales engineer. They are a wealth of knowledge and are generally very happy to help you learn what is available. For instance, I think you will find that you cannot get a 150# orifice flange. This is not a standard rating for the very reason you question. Also, you will find what taps are available. just do a search for 'orifice flanges' and find all kinds of catalog info.

 

[hacksaw]

traditional orifice flanges generally provide 1" from the center of the tap to the flange face not c-c. The gasket thickness is generally not included.