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API 6A Blind Flange

06/21/2017 10:42 AM

In API 6A 20th Ed. the 6BX blind flanges have flat backs for sizes starting at 5-1/8". If you need one smaller than that you have to incorporate an extrusion at the back to accommodate a test port, but the port is optional. If you remove the port you don't remove the extrusion (it seems from all the company drawings I've seen).

Question is, why do the flat backed flanges only start at 5-1/8"?

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#1

Re: API 6A Blind Flange

06/21/2017 11:03 AM
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#2
In reply to #1

Re: API 6A Blind Flange

06/21/2017 11:53 AM

Hi solar eagle. Yes this is the same as a API 6A BX flanges which have a raised face, as opposed to 6B flanges which are flush but I'm asking about the extrusion on the back of the flange. What would be the outside face when the blind flange is made up.

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#3
In reply to #2

Re: API 6A Blind Flange

06/21/2017 12:25 PM
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#4

Re: API 6A Blind Flange

06/21/2017 4:18 PM

Is there any way to contact the person or entity that authored the standard?

This may have something to do with having enough threads to accommodate a pipe nipple.

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#5

Re: API 6A Blind Flange

06/22/2017 5:32 AM

Pressure.

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#6

Re: API 6A Blind Flange

06/22/2017 6:02 AM

So for flanges up to 5-1/8" we have this

For blind flanges 5-1/8" and bigger we have

I know why the extrusion at the back of the small flanges is there, my question is why don't the flat backed blind flanges go down smaller than 5-1/8"? If it were because of pressure you'd assume it were the larger flanges which would need the support of more material.

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#7
In reply to #6

Re: API 6A Blind Flange

06/22/2017 10:29 AM

The flange thickness does reduce some with diameter, ANSI 300# flanges for 1/2" pipe are 9/16" thick, for instance. My guess is that no one bothered to test a flat version for that particular API standard.

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#8

Re: API 6A Blind Flange

06/22/2017 2:15 PM

That would be an arbitrary, and agreed upon standard, required by major users of such flanges, thus the standard would have been written by a national or international standards organization, thus stipulating such. It could even be a Military Specification.

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