What is the difference between a blind flange and a flange blank? 1

[beh188]

ASME B31.3 defines in 304.5.2 the calculation of thickness for a blind flange. I can see why you would use a blind flange, which would be when you want to close off the end of a pipe. However, in 304.5.3 the code defines the thickness calculation for a flange blank. Fig. 304.5.3 illustrates blanks, but what exactly are they and what are they used for? It looks like they are used for isolating two pipes when they are joined by flanges.

Thanks.

 

[pennpiper]

Not everyone has a copy of ASME B31.3 and you did not show the illustration so I am going to take a guess at what it shows.

"Flange Blanks" are also called "Spec Blind", "Figure 8 Blind" and "Disk-and-Donut".
Go here and you will see various examples:

http://www.google.com/search?q=spec...&biw=1024&bih=665&sei= BwC7TpWJEofqtgeP6sH5DQ

You asked "what are they used for?"
You also answered your own question: "It looks like they are used for isolating two pipes when they are joined by flanges."
That is correct.
The primary motive behind the use of this type of device is Safety.

 

[zdas04]

Not really. You could provide the same level of safety with a skillet blind.

You use a spec blind to provide a visual reference of the flow path. The best use I ever saw of spectacle blinds was on a 2/3 stage compressor. To make it a 2 stage you would turn several blinds to flow and several to no-flow. To make it a 3-stage you reversed all the blinds. It is very easy to verify the number of compression stages by looking at the spec blinds.

David

 

[pennpiper]

zdas04,
The term "Skillet Blind" is just another name for the "Disk" part of the "Disk-and-Donut"

 

[chicopee]

A blind flange dead ends the tubing flow; a blank flange is one that is to be machined to a finished product.
Or,it is that can not see and the other has no facial expression.