large size Flanges serie A or B ?

[ENPMAT]

Dear All,
Can anyone advise what are the main differences between serie A & B large size ANSI flanges.
As a general rules we shall specify serie A or B ?

Regards,

 

[pennpiper]

Look here:

http://pipingdesigners.com/downloads/texas Catalog.pdf

prognosis: Lead or Lag