Just to complete this, you also clearly don't have a copy of ASME B 16.47 - I would recommend that you get one....
It is very important that you know which one is which when connecting to any existing flange >24" as whichever one you assume will be the wrong one when you get to site.... Or take both.
The following is in the foreword of ASME B 16.47.
In November 1980, a task force was appointed within Subcommittee C of the American National
Standards (ANSI) B16 Committee to develop a standard for pipe flanges in size NPS 26 through
NPS 48. Every attempt was made to standardize those dimensions that existed within the industry
for the materials covered by ANSI B16.5.
Prompted by suggestions received from committee members, the task force was authorized to
increase the size range to NPS 60. The first draft was developed in December 1982 to include
Class 75 through Class 1500 for the size range NPS 26 through NPS 60. Flange dimensions were
based on the Manufacturers Standardization Society Standard Practice (MSS SP) 44 flanges, except
for Class 75 flanges that are ANSI/API 605 flanges.
At the request of the American Petroleum Institute (API), flange dimensions, in accordance
with the API Standard 605, were included in the subsequent drafts. Class 1500 flanges were
deleted due to a lack of interest in using large size flanges in that pressure–temperature rating.
The API-605 flanges for Class 150 and 300 and for sizes NPS 36 and smaller for classes higher
than Class 300 are not compatible with the MSS SP-44 flanges. Thus, the MSS SP-44 flanges are
designated as Series A flanges and the API-605 flanges are designated as Series B flanges in this
Standard. Materials covered in this Standard are as in ANSI B16.5, except nickel base alloys are
excluded. Pressure–temperature ratings are in accordance with ANSI B16.5.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
