A Series or B Series for Large Diameter Flanges
Above DN600 a large diameter flange has to be specified as A series or B series. Designers who leave that off the drawing buy the wrong forging, and large forgings are expensive to get wrong.
When the Question Arises
When selecting American standard flanges, a large diameter flange is needed above DN600. National standard selection generally follows HG/T 20623-2009, and ASME selection follows ASME B16.47-2020. It is common for designers to choose a large diameter flange model without stating whether it is A series or B series, which leads to the wrong flange being purchased and to significant economic loss.
Related product: Stainless Steel Flange DN15 to DN1200
Where the Two Series Came From
The ANSI B16 committee developed flanges from 26 to 60 inches in December 1982, with dimensions based on MSS SP-44 steel pipe flanges. The later B16.47 update added flange dimensions for API 605 large diameter carbon steel flanges. For Class 150 and 300 and for NPS 36 or smaller sizes, API 605 and MSS SP-44 flanges are not compatible and cannot be paired at all. To distinguish them, MSS SP-44 flanges are designated A series and API 605 flanges are designated B series.
How They Differ in Practice
At the same size and pressure rating, ASME B16.47 A series flanges are thicker, heavier and stronger than B series flanges, which is why A series is generally more expensive. B series flanges require more but smaller bolts and nuts than A series, and their bolt circle diameter is smaller.
How to Avoid the Mistake
Put the series on the drawing and on the purchase order, not just the size and class. Confirm the mating flange series before ordering, because an A series flange will not bolt to a B series flange of the same nominal size and rating. Forgings are expensive and large forgings more so, which makes this a cheap check to run.
What We Supply
Our flange programme runs DN15 to DN1200 in Class 150, 300, 600, 900 and 1500, in plate, slip on, weld neck, blind and threaded types, with bolt hole centre circle diameters from 50 mm to 2130 mm, 4 to 48 bolt holes and thread sizes M10 to M27. Tell us the series and the standard and the correct table is used.
Products Covered in This Guide
Stainless Steel Flange DN15 to DN1200
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Stainless Steel Elbow 45 90 and 180 Degree
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View specifications →Frequently Asked Questions
When do I need to choose between A and B series
Which series is stronger
Can an A series flange bolt to a B series flange
Which standards apply
Apply This to Your Own Specification
Send the service conditions and the grade recommendation comes back with a quotation for the sizes you need.