The selection of national standards
generally follows the standard HG/T 20623-2009.
ASME is selected according to ASME
It is common for designers to choose a large-diameter
flange model without specifying whether the flange should be labeled as A
series or B series, resulting in the purchase of the wrong flange and causing
huge economic losses.
Forgings are expensive, while large
forgings are even more expensive.
So why do large-diameter flanges need to be
divided into A series or B series, and why not unify them?
From the preface of the specification, we
can understand that:
The American National Standards (ANSI) B16
Committee developed flanges ranging from 26 "to 60" in December 1982,
with flange dimensions based on the manufacturer's standardization
association's standard practice MSS SP 44 Steel Pipe flanges.
The subsequent B16.47 update includes
flange dimensions for API 605 Large Diameter Carbon Steel flanges.
Used for Class150 and 300, as well as NPS36
or smaller sizes, API 605 and MSS SP-44 flanges are not compatible and cannot
be paired at all.
For ease of differentiation, MSS SP-44
flanges are designated as A-series. API 605 flanges are designated as B-series.
What is the difference between the A series
and the B series?
Generally speaking, under the same size and
pressure rating, ASME B16.47 A series flanges are thicker, heavier, and
stronger than B series flanges.
So, from a business perspective, A-series
flanges are generally more expensive than B-series flanges.
From the figure below, with the same
pressure rating and nominal diameter, it can be intuitively felt that the A
series is more majestic and enthusiastic. In contrast, the B series is more
exquisite and compact.
B-series flanges require more but smaller
fasteners (bolts and nuts) than A-series flanges, and the center circle
diameter of the bolts is smaller than A-series flanges.
Both the A series and B series defineraised face (RF) butt welding flanges and flange covers, but only the A series
has ring connection face (RJ) flanges ranging from Class300 to Class900.
The size of the connecting pipe provided by
the A series is completely different from that of the connecting pipe provided
by the B series. The outer diameter of the A series nozzle for DN650 Class150
is 660.4, and the B series nozzle is 661.9.
It is worth noting that the outer diameter
of the flange welding end (connecting pipe outer diameter) of the A series is
independent of the pressure level. In contrast, the outer diameter of the
flange welding end of the B series varies among different pressure levels.
For example, for the B series flange of
DN800, the outer diameter of Class150 is 814.3, the outer diameter of Class300
is 819.2, and the outer diameter of Class600/900 is 812.8.
For DN1500, the connecting pipe of Class150
is 1527, and the outer diameter of the connecting pipe of Class300 is 1557.3,
with a difference of 30mm. I have encountered a friend who used to check the
standard for errors but made a mistake in the outer diameter of this DN,
resulting in the scrapping of the paired connection.
Generally, the owner will provide flange
requirements for A series or B series according to the owner or contract
Due to the large redundancy of the
A-series, uniform pipeline size, and the addition of an RJ sealing surface,
most pipeline users or designers may choose A-series flanges for new pipelines
In general, the B series is affordable and compact
in structure, or previous devices that used API 605 need to be refurbished or
replaced, or the equipment itself has flanges or maintenance holes. Using the B
series can save construction costs.
Of course, the B series may sometimes be
cheaper than the A series; for example, for Class300 and larger than DN950, the
B series flange is heavier than the A series.
Of course, not all high-pressure levels are
heavier than low-pressure levels. For example, the A series DN950 weighs
326.9kg for Class150 and 315.6kg for Class300.
Of course, not all large-diameter ones are
heavier than small-diameter ones; for example, the DN900 of the A-series
Class300 is 578.9kg, and the DN950 is 315.6kg. The weight of DN650 for Class150
and B series is 54.5kg, and the weight of the WN flange for DN600 is 121.7kg.
There are too many exceptions in the world.
So many times, we need specific analysis.
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