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History of Flanges
(To Identify API
Wellhead Flanges, Click Here)
(Jump down to:
ANSI Flanges, API 6AB Flanges,
Today API Spec 6A and MSS SP-44 specify all flanges commonly
used in surface drilling and production. These flanges have a long history and
many flanges used in the past have been
replaced by more modern configurations. Originally, all flanges related to pipe
and became standard as
As equipment with
integral flanges came to the oilfield, standardization became necessary for
In the late 1930’s, the
American Petroleum Institute
(API) adopted the then ASA B16.5 flanges. For 720 psi and 960 psi applications
API specified no changes to the ASA B16.5 Standard, using the 300 lb. and 400
lb. flanges respectively. For 2000, 3000, and 5000 psi applications, API
specified an increase in material
yield strength to the respective ASA B16.5 flanges: 600, 900, and 1500 lb.
API distinguished their flanges from the
original ASA flanges through the method of changing the ASA term "lb." to the
API term "SERIES", (e.g. ASA 4" 900 lb. flange, 2160 psi
working pressure, compared to API 4" SERIES 900 flanges, 3000 psi working
pressure), dimensionally the same but differing in name, material strength, and
working pressure. API issued the first specification for wellhead flanges as 6B,
later incorporated into API 6A. The original flanges specified, retained the
designation "6B". All API flanges adopted for
wellhead use have Ring Type Joint
(RTJ) facing. API flanges may have Full
Face or Raised Face geometry, with
either case having the specified ring groove. Most wellhead manufacturers make
their 6B flanges full face.
Note: The ASA
terms 300 lb. through 1500 lb. represented working pressures of flanges in
elevated temperature service. API assumed the ambient temperature working
pressure for the 300 lb. and 400 lb. CLASS and assumed ambient temperatures for
2000, 3000, and 5000 psi flanges also. ANSI has since dropped the previous
ASA term "lb." and now refers to flanges by "CLASS". Today, API Spec 6A
specifies standard service temperatures of -75°
F to 250° F. Current API Spec 6A
flanges classed as 6B
by API (easily identified by the fact that they have ring grooves that accept
have identical dimensions with ANSI B16.5 flanges.
Caution: A connection between mating ANSI and API flanges
requires a rating of the connection no higher than the ANSI pressure rating. See
the notes and cautions below the illustrations on the
Flange Slide Rule Program pages on this web-site.
In 1945 API introduced flanges rated at 7500
psi, and by 1949 these flanges were given new material specifications, a 10,000
psi working pressure, and the classification "SERIES" 2900. Then API included
them with the earlier flanges under the new specification designation
6B. By 1957 API adopted new flanges from the
Association of Well Head Equipment Manufacturers (AWHEM)
designs to replace the "SERIES" 2900. These new 10,000 psi flanges were
specified in API STANDARD 6BX. In 1961, STANDARD 6B and STANDARD 6BX were
combined into STANDARD 6A, now designated Spec 6A. API included 15,000 psi and
20,000 psi flanges in more recent editions of API Spec 6A. API classes all
flanges that accept BX ring
gaskets as 6BX flanges. API 6BX open face flanges must have raised
faces, while API 6BX Studded Face
flanges may have their raised faces omitted. Most manufacturers make API 6BX
studded face flanges without raised faces.
API Spec 6AB, introduced in
1983, specified 30,000 psi flanged equipment. Spec 6AB has failed to achieve
reaffirmation by API so it has the current status of "withdrawn".
API Spec 17D, 1st edition,
appeared in 1992. This specification introduced 5,000 psi working pressure Type
17SS and 17SV swivel flanges and 10,000 psi swivel flanges that connect to API
Spec 6BX flanges of the same working pressure. These flanges for subsea
applications have dimensions to accept BX ring gaskets. Spec 17D requires all
flanges used for subsea applications to have ring grooves manufactured from, or
alloy. This specification also introduced
and SRX ring gaskets designed to
allow reliable make-up of flanges underwater. For more information specific to
API Spec 17D connectors, see About API 17D
SS and SV Swivel Flanges on this Web Site.
Low pressure Drilling
Diverter Systems use MSS
SP-44 flanges for 30" 500 psi and 30" 1,000 psi service.
for API flange specification source information.
WOODCO USA can supply most types of
flanged equipment, and
flange accessory items.
For Q. & A. about related
matters: Click Here.
Click here to
view a Flange Cross Reference Chart listing "Series" flanges and the current API
Spec 6A designations for these flanges.
Click here to view the WOODCO USA Catalog for Pressure Control Equipment.
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