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A Brief History of Flanges
(To Identify API Wellhead Flanges, Click Here)
to: ASA Flanges,
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 discontinued,
obsoleted and replaced by more
modern configurations. Originally, all flanges related to pipe and became
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
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 (now
terms 300 lb. through 1500 lb. represented working pressures of flanges in
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 R or
ring gaskets) 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
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 STANDARD
6B. By 1957 API adopted new flanges from the Association of Well Head Equipment Manufacturers
(AWHEM, See Related Links)
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 inlayed with,
alloy. This specification also introduced SBX
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.
See Related Links
for API flange specification source information and AWHEM recommendations for
stud bolts and tap end studs as well. WOODCO USA can supply most types of
API flanges and many types of flanged equipment.
& A. about related matters: Click
Click here to
view a Flange Cross Reference Chart listing "Series" flanges and the current API
Spec 6A designations for these flanges.
here to view the WOODCO USA Catalog for Pressure Control Equipment.
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