Revised: 12/28/2007 Provided links give access to illustrations and/or additional information. To return to this page use your browser back button.
API Spec 6A, 6B weld neck flanges, do not have full bores, they have restricted bores that match nominal pipe sizes. As an example, 4-1/16" 5M, 6B flanges have a maximum bore of 3.47" approximating the I.D. of 4 inch schedule 160 line pipe, 4-1/2" O.D. An illustration of a conventional flow line composed of line pipe welded to compatible weld neck flanges, as described, and joined by bolting these flanges together with an R-39 ring gasket, appears below.
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Standard API Spec 6A, 6B weld neck flanges present some interesting fluid dynamic problems when connected to full bore valves or flow lines. When bolted downstream onto flanges of full bore equipment, these weld neck flanges present a restrictive shoulder in the flow bore. Rapidly moving fluids will experience turbulence upon contacting this shoulder, premature failure of equipment may result. To prevent erosion problems weld neck flanges may have a special entrance opening bevel, or they may have full bores and special weld necks which may or may not be compatible with commercial pipe sizes. See illustrations below. |
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Special API Spec 6A, 6B weld neck flanges may have full bores, All API Spec 6A, 6BX weld neck flanges have full bores. Users of full bore weld neck flanges should 1 specify the O.D., I.D., and strength of tubular material used for attachment to any of these special weld necks.
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Regardless of published specifications, to satisfy their field
service needs, many users specify special weld necks that match standard pipe sizes on 6BX flanges. Such users do so at high risk unless they include
engineering and welding considerations in their decision process. WOODCO
USA provides a Flange Slide Rule, which includes links to
Weld
Neck Dimensions on most of the popular API flanges. All of the weld
necks shown meet API requirements but some 6B flanges illustrated have bores
smaller than the maximum allowed by API Spec 6A. WOODCO USA recommends that pipe of 2" nominal size (2-3/8" O.D.) or larger, used for pressure service of 960 psi or more, have a minimum wall thickness of .200 inches. This wall thickness can resist some external damage and internal erosion. All bores of 2" nominal size and larger weld neck flanges shown on this web site match pipe with a wall thickness equal to or greater than .200 inches. API
Spec 6A does not specify compatible pipe. 6B flange weld necks shown on this web site
match commonly available pipe which WOODCO USA identifies. Joining these flange weld
necks to the identified pipe should 1 allow full rated working pressure as
indicated for the flange. API Spec 6A does not specify test pressure for weld neck flange to pipe, welded assemblies. Logic would indicate 1 that 6B flanges with 45K material should experience a Test Pressure of 1.5 times Maximum Service Pressure (compared to 2 times maximum service pressure for 6B flanged equipment with 60K material integral flanges). Note: Test 16 inch nominal and larger assemblies with 6B flanges 1.25 times maximum service pressure (API Spec 6A specifies 1.5 times maximum service pressure for 6B flanged equipment with 60K material integral flanges in these sizes. Recent [2005] changes in the API specified test pressure of 5M working pressure equipment to 7,500 psi has not resulted in any change in 45K Weld Neck Flanges). 6BX weld neck flanges meet all material and design
requirements for Integral flanges so welded assemblies using these
flanges, joined to equal strength tubing of the indicated size, may experience a test pressure equal to that specified for the same pressure
rated flanged equipment with integral flanges. For
flanges which have Weld Neck
Dimensions other than
those shown on this
web site, determine matching pipe size by referencing Carbon Steel Pipe
Dimensions and Weights on this web site. WOODCO USA suggests no
grade or strength for pipe so selected and suggests no maximum service
pressure or test pressure for flanges joined to such selected pipe. Always
use Qualified Welding Procedures supported by a
Performance Qualification
Record and performed by Qualified Welders when joining weld
neck flanges to pipe or tubing. For Q. & A. about this page, Click Here. Click here for tips on Weld Neck Flange Attachment
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Information above, and in other
parts of this Web Site, may help persons who really seek to know. If you
have a question, and you think WOODCO USA may have the capacity to answer
it, please use our
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chance to help. WOODCO USA provides Web Site Tools for identification, estimating, and reference only. Do not use this information for manufacturing or inspection. Users of these tools should not use them as a substitute for professional engineering advice. Anyone making use of the information presented does so at his own risk and assumes any and all liability resulting from such use. FOR FURTHER INFORMATION, OR TO LEARN MORE ABOUT WOODCO USA PRODUCTS AND SERVICES, CONTACT: WOODCO USA
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