17

To:
Subject: Different bores in the same nominal size flange

Question:

Please advise why the 9" - 5M - BX157 bore is shown as 9" and yet the ID in the Weld Neck Dimensions is less at 6.813"

Answer:

Check out http://www.woodcousa.com/flange_history.htm and http://www.woodcousa.com/about_wnf.htm. These Web Pages will provide some background on API 6A Flanges.

API adopted API 6B Flanges (those flanges in API Spec. 6A that utilize R or RX ring gaskets) directly from the old ASA Standard. These old flanges were made in weld neck, blind, and threaded versions, all compatible with standard pipe sizes. The ASA originally identified the "Grandfather" of the flange mentioned as 8" 1500 lb., later API 6B adopted the dimensions and increased the material strength requirements, API then identified this flange as, 8" Series 1500, 5,000 lb. working pressure.

As Blowout Preventer design developed, convenience dictated that the bore of these flanges should be as large as the maximum diameter of the flange neck would permit. This enlargement would allow the passage of casing slips and hangers into wellhead tapered or shouldered bores below the Blowout Preventers. These full bore "integral" flanges require 60K minimum yield material to provide adequate strength for the increased bore size and the increased working pressure above that of the old ASA rating. Weld neck flange dimensions remained as originally specified (compatible with pipe sizes) but the material requirement increased to 45K yield due to the increase in pressure rating.

The particular flange in question has a BX ring groove normally used in a subsea application. When the flange has this BX groove it should comply with API Spec 17D. API 17D refers back to API Spec 6A for all but the ring groove. 17D requires the BX 157 ring groove to have a corrosion resistant inlay.

Click here for another related Q & A.
 

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 link and give us a 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.