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ABOUT FLANGES 


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Flange Bolt Hole Orientation
For Stack or System Assembly

 

When assembling equipment, operators sometimes find it necessary or advantageous to join flanged equipment of different nominal size or working pressure. Adapter Flanges or Adapter Spools necessary for this may have a different number of bolt holes on their opposite connections. When this case occurs, a problem of proper orientation presents itself. API 6A, 20th Edition contains the following. "10.5.4.2.7 Bolt Location For Flanges. A pair of bolt holes in both end flanges shall straddle the common centreline. " This design requirement assures that operators can maintain a proper orientation of equipment if they understand this requirement and how it applies to field assembly.

The following illustrations will make clear a method of recognizing the points of common center line that will assure proper orientation of the next piece of equipment joined in an assembly.

The rule is as follows: For a horizontal flange face (the flange face in the horizontal position and the bore vertical) the bolt holes shall be oriented to straddle the centerlines, both ends.

For a vertical outlet flange face (the flange face in vertical position and the line horizontal) the bolt holes shall be oriented to straddle vertical and horizontal centerlines.

BOLT CIRCLE LAYOUT, FLANGED DRILLING SPOOL
(13-5/8"15M x 13-5/8"15M with 4-1/16"15M Outlets)

(To see a catalog page click here)

Photo                   

 

 

BOLT CIRCLE LAYOUT, FLANGED ADAPTER SPOOL
(11"3M x 7-1/16"5M)

(To see a catalog page click here)

Photo                   

 

This Flanged Adapter Spool with 16 bolt holes in one flange and 12 bolt holes in the other will have 4 points around its' circumference where two bolt holes will equally straddle a common centerline.


BOLT CIRCLE LAYOUT, DOUBLE STUDDED ADAPTER
(7-1/16"5M x 4-1/16"5M)

(To see a catalog page click here)

Photo                   

 

This Double Studded Adapter with 12 studs extending from one connection and 8 studs extending from the other will have 4 points around its circumference where two studs in each connection will straddle a common centerline.


Although they have different configurations, both the Flanged Adapter Spool and the Double Studded Adapter illustrated conform to the API Spec 6A requirement for bolt circle orientation (Single Studded Adapters, not illustrated also conform).

API flange connections always have a number of holes (or tap end studs) divisible by 4, so regardless of the flange size or pressure or number of holes, this rule applies.

Persons making an assembly of flanged equipment should visually identify the 4 common center lines on all pieces of equipment. Maintaining strict alignment of this set of center lines through any assembly that requires an adapter will assure predictable orientation of the next connected unit.


Note: When adapters built to API Spec 6A requirements have the same number of holes, or studs, on each connection, all of these holes will straddle common center lines. The orientation of such an adapter does not effect the orientation of the next equipment connected. As a general rule any outlet connection on a Spool or Blowout Preventer will fall on the same center lines as the connection bolt holes. Except for special requirements outlets project at 90 from the Run bore and two outlets, 180 apart.


The following illustrations provide examples of bolt hole arrangement and outlet position on different types of Well Head and Blowout Preventer equipment.

BOLT CIRCLE LAYOUT, BLOWOUT PREVENTER (BOP)

 

BOLT CIRCLE LAYOUT, STUDDED TEE AND CROSS

BOLT CIRCLE LAYOUT, FLANGED TEE AND CROSS

BOLT CIRCLE LAYOUT, FLANGED GATE VALVE


As an example of a problem situation, observe the following illustration of an out of orientation installation made for a Flow Line connection extending to a Studded Cross in a Choke Manifold.

REFERENCE TO CENTER LINE OF BOP EQUIPMENT
FOR INSTALLATION ON OUTLET

The above illustration shows a 7-1/16" 5M x 4-1/16" 5M Flanged Adapter Spool installed without proper reference to center lines. An attempt to install a Studded or Flanged Cross onto any Spacer Spool extending from the 4-1/16" 5M flange will result in cross outlets 30 out of level plane. Unless the operator intended this orientation, disassembly and reassembly must take place.

If persons making assemblies using adapters do not have awareness of this information, they may consume valuable operator time investigating a non-existent, but suspected, equipment defect.

For more information about joining equipment units having differing flange connections, see Crossover Connections and Double Drilled Flanges.

For more information about Flange Make-up, Stand-off and Drift, Click Here.

 

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