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Prior to assembling a flanged connection, clean the ring grooves and inspect for damage (see Field Appraisal of Ring Grooves). Select a new ring gasket of the specified size (To identify the flange see Flange Slide Rule, For known flanges see Flange Reference Chart). Light lubrication of the ring gasket with a multi-purpose grease will not hurt, and may help, if the ring groove has a rougher 1 than specified surface finish. Take special care to avoid over lubrication of the gasket, so as not to fill the bottom of the ring groove with grease and block the downward travel of the ring gasket into the groove and limit the coining effect (also limiting the width of intimate contact between the gasket and the groove). Install the gasket and set the flanges together. Place bolts lubricated with API RP 5A3/ISO 13678 thread lubricant into bolt holes and install nuts, also lubricated on their back face, by hand. Tighten bolts by hand until nuts on both sides touch the backs of their respective flanges and have equal engagement on the ends of the stud bolts. At this point observe the stand-off between flanges for equal appearance all around, make any adjustment necessary to equalize the stand-off all around. This may require hand or hammer wrenches to achieve this equal stand-off.
Begin tightening by rotating nuts clockwise, choosing one bolt first, then choosing the bolt 180° opposite second. then one at 90° and then the one 180° from that. Then step over one nut from the first nut tightened (decide for yourself clockwise or counter-clockwise) and continue the same pattern as with the first four. See illustration below for tightening order of a 12 bolt flange:
Continue to monitor the stand-off and keep it equal all around during the tightening process. Judge make-up by observing the stand-off or if using a torque wrench, by achieving specified torque. Reference torque information when available (see Flange Slide Rule for API specified lubricant and torque on current API Spec 6A flanges). In the event the connection joins a Studded Flange with an Open Face Flange, then everything remains the same except that the studs have only one nut to tighten, eliminating the difficulty of keeping nut engagement equal on both ends of stud bolts.
If any properly made up connection leaks on test, it should be disconnected, inspected and if OK 1 , reassembled with a new gasket and retested. Any attempt to retighten a leaking connection, without disassembly, traps test fluid under the ring gasket limiting ring gasket coining and reducing the reliability of the connection. For more information see Test Rack Tips on this web site.
Those flanges for which API Spec 6A specifies R or RX Ring Gaskets (included here find information on 30" 300 and 600 MSS RTJ flanges also). Ring Gaskets (included here find information on 30" 300 and 600 MSS RTJ flanges also).
These flanges (usually without raised faces) have designs that leave a stand-off (gap) between the flanges after bolts have reached the required torque.
To plan the overall dimensions of assembled API 6B flanged equipment, operators must allow for this measured stand-off between flanges. This stand-off varies with the choice of R or RX gaskets. See illustration below:
6B flanges must always stand apart after assembly. Under normal circumstances no reason to accurately measure the stand-off of made-up API 6B flanges occurs. For most 6B flanges, operators can estimate the stand-off measurement by observing the gap between the flanges along their outside circumference. When one or both API 6B flanges have a raised face, the stand-off gap appears wider than normal and observation of the actual gap requires looking between the flanges to observe the space between the raised faces. In any case, the observed stand-off should appear uniform all around.
Caution: The difference in stand-off between R and RX gaskets can cause alignment problems on close coupled manifolding or pressure controlling loops. Assembly designers specify component dimensions which allow for the difference in stand-off between flanges when choosing either R or RX gaskets. When operators perform maintenance that involves disassembly, trouble free reassembly requires using gaskets the same as the gaskets originally chosen.
6 BX FLANGES
Those flanges for which API Spec 6A specifies BX Ring Gaskets.
These flanges have raised
faces that the design may permit to meet or
touch when the connecting bolts have reached the required torque. API
Spec. 6A requires that all 6BX open
face flanges have a raised face, 1/8" minimum height, and no
higher than the flange ring groove depth. See illustration below:
Made-up 6 BX Flanges
6 BX flange raised faces shown in contact after assembly. In actual field situations any small gap present after achieving specified torque should appear uniform all around.
6 BX Flange X 6BX Studded Face
On 6 BX studded face flanges API Spec 6A permits manufacturers to omit any raised face. As a practical matter almost all manufacturers do omit the raised face on studded face flanges.
The 6BX flange design requires that at least one of the joining connectors have a raised face. This raised face permits a face to face make-up of the connection near the ring groove while leaving a gap between the flange over most of the area of the flange out to the outside diameter. This gap allows for strain (flexing) in the flange as a result of the bolt tension after tightening without compromising the face to face and ring gasket compressive forces. Since a minimum 1/8" gap accomplishes this, only one connector must have a raised face. If all open face flanges have a raised face, and only an open face flange can join with a studded face flange, this permits the omission of the raised face on the studded face flange as a Defacto Standard.
Two distinct advantages exist as a result of this Defacto Standard: uniformity of tap end stud length among manufacturers, and elimination of machine time necessary to remove metal in order to produce the raised face. Lower cost of manufacture and greater interchangeability results, with no reduction of quality. See illustration below:
Made-up 6 BX Flange and 6BX Studded Face Flange
6 BX flange faces, with raised face omitted on studded face flange, shown in contact after assembly. In actual field situations any small gap present after achieving specified torque should appear uniform all around.
DRIFT TESTING OF ASSEMBLED EQUIPMENT
In the case of 6 B flanges (or 6 BX flanges that have not been pulled fully face to face), non-uniformity of stand-off may prevent the passing of a Drift past the connection even though the flanges may hold pressure. See the exaggerated illustration below:
If the equipment bore has the minimum I.D. and the stand-off does not appear uniform (or the flange faces do not appear to run parallel), a passing Drift may contact the wall of the connected piece of equipment and bind 1 or stick 1 instead of passing freely.
API Spec 6A or Spec 16A requires manufacturers that apply the API Monogram to the product, to drift test each piece of such equipment. However, when separate units of equipment require field assembly, the person(s) making the assembly may create an unexpected problem by not keeping any stand-off between flanges uniform all around. Rarely do field personnel have a Drift Gage available, so the best insurance against a stuck working tool comes from careful make-up of flange connections. Even if the job doesn't require close fitting tools, such tools may come into play should a well emergency occur.
Additionally, Blowout Preventer stacks frequently experience Kelly wear on their I.D. because flange make-up lacked uniformity all around and all, or a portion, of the stack leaned from the vertical, allowing the Kelly to rub against the side leaning in.
When operators anticipate the need for running tools which may have a small clearance with the I.D. of Blowout Preventers or Christmas Trees, having a Drift Gage available and used at the make-up site will provide cheap insurance against later downtime.
To determine a suitable ring gasket for a specific service application, see Ring Gasket Selection.
For Q. & A. 54 Stud Bolt Extension Beyond Nut, Click Here.
For Q. & A. 58 API Bolt Tension for Surface and Subsea Applications.
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