U.S. patent application number 09/729746 was filed with the patent office on 2001-04-12 for apparatus for reducing fastener bending stress in flanged connections.
Invention is credited to Nguyen, Lan T..
Application Number | 20010000225 09/729746 |
Document ID | / |
Family ID | 22806142 |
Filed Date | 2001-04-12 |
United States Patent
Application |
20010000225 |
Kind Code |
A1 |
Nguyen, Lan T. |
April 12, 2001 |
Apparatus for reducing fastener bending stress in flanged
connections
Abstract
An apparatus for reducing the bending stress imparted to
threaded fasteners in flanged connections is disclosed. The
apparatus includes a radially tapered surface machined in the
backface of the flanges to coact with the head of the threaded
fastener as the threaded fastener is tightened to a predetermined
torque value. This coaction compensates for flange deflection as
the threaded fastener is tightened.
Inventors: |
Nguyen, Lan T.; (League
City, TX) |
Correspondence
Address: |
JACKIE LEE DUKE
ATTORNEY COUNSELOR AT LAW
SUITE 100
1001 WEST LOOP SOUTH
HOUSTON
TX
77027
US
|
Family ID: |
22806142 |
Appl. No.: |
09/729746 |
Filed: |
December 5, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09729746 |
Dec 5, 2000 |
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09216201 |
Dec 18, 1998 |
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6176663 |
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Current U.S.
Class: |
411/145 |
Current CPC
Class: |
F16L 23/003 20130101;
Y10S 411/916 20130101; F16L 23/006 20130101; F16L 23/036
20130101 |
Class at
Publication: |
411/145 |
International
Class: |
F16B 039/282 |
Claims
What is claimed is:
1. A flanged connection fastener bending stress reduction
apparatus, comprising: first and second flanges in facing
relationship, said first flange having a plurality of fastener
holes therethrough, said second flange having a plurality of
complementary fastener holes therein; said first flange fastener
holes having a radially tapered surface on the back face of said
first flange; a fastener extending through said first flange
fastener holes; said radially tapered surface of said first flange
fastener holes configured to minimize bending stress on said
fastener when said fastener is tensioned; said fastener including
first and second preload retaining means; and, said fastener first
and second preload retaining means engaging said first and second
flanges, respectively, whereby tensioning of said fastener preloads
said fastener and maintains said first and second flanges in
preloaded abutting relationship.
2. A flanged connection fastener bending stress reduction apparatus
according to claim 1 wherein: said first fastener preload retaining
means includes a flanged end, said flanged end having an upper end
configured to receive a wrenching means for tightening said
fastener, said lower end of said flanged end of said first fastener
preload retaining means having a flat face; said second fastener
preload retaining means includes a threaded end; and, said second
flange complementary holes are threaded to receive said second
fastener preload retaining means threaded end.
3. A flanged connection fastener bending stress reduction apparatus
according to claim 2 wherein: tensioning of said fastener causes
said radially tapered surface to engage said flat face of said
lower end of said flanged end of said first fastener preload
retaining means in face to face contact.
4. A flanged connection fastener bending stress reduction apparatus
according to claim 1 wherein: said first fastener preload retaining
means includes a threaded end and a nut positioned thereon, said
lower end of said nut having a flat face; said second fastener
preload retaining means includes a threaded end; and, said second
flange complementary holes are threaded to receive said second
fastener preload retaining means threaded end.
5. A flanged connection fastener bending stress reduction apparatus
according to claim 4 wherein: tensioning of said fastener causes
said radially tapered surface to engage said flat face of said nut
of said first fastener preload retaining means in face to face
contact.
6. A flanged connection fastener bending stress reduction apparatus
according to claim 1 wherein: said first fastener preload retaining
means includes a threaded end and a nut positioned thereon, said
lower end of said nut having a flat face; and, said second fastener
preload retaining means includes a threaded end and a nut
positioned thereon.
7. A flanged connection fastener bending stress reduction apparatus
according to claim 6 wherein: tensioning of said fastener causes
said radially tapered surface to engage said flat face of said nut
of said first fastener preload retaining means in face to face
contact.
8. A flanged connection fastener bending stress reduction apparatus
according to claim 1 wherein: said second flange fastener holes
having a radially tapered surface on the back face of said second
flange; said first fastener preload retaining means includes a
threaded end and a nut positioned thereon, said nut having a flat
face; and, said second fastener preload retaining means includes a
threaded end and a nut positioned thereon, said nut having a flat
face.
9. A flanged connection fastener bending stress reduction apparatus
according to claim 8 wherein: tensioning of said fastener causes
said radially tapered surfaces to engage said flat faces of said
nuts of said first and second fastener preload retaining means in
face to face contact.
Description
1. This is a divisional application of application Ser. No.
09/216,201 filed Dec. 18, 1998, hereby incorporated herein by
reference.
BACKGROUND OF THE INVENTION
2. 1. Field of the Invention
3. This invention relates to a novel apparatus for reducing
stresses due to bending in threaded fasteners, particularly bolts
and cap screws, used in connecting flanged connections. Such
flanged connections have a wide variety of industrial uses
including connecting structural members that will be subjected to
critical external loads and in sealing high pressure vessels. The
flanges used in such applications must be maintained in face to
face contact to ensure proper operation. This face to face contact
is maintained by the plurality of threaded fasteners that are
tightened to a high percentage of their yield strength to ensure
this contact is maintained. It is well known in the art that such
flanges bend in an axial or meridional direction during this
tightening procedure. This meridional bending is transmitted to the
threaded fasteners and is known to contribute significantly to the
stress in the threaded fastener and reduces the amount of
tightening to which the threaded fastener can be safely subjected.
This in turn reduces the face to face contact between the flanges
and therefore the load to which the flanged connection can be
subjected.
4. The present invention has particular applicability in the oil
and gas industry where large diameter tubular members with flanged
end connections, called "risers" or "riser joints", are used. These
risers are used in offshore drilling and production operations and
extend from the wellhead at the ocean floor to a surface vessel.
These risers have typically been manufactured in fifty and eighty
foot lengths. During normal operation the flanged connection
between adjacent riser joints must contain internal pressure along
with enormous external loads due to environmental conditions. It is
critical that these flanged connections, and the threaded fasteners
holding them together, function flawlessly. These flanged
connections and the threaded fasteners connecting them are the area
to which the present invention most closely applies.
5. 2. Description of Related Art
6. An apparatus for stretching threaded fasteners is shown in U.S.
Pat. No. 3,749,362 (O'Connor et al.) The apparatus shown by
O'Connor et al. uses an external fastener stretcher threaded onto a
bolt to apply an axial load to the bolt wherein the bolt's nut can
then be tightened with minimal torque. Removal of the fastener
stretcher allows the bolt and nut to retain the load induced in the
bolt.
SUMMARY OF THE INVENTION
7. The current invention uses a radially tapered surface that is
machined into the backface of the flange, adjacent to the bolt or
stud holes, to compensate for the axial or meridional direction
bending that the flange undergoes during fastener tightening. The
machined radially tapered surface ensures that as the flanges bend
the threaded fastener remains straight and thereby minimizes the
bending stress transmitted to the fastener.
8. According to the present invention, in a first embodiment a
radially tapered surface is machined into the backface of the upper
flange adjacent each of the bolt holes. The lower flange has a
plurality of complementary holes threaded to receive the bolt. As
the bolt fastener is tightened to its predetermined value and the
flange deflects, the head of the fastener remains vertical while
the radially tapered surface moves downwardly. At maximum fastener
torque and flange deflection, the machined radially tapered surface
of the backface of the flange is in substantially face to face
contact with the head of the fastener and perpendicular to the axis
of the fastener.
9. In a second embodiment of the invention, an all thread stud with
a single nut is used in place of the bolt of the first embodiment.
A radially tapered surface is machined into the backface of the
upper flange adjacent each of the stud holes. The lower flange has
a plurality of complementary holes threaded to receive the all
thread stud. As in the first embodiment, as the nut of the fastener
is tightened to its predetermined value and the flange deflects,
the head of the fastener remains vertical while the radially
tapered surface moves downwardly. At maximum fastener torque and
flange deflection, the machined radially tapered surface of the
backface of the flange is in substantially face to face contact
with the nut of the fastener and perpendicular to the axis of the
fastener.
10. In a third embodiment of the invention, an all thread stud with
a pair of nuts is used in place of the fasteners of the previous
embodiments. A radially tapered surface is machined into the
backface of the upper and lower flanges adjacent each of the stud
holes. As in the previous embodiments, as the nuts of the fastener
are tightened to their predetermined value and the flange deflects,
the fastener remains vertical while the radially tapered surface
moves downwardly. At maximum fastener torque and flange deflection,
the machined radially tapered surfaces of the backface of the
flanges are in substantially face to face contact with the nuts of
the fasteners and perpendicular to the axis of the fastener.
11. A principal object of the present invention is to provide an
apparatus to reduce the bending stress transmitted to threaded
fasteners due to deflection of the flange.
12. Another object of the present invention is to provide an
apparatus for increasing the fatigue life of threaded fasteners
used in flanged connections.
13. A final object of the present invention is to provide an
apparatus for reducing the bending stress in threaded fasteners
without requiring the use of special fasteners.
14. These with other objects and advantages of the present
invention are pointed out with specificness in the claims annexed
hereto and form a part of this disclosure. A full and complete
understanding of the invention may be had by reference to the
accompanying drawings and description of the preferred
embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
15. These and other objects and advantages of the present invention
are set forth below and further made clear by reference to the
drawings, wherein:
16. FIG. 1 is an isometric view of a riser connector used in subsea
oil and gas drilling operations with the backface of the flanges
machined with a radially tapered surface.
17. FIG. 2 is a sectional view of the first embodiment of the
radially tapered surface bending stress reducing apparatus using a
threaded bolt fastener with the riser connectors unloaded.
18. FIG. 3 is a sectional view of the first embodiment of the
radially tapered surface bending stress reducing apparatus using a
threaded bolt fastener with the riser connectors loaded.
19. FIG. 4 is a sectional view of the second embodiment of the
radially tapered surface bending stress reducing apparatus using a
threaded stud and single nut with the riser connectors
unloaded.
20. FIG. 5 is a sectional view of the second embodiment of the
radially tapered surface bending stress reducing apparatus using a
threaded stud and single nut with the riser connectors loaded.
21. FIG. 6 is a sectional view of the third embodiment of the
radially tapered surface bending stress reducing apparatus using a
threaded stud and two nuts with the riser connectors unloaded.
22. FIG. 7 is a sectional view of the third embodiment of the
radially tapered surface bending stress reducing apparatus using a
threaded stud and two nuts with the riser connectors loaded.
DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
23. With reference to the drawings, and particularly to FIG. 1,
riser connector 100 is shown in an isometric view. Riser connector
100 includes first or upper flange 102 and second or lower flange
104. Upper flange 102 and lower flange 104 include butt weld
preparations 106 and 108, respectively, for attaching appropriate
sized tubular members (not shown) as is well known in the art. Seal
element 110 is disposed in the bores of upper flange 102 and lower
flange 104. A plurality of fastener holes 112 are spaced
circumferentially around upper flange 102 and lower flange 104 with
threaded fasteners 114 disposed therein. Upper flange 102 and lower
flange 104 include raised faces 116 and 118, respectively, that are
held in face to face contact when threaded fasteners 114 are
tightened to a specified torque value.
24. As best seen in FIG. 2, the first embodiment of the present
invention includes upper flange 102 and lower flange 104 with
raised faces 116 and 118, respectively. Fastener hole 112 in upper
flange 102 receives threaded fastener 120 in close fitting
relationship. Fastener hole 112 in lower flange 104 includes
threads 122 to engage threads 124 of threaded fastener 120. Upper
flange 102 includes backface 126 with radially tapered surface 128
machined thereon.
25. The radially tapered surface 128 is tapered radially as shown
to define angle .theta. between tapered surface 128 and the
underside 130 of the head 132 of threaded fastener 120. When
threaded fastener 120 is initially installed and threaded into
lower flange 104, the underside 130 of the head 132 of threaded
fastener 120 contacts tapered surface 128 at the outer edge and
angle .theta. as shown.
26. Referring to FIG. 3, when threaded fastener 120 is fully
tightened, the flange 102 has deflected downwardly by the angle
.theta.. Radially tapered surface 128 is in face to face contact
with underside 130 of the head 132 of threaded fastener 120 and
perpendicular to the axis of the fastener 120. This radially
tapered surface 128 minimizes the bending stress from meridional
bending of upper flange 102 transmitted to threaded fastener 120.
This reduction in bending stress on threaded fastener 120 is a
significant factor in increasing the fatigue life of threaded
fasteners 120.
27. A second embodiment of the present invention is shown in FIG.
4. Those items that are the same as in the first embodiment retain
the same numeric designation. As in the first embodiment, riser
connector 200 includes upper flange 102 and lower flange 104 with
raised faces 116 and 118, respectively. Fastener hole 112 in upper
flange 102 receives threaded stud 202 in close fitting
relationship. Fastener hole 112 in lower flange 104 includes
threads 122 to engage threads 204 of threaded stud 202. Upper
flange 102 includes backface 126 with radially tapered surface 128
machined thereon.
28. The radially tapered surface 128 is tapered radially as shown
to define angle .theta. between tapered surface 128 and the
underside 206 of nut 208 of threaded stud 202. After threaded stud
202 is initially installed and threaded into lower flange 104, nut
208 is tightened and the underside 206 of nut 208 contacts tapered
surface 128 at the outer edge and angle .theta. as shown.
29. As best seen in FIG. 5, when nut 208 is fully tightened, the
flange 102 has deflected downwardly by the angle .theta.. Tapered
surface 128 is in face to face contact with underside 206 of nut
208 of threaded stud 202 and perpendicular to the axis of the stud
202. This tapered surface 128 minimizes the bending stress from
meridional bending of upper flange 102 transmitted to threaded stud
202. This reduction in bending stress on threaded stud 202 is a
significant factor in increasing the fatigue life of threaded studs
202.
30. A third embodiment of the present invention is shown in FIG. 6.
Those items that are the same as in the first two embodiments
retain the same numeric designation. As in the prior embodiments,
riser connector 300 includes upper flange 102 and lower flange 104
with raised faces 116 and 118, respectively. Fastener hole 112 in
upper flange 102 and lower flange 104 receives threaded stud 302 in
close fitting relationship. Upper flange 102 and lower flange 104
include backfaces 304 and 306, respectively, with radially tapered
surfaces 308 and 310 machined thereon, respectively.
31. Radially tapered surfaces 308 and 310 are tapered radially as
shown to define angle .theta. between radially tapered surfaces 308
and 310 and the underside 312 of nuts 314 of threaded stud 302.
After threaded stud 302 is initially installed, nuts 314 are
tightened and the undersides 312 of nuts 314 contact tapered
surfaces 308 and 310 at the outer edge and angle .theta. as
shown.
32. As best seen in FIG. 7, when nuts 314 are fully tightened, the
flanges 102 and 104 are deflected by the angle .theta.. Radially
tapered surfaces 308 and 310 are in face to face contact with
underside 312 of nuts 314 of threaded stud 302 and perpendicular to
the axis of the stud 302. These radially tapered surfaces 308 and
310 minimize the bending stress from meridional bending of upper
flange 102 and lower flange 104 transmitted to threaded stud 302.
This reduction in bending stress on threaded stud 302 is a
significant factor in increasing the fatigue life of threaded studs
302. Although shown with both flanges having radially tapered
surfaces, the present invention envisions and claims a construction
with only one flange having the radially tapered surfaces machined
therein.
33. My improved apparatus to reduce the bending stress transmitted
to threaded fasteners due to flange deflection and the methods of
its application will be readily understood from the foregoing
description and it will be seen I have provided an improved
apparatus requiring minimal modification to existing flanges to
reduce the bending stresses transmitted to the threaded fasteners.
Furthermore, while the invention has been shown and described with
respect to certain preferred embodiments, it is obvious that
equivalent alterations and modifications will occur to others
skilled in the art upon the reading and understanding of the
specification. The present invention includes all such equivalent
alterations and modifications, and is limited only by the scope of
the appended claims.
* * * * *