Note: Descriptions are shown in the official language in which they were submitted.
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1 METHO~ AND APPARATUS FOR SEALING A PIPELINE
2 BACKGROUND OF THE INVENTION
3 1. Field of the Invention
4This invention relates to a method and apparatus for sealing a
pipe. More particularly, this invention relates to a method and apparatus
6 for separatiQg and sealing a first section of a submer~ed pipeline from a
7 second section of a submerged pipeline.
8 2. Description of the Prior_Art
9 In the offshore production of oil and gas, pipelines are used to
transport produced hydrocarbons to onshore storage and refining facilities.
11 Occasionally, in maintaining the pipelines i~ is necessary to check the
12 pressure integrity of the pipeline or a section of the pipeline. ~ne
13 method to accomplish such a check is to divide and seal the pipeline into a14 series of sections by means of a pressure-moveable plug member commonly
referred to as a "pig means" (see U.S. Patent Nos. 3,561,490; 3,903,730;
16 and 4,077,435). Pressure may then be introduced sequentially into each
17 section to check for leaks. However, for specific applications such as
18 sealing a section of a pipeline which has a bend with a very small radius
19 of curvature, the use of such conventional pig means may be difficult. In
addition, the pig means disclosed in U.S. Patents Nos. 3,561,490 and 4,077,435
21 are complicated and e~pensive to manufacture and maintain.
22 Therefore3 the need exists for an improved method and apparatus
23 for sealiug a pipeline which is simple to manufac~ure and maintain and
24 capable of passing through pipelines which have unusual geometic configura- tions or operating requirements.
26 SUMMARY OF THE INVENTION
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27 The present invention is directed to a method and apparatus for
28 separating and sealing a first section of a submerged pipeline from a
29 second section of a submerged pipeline.
The apparatus comprises a spherical member adapted for movemen-t
31 along the interior of a pipeline by induced pressure. Preferably, the
32 speciflc gravity of the spherical member is substantially the same as the
33 specific gravity of the fluid flowing within the pipeline so that the
34 spherical member is neutrally buoyant and, therefore, more easily advanced.
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1 The apparatus also includes a restraining member adapted to be2 attached between first and second sections of the pipeline. The restrain-
3 ing member includes a central protruding portion having a lip surface at
4 one end for co~tacting the spherical member and thereby stopping the
advancement of the spherical member. The lip surface has a cur~ed profile
6 at a radius substantially the same as the radius of the spherical member.
7 Thus, upon contact between the spherical member and the lip surface, a
8 pressure-tight seal is formed between the first and second sections of the
9 pipeline.
The method comprises the steps of initially installing a pig
11 means into one end of the pipeline and pressuring up the pipeline behind
12 the pig means so as to advance the pig means along the interior of the
13 pipeline. The pig means advances until it engages the restraining member,
14 thereby forming the pressure-tight seal between the two sections of the
pipeline. The pressure in the pipeline section upstream the restraining
16 member is then increased, and this pipeline section is monitored for leaks.17 Upon completion of the monitoring phase, the pressure in the first section
18 of the pipeline upstream the restraining member is released. A pressure
19 differential is then formed with the higher pressure being in the second
section of the pipeline to dislodge the pig means from the restraining
21 member. This pressure differential may be formed by back-up pressure
22 injected into the second section of the pipeline or a suction created in
23 the first section of the pipeline. In this manner, the pig means is then
24 advanced back through the first section of the pipeline and retrieved.
Examples of the more important features of this invention have
26 been summarized rather broadly in order that the detailed description which27 follows may be better understood. There are, of course, additional features
28 of the invention which will be described hereafter and which will also form29 the subject of the claims appended hereto.
BRIEF DESCRIPTION OF THE DRAWINGS
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31 In order to more fully understand the drawings used in the detailed
32 description of the present invention, a brief description of each drawing
33 is provided.
34 FIG. 1 is a sectional view of the present invention wherein a
spherical.member is seated against a restraining member.
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1 ~IG. 2 is a detailed drawing of that portion of FIG. 1 which
2 illustrates the contact area between the restraining m~mber and the spher-
3 ical member.
4 FIG. 3 is a graph of sphere velocity (feet per second) versus
pump rate (gallons per minute) generated in the experiments described
6 below.
7 DETAI~ED DESCRIPTION OF THE PREFERRED EMBODIMENT
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8 Briefly, the present invention is a Inethod and apparatus for
9 sealing a submerged pipeline which method and apparatus are reversible and
capable of operating in pipelines having unusual geometric configurations,
11 specifically bends with a small radius of curvature.
12 Referring to FIG. 1, a spherical member 10 (also referred to as a13 sphere) is illustrated inside of a pipeline 12. The sphere 10 is seated
14 against a circular restraining member 14 (also referred to as a seal trap).The member 14 is attached between first and second sections 16 and 18 of
16 the pipeline 12 by conventional methods, i.e., welding.
17 FIG. 2 is a detail of the restraining member 14 and the spherical18 member 10 as illustrated in FIG. 1. The restraining member is thicker at
19 its central portion 20 than at its end portions 22 and 24. The inner
diameter 26 of the restraining member at the central portion 20 is selected
21 so that the spherical member cannot pass by the restraining member when it
22 is advancing in the direction of the arrow 28. The central portion includes
23 a curved lip surface 30 at one end having substantially the same radius of
24 curvature as the spherical member. Thus, once the spherical member 10
engages the lip surface 30, a pressure-tight seal is achieved.
26 The relationship between the diameter of the spherical member and27 the inner diameter 32 of the first section is important due to the resulting
28 annular clearance between the spherical member and the inside of the pipe-
29 line. As verified by the experiments described below, the diameter of the
spherical member preferably should be 1/8 to 1 inch (3.2 to 25.4 mm) less
31 than the inner diameter 32 of the first section 16 of the pipeline and,
32 most preferably 1/6 to 1/2 inch (4.23 to 12.7 mm) less than the inner
33 diameter 32. In selecting the annular clearance between the spherical
34 member and the inner diameter of the pipeline, any irregularities on the
inner surface 34 of the pipelinej such as protruding field welds, as well
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1 as the desired flow velocity of the spherical member should be taken into
2 account. The greater the annular clearance between the spherical member
3 and the inner diameter of the first section, the greater the loss in pumping4 capacity due to the increased flow path available around the spherical
member (referred to as "blow-by loss"). Therefore, while it is advantageous
6 to increase the annular clearance to accommodate for irregularities on the
7 inner surface of the first section, the annular clearance cannot be too
8 large because of the blow-by loss. Thus, for pipelines with an inner
9 diameter between approxima~ely 6 and 18 inches ~15.2 and 45.7 cm), the
preferred annular clearance is 1/6 to 1/2 inches (4.23 to 12.7 mm) and,
11 most preferably, 1/12 to 1/4 inches (2.1 to 6.4 mm).
12 To facilitate the advancement of the spherical member through the13 pipeline, the specific gravity of the spherical member with respect to the
14 specific gravity of the fluid flowing in the pipeline should be considered.The specific gravity of the spherical member should be between 0.70 and
16 2.00 of the specific gravity of the fluid flowing through the pipeline.
17 Preferably, the specific gravity of ~he spherical member is between 0.75
18 and 1.25 of the specific gravity of the fluid flowing through the pipeline
19 and, more preferably, between 0.85 to 1.15. Most preferably, the specific
gravity of the spherical member is approximately 1Ø Thus, the spherical
21 member is substantially neutrally buoyant, and the amount of friction
22 between the spherical member and the bottom side of the inner surface of
23 the pipeline is minimized. In addition, the pumping-capacity requirement
24 is reduced because the annular clearance is maintained substantially constant
around the sphere. A neutrally buoyant sphere will also minimize blow-by
26 loss around only one side of the sphere that may otherwise occur because of27 a disproportionate gap in the annular clearance, thereby causing an increased
28 pumping requirement.
29 The diameter of the spherical member should not be too small;
otherwise, it might be forced past the central portion 20 of the restraining
31 member. The inner diameter of the central portion should be preferably
32 80-95% of the diameter of the spherical member, more preferably 90-95%.
33 Otherwise, as verified by the e~periments, if t~e inner diameter is more
34 than 95% of the diameter of the spherical member, there may not be enough
contact area available on the lip surface 30 tc keep the stresses in the
36 spherical member below its yield point, and the spherical member may be
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1 deformed and forced past the restraining member. The preferred ratio of
2 th~ dia~eter of the spherical member to the inner diameter o~ the restrai~ing
3 member at the central portion is 1.05 to 1.20 and, more preferably, 1.05 to
4 1.10.
Through-the-Flowline (TFL) tools (which are used to perform
6 various well completion functions) and various types of pigging means are
7 frequently run through the pipeline 12 to a well site or other facilities.
8 Such TFL tools and pigging means generally require a minimum annular
9 clearance between the inner diameter o~ the pipe and their outer diameters.
Therefore, in selecting the inner diameter of the central portion of the
11 restraining member, the minimum clearance requiremen~s of ~he types of TFL
12 tools and piggin~ means that must be run past the central portion also
13 should be considered.
14 EXPERIME~TS
Experiments were conducted to test the present iuvention as
16 indicated in FIGS. 1 and 2. Basically, the experiments were conducted in
17 two phases. The first phase (Phase I) consisted of three tests using
18 pipelines with an inner diameter of 11.375 and 11.94 inches (28.9 and 30.3
19 cm) a~d spheres of 10.95 to 11.~25 inches (27.8 to 30. cm) in diameter.
The second phase (Phase II) also consisted of three tests using a pipeline
21 with an inner diameter of 7.625 inches (19.4 cm) and spheres of 7.40 to
22 7.45 inches (18.8 to 18.9 cm) in diameter.
23 Each sphere was manufactured from aluminum. The spheres were
24 made of aluminum due to the availability, cost, strength-to-weight ratio,
and workability of the material. However, the spheres may be made of any
26 kind of material which satisfies the specific requirements of the present
27 invention.
28 In both Phases I and II the fluid flowing through the pipeline
2~ was fresh water with a density of 62.4 pounds per cubic foot (1 gram per
cubic cm). To provide for substantially neutral buoyancy, each sphere
31 included a hollow inner chamber 38. To create such a chamber 38, each
32 sphere was made in two halves. Each half was hollowed out to form part of
33 the chamber, and the halves were then welded together to form the sphere.
34 The e~periments indicated that the inner chamber 38 preferably
should be filled with a hard material to strengthen the sphere and prevent
36 it from being deformed and extruded past the restraining member. For
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1 example, the chamber 38 could be filled with woods-metal or an epoxy resin
2 such as Brutum 78 tTM). In some of the tests 7 the spheres were filled with3 Br~tum 78 epoxy. The epo~y was injected into the chamber 38 through a
4 small 1/4 inch ~6.4 mm) diameter hole in the wall of the sphere, after both
halves were welded together. The 1/4 inch (6.~ mm) diameter hole was then
6 tapped and plugged. However, other methods may be used to internally
7 strengthen the sphere. ~or example, the chamber 38 may be pressured-up to
8 a level greater than the anticipated local stresses caused by contact with
9 the seal trap. Alternatively, the hollow chamber may be internally strength-
ened w-th a series of plates or braces.
11 Phase I
12 Phase I consisted of a flow test in a vertical and hori~ontal
13 orientation and two pressure tests.
14 The flow test indicated that the velocity of the sphere is directly
proportional to the flow or pump rate of the fluid in the pipe. Referring
16 to FIG. 3, the flow tests indicated that a sphere will travel vertically
17 through the pipeline with a pump rate as low as 290 gallons per minute
18 tlO98. liters per minute). For the test sphere, this represented a minimum19 velocity of 0.8 feet per second (0.24 meters per second). The line 40 in
FIG. 3 was generated by a least squares statistical summary and illustrates
21 that there is a linear relationship between the pump rate and the velocity
22 of the sphere.
23 The flow test also indicated that the specific gravity of the
24 sphere should be most preferably approximately 1Ø The relatively easy
movement of the flow test sphere is attributed to the fact that the specific
26 gravity of the sphere was 0.996.
27 The pressure tests indicated that the seal trap should include a
28 circular lip surface 30, as illustrated in FIG. 2, to achieve a pressure-
29 tight, metal-to-metal seal. In the first pressure test, a straight 20
tapered surface, as illustrated on the down-stream end 24 of the central
31 portion with the angle ~ (see FIG. 2), was used as the contact surface with32 the sphere; however, the straight tapered surface was not capable of main-
33 taining a pressure-tight, metal-to-metal seal. The lip surface 30 was
34 reshaped to conform with the radius of curvature of the sphere. The secondpressure test indicated that the curved lip surface was capable of maintain-
36 ing a pressure-tight, metal-to-metal seal.
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1 As an added sealing means, the sphere may be coated with a thin
2 layer (i.e., 1/8 inch (3.2 mm) thick) o~ elastomeric material 42 (shown
3 partially in FIG. 2) such as neoprene or polyurethane. Thus, upon the
4 sphere's engagement with the lip surface, a tight elastomeric seal is
achieved. The tests of Phase I indicated that such a coating would be
6 helpful in assuring a pressure-tight seal; however, the elastomeric coating
7 must be carefully applied to ensure adequate bonding with the outside
8 surface of the sphere. Otherwise, contact with the inside wall of the
9 pipeline may damage the coating by peeling it off.
The pressure tests were of a static nature. That is, the spheres
11 were seated by hand in a seal trap test fixture. Pressure was then intro-
12 duced on the upstream side of the sphere. The second pressure test indicated
13 that the present invention is capable of holding a pressure of 3900 psi
14 (274 kilograms per square cm (kg/cm2)) for over 18 hours with a minimum of
deformation to the sphere (less than 1.4 percent of the sphere's diameter
16 along any axis). Such deformities are acceptable standards for industry
17 application of the present invention.
18 The more significant dimensions for the three tests of Phase I
19 were:
A. Flow tests:
21 Pipeline inner diameter: 11.94 inches (30.3 cm)
22 Sphere diameter with elastomeric coating: 11.825 inches
23 t30. cm)
24 Sphere diameter without elastomeric coating: 11.575 inches
(29.4 cm)
26 Specific gravity of sphere without elastomeric coati~g:
27 0.996 (compared to fresh water)
28 B. First pressure test:
2~ Pipeline inner diameter within test fixture: 11.375 inches
(28.9 cm)
31 o Sphere diameter: 10.950 inches (27.8 cm)
32 o Specific gravity of sphere: 0.997 (compared to fresh water)
33 Seal trap inner diameter at central portion: 10.375 inches
34 (26.4 cm)
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1 C. Second pressure test;
2 0 Pipeline inner diame~er within test fixture: 11.375 inches
3 (28.9 cm)
4 Sphere diameter: 11.200 inches ~28.5 cm)
Specific gravity of sphere: 0.82 (compared to fresh water)
6 o Seal trap inner diame~er at central portion: 10.375 inches
7 (26.4 cm)
8 Phase II
9 Phase II consisted of three pressure tests. These tests confirmed
that the sphere was capable of holding a pressure differential of over 4500
11 psi (316 kg/cm2) for extended periods of time with no leakage.
12 The first test was a static test, as discussed above. The second13 and third tests were dynamic. That is, a sphere was pumped through a 80
14 foot ~24.4 meters) section of 8 inch schedule 80 pipe (21.9 cm outer diameter)
and seated on the seal trap with the pressure head. As nated above, the
16 three tests indicated that the present invention is capable of sealing and
17 holding a pressure differential of over 4500 psi (316 kg/cm2) for extended
18 periods of time. Pressure loss due to leakage past the sphere/seal trap
19 never occurred.
The dynamic tests were also valuable because they indicated the
21 amount of differential back pressure required to unseat the sphere. Once
22 the test pressures of 4500 psi ~316 kg/cm2) were xeleased, the second
23 pressure test indicated that only about 300 psi (21.1 kg/cm2) back pressure24 was required to unseat the sphere for retrieval. The third pressure test
did not indicate a noticeable back-pressure requirement to unseat the
26 sphere.
27 In Phase II, the inner diameter of the pipeline was 7.625 inches
28 (19.4 cm), while the inner diameter of the central portion of the seal trap29 was 6.70 inches (17. cm). The diameters and specific gravities of the
three spheres were:
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31 A. First pressure test (Static test):
32 Sphere diameter: 7.45 inches (18.9 cm)
33 Specific gravity- 1.7 (compared to fresh water)
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1 B. Second pressure test (Dynamic test):
2 o Sphere diameter: 7.402 inches (18.8 cm)
3 Specific gravity: 1.7 (compared to fresh water)
4 C. Third pressure test (Dynamic test):
Sphere diameter: 7.402 inches (18.8 cm)
6 0 Specific gravity: 1.7 (compared to fresh water)
7 The dynamic tests indicated that even with a specific gravity of
8 1.7 the tes~ spheres performed well as a pressure-sealing means. To minimize
9 the pumping-capacity requirement and frictional damage to the sphere and
pipeline, the flow test of Phase I clearly indicated that most preferably
11 the specific gravity should be approximately 1Ø
12 In addition to the pressure tests, three types of commonly used
13 pipeline pig means (cleaning, paraffin-removal and scraper) were run down
14 the 8 inch test pipe and past the restraining means several times. These
tests indicated no visible damage to the pig means in advancing past the
16 restraining means. In addition, it took less than 300 psi (21.1 kg/cm2) to17 advance each pig means past the restraining means which is an acceptable
18 pressure for moving pipeline pig means.
19 The test environment for Phases I and II was an accurate represen-
20 tation of an actual field environment. The working pressures were represen- ~-
21 tative of actual well production pressures for the testing of pipeline
22 leaks. In addition, the dimensions for the pipelines tested in Phases I
23 and II are similar to those actually in place in present well production
24 facilities.
Summarily, the experiments indicated that the present i~ven~ion
26 performed very well as a pressure-sealing means.
27 OPERATION
28 To practice the present invention, the sphere is inserted at an
29 entry point upstream the first section of the pipeline. Pressure is exerted
against the back side of the sphere to advance it along the interior of the
31 pipeline toward the seal trap. As mentioned above, since the sphere is of
32 substantially neutral buoyancy, only a small pump rate is required to
33 advance it.
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l Once the sphere approaches the seal ~rap and engages the lip
2 surface, the pressure in the first section is increased, ~nd the first
3 section is monitored for leaks. Thereafter, the pressure in the first
4 section of the pipeline is released, and a back pressure is introduced into
the second section of the pipeline. As mentioned above, the Phase II tests
6 indicate that a maximum pressure differential of only about 300 psi (21.1
7 kg/cm2) was required to dislodge a sphere (equivalent to 100 gallons per
8 minute (378.5 liter per minute) for the 7.625 inches (19.4 cm) inner
9 diameter pipeline). Once dislodged, the sphere is advanced back up the
first section and retrieved.
ll The present inventio~ has been described in terms oi a preferred
12 embodiment. Modifications and alterations to this embodiment will be
13 apparent to those skilled in the art in view of this disclosure. It is,
14 therefore, intended that all such equivalent modifications and variations
fall within the spirit and scope of the present invention as claimed.
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