GB2070188A - Pigging of pipelines - Google Patents

Abstract

There is described a fluid pipeline system including branch bends (3, 5) to and from a compressor station (2) wherein the fluid pressure drop at the bends is reduced by the presence of flow-diverting vanes (5) in the angles of the bends. Pigging of the system is made possible by arranging for the vanes (5) to be movable out of the working bore of the pipeline. The vanes (5) may be mounted in a sleeve (12, Fig. 3 not shown) and moved by a mechanism (16, Fig. 3) mounted in a movable chamber (20, Fig. 4 not shown) which is sealingly lockable to the pipeline adjacent the branches and is also used to receive pigs from, and launch them into, the pipeline. The vanes may be arranged as a pivotally mounted unit (40 Fig. 6 not shown) so that they may be pivoted out of the pipeline bore into an enlargement (44) of the pipe wall. Each bend (3, 5) may be closed by an inner door (11, Fig. 4 not shown) and an outer safety door (6). The inner door (11) maybe removed by a mechanism (21, Fig. 4). <IMAGE>

Description

SPECIFICATION Pigging of pipelines This invention relates to pipelines, for example those which carry fluids, for example gas, water, oil and the like, in bulk from one locality to another. It is usual for such pipelines, which may for example have diameters of the order or 28", 48", 56" and 72", to be cleaned and/or inspected by means of pigs or spheres which pass along them. The invention is especially concerned with pigging systems, and more especially with a pipeline system which enables the efficient use of pigs without substantial disruption in the flow of fluid through the system.

In any pipeline system, for example a natu ral gas pipeline, it is normal for compressor stations to be located at spaced positions therealong. Such compressor stations conveniently coincide with pigging stations, i.e. pigreceiving and pig-launching stations. At these stations it is required that the pipeline flow should go through the compressor, whereas pig trapping, or pig reception, should occur upstream of the compressor station and piglaunching downstream thereof. Thus, a common feature of natural gas pipelines at compressor stations is the use of right-angle branch bends. These bends perform the task of diverting the flow of fluid from the pipeline into the compressor station and returning the compressor discharge back to the pipeline on the downstream side of the compressor station.Whilst the pipeline flow negotiates these branch bends, the pigs or spheres do not and are trapped at the branch bends. It is known that such branch bends, which occur twice per compressor station, are associated with high loss coefficients. Since pumping stations are normally fuelled by a proportion of the transported gas, the reduction in pressure resulting from the branch bends represents a considerable operating cost.

Thus, even a modest reduction in these losses will amount to a substantial reduction of the running costs of a pipeline if taken over an average 25 year operating life.

Such losses can be reduced by incorporating in the branch bend a cascade, which comprises a number of flow-diverting vanes situated in the bend, which divert the flow of fluid from the main pipe line to the branch line through the compressor station. It is equally clear, however, that such a set-up does not lend itself to cleaning by means of pigs or spheres, since the passage of the pigs or spheres would be interrupted by the vane cascades situated in the branch bends. It has not hitherto been possible, therefore, to reduce the pressure drop of fluids flowing from a main pipeline into a branch bend and at the same time clean/inspect the pipeline by means of pigs or spheres. The object of the invention is to provide a system in which this is possible.

According to the present invention, in a fluid pipeline, e.g. a natural gas pipeline, having branches leading to a compressor station, there is situated in the angle of the branch a plurality of flow-diverting vanes, which vanes are movable out of the path of a pig or sphere passing along the pipeline.

In one form of the invention, the vanes are mounted on a support which is pivotable about an axis contained in the wall of the pipeline, so that when a cleaning/inspecting pig or sphere approaches the vanes the vane structure may be pivoted out of the path of the pig or sphere, for example into a chamber formed by a portion of the pipeline wall. In another embodiment, the vane cascade is mounted on a sleeve which is retractable out of the pipeline by means external thereof In either case, the vane unit is movable in order that it can control the fluid flow during normal operation of the pipeline, and can be removed, i.e. out of the pipeline, when a pigging operation is in progress.

As is known, the reception of pigs at one part of the pigging station, e.g. upstream of the compressor station, and the launching of pigs at another station, e.g. downstream of the compressor station, involves careful control of the fluid flow and a considerable amount of ancillary equipment is required to effect this. External valves and loops, e.g.

bypass and kicker lines and valves, are normally required. Such costly ancillary equipment is rendered unnecessary by a further aspect of the present invention, which comprises a movable pigging chamber. Such a chamber comprises a pressure vessel adapted to be attached to and removed from the pipeline, and housing a movable sleeve for reception or launching of a pig. By means of such a movable pigging chamber it is possible to control the subsidiary fluid flows, whereby to drive the pig out for launch or to force it into the sleeve for reception.

The movable pigging chamber preferably includes means for withdrawing the cascade or vane unit. The movable pigging chamber thereby constitutes a "trap" which can be fixed to and taken from the pipeline without mainline valving, and which incorporates internal bypassing, can be located directly against the main flow connection and, by using the same internal movement mechanisms, can remove a cascade or vane unit to prepare for a pigging operation.

Cascade or vane units per se, consisting of a number of guide blades or vanes, are known. The vanes normally have a narrow chord compared with their length, and are arranged along the intersection line of the main pipe line and the branch bend. The effect of a cascade is to reduce separation of the fluid flow at the inner wall and to sup press any tendency to set up secondary flows.

The construction and effect of the vanes in the cascade of vane unit depend upon a number of variables, e.g. the number of vanes and the vane spacing, the vane shape, e.g. a parabolic or circular arc aero-foil section or a constant thickness section of parabolic or circular arc curvature, the chord length, the inclination of each vane to the pipe walls, and the leading and trailing edge geometry of the vanes. Preferably, the vanes are adjustable on their support in order to vary their inclination as appropriate to the particular job in hand.

The effect of flow-diverting vanes upon fluid flow has been investigated in other areas, and much is known of the effect of various configurations of vane. A consideration of the relevant factors in any particular case will enable the determination of the most efficacious vane configuration for use.

Since it is a preferred feature of the invention that the movable pigging chamber, which is preferably provided with means for inserting and removing the vane cascade into and from the pipeline branch bend, is also used both to receive and launch a pig, the pig launch and pig reception stations are preferably situated in axial alignment and sufficiently close together that a turntable can be positioned between them and used to move the pigging chamber from its pig-receiving position to its pig-launch position, through a neutral position in which the pig and debris may be removed from the chamber and the pig re-loaded therein.

It is thus also a preferred feature of the invention that the upstream and downstream portions of the pipeline, i.e. the portions of the pipeline on either side of the compressor station, should be rigidly held together. This is preferably effected by means of a rigid anchor structure, which eliminates the need for large and costly ground anchors at both the incoming and outgoing portions of the line.

The accompanying drawings are given for the purpose of illustrating the invention and its method of use.

In the drawings, Figure 1 is a diagrammatic representation of a pipeline showing an intermediate compressor station connected by conventional rightangled branch bends to the main pipeline; Figure 2 is a diagrammatic representation similar to that of Fig. 1, but wherein the rightangled bends include movable vane cascade structures in accordance with the present invention; Figure 3 is a part-sectional elevation of a branch bend, downstream of a compressor station, showing the position of the vane structure therein; Figure 4 is a part-sectional elevation of a movable chamber for reception/launch of a pipeline pig and manipulation of the movable vane cascade unit; Figure 5 is a detail of the movable chamber locked on to the end of the pipeline;; Figure 6 is a sketch of a right-angled branch bend on the upstream side of a compressor station, containing an alternative constr,uction of vane unit; Figure 7 illustrates a right-angled branch bend containing a vane unit and being closed by means of a main door and a safety door; Figures 8 to 13 illustrate various stages in the operation of the movable pigging chamber, including the removal of the main and safety doors, the withdrawal of the vane unit from the bend, the reception of a cleaning/inspecting pig, the re-launch of a pig and the replacement of the vane unit; Figure 14 illustrates the disposition of pig receiving and pig launching stations above ground level; and Figure 15 illustrates a below-ground level station at which the incoming and outgoing ends of the pipeline are rigidly held together by an anchor structure.

Referring to the drawings, Fig. 1 shows a conventional pipeline/compressor station setup. The main pipeline is indicated at 1, and fluid flows from the pipeline 1 into a compressor station 2 by means of a right-angled branch 3, and is discharged from the compressor station back into the main pipeline through a second right-angled branch 4. The branches 3 and 4 are formed by T-pieces, which terminate in conventional pig traps (not shown), one for receiving a pig passing along the line 1 and the other for re-launching the pig, or another pig, into the downstream side of the line. In the system according to the invention, illustrated in broad outline in Fig.

2, movable vane units 5 are situated in both the upstream and downstream branch bends 3, 4, and the line beyond each bend is capped by a door 6.

Fig. 3 illustrates in greater detail a rightangled branch bend on the downstream side of the compressor station. The bend comprises an adaptor body or lateral tee 10 welded to the main pipeline 1, and closed and sealed by an inner door 11 which in normal operation is covered by a safety door or cap 6. Mounted within the bend is a vane unit comprising a sleeve 1 2 across the angle of which are a series of vanes 1 3 mounted on support bars 14. The movement of the sleeve 1 2 in the body 10 is iimited by a shoulder 1 5 against which the free end of the sleeve 1 2 abuts. The sleeve 1 2 is otherwise axially movable within the body 10 by a mechanism generally indicated at 1 6.

in the Fig. 3 construction the vanes 1 3 are shown as equally spaced across the mitre bend. In some conditions it may be advantageous for them to be spaced according to an arithmetic progression, the vanes being closer together on the inside of the bend than on the outside. Each vane has a radiussed edge 1 7 and a tapered trailing edge 1 8. In one embodiment the optimum inter-vane passage aspect ratio is between 6 and 8, the optimum pitch/ chord ratio is about 0.3 - 0.4, the optimum incidence angle is between + 1" and - 5", and the optimum chamber angle is between 90 and 107".

Fig. 4 shows a pigging chamber 20, which is attachable to the end of the adaptor body 10. This locking/sealing attachment is better illustrated in Fig. 5. Mounted within the chamber 20 is a mechanism, indicated generally at 21, which, when chamber 20 is attached to the adaptor body 10, operates to remove the inner door 11 from the adaptor body and stow it clear of the working bore of chamber 20 in an increased diameter portion of the chamber, 22. The door 11 is shown in its fully stowed position at 11 b, an intermediate position being shown at 1 1a. The doorremoval mechanism 21 comprises a 3-point attachment 23, 24, the brackets 23 being attached to the caliper drive 25 by struts 26 and the bracket 24 being attached to a tilting gear 27 by a strut 28. The caliper drive 25 and tilting gear 27 are mounted on forks 29.

The door-manipulating mechanism 21 is movable on longitudinal and transverse rails.

Thus, the operation of removing the door 11 from the adaptor body involves a linear movement of the manipulating mechanism, to place the door at its position 11 a, followed by a transverse movement, accompanied by an angular movement of the door 11 to its fullystowed position at 11 b. It will be appreciated that the struts 26 and 28 are attached to brackets 23 and 24 respectively, manually.

As seen in Fig. 5 when the chamber 20 is sealingly-locked to the adaptor body 10, locking is by means of inner and outer locking rings 30, 31 respectively, and sealing is by means of bi-face seals 32 and 33. The locking rings 30 and 31 may typically be of the type described in U.K. Patent Application No.

45281/76; and the bi-face seals 32 and 33 may typically be of the type described in U.K.

Patent Application No. 80201 78. The seal is completed by means of a security ring 34.

Once the door-removal gear has been manually attached to the inner door 11, the safety cap 6 having been removed following the usual safety procedures, and the movable chamber 20 has been sealingly-locked onto the end of adaptor body 10. The door-removal mechanism 21 is manipulated to remove the door 11 from the position shown at the lefthand side of Fig. 4, into its intermediate position at 11 a, and then into its final stowed position, at 11 b.

Fig. 6 shows an alternative form of right- angled branch bend, wherein the vane unit is movable by pivoting it. Thus, Fig. 6 shows a vane unit 40 comprising a series of vanes 41 mounted across the mitre bend of a branch 42, the unit 40 being pivoted about a pivot 43 disposed within the pipeline but outside the working bore thereof. The pipeline is enlarged to provide a well 44 into which the vane unit 40 may be pivotally moved by a piston rod 45 to enable a pipeline pig 46 to pass unimpeded from the upstream, to the downstream side of the branch bend.

The operation of a branch bend having a movable vane unit in accordance with the invention is illustrated in Figs. 7 to 1 3.

Fig. 7 shows the normal non-pigging operation of the branch bend. Thus, the body 10 is fitted with the flow-directing vane unit 1 2 and is closed at its downstream end by main door 11 and safety door 6. When a pigging operation is to be carried out, it is necessary to remove the vane unit 1 2 from the branch bend. The integrity of the main door seal is tested by means of guage 50 and the safety door 6, which is equipped with dual safety bleed locks, is removed. The movable chamber 20 is then placed in the position shown in Fig. 8, after the door removal mechanism has been manually attached to the main door 11 (see Fig. 4). The chamber 20, suitably movable on runners, rails or wheels, is equalised to the main line pressure and the main door 11 is then unlocked and stowed as described hereinbefore with reference to Fig. 4.The vane unit 1 2 is then removed by means of the mechanism 1 6, operated from outside the chamber 20, the main door 11 is replaced onto the adaptor body 10, the chamber 20 is then blown down, and is removed from locking engagement with the adaptor body 10, namely to the position shown in Fig. 9.

The vane unit 1 2 can then be removed from the chamber 20., and a pig trap unit 51 placed therein.

The chamber 20 is then refitted to the adaptor body 10, the main door 11 once again removed and stowed, and the trap unit 51 moved into pig-receiving position with the end of the unit 51 within the adaptor body 10. An annular gap 52 is left between the end of the trap unit 51 and the adaptor body 10 to enable fluid to by-pass the trap unit 51 and damp the reception of the pig 46 entering the trap unit and moving with the trap unit to the closed end 53 of chamber 20. The final position of the pig 46 and trap unit 51 is shown in the lower part of Fig. 10.

The main door 11 is once again replaced, the chamber 20 rolled back to the position shown in Fig. 11, and the pig 46 and trap unit 51 removed. The vane unit 12 can then be replaced in the chamber 20, the chamber 20 re-locked onto adaptor body 10 and its pressure equalised with main line pressure, the main door 11 once again removed and stowed, the vane unit replaced in the branch bend, the main door 11 replaced, and the chamber 20 unlocked from the adaptor body 10 and removed therefrom. The safety door 6 can then be replaced.

Figs. 1 2 and 1 3 illustrate the use of the removable pigging chamber 20 to launch a pig 46 into the downstream portion of the pipeline 1. The trap unit 51 and pig 46 are placed in the chamber 20, which is locked on the adaptor body 110 of the branch bend.

The main door is removed and stowed in the chamber 20, the trap unit moved to close the fluid by-pass, and the pig launched. The trap unit 51 is then moved back into the chamber 20, the main door replaced, the chamber 20 removed from the adaptor body 110, a vane unit 112 placed therein, the main door once again removed and stowed, the vane unit manipulated into position in the adaptor body 110, the main door replaced and the removable chamber removed therefrom.

It will be appreciated that the pressure inside the chamber 20 should be equalised to main line pressure before main door 11 is removed, and that when main door 11 has been replaced, and before chamber 20 is removed from the adaptor body, it should be blown down.

Figs. 14 and 1 5 illustrate possible layouts of the branch bends 5. In Fig. 14 they are situated above ground level, whilst the major portion of the pipeline 1 is below ground level and is rigidified by thrust anchors 60. Although not shown, a turntable is preferably situated between the ends of the pipe, in order readily to move pigs, traps and vane units between one end of the pipe and the other.

In the layout shown in Fig. 15, both the pipeline and the other ancillary mechanisms are situated below ground level. The adaptor bodies 10, 110, are provided with reinforcing collars 120, and the collars 1 20 are rigidly attached to each other by longitudinal members 121, e.g. steel girders, suitably of strength equivalent to that of the line pipe. By this means the adaptor bodies 10, 110 are maintained in rigid axial alignment, which enhances the efficiency of the pig-receiving and pig-launching operations.

It will be appreciated that by virtue of the this invention there is provided a method of reducing the pressure loss at both the main line compressor station tee branches, and at the same time enabling the efficient use of cleaning/inspecting pigs. The use of a turntable pig handling arrangement between the traps facilitates the movement of the pressure loss equipment, minimises the space required for the overall machinery, and makes weather protection feasible. By rigidily coupling the ends of the pipeline together the need for massive concrete pipeline anchoring arrangements is obviated.

Claims (14)

1. A fluid pipeline comprising a branch wherein there is situated a plurality of fluid flow diverting vanes, the vanes being movable out of the path of travel of a pig or sphere passing along the pipeline-.

2. A pipeline as claimed in claim 1 wherein the vanes are mounted or a support which is pivotable about an axis contained in the wall of the pipeline.

3. A pipeline as claimed in claim 1 wherein the vanes are mounted on a sleeve which is movable into and out of the branch.

4. A pipeline as claimed in any of claims 1 to 3 wherein the individual vanes are adjustable as to their inclination relative to the pipeline walls.

5. A pipeline as claimed in claim 3 wherein there is associated with the branch a movable chamber sealingly attachable to the pipeline and having means for moving the vanes into and out of the branch.

6. A pipeline as claimed in claim 5 wherein said chamber also comprises means for permitting access to said branch.

7. A pipeline as claimed in claim 5 or 6 comprising also a turntable for rotational movement of said chamber.

8. A pipeline as claimed in claim 5 wherein said chamber includes first means for attaching to and moving a closure member of said pipeline into a stowed position within said second chamber but out of axial alignment therewith, and second means for attaching to and moving said vanes into and out of said branch, said first and second means being operable externally of said chamber.

9. A pipeline as claimed in any of claims 5 to 8 wherein said chamber comprises an internal fluid flow control system.

10. A pipeline as claimed in claim 9 wherein said fluid flow control system comprises a substantially cylindrical sleeve axially movable within said chamber.

11. A fluid pipeline comprising an intermediate compressor station and branches diverting the fluid flow into the compressor station and returning the compressor discharge to the pipeline, a movable chamber sealingly attachable to the pipeline at or adjacent the branches, and means operable externally of the chamber for coupling the chamber to the pipeline.

1 2. A pipeline as claimed in claim 11 wherein said movable chamber includes an internal fluid flow control system.

1 3. A pipeline as claimed in claim 1 2 wherein said fluid flow control system comprises a substantially cylindrical sleeve axially movable within said chamber.

14. A pipeline as claimed in any of claims 11 to 1 3 comprising means rigidly coupling said brar.ches together.

1 5. A pressure chamber having means for sealingly locking it to the closed end of a pressure fluid pipeline, and means operable externally of the chamber for effecting fluid communication between the pipeline and the chamber.

1 6. A chamber as claimed in claim 1 5 including an internal fluid flow control system in the form of a substantially cylindrical sleeve axially movable with the chamber.

1 7. A chamber as claimed in claim 15 or 16, made of high tensile steel of thickness 50 to 65 mms.