GB2196715A - Method of launching a pig into a pipeline - Google Patents

Abstract

A pig 112 e.g. made up of two pivotally interconnected modules is pulled into a cassette 110 by a winch. The cassette is lifted by a crane hoist with the pig held captive and lowered into or onto a pipe 124. A flange 126 on the cassette engages a flange 128 on a guide 130. The pig descends until the leading seal engages the small diameter 136 of the pipe. The cassette and guide are removed and the door 140 is closed. Pressurised 124 fluid is admitted through a connection 146 to drive the pig out of the pipe into then main pipeline. The cassette may be of non- magnetic steel to reduce pig drag. The descent of the pig after the flanges 126, 128 engage is controlled by the crane hoist connected to the pig by the sling 118. <IMAGE>

Description

SPECIFICATION Method of launching a pig into a pipeline The invention relates to methods of launching pigs into pipelines.

Many kinds of pigs are used for cleaning and inspecting pipelines and for separating different products flowing through the same pipeline. A pig is driven along the pipeline by the product flowing in the line. Many kinds of pigs have circumferential seals which engage the inside of the pipe. Another kind of pig is a sphere of elastomeric material, such as polyurethane. It is common practice for a pipeline to be connected to pipes, known as "traps", by means of which pigs can be launched into, and received from, the pipeline. Such traps are often of greater diameter than the pipeline to facilitate entry and removal of the pig and include a tapered section or throat by which the larger diameter part is joined to the remainder of the branch pipe of diameter equal to the pipeline.Where the trap is horizontal-the launching of a pig is greatly facilitated because the pig is readily supported, for example, in a shallow purpose-built concave support or tray.

The pig can quite easily be pushed along the tray and into the trap at the same level. Such a technique is applicable to specialised inspection pigs which are either of the kind consisting of a single module or of the kind consisting of at least two or more pivotally interconnected modules.

In some cases, for example on offshore installations where space is severely restricted, the launch trap is vertical. It has already been proposed to launch pigs of the sphere type by using a so-called basket containing a sphere or several unconnected spheres, the basket being raised by a crane hoist and lowered into a vertical trap.

In other cases the diameter throughout the length of the trap may be only slightly greater than the same as that of the pipeline so that it is very difficult for a pig to be inserted into the trap by pushing action. Where the pig consists of interconnected modules pushing action tends to cause the train of modules to jack-knife and become jammed. The seals in such cases fit very closely against the trap wall and commonly are of larger diameter than the inside trap diameter while in their free, non-deflected condition. Where the pig is of the magnetic type there is very high drag between the pig and the trap wall making insertion even more difficult.

In this specification the term "pipe" means any pipe such as a trap, for example, connected to a pipeline through which a pig can pass into the pipeline.

The object of the invention is to provide a method of launching into a pipeline a pig having two or more circumferential seals.

A method according to the invention of launching into a pipeline a pig having two or more circumferential seals using a cassette to facilitate installation of the pig in a pipe connected to the pipeline comprising moving the pig into the cassette through a first end thereof, moving the cassette with its second end- leading to effect coaxial engagement between the cassette and the pipe while the pig is prevented from moving out of the cassette and driving the pig out of the pipe by fluid pressure difference applied across at least one of the circumferential seals.

Examples of how to perform the method will now be described with reference to the accompanying drawings in which: Figure 1 is a vertical elevation, partly in section, of a pipe, a cassette mounted on the pipe and a pig in the cassette; Figure 2 is an elevation similar to Fig. 1 but showing a different type of cassette; Figure 3 is a vertical section through another type of cassette and a pig supported on a tray preparatory to the transfer of the pig from the tray into the cassette; Figure 4 is a vertical section through the cassette shown in Fig. 3 the cassette containing the pig and being shown already inserted fully inside a pipe; Figure 3 is a scrap section showing details of the cassette and pipe shown in Figs. 3 and 4; and Figure 6 is a vertical section through another type of cassette shown inserted with a pig inside a pipe.

Fig. 1 shows a pipe 10 in the form of a trap with a hollow cylindrical steel (i.e. ferromagnetic) cassette 12 secured to the pipe 10 in coaxial end-or-end relationship. The pipe 10 has an upper part 14 of slightly enlarged diameter joined to a lower part 16 of lesser diameter by a tapering section 18. The lower end of the part 16 has an external flange 20 by which the pipe 10 is secured to a pipe section (not shown) containing a ball valve.

The diameter of the part 16 equals the stan dard diameter of the pipeline (not shown) to which the pipe 10 is connected. The pipe 10 has a connection 22 for pressurised fluid. A reaction band 24 is bolted onto the pipe 10 and chains 26 secured the band 24 to a cross-beam 28 secured to the outside of the lower end of the cassette 12. The cassette 12 has a locating flange 30 engaging the upper end of the pipe 10 and the lower extremity of the cassette 12 fits closely within the recess in the top of the pipe 10 which recess receives a closure lid (not shown) for closing the pipe 10 after the cassette 12 has been removed.

The cassette 12 contains a pig made up of three modules 32, 34, 36 which are pivotally interconnected by Hookes joints. The lowermost module 10 has powerful permanent magnets (not shown) and two arrays of steel bristles 38, 40 forming a magnetic path between the magnets and the cassette 12. The module 32 has two circumferential elastomeric seals 42, 44. The module 32 carries sensors (not shown) for detecting the magnetic field created by the magnets. The module 32 is drive by pressure differences across its seals when the pig is travelling along the pipeline and the module 32 tows the other two modules 34, 36. The module 34 is an instrumentation module and also carries sensors for detecting the magnetic field. The module 36 is a battery module. The modules 34 and 36 have wheels 46 running on the inside of the cassette 12 or pipeline.

The pig is first moved into the cassette 12 in the horizontal position (see below) through the end 48. The cassette 12 is then lifted by a crane hoist (not shown) to the vertical position and assembled onto the pipe 10 as shown in Fig. 1.

The cassette 12 has longitudinal slots (not shown) and while the cassette is horizontal and after the pig has moved into the cassette, a cross-beam 50 is passed through the slots past the end of the module 36. Cables 52 are secured to the cross-beam 50 and to the cross-beam 28 and are also connected to winches 54.

The cassette 12 is lifted by a crane hoist (not shown) with the hoist cable 56 connected to both the cassette and the pig. The cassette 12 is lowered, with its other end 58 leading, to effect coaxial engagement between the cassette 12 and the pipe 10 as shown.

Once the cassette 12 is engaged with the pipe 10 and the chains 26 have been secured, operation of the winches 54 draws the crossbeam 50 downwardly against the upward pull of the crane hoist cable 48. The crane hoist renders during this stage. The reduced upward pull on the pig allows the weight of the pig to overcome the drag which is generated by friction and magnetic attraction between the pig and the cassette 12.

Once the pig is completely in the pipe 10 the cross-beam 50 and cable 48 are removed and the closure lid (not shown) is secured in its recess at the upper end of the pipe 10.

Pressurised fluid is admitted through the connection 22 (not shown). The ball-valve is then closed and another connection is used to admit fluid to drive the pig further into the pipeline.

The pig is supported in the pipe 10 out of contact with the ball-valve (while the cable 48 and cross-beam 50 are removed) by friction and magnetic drag and by the engagement of the leading seal 42 with the throat formed by the decreasing diameter of the section 18.

The cassette 12 keeps the pig straight and prevents jamming or jack-knifing as the pig is moved into the pipe. The entry of the seals 42, 44 into the pipe 10 is facilitated and damage to the pig is prevented. It will be noted that the leading seal 42 is brought into engagement with the pipe 10 while the module 32 and the modules 34 and 36 still engage the cassette 12. The internal diameter of the cassette 12 equals that of the section 14 of the pipe 10 to facilitate transfer of the seals between the two surfaces.

Fig. 2 shows a number of parts corresponding to the parts described with reference to Fig. 1 and they need not be described again.

The same reference numerals are used in Fig.

2 for such parts. Fig. 2 shows a cassette 60 which is secured to the pipe 10 by bolts 62 clamping together flanges on the cassette and pipe. The lower end of the cassette 60 engages an annular seal 64 in the recess at the top of the pipe 10. The upper end of the cassette 60 is closed by a demountable housing 66 containing a winch barrel 68. The winch cable 70 is secured to the upper end of the module 36. The housing 66 provides an eye 72 for securing the cable of a crane hoist (not shown). The winch barrel is driven by an external hydraulic motor 74.

The cassette 60 has a connection 76 for pressurised fluid. The axle of the.winch barrel 68 passed through a pressure-tight gland. The connection leads to a valve 80 and is connected via a valve 82 to the section 16 of the pipe 10. Two further valves 84, 86 are provided in lines leading, respectively, to a source of fluid at pipeline pressure and to atmosphere.

The pig is pulled into the cassette 60 in the horizontal position (see below) through the open end of the cassette available when the housing 66 is removed. The housing 66 is secured to the other end of the cassette and used to pull the pig into the cassette. The housing is finally secured once more to the first end after the cable 70 has been secured to the module 36 and drawn tight. The cassette is lifted by a crane hoist cable attached to the eye 72 and secured in position on the pipe 10 as shown. The valves 80, 82 and 84 and the ball-valve below the flange 20 are closed and pressurised fluid e.g. air, nitrogen or oil, for example, is admitted through a valve (not shown) and the connection 76 into the cassette 60. The pressure difference across the seals 42, 44 drives the pig downwardly. The hydraulic motor 74 is used to brake the winch barrel 68 and control the rate of descent of the pig. Typically, for example, the pressure of the fluid admitted to the cassette 60 is some 30 pounds per square inch maximum. The cassette 60 typically has a pressure rating of (100 psi).

Uitimately, the pig is fully within the pipe 10 with the leading seal 42 engaging the throat within the section 18 of the pipe 10. The valves are manipulated to purge the cassette and pipe of the fluid used to move the pig into the pipe 10. Also the valves are used to slowly pressurise both sides of the module 32 using pipeline supply to prevent premature pig movement resulting from transient pressure differentials. The pig is supported in the pipe 10 (before being driven through the open ballvalve) by friction and magnetic drag and engagement of the seal 42 with the throat in the section 18.

Figs. 1 and 2 show embodiments suitable for use where the bore of the trap is not large enough to accommodate a cassette.

Figs. 3 to 5 show apparatus applicable in a new installation. Fig. 3 shows a cassette 80 similar to the one shown in Fig. 2 which has just received a pig in the horizontal position.

The pig was pulled from a concave tray 82 by a winch cable 84 extending from a winch barrel 86. The barrel 86 is carried in a demountable housing 88 secured to one end of the cassette 80.

After the pig has entered the cassette 80 the housing 88 is demounted and mounted on the left-hand end of the cassette 80. The cable 84 is secured to the left-hand end of the module 36 and drawn tight.

The cassette 80 is then lifted by a crane hoist and lowered into a vertical pipe 90 (Fig.

4). The cassette 80 has an external flange 92 at its upper end which engages a shoulder in the upper end of the pipe 90 (Fig. 5). An internal groove in the wall of the pipe 90 immediately above the shoulder provides location for a locking ring 94 to retain the cassette 80 in position.

The cassette 80 has an external annular elastomeric seal 96 (Fig. 5) which engages the inside surface of the pipe 90. The seal 96 also protects the cassette 80 during loading into the pipe 90.

The cassette 80 has vents 98 (Figs. 3 and 4) to admit pressurised fluid from the interior of the pipe 90, which has connections 100, 102 (Fig. 4).

Once the cassette 80 is in position in the pipe 90, the housing 88 is removed and the winch cable 84 is disconnected from the module 36. At this stage the pig is supported in the cassette 80 by friction and magnetic drag.

The pig 90 is then closed by a door (not shown) fitted into the recess at the upper end of the pipe 90. Pressurised fluid is admitted and the pressure difference across the seals on the module 32 drives the pig downwardly through the ball-valve below the pipe 90 and into the pipeline.

Fig. 6 shows apparatus for use in existing or new installations. Fig. 6 shows a cassette 110 into which the two-module pig 112 is pulled while the cassette 110 is horizontal and supported substantially at ground level. The trailing end of the trailing module 114 has a lifting bar 116 to which one leg 118 of a three-legged sling set is secured. The other two legs 120 of the sling set are secured to lugs at one open end of the cassette 110 through which end the pig 112 was moved into the cassette. The cassette 110 is then lifted by a crane hoist having a hook connected at 122 to the sling set, the pig 112 being lifted independently by the leg 118.

The pig 112 is typically, for example, suitable for inspecting a pipeline having an internal diameter of 915 millimetres (36 inches). Such a pig weighs some 3.7 Tonnes but the magnetic and frictional drags can commonly exceed the weght of the pig. In this example, the cassette 110 is made of stainless steel; it may alternatively be made of some other material which is not ferromagnetic or which is substantially non-ferromagnetic so that the pig is insulated magnetically from the trap and the total drag is reduced to a value less than the weight of the pig.

The cassette 110 and pig 112 are lowered into the pipe 124 until an external flange 126 on the upper end of the cassette 110 engages an inwardly-directed flange 128. The flange 128 is part of a cassette guide 130 which is positioned on the end of the pipe 124 to facilitate entry of the lower end of the cassette 110 into the pipe 124. After engagement of the flanges 126, 128 which act as stops the cassette 110 descends no further but is supported by the pipe 124. At this stage the leading module 134 of the pig occupies the upper position shown in ghost outline in Fig. 6. The two sling legs 120 are released from the cassette 110 and the crane hoist continues to be lowered to lower the pig 112 inside the cassette 110 until the leading seal 132 on the leading module 134 engages the smallest diameter part 136 of the pipe 124.

There is now sufficient friction and magnetic drag acting on the seal 132 and the bristles 138 of the leading module 134 to prevent further descent of the pig 112. The leading module 134 is now in the lower position shown in ghost outline in Fig. 6.

The hook on the lower end of the sling leg 11 8 is released from the bar 116, preferably by remote control. The two sling legs 120 are re-attached to the cassette 110 and the crane hoist is operated to lift the cassette 110 out of the pipe 124 and return it to the ground.

The pig 112 remains generally stationary as the cassette 110 is withdrawn but the other seal 142 and array of bristles 144 on the leading module come into engagement with the inside of the pipe 124.

The cassette guide 130 is then removed and the trap door 140 is closed and secured.

The pipe 124 has a connection 146 to admit pressurised fluid into the pipe 124 to drive the pig 112 into the pipeline downstream of the pipe 124.

Although the description given above is concerned with launching a pig from a vertical position, the invention is not limited to that condition and is applicable to launching pigs from any position. Furthermore, the invention is applicable to launching pigs into oil, gas or water pipelines or pipelines conveying or intended to convey other products or materials.

Although the pigs shown each comprise two or more modules the invention is also applicable to pigs comprising a single module, particularly though not exclusively large and heavy magnetic pigs of that type. As already described the cassette is of either ferromagnetic or non-ferromagnetic material. A typical non-ferromagnetic material is stainless steel.

Alternatively the cassette is of non-metallic material. The pig generally is a magnetic inspection pig but the invention is applicable also to non-magnetic pigs.

Claims (15)

1. A method of launching into a pipeline a pig having two or more circumferential seals using a cassette to facilitate installation of the pig in a pipe connected to the pipeline comprising moving the pig into the cassette through a first end thereof, moving the cassette with its second end leading to effect coaxial engagement between the cassette and the pipe while the pig is prevented from moving out of the cassette, and driving the pig out of the pipe by fluid pressure difference applied across at least one of the circumferential seals.

2. A method according to claim 1, a crane hoist being used to move the cassette to the pipe and to control the movement of the pig from the cassette into the pipe.

3. A method according to claim 2, the cassette having external winch means which exert force on the pig assisting gravity as the pig moves out of the cassette.

4. A method according to claim 1, the cassette having a demountable winch which is used at said second end of the cassette to pull the pig into the cassette and which is used at said first end of the cassette to secure the pig to prevent its movement in the cassette while the cassette is moved to the pipe and to control the movement of the pig out of the cassette into the pipe.

5. A method according to claim 4, the cassette having a connection through which pressurised fluid is admitted to drive the pig out of the cassette into the pipe.

6. A method according to claim 4, in which the cassette has vents and is moved into the pipe to position the pig therein, the winch being removed before the pipe is closed and pressurised fluid admitted into the pipe and cassette to drive the pig from the pipe.

7. A method according to claim 1, the cassette and the pig being separately suspended from a crane hoist by which the cassette is moved to the pipe.

8. A method according to claim 7, the cassette being lowered into the pipe until a stop on the cassette engages the pipe, the pig continuing to be lowered until the seal engages the inner surface of the pipe.

9. A method according to claim 8, the cassette being withdrawn by the hoist before the pig is driven from the pipe.

10. A method according to claim 8, the cassette remaining in the pipe while the pig is driven from the pipe.

11. A method according to any preceding claim, the pig being a magnetic pig and the cassette being of non-metallic or other nonferromagnetic material.

12. A method according to claim 1, substantially as herein described with reference to Fig. 1 of the accompanying drawings.

13. A method according to claim 1, substantially as herein described with reference to Fig. 2 of the accompanying drawings.

14. A method according to claim 1, substantially as herein described with reference to Figs. 3, 4 and 5 of the accompanying drawings.

15. A method according to claim 1, substantially as herein described with reference to Fig. 6 of the accompanying drawings.