Background of the Invention Pipelines used to transport products such as fuel, gas or hazardous liquids, particularly fuel pipelines, require periodic maintenance which involves cleaning their outer surfaces and providing them with protective coating, e. g., coating for protecting the outer surfaces of the pipes from corrosion. Since these pipelines reach thousands of kilometers in length, the maintenance is effected in stages, viz. successively on sections thereof, which have a length in the order of tens of meters. Each section is subjected to maintenance at intervals of a few years, but in view of the great length of the pipelines, the overall maintenance operations are extremely heavy and costly.

Currently, each pipeline section is exposed by digging at the sides and under the pipeline, to distance the outer surfaces of the pipes from the surrounding ground sufficiently to permit to carry out on said outer surfaces the required maintenance operations. In many cases, the pipeline is laid in or crosses hard ground, such as rock formations, which is very difficult to dig out, and requires lengthy and expensive operations.

It will be appreciated that while the ground may have been comminuted to some extent on the sides, when a trench was dug for the laying of the pipeline, the bottom of the trench is intact and can be formed by a hard rock mass. In addition, digging underneath the pipeline in any ground type will compromise the integrity of the trench bed and additional costs are incurred in restoring the trench bed to a state suitable for supporting the pipeline. So far, no method or apparatus is known in the art that will overcome these difficulties and render the maintenance of the pipelines easier and more economical. More specifically, no method or apparatus is known that will permit to avoid having to dig below the pipeline, often into hard rock beds.

It will be appreciated that any damage to a pipeline, involving failure thereof and spillage of the transported liquid, would constitute, apart from the economical damages, a major economical disaster, and therefore those responsible will never carry into practice a maintenance method that involves even a very small probability of such damage and failure.

It is therefore a purpose of this invention to provide a method that will permit to avoid digging under the pipeline into the trench bed, particularly when it is hard rock bed.

It is another purpose of the invention to provide such a method that avoids with absolute certainty any damages to the pipeline, that might result in failure thereof. It is a further purpose of this invention to provide such a method which involves considerable savings in terms of time and costs in the maintenance of pipelines.

It is a still further purpose of this invention to provide an apparatus for carrying out the aforesaid method.

It is a still further purpose of this invention to provide such an apparatus which is error-proof, so that it eliminates any danger of damage or failure of the pipeline as a consequence of the maintenance operations.

It is a still further purpose of this invention to provide such an apparatus that can be easily transported from section to section of the pipeline.

It is a still further purpose of the invention to provide such an apparatus that can be easily operated by workers who have no particular skill.

Other purposes and advantages of the invention will appear as the description proceeds.

Summary of the Invention In order fully to understand the invention, it must be recalled that pipelines have a certain flexibility which, small as it is, can result in significant bending over length of pipeline of tens of meters. International standards limit the permissible degree of bending in a very strict manner to assure that it should not be so great as to create a danger to the integrity of the pipeline. For example, such standards permit vertically to displace a cross-section of a standard fuel 42"pipeline by up to and no more than 22 cm over a length of 30 meters. This means that if one cross-section of the pipeline is kept still, another cross-section which is spaced from the first one by 30 meters may be raised, without danger of failure or damage to the pipeline by up to and no more than 22 cm. The following description will be based on these numerical data, but it should be understood that this is done by way of illustration, and that while those data are the usual ones and are assumed in the embodiments of the invention to be described, they do not constitute a limitation. Therefore, the invention might be carried into practice on a 42"fuel pipeline by effecting vertical displacements different from 22 cm over lengths of pipeline different from 30 meters, provided that the ratio between the vertical displacement and the pipeline length is such as to be permitted by the international standards and such as not to exceed what is permitted by the elasticity of the pipeline. Likewise, different ratios of vertical displacement to pipeline length are permissible for different pipeline, depending on their structure and dimensions.

The method according to the invention for effecting maintenance of pipelines comprises selecting a number of points along the pipeline and raising the pipeline at these points by an amount that the height difference between these points does not exceed the international flexibility standards. More specifically, in a preferred embodiment, the segment of a standard 42"fuel pipeline selected is 30 meters long and the extent to which the terminal cross-section is raised is not more and preferably close to 22 cm. The initial cross-section of the selected segment rests on the bed of the trench because of its weight and no action is required to cause this to occur. Therefore, if a cross-section of pipeline is raised by more than what is permitted by the international standards, which reflect the typical elasticity of pipelines, there is danger that the pipeline will fail and the transported liquid will spill out. Presently, said standards allow a standard 42"fuel pipeline cross-section to be raised by no more than 22 cm. Raising a cross-section by said amount, will cause the pipeline to bend upwards over a length of 30 meters.

Maintenance of a given pipeline segment requires a clearance on all sides, typically a clearance of 63 cm for a standard 42"fuel pipeline. Thus, the maintenance of a pipeline according to the invention is a multi-step process, as schematically illustrated by way of example in Figs. 8a to 8e.

After exposure, the pipe is initially raised at one point by 22 cm (Fig. 8a), by means of a lifting apparatus not shown in the drawings and hereinafter described, and a support, schematically indicated at 90, the preferred structure of which will be described hereinafter, is placed thereunder. The lifting apparatus is then relocated to another point and the pipe is there raised by 22 cm (Fig. 8b). The second point will be at most 30 m distant so that the length of pipe suspended between the two supports can bear its own weight without being structurally compromised. This is repeated three times so that the pipeline segment is raised at six points along its length (Fig. 8c). The pipe is then raised by another 22 cm at each of the four inner points (ii, iii, iv, v) and additional supports are stacked onto those already present at the aforesaid points (Fig. 8d). The lifting and supporting procedure is repeated at the two innermost points (iii, iv), yielding a situation where the middlemost pipe segment is suspended by no more than 66 cm above the trench bottom (Fig. 8e). Maintenance can then be performed on that segment. When maintenance is completed, the pipe can be lowered by reversing the raising procedure.

It is clear to one skilled in the art that this procedure can be continued along the pipeline section that is to undergo maintenance by carefully raising and lowering the pipeline segments and adding or removing the pipeline supports. It is equally clear that the procedure is only one of many possibilities of combining the raising, supporting and lowering steps to perform maintenance along the pipeline. One variation might be to raise long sections of the pipeline to a height sufficient to perform maintenance.

The figures of 30 meters and 22 cm reflect the present international standards, and would be changed if such standards were changed, based on a different evaluation of the pipelines elasticity. Likewise, different figures would apply to different pipelines.

Preferably, the method according to the invention also comprises supporting the pipeline, which is subjected to maintenance, on the sides thereof against the sides of the trench, so as to maintain it in the desired alignment.

More particularly, the method of the invention preferably comprises tightly engaging the bottom of a cross-section or a short length of the pipeline, which is to be raised, with raising means, so as to establish an initial or reference vertical position of said cross-section, and then actuating the raising means to effect a predetermined lifting of said cross-section or short length, for a standard 42"fuel pipeline being typically by 22 cm for each length of pipeline of 30 meters.

The apparatus according to the invention comprises: a) a lifting frame, having telescopic legs and a transverse top beam; b) telescopic lifting arms supported in said top beam; c) flexible means, typically chains or the like, connected to the lifting arms for engaging the bottom of the pipeline; d) first hydraulic means for telescopically extending and retracting the legs of the lifting frame; and e) second hydraulic means for telescopically extending and retracting said lifting arms thereby lifting the pipe.

Preferably, said first hydraulic means have a limited power so that they can exert only the force required for placing the frame in the desired configuration with respect to the trench bed, but cannot exert a force sufficient to raise the pipeline; whereas said second hydraulic means have sufficient power to exert the force required to lift the pipeline.

Further, said second hydraulic means have a limited stroke and, when actuated, will retract the lifting arms and therefore raise the pipeline by the exact predetermined amount permitted by the international flexibility standards, typically 22 cm.

In a preferred embodiment of the invention, the apparatus comprises two parallel frames, each comprising the aforesaid elements, so as to exercise the lifting action on a short length of pipeline comprised between the two parallel frames.

Further, the apparatus of the invention also preferably comprises supports for the section of pipeline that is lifted, which supports are preferably composed of several stackable sections, so that they can be placed under the pipeline successively as the pipeline is gradually lifted.

Also preferably, the apparatus comprises lateral supports adapted to be placed on the sides of the pipeline and to be operatively connected thereto by flexible means, said supports being provided with extendable arms for engaging the sides of the trench, so as to determine the distances between said sides and the pipeline and therefore guaranteeing the desired alignment of the pipe.

Preferably, two parallel and equal lifting frames are connected to one another and are attached to a common hook or like element for lifting them and transferring them from one location to another.

Brief Description of the Drawings In the drawings: Fig. 1 is a schematic vertical view of an apparatus according to an embodiment of the invention, seen from a plane perpendicular to the axis of the pipeline; Fig. 2 is a schematic vertical view of the same apparatus, seen from a plane parallel to the axis of the pipeline; Fig. 3 is a schematic perspective view of the same apparatus; Figs. 4A, B and C are schematic perspective views of three successive stages of the installation of a support for a lifted section of the pipeline; Figs. 5 and 6 schematically illustrate two stages of the lifting of the pipeline ; Fig. 7 is a perspective detail of the lifting apparatus; Figs. 8a to 8e schematically illustrate the pipeline lifting procedure.

Fig. 9 is a schematic vertical view of an apparatus according to another embodiment of the invention, seen from a plane perpendicular to the axis of the pipeline; and Fig. 10 is a schematic vertical view of the apparatus of Fig. 9, seen from a plane parallel to the axis of the pipeline.

Detailed Description of Preferred Embodiments The lifting apparatus according to the invention, as schematically illustrated in Figs. 1-3, comprises in the embodiment illustrated two lifting frames that are equal and parallel to each other, and that are generally indicated at 10 and 10'. They are interconnected by a beam 11.

When the apparatus is placed in the pipeline trench, the frames are perpendicular to the trench and consequently the beam 11 is parallel to the trench. In the following description, for clarity's sake, the term "longitudinal"will mean approximately parallel to the axis of the trench and the term"transverse"will mean approximately perpendicular to the axis of the trench. One of the frames (frame 10) is shown in vertical view in Fig. 1. It comprises two telescopic legs 12 and 13. Each leg rests on a foot, 14 and 15 respectively, to which are connected pistons 16 and 17 respectively, actuated by hydraulic systems schematically indicated at 18 and 19 respectively. Legs 12 and 13 are connected by a transverse beam 20 to which may be connected a link 21 having an opening 22 for lifting the frame by means of a crane. The crane will be equipped with lifting fingers, not illustrated, that concurrently seize link 21 of frame 10 and the corresponding link 21', not visible in the drawings, of frame 10', to lift the entire apparatus as a single body. Such crane operations are conventional and need not be further described or illustrated.

In the transverse beam 20 are housed cylinders 23 and 24 respectively of two hydraulic, extendable lifting arms, generally indicated at 31 and 32, which comprise pistons 25 and 26 respectively. Said pistons are bidirectional pistons which can extend and retract with sufficient power.

The lifting arms also comprise lifting fingers attached to said pistons, for connecting thereto a chain 29 which is adapted to be placed about the pipeline, the cross-section of which is illustrated at 30. Said fingers are schematically indicated in Figs. 1,5 and 6 as rings 27 and 28, but may, and generally will have different structures, an example of which is given in Fig. 7. In said example, each piston 25-26 is connected to a pair of clips 33-33'and 34-34'respectively, to which are attached two chains 35-35', or other belts, which are placed around the lower half of pipe 30.

The operation of the apparatus is as follows. The apparatus is placed in the trench astride the pipeline, as seen in Fig. 1. A few centimeters are removed from the trench bed under the section of the pipe that has to be engaged by the lifting apparatus, and the chain 29 (or the pair of chains 35-35'or belts) is passed underneath the pipe and is connected to the lifting fingers 27 and 28 (or 33-33'and 34-34'). Then the hydraulic apparatus 18 and 19 are actuated so as to extend the telescopic legs 12 and 13 until the chain 29 is tight or the chains 35-35'or belts are tight.

The actuation of the hydraulic apparatus also serves to set the lifting frames in the proper positioned relationship to the trench, with their legs vertical as far as possible. The power of the hydraulic systems 18 and 19 is so limited that they can cause the legs 12 and 13 to be telescopically extended to place the frame in a correct positioned relationship to the trench and to tighten the chain or chains or belts, but they cannot raise the pipe, the weight of which is in the order of tens of tons and is much greater than that of the lifting frames. What has been said of one lifting frame applies to both of them, when the apparatus comprises two lifting frames, as in this embodiment.

Thereafter, the lifting arms are hydraulically actuated so as to retract and lift the pipe 30 (see Fig. 6). The apparatus is so dimensioned that the entire stroke of the lifting arms is 22 cm or whatever other amount might be determined by international standards. The apparatus cannot lift the pipe by more than said amount, because its stroke is structurally limited, by any suitable structural means, and cannot be exceeded as a result of operating errors. For example, the piston of the lifting arm may be so manufactured so that its stroke is only 22 cm.

The hydraulic pumps which supply the lifting power to the telescopic legs on the one hand and to the lifting arms on the other hand, are mutually independent. In this way it can be guaranteed that the power of the telescopic legs will always be well below that necessary to lift the pipe.

At this point, it is necessary to support the bottom of the pipe in the way illustrated in Figs. 4A, B and C. Initially, as in Fig. 4A, two supports 40 and 41 are placed under the pipe. Each support comprises a parallelepipedal portion 42-43 and a concave portion 44-45 shaped as a cradle to conform to the surface of the pipe. Thereafter, as the pipe is further raised, two additional parallelepipedal elements 46 and 47 are placed under elements 40 and 41, as shown in Fig. 4B. Subsequently, two more parallelepipedal elements 48 and 49 can be placed under elements 46 and 47, as shown in Fig. 4C. The use of these stackable supports during the maintenance procedure has been described hereinbefore and schematically illustrated in Figs 8a to 8b.

Figs. 9 and 10 illustrate another embodiment of the invention. This comprises two lifting frames that are equal and parallel to each other, one of which is generally indicated at 60 in Fig. 9. They are interconnected by a beam such as 11 in Fig. 3. When the apparatus is placed in the pipeline trench, the frames are perpendicular to the trench and consequently the beam is parallel to the trench. The frame shown in Fig. 9 comprises two telescopic legs 62 and 63. Each leg rests on a foot, 64 and 65 respectively, to which are connected pistons 66 and 67 respectively, actuated by hydraulic systems. Legs 62 and 63 are connected by a transverse beam 70 to which may be connected a link for lifting the frame by means of a crane.

The operation of this embodiment is essentially the same as that of the embodiment of Figs. 1 to 7.

The transverse beam 70 supports cylinders 73 and 74 respectively of two hydraulic, extendable lifting arms generally indicated at 80 and 81. The lifting arms are connected, in any suitable way, to a chain 79 (shown in broken lines in Fig. 9) which is adapted to be placed about the pipeline, the cross-section of which is illustrated at 83. Fig. 10 shows two such chains 79 and 79'. Two hydraulic fingers 84 and 84'engage the top of the pipe to steady it.

While embodiments of the invention has been shown has been described by way of illustration, it will be understood that the invention may be carried into practice with many modifications, variations and adaptations, without departing from its spirit or exceeding the scope of the claims.