Patent Publication Number: US-2015078832-A1

Title: Pipeline Lifting and Supporting Apparatus For Maintenance and Restoration Purposes

Description:
FIELD OF THE INVENTION  
     This invention refers to an apparatus for lifting and supporting pipelines through which is flowable fuel, gas or hazardous industrial liquids, in order to carry out maintenance and restoration. 
     BACKGROUND OF THE INVENTION 
     Pipelines used to transport products such as fuel, gas or hazardous industrial liquids, particularly fuel pipelines, require periodic maintenance which involves cleaning their outer surfaces, performing the required repairs and providing them with new and advanced protective coating, e.g., coating for protecting the outer surfaces of the pipes from corrosion. 
     Generally, the decision when to perform pipeline maintenance is made according to one of two approaches—according to the preventative maintenance approach or the post damage repair approach. Many companies carry out systematic examinations of pipelines, using advanced instrumentation in order to prevent recurrence of failure events by taking preventive maintenance measures. On the other hand, some companies prefer to take emergency restoration measures, due to cost saving considerations, only once a failure occurred or is about to take place. 
     Regardless of the approach, the overall maintenance and restoration operations are extremely heavy and costly since a relevant global pipeline network may extend for hundreds of miles in length. 
     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 damage, a major ecological disaster including a significant risk of fire, explosions and loss of life. Therefore those responsible will never initiate a maintenance operation that involves even a very small probability of such damage and failure. 
     Each pipeline section that requires a maintenance operation is generally exposed by excavating soil from the sides of a trench in which the pipeline is embedded and under the pipeline, in order to provide sufficient space within the trench and on both sides of the exposed pipeline, in order to enable performance of the required maintenance operations. 
     In many cases, the pipeline trenches cross rough ground such as rock formations or difficult topographic conditions that 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, filled with carefully selected padding material, is intact. It should be pointed out that digging underneath the pipeline in any ground type will compromise the integrity of the original trench bed and additional costs are incurred in restoring the trench bed to a state suitable for supporting the pipeline in the future. 
     U.S. Pat. No. 7,845,881 discloses a method and apparatus for lifting pipelines without having to dig significantly therebelow, often into hard rock beds. The apparatus includes at least one lifting frame having telescopic legs and a top beam connecting the legs, telescopic lifting arms supported by the beam, and a chain or a belt connected to the lifting arms for engaging the bottom of the pipeline. The telescopic legs are extended until the chain or belt is tightened. The lifting arms are then retracted to raise the pipeline. A number of points are selected along the pipeline, and the pipeline is raised at these points by an amount that the height difference between these points does not exceed the international flexibility standards regarding the maximum allowable stress for oil and gas pipelines. Other standards have been determined, for safety and integrity of pipelines for carrying hazardous materials, such as:
         European standard BS EN 14161 (Petroleum and natural gas industries)   European standard BS EN 1594 (Gas supply systems)   British Standard Code of Practice for Pipelines BS PD 8010   American Petroleum Institute standards API 17B, API 17TR2, API RP 579 and others       

     Although this method is effective in terms of raising a pipeline segment in order to perform a maintenance operation thereto while complying with international flexibility standards, the chain or belt engaged with the bottom of a pipeline segment constitutes a significant safety hazard. 
     A chain comprising a plurality of interconnected elliptical links has maximum tensile strength along the major axis of each link. However, the orientation of may of the links may be changed to a position that does not exploit this maximum tensile strength when the chain is caused to be engaged with the bottom of a curved pipeline segment. 
     At times, as shown in  FIG. 1 , a link  2  of a chain  9  adapted to support a pipeline segment  5  from the bottom is liable to change its orientation by as much as 90 degrees from an adjacent link  4  with which it is interconnected. The bottom periphery of pipeline segment  5  therefore becomes in contact with the upper end of link  2  while is spaced from link  4 . As a result, the protruding link  2  supports the entire weight of pipeline segment  5  by point contact and eventually causes portion  8  of the pipeline segment contacted by link  2  to be damaged, or even collapse. Such damage can seriously compromise the structural integrity of the pipeline and lead to an ecological disaster. Additionally, the tensile force of chain.  9  is transmitted through the minor axis of link  2 , leading to a relatively high stress concentration that can cause structural failure. 
     Monolithic belts made of a web, such as woven material or rope, are more advantageous for supporting the bottom of a pipeline segment than hard metal chains that consist of a plurality of angularly displaceable links. However, belts have a tendency of stretching to a certain extent. Accordingly, a pipeline segment at times may be unknowingly raised more than the maximum height difference permitted by the international flexibility standards as a result of the belt elongation, leading to pipeline failure. Furthermore, the belt elongation cannot always be anticipated since a belt generally exhibits non-linear elongation characteristics that may result in a different value of elongation for a same load. 
     It is therefore an object of the present invention to provide an apparatus and method for lifting and supporting pipelines by which any danger of damage or failure to the pipeline is eliminated as a consequence of the lifting and maintenance operation. 
     It is an additional object of the present invention to provide an apparatus and method that will obviate the need for considerable digging under the pipeline into the trench bed, particularly when it is hard rock bed. 
     It is an additional object of the present invention to provide such an apparatus and method which involve considerable savings in terms of time and costs during maintenance of pipelines. 
     It is yet an additional object of the present invention to provide such an apparatus that can be easily operated by unskilled workers, to minimize the risk of human error. 
     Other purposes and advantages of the invention will become apparent as the description proceeds. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to apparatus for lifting and supporting pipelines through which is flowable fuel, gas or hazardous industrial liquids, for maintenance and restoration purposes, comprising a hybrid sling for supporting a pipeline segment when being raised, said sling comprising a flexible belt portion contacting an underside of said pipeline segment and a chain portion vertically extending from each end of said belt portions to an element through which a lifting force is transmittable, wherein said sling is assured of being sufficiently structurally strong and dimensionally stable to ensure that the difference in height of any two points of said segment when being raised is not so great as to create a danger to the integrity of the pipeline. 
     In one aspect, each of the chain portions is connected to a raisable member of a lifting apparatus through which the lifting force is transmittable, said lifting apparatus comprising two transversally spaced lifting frames awl a transversally extending beam interconnected with said two lifting frames. 
     The apparatus preferably comprises a first hydraulic system for telescopically extending and retracting a corresponding foot on which each of the two lifting frames rests, wherein said first hydraulic system has insufficient power to extend said foot to lift the pipeline, and a second hydraulic system independent from said first hydraulic system for applying the lifting force to lift the pipeline or a lowering force to lower the pipeline. 
     In one aspect, the first and second hydraulic systems are positioned with an interior of each of the two lifting frames and a piston of the first hydraulic system is connected to the corresponding foot. 
     In one aspect, the raisable member is a longitudinally extending beam that passes through, and is engaged by, a corresponding lifting frame and a piston of the second hydraulic system is configured to apply a lifting or lowering force to a pin attached to the corresponding lifting frame, the lifting or lowering force applied to said pin being transmitted to the longitudinally extending beam. 
     In one aspect, the pin is releasably attachable to a block which is positioned in abutting engagement with an inner face of the corresponding lifting frame and is connected to the piston of the second hydraulic system, a selected attachment position of the pin in one of a plurality of apertures formed in the corresponding lifting frame defining a stroke of the piston of the second hydraulic system and a height to which the pipeline segment is raised. 
     In one aspect, a reinforcing element is welded to an outer face of the corresponding lifting frame in the vicinity of the pin and the longitudinally extending beam. 
     In one aspect, the raisable member is a telescopic lifting arm. 
     In one aspect, the transversally extending beam is dimensionally adjustable. 
     In one aspect, the apparatus further comprises two longitudinally separated and manually actuated force applicators that are engageable with a top of the pipeline segment. 
     In one aspect, a longitudinally extending support beam passes through a corresponding lifting frame and is raisable by a crane. 
     In one aspect, the apparatus further comprises a crane related chain connected to, and extending upwardly from a corresponding support beam disposed at a same angular disposition with respect to a horizontal plane as the pipeline segment and a hook element connected to a crane, for supporting a central portion of the two crane related chains and thereby allowing the pipeline segment to be raised by the crane in a direction parallel to an inclined disposition of terrain in which the pipeline is embedded. Each crane related chain is connected to the corresponding support beam by means of partially open eyelets protruding from the corresponding support beam. 
     In one aspect, the belt portion is resistant to acids and has an elongation ranging from 3 to 5%. 
     In one aspect, the belt portion is made from polyester. 
     In one aspect, two longitudinal ends of the pipeline segment are supported by a corresponding sliding cradle assembly. 
     In one aspect, a support is in contact with the pipeline at a corresponding lifting location, said support including one or more stackable elements including a concave element for engaging the bottom of the pipeline, wherein said concave element has a substantially similar curvature as that of the pipeline to conform to the surface of the pipeline. 
     In one aspect, the difference in height between any two adjacent points of the pipeline is less than a permissible vertical displacement value in accordance with a flexibility standard. 
     The present invention is also directed to a support assembly for a longitudinal end of a raised pipeline segment through which is flowable fuel, gas or hazardous industrial liquids, comprising a sliding cradle assembly that includes a concave portion for engaging a bottom of a raised pipeline segment and that is transversally slidable in response to an applied temperature related, pipe derived force. 
     In one aspect, the sliding cradle assembly comprises a monolithic member configured with the concave portion and two rectilinear portions between which the concave portion is interposed, at least one rectilinear supporting block, a plurality of transversally spaced rollers placed on top of an uppermost layer of said at, least one supporting block, and two longitudinally extending position limit elements affixed to said uppermost layer of supporting blocks and transversally spaced from transversal ends, respectively, of said monolithic member, a maximum transversal displacement of said monolithic member being defined by a position of said two position limit elements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
       In the drawings: 
         FIG. 1  is a front view of a prior art chain supporting the bottom of a pipeline segment, showing the damage that the chain can cause to the pipeline segment; 
         FIG. 2A  is a schematic vertical view of a lifting apparatus according to an embodiment of the invention, seen from a plane perpendicular to the axis of the pipeline; 
         FIG. 2B  is a schematic vertical view of the apparatus of  FIG. 2A , seen from a plane parallel to the axis of the pipeline; 
         FIGS. 2C and 2D  schematically illustrate two stages of the lifting of the pipeline with the apparatus of  FIG. 2A ; 
         FIG. 2E  is a schematic vertical view of a lifting apparatus according to another embodiment of the invention, seen from a plane perpendicular to the axis of the pipeline; 
         FIG. 3  is a perspective view of a lifting apparatus according to another embodiment of the invention; 
         FIGS. 4-6  are a front view of the lifting apparatus of  FIG. 3 , shown in three successive stages, respectively, of a lifting operation; 
         FIG. 7A  is a side view of the lifting apparatus of  FIG. 3 ; 
         FIG. 7B  is an enlarged cross sectional view of the lifting apparatus of  FIG. 3 , cut about plane A-A; 
         FIG. 8  is a top view of the lifting apparatus of  FIG. 3 ; 
         FIGS. 9   a - e  schematically illustrate a pipeline lifting procedure; 
         FIG. 10  is a perspective view of the lifting apparatus of  FIG. 3  being involved in a lifting operation over inclined terrain; 
         FIG. 11  is a front view of a sliding cradle assembly; 
         FIG. 12  is a perspective view of the sliding cradle assembly of  FIG. 11 ; and 
         FIGS. 13A and 13B  are side views of a lifted pipeline segment when being supported at each longitudinal end thereof by a corresponding sliding cradle assembly of  FIG. 11 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention is directed to a novel elongated and flexible element for supporting the bottom of a pipeline segment (hereinafter referred to as a “sling”) which is hybrid in the sense that it comprises two portions, a belt portion that contacts the underside of the pipeline segment and a chain portion having links that are assured of remaining in vertical alignment without being angularly displaced. The sling is connecting to a lifting apparatus that is able to limit the degree of bending of a pipeline segment to a permissible value. 
     Reference is first made to  FIG. 2A , which schematically illustrates a sling  29 , according to one embodiment of the invention, when connected to the lifting apparatus and in supporting relation with a pipeline  30 . Sling  29  comprises belt portion  34  which is in engagement with the underside of pipeline segment  30  instead of chain, the links of which are liable to be angularly displaced and to damage the pipe. In addition, sling  29  comprises two vertically disposed chain portions  37 , each of which extending from a corresponding end of belt portion  34  and terminating at a free end that is connected to the lifting apparatus. The chain portions  37  provide good strength during a lifting operation and their links are retained in vertical alignment. 
     Since sling  29  comprises chain portion  37  that vertically extends from pipeline segment  30  to the lifting apparatus, the length of belt portion  34  contacting the underside of pipeline segment  30  is able to minimized. The elongation of belt portion  34  is therefore able to be minimized due to its reduced length, thereby ensuring that pipeline segment  30  will not be raised more than the maximum height difference permitted by the international flexibility standards as a result of unforeseen elongation. In addition, using a belt portion  34  allows compensating for possible deformations in the cross-sectional area of the pipeline. Such deformations may occur due to the fact that the pipeline is full or empty. When being full with oil, the oil weight may cause the pipeline to be slightly oval, rather than circular (when empty), depending on the weight and the thickness of the pipeline wall. In this case, the belt portion  34  adjusts itself to any deformation, so as to maintain good grasp under any condition. 
     Although belt portion  34  may he made of many different types of material, it has been found that polyester is a preferred material due to its relatively high load capacity, good flexibility that facilitates engagement with pipeline segment  30 , resistance to acidic environments, and a low elongation ranging from 3-5%. 
     Belt portion  34  may he connected to the two chain portions  37  by any suitable means, for example by a triangular fitting  39  shown in FIGS.  3  and  7 A-B. 
     An embodiment of the lifting apparatus is illustrated in  FIGS. 2A-D  and comprises two longitudinally spaced and vertically extending lifting frames that are equal and parallel to each other. The two lifting frames are generally indicated at  10  and  10 ′ and are interconnected by a longitudinally extending beam  11 . When the lifting 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&#39;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. 2A . 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 he 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 sling  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  FIG. 2A  as rings  27  and  28 , but may, and generally will have different structures. 
     The operation of the apparatus is as follows. The apparatus is placed in the trench astride the pipeline, as seen in  FIGS. 2A and 2C . 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 sling  29  is passed underneath the pipe and is connected to the lifting fingers  27  and  28 . Then the hydraulic apparatus  18  and  19  are actuated so as to extend the telescopic legs  12  and  13  until the sling  29  is 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 sling, but they cannot raise a pipeline segment loaded with a hazardous industrial liquid, 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. 2D ). 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. 
     The use of these stackable supports during the maintenance procedure is schematically illustrated in  FIGS. 10   a  to  10   e.    
     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 pipelines, depending on their structure and dimensions, and the characteristics of the metal from which they are made. 
     Maintenance of pipelines is first carried out by selecting a number of points along the pipeline segment that requires maintenance. The pipeline segment at these points may be raised by an amount that the height difference between these points does not exceed the international flexibility standards. For example, 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 reflects 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 clearance on all sides, typically a clearance of 60 cm for a standard 42″ fuel pipeline. Thus, the maintenance of a pipeline involves a multi-step process, as schematically illustrated by way of example in  FIGS. 9   a  to  9   e.  After exposure, the pipe is initially raised at one point by 22 cm ( FIG. 9   a ), by means of the lifting apparatus described hereinafter, and a cradle support such as a sliding cradle, 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. 9   b ). 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 several times so that the pipeline segment is raised at six points along its length ( FIG. 9   c ). 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. 9   d ). 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 45-50 cm above the trench bottom ( FIG. 9   e ). Maintenance operations can then be performed on that segment. When the maintenance operations are completed, the pipeline can be lowered and returned to its original position on the padding material at the bottom of the trench by carefully reversing the raising procedure. 
     It is clear to one skilled in the art that this method 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 values of 30 meters and 22 cm reflect the present international flexibility standards for 42″ carbon steel pipeline, 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. 
     The difference in height between any two adjacent points of the pipeline is less than a permissible vertical displacement value in accordance with said flexibility standard. 
     Alternatively, the bottom of longitudinal ends  36  of a pipeline segment  30 , e.g. having to length of 200 ft, may be supported by two longitudinally spaced sliding cradles  155 , as illustrated in  FIG. 11  and  FIG. 13A .  FIG. 13B  shows the pipeline segment  30  when supported by 3 sliding cradles  155 . The sliding cradles  155  are used to relieve the stress normally experienced by a pipeline during thermal elongation during periods of extreme temperature fluctuations of as much as 30° C., often causing the pipeline to curve and at even at times to structurally fail. 
     Each sliding cradle  155  has two parallelepipedal portions  157  and a central concave portion  159  interposed between the parallelepipedal portions in which the bottom of pipeline segment  30  is received. Each sliding cradle  155  extends transversally and may be positioned on top of one or more transversally adjacent rectilinear supporting blocks  161 . A balancing plate  169  placed below a lowermost supporting block  161  may be used when the underlying terrain is not level. 
     After stacking and immobilizing one or more levels of supporting blocks  161  in the manner shown in  FIGS. 9   a - e,  a plurality of transversally spaced rollers  164  are placed on top of the uppermost layer of supporting blocks  161 . Transversally spaced from each transversal end  156  of sliding cradle  155  is affixed a corresponding longitudinally extending position limit element  166  to the uppermost supporting block  161 . If two longitudinally spaced stacks  167  and  168  of supporting blocks  161  are employed at each longitudinal end  36  of pipeline segment  30 , the rollers  164  and limit elements  166  may be placed on top of both stacks. Cradle  155  remains in contact with rollers  164  when pipeline segment  30  is lifted. 
     The pipeline normally becomes deformed when subjected to temperature fluctuations. By virtue of the presence of the sliding cradle  155 , however, a force is applied onto the cradle when the pipeline becomes elongated. The cradle  155  is caused to transversally slide in response to the applied pipe derived force. The maximum transversal displacement of the cradle  155  is defined by the position of the two limit elements  166 . In this fashion, pipeline deformation is minimized. 
       FIG. 2E  illustrates 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 . They are interconnected by a beam such as  11  in  FIG. 2B . 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. Each frame 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 $ 3  are connected by a transverse beam  70  to which may be connected a link for lifting the frame by means of a crane. 
     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 sling  79  (shown in broken lines) which is adapted to be placed about the pipeline, the cross-section of which is illustrated at  83 . Two hydraulic fingers  84  may engage the top of the pipe to steady it. 
       FIGS. 3-8  illustrate another embodiment of the lifting apparatus to which the sling is connected, and is generally designated by numeral  110 .  FIG. 3  illustrates a perspective view thereof. A front view of the lifting apparatus is illustrated in  FIGS. 4-6 , a side view thereof is illustrated in FIGS.  7 A.-B, and a top view thereof is illustrated in  FIG. 8 . Lifting apparatus  110  is made of steel or of any other structurally strong material, and is used for raising pipeline segment  30 . 
     Lifting apparatus  110  comprises two transversally spaced and vertically extending lifting frames  101  and  105 , a transversally extending adjustable beam  102  interconnecting lifting frames  101  and  105 , two longitudinally extending and transversally spaced support beams  108  which pass through a corresponding frame and are raisable by a crane, a longitudinally extending balance beam  113  for suspending a corresponding chain portion  37  of two longitudinally separated slings  29  that engage the bottom of pipeline  30 , and two longitudinally separated manually actuated force applicators  116  that are engageable with the top of pipeline  30 . Adjustable beam  102  may be perpendicular to lifting frames  101  and  105 , and each support beam  108  may be perpendicular to the corresponding lifting frame. 
     The following description is made with respect to lifting frame  105 , but it will be appreciated that the description similarly applies to lifting frame  101 . 
     Lifting frame  105  comprises two identical longitudinally spaced plates  118  and  119 , which have a relatively narrow lower portion  123  and a relatively wide upper portion  124  configured with a common straight outer edge  126 . A plurality of vertically spaced rods  127  extend between plates  118  and  119 . Each support beam  108  and balance beam  113  passes through a corresponding wide upper portion  124  of the frame, and is configured such that the support beam  108  is positioned above, and outwardly spaced from, the corresponding balance beam  113 . Lifting frame  105  rests on an extendable foot  107 , to which is connected a piston  132  actuated by a hydraulic system. 
     The first stage of the lifting operation for this embodiment is essentially the same as described hereinabove. Piston  132  of each frame is actuated so as to telescopically extend the corresponding foot  107  until sling  29  is tight. Thereinafter, pipeline segment  30  is raised during the second stage. 
     Prior to raising pipeline segment  30 , force applicators  11 . 6  are separated from the top of the pipeline by manipulating the corresponding mechanical actuator  128  or by raising cross element  141  extending from actuator housing  142  to vertical guide elements  146  attached to side wall  148  of beam  102 . 
     With reference particularly to  FIGS. 3 and 7B , two adjacent hydraulically actuated pistons are positioned within lifting frame  105 . Piston  132  is connected to foot  107  and piston  136  is located thereabove for raising pipeline segment  30 . A divider  133  is fitted in cylinder  131  within which pistons  132  and  136  are housed, separating cylinder  131  into two sections. Bottom piston  132  is therefore forced to extend downwardly while upper piston  136  is forced to extend upwardly. 
     A single pin  137  extending between, and protruding outwardly from, plates  118  and  119  at an upper region thereof is used to raise lifting frame  105 . Pin  137  is inserted within an aperture  143  formed in each of plates  118  and  119  and also by a frictional fit within a cavity formed within rectilinear block  139 , which is brought in abutting engagement with the inner face of plates  118  and  119 . Upper cylinder  136  is connected to block  139  at a recess formed at the bottom thereof. 
     A vertical slot  151  is formed within plates  118  and  119 , proximate to short inner edge  112  thereof and above oblique edge  114  extending from upper portion  124  to lower portion  1 . 23 . A balance beam  1 . 13  having a straight upper edge  115  and a varying lower edge  117  for increased structural strength is inserted within the two slots  151 . The chain portion  37  of a sling  29  is connected to a corresponding narrow terminal end  121  of balance beam  113  by a fastener  122 . Consequently when upper piston  136  is actuated and extended, pin  137  is raised together with lifting frame  105 . After lifting frame  105  is slightly lifted, the bottom wall  153  of slot  151  contacts lower edge  117  of balance beam  113 , causing balance beam  113  together with pipeline segment  30  to be also raised. 
     Assistance in ensuring stability of lifting apparatus  110  during the second stage of the lifting operation may be provided by a crane associated element connected to eyelets  95  provided with each of the two support beams  108 . Each eyelet  95  is located near a corresponding end  106  of a support beam  108 , and protrudes upwardly from the upper face thereof. 
     A corresponding reinforcing element  129  is welded to the outer face of plates  118  and  119 , in order to reinforce each plate at high stress regions, namely in the vicinity of pin  137  and slot  151 . Reinforcing element  129  may be embodied by a thin triangular plate positioned between support beam  108  and balance beam  113 . Vertically separated apertures  134 ,  135  and  138  may be formed within reinforcing element  129  in order to coincide with apertures  143 - 445 , respectively, formed within each of plates  118  and  119 . Thus pin  137  may be removed from apertures  134  and  143  and inserted into a different pair of apertures when it is desired to raise a pipeline segment having a different diameter. 
     It will be appreciated that the pipeline may be supported by the cradle shown in  FIG. 11 . 
     As shown in  FIG. 1.0 , lifting apparatus  110  may be advantageously employed to raise a pipeline segment  30  embedded in terrain  96  that is disposed at an incline of angle I with respect to a horizontal plane  93 . After some of terrain  96  is removed to form a small clearance C below pipeline segment  30 , a pair of spaced hybrid slings  29 A and  29 B are passed underneath the pipe such that the belt portion  34  of each is brought in engagement with the bottom of pipeline segment  30 . 
     A crane then lowers lifting apparatus  110  onto inclined trench bed  92  until lifting frame  105  is perpendicular thereto. A hook element  103  having a vertically disposed rod  104  connected to the crane (not shown) facilitates this procedure. Hook element  103  is engageable with two chains  107 A and  107 B connected to, and extending upwardly from, lifting apparatus  110 . The terminal link  109  at each free end of a chain is connected to a corresponding eyelet  95  of support beam  108 , and a central portion  111  of the chains is passed over, and in contact with, hook element  103 . 
     In order to accommodate the inclined terrain, the height of each force applicator  116  with respect to trench bed  92  may then be adjusted to ensure that the top of the pipeline will be engaged thereby. 
     Support beams  108  are positioned to be at the same angular disposition with respect to horizontal plane  93  as pipeline segment  30 , i.e. they are spaced by a uniform height H from the longitudinal axis  33  of pipeline segment  30 . After support beams  108  become correctly positioned, the sling chain portions  37  and the overlying chains  107 A-B become automatically repositioned with respect to the relative location of hook element  103 . Since rod  104  extending upwardly from hook element  103  is vertically disposed, the crane is able to apply an easily generated vertical lifting force L while pipeline segment.  30  can be raised parallel to the disposition of trench bed  92  and obviating the need of having to dig in some regions a large clearance trench if the pipeline were vertically raised. 
     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 exceeding the scope of the claims.