Abstract:
To separate relatively long upright pipes ( 13 ) which have a relatively large diameter, the lower end thereof being fixed in the ground, in particular of support legs ( 3 ) of an off-shore oil bore or conveying platform ( 100 ), a cutting unit is lowered down into the pipe ( 13 ) to a separation point. The cutting unit ( 40 ) acts gradually from the inside across the periphery to the internal periphery of the pipe ( 13 ) and cuts through the pipe ( 13 ) by removing metal. A bore tool head ( 60 ) is mounted upstream of the cutting unit ( 40 ), viewed from the lowering position, and is used to bore out material in the pipe such as ocean bed or concrete.

Description:
SUMMARY 
     For separation of upright pipes ( 13 ) with their lower ends anchored in the ground having a longer length and larger diameter, particularly of support legs ( 3 ) of an offshore oil rig or oil platform ( 100 ), a cutting unit is lowered into the pipe ( 13 ) down to a separation point ( 9 ). The cutting unit acts upon the circumference advancing from the inside against the inside circumference of the pipe ( 13 ) and cuts through the pipe ( 13 ) using chip removal. In the lowering direction, seated downstream from the cutting unit ( 40 ) is an auger head ( 60 ), which serves to drill out material, such as ocean floor matter or cement, found in the pipe. (FIG. 8) 
     BACKGROUND OF THE INVENTION 
     Method and device for separating pipes or columns that are anchored into the ground The invention relates to a device and a method for separating upright pipes having their lower end anchored into the ground, particularly for support legs of an offshore oil drilling or oil supply platform. 
     To win the numerous crude oil reservoirs, drilling has been conducted for some time not only from oil fields accessible by land, but also offshore fields located under the ocean floor and other bodies of water. Such drills have been sunk at various water depths and, in part, far from the coast. In principle, the structure above the water surface, is the same drilling rig as is used on land, only on a supply platform positioned above the water surface. The type of support for the supply platform on the ocean floor is dependent, in part, on the water depth. Most offshore oil supply platforms are anchored into the ocean floor by means of support legs formed from large pipes. 
     Depending on the condition of the ocean floor, the support legs are embedded into the ocean floor, for example, rammed in or retained by the friction in the ocean floor. If this is insufficient, there is an alternative in which the embedded base of the support legs is installed in underwater cement or something similar, which also partially has an outlet in the surrounding ocean floor from the lower end of the pipe and which forms an artificially created ocean floor after hardening, the anchoring effect of which is contributed to by the effect of the weight of the cement, which fills up the lower part of the respective pipe up to a certain height. Using these measures, the supply platforms obtain stability under load even in problematic underground situations, which provide resistance to the platforms under the extreme loads in high seas. 
     The first of these platforms has operated in the North Sea for approximately 20 to 25 years. They are no longer needed in the meantime because the oil fields that were drilled with these platforms have been exploited. They cannot simply be left standing because they pose a hazard for ship travel. 
     Therefore, there is a need for a method and devices with which the oil supply platforms can be removed from the ocean after their service life has passed. While the removal of the structures of the platform and the platform itself are similar in principle to those used for land-based oil rigs, the support structures or platforms that are, in part, in deep and moving water, pose considerable problems. The support legs also need to be removed, but for the reasons indicated, cannot simply be cut off above sea level or just below the ocean surface, rather the specifications from the responsible authorities require that the support legs be cut off a section below the ocean floor. 
     From DE-PS 671 660, a device for cutting through pipes embedded in well drill holes is known, the cutting tool of which is lowered into the pipe to the separation point by means of a rod assembly. The cutting tool is used at the inside wall of the pipe and cuts through it from the inside to the outside. 
     This device is not suited for separating support legs of the platform indicated because the separation point is always in a region of the support leg that is filled with ocean floor matter, cement, and other things and thus does not permit lowering of the separation point. 
     Therefore, it was attempted to have diving teams dive to the ocean floor with suitable equipment and to cut the support leg from the outside using a diamond wire placed about the support leg driven in a longitudinal direction. Due to the large thickness of the pipe wall, this is a time-consuming and not necessarily non-dangerous process for the dive teams. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to accomplish a device and a method with which the pipe of long length and large diameter, such as the support columns of offshore oil supply platforms, can be cut off quickly and economically, in spite of materials found in the pipes, such as dirt or cement, even when below the ocean floor. 
     This object is accomplished methodologically by the subject of claim  1 . 
     According to the invention, a cutting unit is used for this purpose, which is inserted through the upper open end of the support leg and is lowered therein to the separation point, whereby when lowering the cutting unit, the material found in the pipe is drilled out down to the separation point. With this measure, the drilling and cutting are achieved in one work action and thus can be implemented particularly quickly and economically. 
     A configuration of this method as defined in claim  2  is particularly advantageous, in which a cutting unit is brought into action by means of a chip-removing cutting tool at the inside circumference of the pipe and cuts through the pipe in a circumferential direction advancing from the inside toward the outside. A chip-removing separation method is fast because in this way, thick chips are removed from the relatively soft structural steel of the pipe and a groove with high advance and high clearing output can be created in the narrow separation zone extending in a circumferential direction until the separation of the entire material cross-section. Since the separation is achieved from the inside, it is irrelevant where the separation point is with regard to the ocean floor; the method is not influenced in its function by the existing outside relationships. 
     To prevent the weight of the support legs and the other construction points still associated with it from causing the pipe being cut to sink, which could wedge the cutting unit in and cause damage to the cutting unit, it is useful to stay the weight of the pipe as defined in claim  3 , which can be achieved using a method still to be described by supporting the parts of the support structure on the adjacent support legs still standing. 
     The object is instrumentally achieved by means of a device as defined in claim  4 , which is characterized in that a rotatable, drivable auger head is disposed below the cutting unit, by means of which head, material located in the lower region of the pipe, such as ocean floor matter or cement, among other things, that are somewhat above the inside cross-section of the pipe down to the separation point or somewhat above, can be drilled out. The diameter of the bore corresponds at least to the diameter of the cutting unit. This allows for the cutting unit to be lowerable to the separation site. Hence, the lowering movement by the cutting tool is not hindered. 
     The cutting unit as defined in claim  2  preferably comprises at least one radially chipping cutting tool that can be pressed against the inside circumference of the pipe and that is movable by means of a mechanical drive, having a contact point that can be displaced in a plane progressing in a circumferential direction essentially vertical to the pipe axis. Only after the cutting point has been reached is the cutting tool extended out radially and set for chip cutting the pipe by creating an inside circumferential groove against its inside circumference that ultimately goes through the thickness of the wall. 
     To accelerate the actual cutting process, a configuration of the device as defined in claim  6  is recommended in which the cutting unit comprises a plurality of cutting tools distributed symmetrically about the pipe axis, which tools are simultaneously brought into action in the same separation groove. 
     In a preferred specific embodiment as defined in claim  7 , the mechanical drive is configured as a fluid-driven piston/cylinder unit. 
     As defined in claim  8 , this configuration can be driven by means of hydraulic fluid or, as defined in claim  9 , by means of compressive force. 
     In the latter example, a configuration as defined in claim  10  is advantageous. This configuration acts such that air rising through the hollow rod assembly above the platform signals the complete separation of the pipe. Hence, the cutting action can be stopped immediately thereafter, thereby preventing increased wear or even breakage of the cutting tools due to friction of the same on the edges of the separation groove and in the ocean floor material found on the outside of the pipe. 
     During the drilling to reach a separation point, it is often not possible to drill out the underwater cement found in the pipe exactly up to the inside circumference of the pipe. This applies particularly if the pipe is no longer completely round. Under some circumstances, a layer of cement could remain on the inside wall of the pipe, which cement could damage the cutting tools during their subsequent use. 
     To prevent this, a cleaning apparatus as defined in claim  11  is recommended, which cleans the work area of the cutting tools of residue from adhering material before engaging the cutting tools. The cleaning apparatus can comprise a brush-like configuration of cleaning elements, for example. 
     Since the support legs of the offshore oil rigs or oil supply platforms of issue can be of considerable weight and can be subject to stress from remaining parts from the actual platform and the framing braces under certain circumstance, it could happen that the support leg gives in axially at the separation point during the separation process and thereby wedging in the cutting tools. 
     It is therefore recommended, as defined in claim  12 , that a support apparatus be provided that stays the weight of the pipe during the separation process. 
     The support apparatus can, according to a configuration as defined in claim  13 , comprise a previously separated adjacent pipe of a support pipe exhibiting an approximately equal length, which pipe rests on the lower end in the pipe on the ocean floor or the pipe foundation formed by the underwater cement and which can be connected at the upper edge to the separated pipe, as can be achieved by means of a hydraulically braced conical-tensioning connection according to the method described in claim  14 . In this way, the separated pipe is held upright with the adjacent platform parts such that the pipe in which the cutting unit is currently working is not so heavily burdened. 
     Specific embodiments of the invention are described in detail below by way of the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 perspectively, a support structure with a supply platform lifted off; 
     FIG. 2 schematically, a side view of a support structure; 
     FIG. 3 schematically, a side view, partially cut away, of a device according to the invention having a first specific embodiment of the cutting unit in a pipe that forms a support leg; 
     FIG. 4 an enlarged section from FIG. 3; 
     FIG. 5 an alternative specific embodiment of the cutting unit with a linear guide for the cutting tools; 
     FIGS. 6 and 7 schematic representations of the coming cutting principles; 
     FIG. 8 schematically, a specific embodiment in which the cutting unit and the auger head are arranged on a drilling rod assembly; 
     FIG. 9 a side view of the auger head from FIG. 6 in an enlarged scale; 
     FIG. 10 a view of the auger head from FIG. 9 from below, as well as 
     FIG. 11 schematically, a support apparatus arranged in one of the previously separated support legs. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 illustrates oil rig or oil platform  100  already separated into its main component parts, comprising actual platform  1 , which is supported in an assembled condition on a support structure designated entirely by  2 . The entire equipment, such as the drill apparatus, housing, etc., which is normally arranged on platform  1 , is already dismantled and no longer indicated in the drawing. For the assembly and dismantle of oil rigs or oil platforms  100  and/or support structures  2 , crane ships  5  are used, which exhibit cranes  6  having a lift height that can be 200 meters or more above the sea level. In the phase illustrated, actual platform  1 , after being disconnected from support structure  2 , is suspended from cranes  6 . 
     Only the part of support structure  2 , which can be 30 to 40 m high, that is above sea level  10  (FIG. 2) is illustrated in FIG.  1 . Support structure  2  is configured as a tower-like or trestle-like framing with support legs  3  and truss-like cross braces  4  and is anchored below the water surface in the ocean floor by means of its support legs  3  that extend downward (indicated by dashed lines) into the water. The water can be over 100 m deep and each support leg  3  can be embedded in, that is rammed into, the ocean floor by a comparable length. Support legs  3  are thus very long. They consist of large pipes  13  with a 1 to 2 m diameter and a considerable wall thickness of 30 to 50 mm. The number of support legs  3  is dependent on the set-up of support structure  2 . 
     FIG. 2 indicates the dismantled situation of support structure  2 , which deviates somewhat in design from FIG.  1 . Upper parts  3 ′ of support legs  3  are cut off at separation point  8  and still belong to actual platform  1 , which is lifted off of support structure  2  by cranes  6  in accordance with FIG.  1 . Support structure  2  projects above sea level  10  and extends downward to ocean floor  11  by a length corresponding to the water depth. Support legs  3  extend deep into ocean floor  11  and can be anchored in a foundation-like manner at their lower ends in ocean floor  11  either by underwater cement or similar means. For oil rig or oil platform  100 , support legs  3  must be separated at separation points  9 , which lie several meters below ocean floor  11  at distance  7 , from their lower ends  12 , which extend deep into ocean floor  11  at separation points  9 . While the separation at separation points  8  poses no problems due to good accessibility, separation points  9  lie below water surface  10  and within ocean floor  11  and are likewise difficult to reach. 
     For this reason, a separation device—designated in its entirety by  50  in FIG.  3 —is provided so that it can be lowered into the inside of respective pipe  13  and that it can be engaged at the inner circumference of the pipe; the separation device further comprising a cutting unit—designated in its entirety by  40 —that has a drive apparatus  30 . Viewed in the lowering direction, provided downstream from cutting unit  40  at the lower end of rod assembly  14  is auger head  60 , the set-up and function of which are described based on FIG.  9  and FIG.  10 . 
     The upper half of FIG. 3 illustrates such drive apparatus  30  disposed at the upper end of pipe  13  to be cut and as part of a customary air-lift drill apparatus as well as rotatingly driven hollow rod assembly  14  extending downward into pipe  13 , wherein cutting unit  40  is non-pivotably mounted in the lower region of the rod assembly, the set-up and function of which unit are described in detail below. 
     Turntable drive  16  can be used in drive apparatus  30 , as is known for the drive of an auger head of an air-lift drill apparatus from the related art. Hence, existing drive apparatuses can be used, which only exhibit modifications if necessary. To drive cutting unit  40  and auger head  60 , rod assembly  14  extends into pipe  13  to be cut over its upper end such that it can be driven from the outside above the upper end of pipe  13  by means of turntable  18  by way of a toothed gear mounted at the circumference of the rod assembly. 
     So-called flushing head  17  is arranged at the upper open end of rod assembly  14 , by means of which head the material loosened on the floor of an earth drilling during the drill operation is flushed away through the inside cross-section of rod assembly  14  straight through in the direction of arrow  14 A in line  15  according to the air-lift method. The functionality of flushing head  17  and the air-lift method are known from the related art and are not clarified further here. Below flushing head  17 , a rotary connection head, designated by  19 , is disposed, by means of which compressed air for the air-lift method and an additional fluid medium (air or a hydraulic fluid) can be delivered even at high pressures into one or a plurality of lines  20  and  22 , which extend parallel in or to rod assembly  14 . 
     FIG. 4 illustrates an enlarged view of cutting unit  40  from FIG. 3 mounted non-pivotably at the lower end of rod assembly  14 . Inside of rod assembly  14 , line  20  for compressed air and line  22  for compressed air or a hydraulic fluid are indicated in outlines. The drilling of loosened material while drilling on the ground can be supplied with compressed air in the direction of arrow  14 A to the surface by means of flushing channel  21  formed in the inside of the rod assembly. To lower cutting unit  40  inside of pipe  13  to be cut, rod assembly  14  is extended downward in stages by means of flange connections  23  (see also FIG.  6 ), until cutting unit  40  is lowered to the level of separation point  9 . The torque (rotary movement) necessary for chipping is introduced to cutting unit  40  by means of turntable  18  and rod assembly  14 , that is entire rod assembly  14  including cutting unit  40  is rotated within pipe  13  about its axis A. Cutting unit  40  comprises a central section  41  inside the interior of which flushing channel  21  is formed and the outside dimension of which is only approximately one-third of the inside diameter of pipe  13  in the exemplary embodiment, such that annular interim area  42  remains. 
     In the example illustrated, cutting unit  40  comprises three pivotable cutting tools  24  distributed symmetrically about the circumference of rod assembly  14 . Each cutting tool  24  in FIG. 3, FIG.  4  and FIG. 8 exhibits one mechanical drive  34  allocated exclusively to it in the exemplary embodiment, which drive can consist of a fluid-driven piston/cylinder unit. The fluid can be compressed air, the pressure of which is limited, however, or a hydraulic fluid, with which higher pressures and thus actuation forces of mechanical drive  34  are achievable. The compressed air or hydraulic fluid is supplied via line  22  such that individual cutting tools  24  are actuated synchronously and with equal forces. It is understood that each mechanical drive  34  can have its own line available. Cutting tools  24  with their mechanical drives are arranged in annular interim area  42 . 
     If mechanical drives  34  are actuated with compressed air, a connection—not depicted in the drawing—can exist between the working volumes of at least of one cylinder and the inside of rod assembly  14 , which connection is configured such that it opens if the piston of this mechanical drive  34  is in its end position corresponding to the extended position of cutting tool  24  assigned to it. This measures affects that air rising in rod assembly  14 , which can be observed for example on flushing head  17 , signals the complete separation of the pipe. The separation process can then be stopped immediately, thereby preventing that the cutting tools wear prematurely from unnecessary friction at the edges of the separation groove or are completely destroyed by penetrating through into the ocean floor outside of the pipe. 
     Each cutting tool  24  consists of a long base body  25  to which one end of cutting plate  26  is secured. Cutting plates  26  are formed from reversible plates consisting of material suitable for heavy chipping. Base body  25 , at its end facing cutting plate  26 , is seated on tangentially swiveling journal  28  disposed on the outside circumference of central section  41  horizontal to a circle about axis A. Connecting rod  29 , which is connected to the mechanical drive, is engaged between swiveling journal  28  and cutting plate  26 , by means of which connecting rod cutting tool  24  can be displaced radially outward during an upward movement of connecting rod  29  by pivoting about swiveling journal  28  downward from transport position  24 ′ indicated in FIG. 4 by a dotted line, until cutting plate  26  comes into contact at the inside circumference of pipe  13  and pipe  13  is chip cut at separation point  9  from the inside toward the outside by forming separation groove  45 , which extends progressively in a plane vertical to axis A. 
     In the specific embodiment illustrated in FIG. 3, FIG.  4  and FIG. 8, mechanical drive  34  is configured as a piston/cylinder unit, which is fixedly arranged in interim area  42  at the outside circumference of the central section parallel to axis A and which has piston rod  32  connected to be movable to connecting rod  29  by means of slide  33  guided on central section  41 . During the lowering movement of cutting unit  40 , the cylinder of the piston/cylinder unit is in its fully extended position (further down than illustrated) such that cutting tool  24  is aligned essentially lengthwise to axis A (position  24 ′) and is free from pipe  13 . To press cutting plate  26  against the inside circumference of pipe  13 , the piston of the piston/cylinder unit is moved upward by means of line  22  and base body  25  of cutting tool  24  pivots radially outward. By means of the pressure supplied by compressed air or hydraulic fluid through line  22 , the contact pressure of cutting plate  26  on the pipe inside wall is adjustable for influencing the cutting result. As soon as pipe  13  is cut through completely, the piston is moved downward and cutting tool  24  is pressed back to its initial position  24 ′, such that cutting unit  40  can be pulled out, upward from separated pipe  13 . 
     The pivoting of cutting tool  24  to the pipe inside wall or the actuation of the piston/cylinder unit can be achieved by numerous methods known to specialists in the field. If a plurality of lines  22  are present, piston  32  can also be impinged upon by pressure alternately in both directions; the restoring moment can be affected by way of springs or similar means. 
     Alternatively to the radial pivot about a horizontal axis, the base body of the cutting tool can also be moved linearly. In FIG. 5, cutting unit  140  is illustrated with a radial guide of base body  125  of cutting tool  124  linear to axis A of cutting unit  140  or pipe  13 , wherein the linear guides are formed in tool guide body  131 , which is disposed at the lower end of central section  141 , exhibiting flange  143  at its upper end for connection to rod assembly  14 . Base bodies  125  of cutting tools  124  can be displaced in radial guide channels  123  of tool guide body  131 . In the left half of FIG. 5, cutting tool  124  is illustrated in is extended condition; in the right half, in its retracted condition. One leg  127  of an articulated lever is connected at the end of base body  125  facing pipe axis A and extends up to articulated joint  133 , while the other leg  128  of the articulated lever is connected centrally near pipe axis A starting from articulated joint  133 . One end of joint rod  129 , which extends lengthwise to axis A, contacts articulated joint  123  of the articulated lever, the other end of the joint rod is connected to mechanical drive  134  by means of pivot pin  132 . 
     In contrast to the specific embodiment according to FIG. 3, FIG.  4  and FIG. 8, only one piston/cylinder unit is provided here as mechanical drive  134 , which jointly drives all of cutting tools  124 . 
     The piston/cylinder unit exhibits pistons  135  configured at central section  141 . The cylinder from the piston/cylinder unit is configured as sliding cylinder  138  surrounding piston  135 , end plates  138 A,  138 B of which sliding cylinder slide on cylindrical outside circumference  142  of central section  141  for both sides of piston  135  projecting out radially and which form pressure chambers  136 , 137  with piston  135 , which are impinged upon by compressed air or hydraulic fluid, as desired. To move base body  125  of cutting tool  124  outward in respective guide channel  123 , compressed air or hydraulic fluid from upper pressure chamber  136  is supplied such that sliding cylinder  138  is pressed upward and articulated joints  127 , 128  are extended by means of connecting rod  129  connected to sliding cylinder  138 , such that cutting inserts  126  of cutting tools  124  are set linearly against the inside circumference of pipe  13  to be cut. 
     If the sliding cylinder is driven by compressed air, then channel  136 ′ extending to the inside of rod assembly  114  can be provided at the upper end of upper compressed air chamber  136 , the outlet of which channel is released into upper pressure chamber  136  if sliding cylinder  138  is in its upper end position limiting the extended position of cutting tools  124 . Air rising in the inside of rod assembly  114  signals in turn the end of the separation process. 
     In the configuration illustrated in FIG. 5, which is dimensioned such that the approach—reproduced on the left side—to the extended position of articulated lever  127 , 128  occurs during the engagement of cutting insert  126  in the wall of pipe  13 , a high contact pressure by cutting inserts  126  against pipe  13  and a corresponding chip thickness at separation point  9  can be achieved in a simple manner. To lower cutting unit  140  with cutting tools  124  retracted into pipe  13  and to lift it therein, lower pressure chamber  137  is supplied with compressed air or hydraulic fluid such that due to the downward movement by sliding cylinder  134 , connecting rod  129  and thus elbow  123  of the articulated joint are moved downward and cutting tools  124  are thereby driven inward into guide channels  123 , as illustrated on the right side of FIG.  5 . 
     The operational method of the cutting unit is illustrated primarily in principle in FIG.  6  and FIG.  7 . 
     FIG. 6 corresponds to the specific embodiment described thus far. Cutting unit  40 , 140 , which can rotate about axis A in pipe  13 , exhibits cutting inserts  26 ,  126 , which can be displaced radially outward from cutting unit  40 , 140  and which conduct a rotary movement along the inside circumference of pipe  13  only about axis A. Cutting inserts  26 , 126  act like interior tapping tools. 
     An alternative specific embodiment is illustrated in FIG. 7, in which cutting unit  240  can rotate about axis A, yet does not carry any radially extendable cutting inserts, rather rotatable cutting tools  224  on a tool carrier  231 , which tools can rotate about axis B parallel to axis A at the edge of the cutting unit and make milling contact at the inside circumference of pipe  13 . Cutting tools  224  thus rotate both about axis A and axis B. They can be configured like a milling-cutter. 
     FIG. 8 illustrates separation device  50  as an entire unit with cutting unit  40 , which can be rotated on rod assembly  14 , in accordance with FIG.  3  and FIG.  4 . The rod assembly consists of a plurality of rod elements  14 ′ placed in stages one after the other on coupling points  14 ″ and extends from the top into pipe  13 , of which only the uppermost part is illustrated in FIG.  8 . To fix rod assembly  14  radially within pipe  13 , stabilizers  35  are arranged in intervals axially to one another, which lie against the inside wall of pipe  13  and in which rod assembly  14  is seated and can rotate freely. Switch valve  47  is installed in rod assembly  14  between two stabilizers  35 , with which valve the change of direction of the radial pivoting movement of cutting tools  24  can be controlled. As is known from drilling operations, stabilization rod or heavy rod  49  can be installed as the lowest rod in rod assembly  14 . At the upper end of rod assembly  14 , free coupling point  14 ′″ is provided for decoupling additional rod elements  14 ′ or drive apparatus  30  (FIG.  3 ). Cutting unit  40  is arranged at the bottom end of rod assembly  14 . 
     With cutting units  40  from FIG.  3  and FIG. 4 and 140 from FIG. 5, respective specified separation point  9  can only be reached if pipe  13  is cleared to that point. In many cases, pipe  13  is filled with ocean floor matter or underwater cement, however, which can lie above separation point  9 . 
     Therefore, auger head  60  is secured below cutting unit  40  or  140 , which can be seen below cutting unit  40  in FIG. 3, FIG.  4  and FIG.  8  and in enlarged view in FIG.  9  and FIG.  10 . 
     The object of auger head  60  is to drill out down to separation point  9  material found in the lower section of pipe  13  to be cut so that cutting unit  40  can reach specified separation point  9 . To transport off material drilled away by auger head  40 , the air-lift method indicated briefly in reference to FIGS. 3 and 4 is used. When drilling out pipe  13 , the apparatus functions like a customary earth drill; cutting unit  40  is thereby without function with its cutting tools retracted. It is only put into operation after the drilling is completed. 
     The separation of pipe  13  therefore occurs by using existing drill units and technology, wherein only cutting unit  40  is to be inserted between auger head  60  and rod assembly  14  and is provided with supply lines. 
     Auger head  60  illustrated in FIG. 9 exhibiting a somewhat annular contour is connected by means of upper flange  43  to a counter flange provided at the lower end of cutting unit  40 . As illustrated in the bottom view in FIG. 10, at the bottom of auger head  60 , drill bodies  46  or roller bits prepared with hard metal are permanently arranged, by means of which the underwater cement found in the inside cross-section of pipe  13  to be cut can be drilled away. Suction opening  48  serves the air-lift method and is connected with the inside cross-section of rod assembly  14  (not illustrated). 
     When drilling out pipe  13 , cement layers adhering to the inside circumference of pipe  13  can remain, which can damage or destroy cutting plates  26 , 126  of cutting tools  24 , 124  when placed against the inside circumference of pipe  13 . To prevent this, a cleaning apparatus having radially extendable brush-like or scraper-like cleaning elements  44  can be provided on auger head  60 , by means of which apparatus adhering cement is removed down to the metal of pipe  13  before cutting tools  24 , 124  are brought into action. 
     FIG. 11 illustrates support apparatus  70  with which the weight of applicable pipe  13 —itself adjacent to previously cut pipe  13 —burdens pipe  13  to be cut, and thereby the remaining platform structures can be stayed. Illustrated is a support leg currently working adjacent at separation point  9  of previously cut pipe  13 . After the cutting unit including the rod assembly or the cable is pulled out, additional support pipe  80 , having a smaller diameter and a longer length than the length of pipe  13 , is lowered into cut pipe  13 , as a result of which it stands above the upper end of pipe  13  and the related remnant  63  of the platform. Pipe  13  is filled below with underwater cement  61  up to upper limit surface  65 . Support pipe  80  rests by its lower end  80 ′ on limit surface  65 . Just below upper end  80 ″ of support pipe  80 , conical-tensioning connection  62 , which can be hydraulically clamped, is arranged in the interim area between support pipe  60  and the inside circumference of pipe  13 . The part of support pipe  80  protruding out of pipe  13  is provided with hydraulic lift cylinder  64 , which contacts remnant  63  of the platform. When activating lift apparatus  64 , remnant  63  is pulled up on support pipe  80 . Thus, the upper part of pipe  13  is taken along. A defined distance is specified between the fastening of lift cylinder  64  and the top of remnant  63  of the platform, which distance shall be maintained during the entire separation process of the other support legs. A gap is thereby formed at separation point  9 . By means of conical-tensioning connection  62 , a constant tension is achieved between the support pipe and pipe  13  such that it is no longer applied to the continuous maintenance of pressure in lift cylinder  64 . The previously cut pipes adjacent to pipe  13  to be cut and the related remnant  63  of the platform are safely lifted up in this way such that the entire structure settles together at separation point  9  of pipe  13  currently being worked on. Without the support apparatus, cutting inserts  26 ,  126  could become wedged inside circumferential groove  45  (FIG. 4) formed at separation point  9  during the separation process of pipe  13  currently being worked on, if the remaining wall cross-section of pipe  13  is no longer equal to the load.