Hydraulic and earth engineering – Marine structure or fabrication thereof
Reexamination Certificate
1998-11-19
2001-02-06
Lillis, Eileen D. (Department: 3673)
Hydraulic and earth engineering
Marine structure or fabrication thereof
C166S055000, C166S055200, C166S055600, C166S055700
Reexamination Certificate
active
06183165
ABSTRACT:
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,
Heinrichs Peter
Tibussek Fritz
Hartmann Gary S.
Lillis Eileen D.
Vickers Daniels & Young
Wirth Maschinen-Und Bohrgerate-Fabrik GmbH
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