Wells – Processes – Assembling well part
Reexamination Certificate
1999-03-09
2001-08-28
Cherry, Johnny D. (Department: 3652)
Wells
Processes
Assembling well part
C166S077520, C294S090000, C294S102200
Reexamination Certificate
active
06279662
ABSTRACT:
BACKGROUND OF THE INVENTION
Coupling-engaging elevators, without slips, have been employed to closely surround the pipe and engage the bottom of the coupling at the pipe end. Lifting the elevator lifts the pipe by exerting force against the base of the coupling. This technique is not suitable for use with heavy strings and couplings that are tapered, slender, or otherwise incapable of withstanding the concentrated axial forces imposed along their lower perimeter. Conventionally, heavy strings and pipe with connections not suitable for use with a coupling-engaging elevator have required the use of slip-type elevators. The slip-type elevators are equipped with dies having teeth designed to increase the frictional resistance between the elevator and the pipe. These teeth exert an increasingly greater radial force against the pipe as the weight of the string increases. Pipe made from certain alloys, including chrome, and nickel and steel, is easily damaged by the effects of the die teeth. Such materials are typically required in highly corrosive environments in which any pipe damage is particularly hazardous.
SUMMARY OF THE INVENTION
A conventional, slip-type elevator is equipped with smooth surface pipe-gripping elements to prevent damage to the pipe surface. The contact elements are made of a material that is softer than that of the pipe. The resultant radial forces between the pipe-gripping elements and the pipe force the softer material of the gripping elements to be slightly deformed into the small irregular surface areas on the external surface of the pipe to increase the frictional gripping force. In one form of the invention, a lift connector is also provided to increase the radial forces acting through the pipe-gripping elements. The lift connector is threadedly engaged with the threaded end of the pipe string and is provided with a sleeve that extends over the threaded end of the pipe and down to the pipe-gripping elements. The axial force exerted by engagement of the lift connector with the pipe-gripping elements is transmitted through the lift connector to the connected threads between the lift connector and the pipe. The lift connector thus prevents the forces supporting the pipe from being concentrated at the base of the coupling, as occurs with non-slip lifting elevators.
Non-slip-type lifting elevators may also be employed with the lift connector of the present invention whereby the sleeve of the lift connector engages the elevator and transmits the elevator lifting force to the connected threads between the connector and pipe. The threaded engagement between the connector and pipe has strength equivalent to that of a conventional threaded connection in the pipe string, and the forces imposed by the lift connector are uniformly distributed through the threaded connection as they would be in a normal connection. The lift connector thus prevents the application of concentrated lifting forces at the base of the pipe coupling to prevent damage to the coupling base and to prevent the possibility of the coupling's separating from the threaded section of the pipe.
In the slip-type elevator of the present invention, spring-loaded slip assemblies are employed to provide a smooth surface contact with the pipe to be engaged and held. The contact or gripping portion of the slip assembly is formed of a material that is softer than the pipe that is to be engaged. The gripping material may, for example, be aluminum when used with steel pipe. Conventional, spring-loaded steel slip segments may be equipped with aluminum dies or facings having smooth pipe contact surfaces to provide a slip assembly in which the pipe-engaging components are softer than the steel material of the pipe. In another form of the invention, the entire slip assembly may be formed as a single body made completely of a softer material, such as aluminum, to provide the desired gripping, non-damaging contact with the engaged pipe.
In the system of the invention, the lift connector and spring-loaded pipe-engaging elements are employed in combination to ensure that the pipe will not slip from the elevator. If the pipe-gripping elements engage the pipe where the elevator is latched (closed), the relative axial movement between the spring-loaded slip segments and the pipe will cause the slip-gripping elements to hold and grip the pipe to prevent additional axial pipe movement. In the event the gripping force is not strong enough, the pipe will move down through the elevator until the lift connector engages and rests on the top of the pipe-engaging assembly, thereby increasing the radial gripping force and stopping the downward pipe movement.
In the method of the invention, a lift connector is threaded to the top of a joint of pipe, and the joint of pipe is made up into the pipe string. The elevator is then engaged about the tubing, below the coupling. Where the gripping elements do not initially engage the tubing, the elevator is raised until the lift connector engages the spring-loaded pipe-gripping elements of the elevator and forces them radially into engagement with the pipe. Subsequently, the additional pulling force is supported by the elevator through the pipe-gripping elements primarily, rather than through the lift connector, thereby minimizing the forces acting through the threaded connection between the lift connector and the pipe while maintaining the pipe firmly within the elevator-gripping elements.
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Browning & Bushman P.C.
Cherry Johnny D.
Torres Carlos A.
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