Metal fusion bonding – Process – Diffusion type
Reexamination Certificate
2000-08-22
2002-04-30
Dunn, Tom (Department: 1725)
Metal fusion bonding
Process
Diffusion type
C228S194000, C228S234100
Reexamination Certificate
active
06378760
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to joining of carbon steel pipes, and more particularly to joining of oil well pipes, such as casing tubes, production tubes or coiled tubes, for use in an oil well or a gas well, joining of pipes for a plant or line pipes for use in the chemical industry, petrochemistry or the like, and a method of enlarging the inner diameter of the joint of carbon steel pipes.
2. Description of the Related Art
conventionally, the oil well pipe, such as the casing tube or the production tube, for use in an oil well or a gas well, has been constituted by joining a multiplicity of carbon steel pipes each having a predetermined length (about 10 m to about 15 m).
For example, when an oil well or a gas well is mined, steel pipes, called casing tubes, are embedded in the shaft to protect the shaft dug in the ground and prevent leakage of crude oil or gas. Since the oil well or the gas well is usually present thousands of meters below the ground or the bottom of the sea, the casing tube must have a length of thousands of meters. Crude oil or gas pumped up from the oil well or the gas well is transported to an accumulating tank or a refinery through a separating unit by using a flow line or a pipe line extended for a distance of several kilometers.
The carbon steel pipes for use in the foregoing case are joined by any one of known methods below: a screw joining method (a mechanical coupling method), a welding method (an orbital welding method), a friction welding method or a diffusion bonding method.
The screw joining method is a method arranged to engage screws formed at the ends of the carbon steel pipes to join the carbon steel pipes to each other. The screw joining method has an advantage that time required to join each pipe takes a short time of about 5 minutes to 10 minutes and satisfactory working efficiency can be realized. The foregoing method, however, suffers from a problem in that oil or gas easily leaks through the joined portion. It leads to a fact that the screws provided for the carbon steel pipes must have excellent accuracy. Moreover, excellent skill is required to perform the screw joining operation. To protect the screw portion formed with excellent accuracy from damage, transportation and handling of the carbon steel pipes having the screw portions require close attention to be paid. Although airtightness of the joined portion can be maintained in a case where tensile stress is exerted, the screw joined portion is undesirably enlarged in the radial direction when compressive stress is exerted. Thus, there arises a problem in that leakage of oil or gas cannot be prevented.
In the welding method, a beveling is provided for the end surface of each of the carbon steel pipes and the beveling is filled with metal which must be welded so that the carbon steel pipes are connected to each other. The welding method is free from any leakage of oil or gas from the welded portion if incomplete fusion is performed or a blow hole is not formed. Moreover, an advantage can be realized in that satisfactory welded portion permits equivalent characteristics to those of the base metal to be obtained against compressive stress as well as tensile stress. The welding method, however, suffers from unsatisfactory efficiency. Since multilayer welding must be performed in a case of thick pipes each having a large diameter, an excessively long time of one to two hours is required to complete one joint. Moreover, there arises a problem in that influences of the environment including the weather and wind are exerted on the welding operation which is performed at the site. What is worse, excellent welding skills are required.
In the friction welding method, the abutted carbon steel pipes are relatively rotated or slid while pressure is being applied. Then, thus-generated fictional heat is used to soften and weld the ends of the carbon steel pipes to each other. The foregoing method is able to realize advantages in that any skill is not required, the joining operation can be completed in a short time and excessive influence of the operation environment can substantially be eliminated. However, the foregoing method cannot prevent flash of the inner and outer surfaces of the joined portion of the carbon steel pipes. Therefore, there arises a problem in that removal of the flash, in particular, removal of the flash formed on the inner surface requires a long time. As a method to solve the foregoing problem, a radial friction welding method has been developed. In the method, a ring having a wedge-like cross section is inserted between the end surfaces of a pair of carbon steel pipes while securing the pair of the carbon steel pipes, the ring is inwards pushed toward the center of the carbon steel pipe to perform pressure-welding. The pressure-welded joint attains only poor characteristic. Therefore, there is no report about the employment of the method to join the oil-well pipes.
The diffusion joining method is able to prevent any leakage of oil or gas through the joined portion if the joining operation is performed under appropriate conditions. Although resistance against compressive stress arises similarly to the foregoing welding method, time required to complete one joint can be shortened to about ⅓ to ½ of the welding method. Thus, advantage can be realized in that joints exhibiting high quality can efficiently be formed. Therefore, the diffusion joining method is a significantly advantageous method as a method of joining oil-well pipes and line pipes.
On the other hand, in order to reduce the oil or gas producing cost, a method has been developed with which a shaft having a diameter smaller than that of the conventional method is formed. Moreover, casing tubes each having a length of hundreds of meters and inserted into the shaft is expanded on the ground (World Oil: P.31, April, 1999).
In the foregoing method, a tool which has been inserted into a casing tube having a long length of hundreds of meters and which has an outer diameter larger than the outer diameter of the tube is moved in the tube by using hydraulic pressure or the like. Thus, the inner diameter of the tube is continuously enlarged. Therefore, the diameter of the shaft is reduced to reduce drilling cost. The distance from the shaft to the casing tube is shortened to reduce the cementing cost. Moreover, the number of the required casing tubes is decreased. Thus, reduction in the production cost of oil or gas is expected.
As described above, the casing tube having the long length of hundreds of meters cannot be constituted by one carbon steel pipe. Therefore, a multiplicity of carbon steel pipes each having a predetermined length are joined to one another to form a joint of carbon steel pipes and expanded. The joints of carbon steel pipes are connected to one another by any one of the foregoing methods, such as the above described screw joining method (the mechanical coupling method), the welding method (the orbital welding method), the friction welding method and the diffusion bonding method. Also the joined portion of the joint of carbon steel pipes is expanded similarly to the base metal of the carbon steel pipe. Therefore, the joined portion must have diameter-expansion characteristic similar to that of the base metal of the carbon steel pipe.
When the joints of carbon steel pipes connected by the screw joining method are expanded, deformation of the joined portion results to loose the clamped screws. Thus, there arises a problem in that oil or gas easily leaks. Therefore, precise screws each having a special shape are employed. However, the foregoing method cannot permit satisfactory characteristics to be obtained. Moreover, machining of the foregoing special screws requires a large cost. To protect the screw portions from damage, there arises a problem in that transportation or handling of the screws require close attention to be paid. Therefore, its applicable range is limited.
The mechanical characteristics of the welded portion of each of
Horio Hirotsugu
Inagaki Shigeyuki
Kitou Kazushige
Shimizu Takao
Yamada Ryuzo
Daido Tokushuko Kabushiki Kaisha
Dunn Tom
Johnson Jonathan
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