Steel pipe joint structure and method for processing steel pipe

A steel pipe joint structure that connects a first steel pipe and a second steel pipe with each other, the first steel pipe having an external thread at least at one end portion of the first steel pipe, the second steel pipe having an internal thread at least at one end portion of the second steel pipe, comprising:

• in the first steel pipe, a pin front part, an external thread part having the external thread, and a pin rear part arranged in this order from a distal end of the first steel pipe, and
• in the second steel pipe, a box front part, an internal thread part having the internal thread, and a box rear part arranged in this order from a distal end of the second steel pipe, wherein
• the external thread part includes
• a pin rear incomplete thread part at an end portion on a pin rear part side, the pin rear incomplete thread part being a tapered thread and an incomplete thread, and
• a pin complete thread part at a center portion of the external thread part, the pin complete thread part being a tapered thread and a complete thread,
• the internal thread part includes
• a box front parallel thread part at an end portion on a box front part side, the box front parallel thread part being a parallel thread and an incomplete thread, and
• a box complete thread part at a center portion of the internal thread part, the box complete thread part being a tapered thread and a complete thread,
• the pin rear incomplete thread part and the box front parallel thread part are threadedly engaged with each other by engagement in which a stabbing flank of the pin rear incomplete thread part and a stabbing flank of the box front parallel thread part are brought into contact with each other, and a load flank of the pin rear incomplete thread part and a load flank of the box front parallel thread part are brought into contact with each other, and
• in cross section including a pipe axis, a root of the box front parallel thread part has a larger width than a root of the box complete thread part.

A steel pipe joint structure that connects a first steel pipe and a second steel pipe with each other, the first steel pipe having an external thread at least at one end portion of the first steel pipe, the second steel pipe having an internal thread at least at one end portion of the second steel pipe, comprising:

• in the first steel pipe, a pin front part, an external thread part having the external thread, and a pin rear part arranged in this order from a distal end of the first steel pipe, and
• in the second steel pipe, a box front part, an internal thread part having the internal thread, and a box rear part arranged in this order from a distal end of the second steel pipe, wherein
• the external thread part includes
• a pin front parallel thread part at an end portion on a pin front part side, the pin front parallel thread part being a parallel thread and an incomplete thread, and
• a pin complete thread part at a center portion of the external thread part, the pin complete thread part being a tapered thread and a complete thread,
• the internal thread part includes
• a box rear incomplete thread part at an end portion on a box rear part side, the box rear incomplete thread part being a tapered thread and an incomplete thread, and
• a box complete thread part at a center portion of the internal thread part, the box complete thread part being a tapered thread and a complete thread,
• the pin front parallel thread part and the box rear incomplete thread part are threadedly engaged with each other by engagement in which a stabbing flank of the pin front parallel thread part and a stabbing flank of the box rear incomplete thread part are brought into contact with each other, and a load flank of the pin front parallel thread part and a load flank of the box rear incomplete thread part are brought into contact with each other, and
• a root of the box rear incomplete thread part has a larger width than a root of the box complete thread part.

A steel pipe joint structure that connects a first steel pipe and a second steel pipe with each other, the first steel pipe having an external thread at least at one end portion of the first steel pipe, the second steel pipe having an internal thread at least at one end portion of the second steel pipe, comprising:

• in the first steel pipe, a pin front part, an external thread part having the external thread, and a pin rear part arranged in this order from a distal end of the first steel pipe, and
• in the second steel pipe, a box front part, an internal thread part having the internal thread, and a box rear part arranged in this order from a distal end of the second steel pipe, wherein
• the external thread part includes
• a pin rear incomplete thread part at an end portion on a pin rear part side, the pin rear incomplete thread part being a parallel thread and an incomplete thread, and
• a pin complete thread part at a center portion of the external thread part, the pin complete thread part being a tapered thread and a complete thread,
• the internal thread part includes
• a box-side parallel thread part at an end portion on a box front part side, the box-side parallel thread part being a parallel thread and an incomplete thread, and
• a box complete thread part at a center portion of the internal thread part, the box complete thread part being a tapered thread and a complete thread,
• the pin rear incomplete thread part and the box-side parallel thread part are threadedly engaged with each other by engagement in which a stabbing flank of the pin rear incomplete thread part and a stabbing flank of the box-side parallel thread part are brought into contact with each other, and a load flank of the pin rear incomplete thread part and a load flank of the box-side parallel thread part are brought into contact with each other, and
• a root of the pin rear incomplete thread part has a larger width than a root of the pin complete thread part.

A method for processing a steel pipe, an external thread part or an internal thread part being processed at an end portion of the steel pipe by the method, wherein

• the external thread part or the internal thread part includes a parallel thread part and a tapered thread part in this order from a distal end of the steel pipe,
• the method comprising:
• making a plurality of normal processing passes in which a thread cutting insert is fed from an initial position at a first feeding speed, thus continuously processing the parallel thread part and the tapered thread part,
• making a first size reduction processing pass in which a stabbing flank of the parallel thread part is processed at a second feeding speed,
• making a second size reduction processing pass in which the stabbing flank of the parallel thread part is processed at the second feeding speed, and a stabbing flank of the tapered thread part is processed at the first feeding speed, and
• making a third size reduction processing pass in which a load flank of the parallel thread part is processed at a third feeding speed, and processing is performed on the tapered thread part at the first feeding speed, wherein
• in the first size reduction processing pass and the second size reduction processing pass, processing is started from a position closer to the steel pipe than the initial position, and
• in the third size reduction processing pass, the processing is started from a position farther from the steel pipe than the initial position.

A method for processing a steel pipe, an external thread part or an internal thread part being processed at an end portion of the steel pipe by the method, wherein

• the external thread part or the internal thread part includes a parallel thread part and a tapered thread part in this order from a distal end of the steel pipe,
• the method comprising:
• making a plurality of normal processing passes in which a thread cutting insert is fed from an initial position at a first feeding speed, thus continuously processing the parallel thread part and the tapered thread part,
• making a first size reduction processing pass in which a stabbing flank of the parallel thread part and a stabbing flank of a portion of the tapered thread part are processed at a second feeding speed,
• making a second size reduction processing pass in which the stabbing flank of the parallel thread part and the stabbing flank of the portion of the tapered thread part are processed at the second feeding speed, and a stabbing flank of portions of the tapered thread part other than the portion is processed at the first feeding speed, and
• making a third size reduction processing pass in which a load flank of the parallel thread part and a load flank of the portion of the tapered thread part are processed at a third feeding speed, and processing is performed on the portions of the tapered thread part other than the portion at the first feeding speed, wherein
• in the first size reduction processing pass and the second size reduction processing pass, processing is started from a position closer to the steel pipe than the initial position, and
• in the third size reduction processing pass, the processing is started from a position farther from the steel pipe than the initial position.