Dual member pipe joint for a dual member drill string

摘要

A dual-member pipe joint having an outer member and an inner member which is disposed coaxially within the outer member. Both the outer member and the inner member have a pin end and a box end. The pin end of the outer member is threadable to the box end of another outer member. The pin end of the inner member is geometrically shaped. The box end of the inner member forms a recess which conforms to the geometric shape of the pin end of the inner member. The box end of the inner member nonthreadably receives the pin end of another inner member in "slip-fit" connection. "Slip-fit" means the pin end of the inner member slides into the box end of a like inner member and forms a connection that is capable of transmitting torque. The advantage of this dual-member pipe joint is that both the inner and outer members of a pipe joint may be connected to a drill string in a single action with just one connection. This dual-member pipe joint reduces boring time as compared to boring with conventional dual-member pipe joints, in which both the inner and outer members are threadably connected and thus require two pipe connections. The dual-member pipe joint is usable as a system of pipe, and as part of a boring machine.