Abstract: A plug member can be mounted to the end of a pipe and removed therefrom by automated operation. A mounting and dismounting device 21 for mounting and dismounting a plug member 11 with respect to an oil country tubular good P. The plug member 11 comprises an outer tube 12 having seal portions 16a and 16b and a circumferential groove 12a, a shuttle 13, a cap 14, and a shuttle biasing spring 15 secured to the cap 14 and the shuttle 13. The mounting and dismounting device 21 comprises a tubular holding body 22, a rod 23 which has a conical end portion 23a and which is disposed so as to move inside the tubular holding body 22, and moving means 24 and 25 which allow the tubular holding body 22 and the rod 23 to independently move. The tubular holding body 22 has ball-receiving holes 22a into which fit balls 26 which engage with the circumferential groove 12a.

Abstract: A seamless tube is manufactured while effectively suppressing the occurrence of carburization in the seamless tube without interfering with operations. A seamless tube is manufactured by a step of washing at least a portion of a conveyor installed in a conveying step of a mandrel bar B which is situated from a lubricant applying device 7 to the entrance of a mandrel mill 8, a step of washing, on the upstream side of the lubricant applying device 7, a mandrel bar B which was used for elongation rolling, and a step of applying a non-graphite-based lubricant to the mandrel bar B with the lubricant applying device 7, wherein the conveyor and the mandrel bar B are each washed such that the amount of graphite C2 (g/m2) adhering to the surface of the mandrel bar B before it is provided to elongation rolling and the amount of carbon C1 (g/m2) contained in the organic binder of the applied lubricant satisfy Equation 1: 0.08×C1+0.05×C2?3 and Equation 2: 3?C1+C2?50.

Abstract: A seamless tube is manufactured while effectively suppressing the occurrence of carburization in the seamless tube without interfering with operations. A seamless tube is manufactured by a step of washing at least a portion of a conveyor installed in a conveying step of a mandrel bar B which is situated from a lubricant applying device 7 to the entrance of a mandrel mill 8, a step of washing, on the upstream side of the lubricant applying device 7, a mandrel bar B which was used for elongation rolling, and a step of applying a non-graphite-based lubricant to the mandrel bar B with the lubricant applying device 7, wherein the conveyor and the mandrel bar B are each washed such that the amount of graphite C2 (g/m2) adhering to the surface of the mandrel bar B before it is provided to elongation rolling and the amount of carbon C1 (g/m2) contained in the organic binder of the applied lubricant satisfy Equation 1: 0.08×C1+0.05×C2?3 and Equation 2: 3?C1+C2?50.