Abstract: A pipe joint comprising: a pin having a tapered male screw section formed on an outer circumferential face of an end of a pipe; a box having a tapered female screw section, which can be screwed to the tapered male screw section, formed on an inner circumferential face of an end of a pipe, wherein the tapered male screw section is screwed into the tapered female screw section, a top face of a male thread ridge of the tapered male screw section and a top face of a female thread ridge of the tapered female screw section have a predetermined width like a square screw thread, trapezoidal screw thread and buttress screw thread, and top faces of both thread ridges are inclined in a direction opposite to a tapered face of screw threads with respect to a face parallel to the pipe axis.

Abstract: An object of the present invention is to provide galling resistance to a threaded joint used for an oil well pipe. On a thread portion and a metallic sealing portion of the joint, there is provided a manganese phosphate chemical formation coating layer, or alternatively there are provided a nitriding layer of 1 to 20 .mu.m thickness and a manganese phosphate chemical formation coating layer of 5 to 30 .mu.m thickness, and also there is coated a solid lubricant which contains powder of molybdenum disulfide or tungsten disulfide and also contains one of epoxy resin, furan resin and polyamide resin as an essential component, and a ratio of composition is maintained at a specific value, so that a solid lubricant coating layer of 10 to 45 .mu.m thickness can be formed by heating.Due to the above surface treatment, even when the frequency of repetition of fastening and unfastening of the joint is increased, the occurrence of galling can be prevented over a long period of time.

Abstract: Quenched steel pipe is first held at a tempering temperature for a given period of time, then cooled relatively rapidly. While carrying the pipe in the direction of its length, cooling water is sprayed from outside onto its external surface at an average water flux of not lower than 0.05 m.sup.3 /min.m.sup.2 and not higher than 2 m.sup.3 /min.m.sup.2. This cooling is started when the pipe temperature is between 400.degree. C. and 700.degree. C. and ended between room temperature and 350.degree. C. Also, the cooling is effected at a mean cooling rate of not lower than 5.degree. C./sec. and not higher than 40.degree. C./sec. This cooling method improves the collapse strength of a pipe by providing an appropriate tensile residual stress to the internal surface of the pipe and reduces the cooling floor area without sacrificing the collapse strength of the pipe.