SCREW JOINT FOR STEEL PIPE

摘要

A screw joint for steel pipe of pin/box type having contact surfaces (30) including a threaded part and an unthreaded metal contact part is improved with respect to the leakage resistance, galling resistance and corrosion resistance, especially that to crevice corrosion. The contact surface of at least one of the pin and the box is covered with a first plating layer (34) of Cu-Zn alloy or Cu-Zn-M1 alloy (M1 is at least one selected from among Sn, Bi and In). The first plating layer on its downside and upside may be provided with a lower layer (32) consisting of Ni plating layer (32a) and/or Cu plating layer (32b) (one or both of the layers) and an upper layer of Sn-M2 alloy (M2 is at least one element selected from among Bi, In, Ni, Zn and Cu) plating layer (36). The plating layers may be overlaid with a lubricant coating (38) selected from among a solid lubricant coating (38a) and a viscous liquid or semisolid lubricant coating (38b).