Patent ID: 8420581

Claim:
A threaded joint for pipes used in the excavation of oil wells and gas wells without using a lubricating grease constituted by a pin and a box each having a contact surface comprising a threaded portion and an unthreaded metal contact portion, characterized in that the contact surface of at least one of the pin and the box has a lubricating coating formed using a composition which comprises a total of 1-30% of one or both of a rosin and calcium fluoride, 2-30% of metal soap, 2-30% of wax, and 10-70% of a basic metal salt of an aromatic organic acid as expressed in mass % based on the total amount of non-volatile components in the composition and further contains substantially no harmful heavy metals, wherein a relative value of ΔT is 90 or more when ΔT in control is 100, wherein ΔT=Ty−Ts, and Ts represents torque at a beginning of shoulder interference when the threaded joint is formed by turns of the pipe, and Ty represents torque when plastic deformation of the shoulder of the threaded joint begins during rotation, and ΔT in control is a value obtained with a compound grease.