Threaded joint for steel pipes having improved galling resistance and rust-preventing properties

摘要

In a threaded joint for steel pipes comprising a pin and a box capable of mating with each other, the pin having an externally threaded portion and an unthreaded metal contact portion as a mating surface, and the box having an internally threaded portion and an unthreaded metal contact portion as a mating surface, the mating surface of at least one of the pin and the box is coated with a lower porous zinc or zinc alloy layer by blast plating and with an upper coating which is either a solid lubricating coating (comprising a lubricating powder in an organic or in organic binder) or a liquid, heavy metal powder-free coating (e.g., a liquid coating based on a highly basic organic acid metal salt such as a highly basic metal sulfonate). The threaded joint exhibits improved galling resistance, rust-preventing properties, and gas tightness even after exposure to a high temperature and makes it possible to perform repeated fastening (make-up) and loosening (break-out) in a high-temperature oil well without application of a compound grease containing a heavy metal powder.