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