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

Abstract

IN A THREADED JOINT FOR STEEL PIPES COMPRISING A PIN (1) AND A BOX (2) CAPABLE OF MATING WITH EACH OTHER, THE PIN (I) HAVING AN EXTERNALLY THREADED PORTION (3A) AND AN UNTHREADED METAL CONTACT PORTION (4) AS A MATING SURFACE (10), AND THE BOX (2) HAVING AN INTERNALLY THREADED PORTION (38) AND AN UNTHREADED METAL CONTACT PORTION (4) AS A MATING SURFACE (10), THE MATING SURFACE (10) OF AT LEAST ONE OF THE PIN (1) AND THE BOX (2) IS COATED WITH A LOWER POROUS ZINC OR ZINC ALLOY LAYER (20) BY BLAST PLATING AND WITH AN UPPER COATING WHICH IS EITHER A SOLID LUBRICATING COATING (30) (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. (FIG 2)

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