Threaded joint for steel pipes and process for the surface treatment thereof
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United States of America Patent
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N/A
Issued Date -
Oct 7, 2004
app pub date -
Apr 22, 2004
filing date -
Apr 11, 2001
priority date (Note) -
Abandoned
status (Latency Note)
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Abstract
This invention relates to a threaded joint for steel pipes which comprises a pin and a box each having a contact surface including a threaded portion and an unthreaded metal contact portion and which can be prevented from galling during repeated fastening and loosening without application of a compound grease. A solid lubricant coating which comprises a lubricating powder such as molybdenum disulfide and a resin binder is formed on the contact surface of at least one of the pin and the box. The coating is formed by applying a coating fluid and drying the applied coating by first stage heating in the temperature range of from 70.degree. C. to 150.degree. C. and second stage heating in the range of from higher than 150.degree. C. to 380.degree. C. The resulting solid lubricant coating has a hardness of 70-140 on the Rockwell M scale and an adhesive strength of at least 500 N/m as determined by the SAICAS (Surface And Interfacial Cutting Analysis System) method, and it exhibits excellent galling resistance even in the environment of high-temperature oil wells. Inclusion of ultraviolet screening fine particles such as titanium oxide fine particles in the solid lubricant coating increases the rust preventing properties of the threaded joint.
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