Joint for steel pipe having high galling resistance and surface treatment method thereof
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United States of America Patent
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-
Feb 22, 2000
Grant Date -
N/A
app pub date -
May 23, 1997
filing date -
Oct 4, 1994
priority date (Note) -
In Force
status (Latency Note)
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Abstract
An object of the present invention is to provide galling resistance to a threaded joint used for an oil well pipe. On a thread portion and a metallic sealing portion of the joint, there is provided a manganese phosphate chemical formation coating layer, or alternatively there are provided a nitriding layer of 1 to 20 .mu.m thickness and a manganese phosphate chemical formation coating layer of 5 to 30 .mu.m thickness, and also there is coated a solid lubricant which contains powder of molybdenum disulfide or tungsten disulfide and also contains one of epoxy resin, furan resin and polyamide resin as an essential component, and a ratio of composition is maintained at a specific value, so that a solid lubricant coating layer of 10 to 45 .mu.m thickness can be formed by heating. Due to the above surface treatment, even when the frequency of repetition of fastening and unfastening of the joint is increased, the occurrence of galling can be prevented over a long period of time.
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