Pipe joints or couplings – With lubrication
Patent
1997-05-23
2000-02-22
Arola, Dave W.
Pipe joints or couplings
With lubrication
285333, 29458, 508150, 508167, 427190, 4273722, F16L 700
Patent
active
060271450
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a threaded joint, the galling resistance of which is high even when it is used under the condition of no lubricant. More particularly, the present invention relates to a threaded joint used for joining oil well steel pipes when crude oil is mined, and also used for joining steel pipes in a pipeline to transport crude oil after it has been mined, and the galling resistance of the threaded joint is high even when it is used under the condition of no lubricant, that is, under the condition in which no lubricant is coated on the threaded joint which is repeatedly fastened and unfastened. The present invention also relates to a method of surface treatment of the threaded joint of steel pipes.
BACKGROUND ART
In general, threaded joints are used for the tubing and casing when an oil well is drilled. When these threaded joints are used in an actual environment, they are given a compound force including an internal and external pressure, an axial force and a bending force. Accordingly, these threaded joints are required not to leak or be damaged even when the compound force is given to them. On the other hand, when the tubing and casing are set in an oil well, threaded joints to join the oil well pipes are unfastened after they have been once fastened. In general, according to API (American Petroleum Institute), it is desired that no galling occurs in the threaded joints even when the tubing is fastened and unfastened 10 times and the casing is fastened and unfastened 3 times. In order to meet the above requirements, it is common at present that the threaded joints are fastened after compound grease stipulated in API BUL5A2 has been coated on the joints. In this case, compound grease works to ensure the galling resistance and enhancing the sealing property of the threaded joints.
In order to further enhance the sealing property of the threaded joints, special threaded joints having a contact portion in which metal comes into contact with metal, that is, premium joints have been actively developed. As disclosed in Japanese Examined Patent Publication Nos. 59-44552 and 5-41876, premium joints having sealing sections of various shapes have been invented. According to the above inventions, gas-sealing properties of the above joints are enhanced to the same level as that of the yield strength of the steel pipe. However, in order to further enhance the sealing property, a surface pressure higher than the yield strength of the mother metal must be given to the metal contact portion of the threaded joint. Accordingly, galling incapable of being repaired tends to occur in the threaded joint.
Therefore, the inventors actively investigated the prevention of galling.
There are provided various measures to prevent the occurrence of galling, which will be described as follows. Compound grease is made to appropriately contain powder of a heavy metal such as zinc, lead or copper; alternatively compound grease is made to appropriately contain powder of an inorganic compound such as mica; a shape of the sealing section is devised so that the local surface pressure on the threaded joint can be reduced as disclosed in Japanese Unexamined Patent Publication Nos. 62-209291 and 4-277392; a characteristic of the sealing surface is controlled as disclosed in Japanese Examined Utility Model Publication No. 6-713; and galling resistance is enhanced by conducting surface treatment on the threaded joint as disclosed in Japanese Examined Patent Publication No. 3-78517 and Japanese Unexamined Patent Publication Nos. 5-117870, 62-258283, 60-26695, 58-31097, 58-17285, 61-124792 and 61-136087. The aforementioned techniques are respectively effective to prevent the occurrence of galling. Especially when an appropriate surface treatment is conducted on the threaded joint and an appropriate compound grease is used to coat the threaded joint, galling resistance can be enhanced to a sufficiently high level to be put into practical use.
According to Japanese Examined Patent Publication No. 3-78517, thr
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Akiyama Toshio
Higuchi Seijun
Inoue Ryusuke
Nagayoshi Haruyuki
Nakashima Akira
Arola Dave W.
Nippon Steel Corporation
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