Oilwell tubing connection

Pipe joints or couplings – Particular interface – Tapered

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Details

285397, F16L 2500

Patent

active

048137170

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The outer diameters of conventional threaded pipe couplings are substantially greater than the outer diameter of the pipe joints that they connect and the same is true for most strings of casing and tubing installed within oilwells, however, several constraints are presented by oilwells that are not normally present in surface piping systems. Each consecutive string including couplings, must pass within a hole bore diameter established by a drill or by a previously set string of pipe. Additionally, there must be sufficient clearance between that bore and the maximum diameter of the string being run so as to lower freely without sticking and to allow sufficient flow area through the annulus then formed for fluids without causing an unacceptable pressure drop caused by friction of the flowing fluid. Thirdly, oilwell strings must withstand axial tension and compression loads caused by the weight of miles of pipe that may be hanging within the well. Further, oilwell strings may be subject to external fluid pressures being greater than internal pressures to thereby introduce tendency to collapse. For these and other reasons, joints with upset ends and high cost "premium connections" have been introduced to work in the presence of such constraints. However, such solutions result with the outer diameters of connections being greater than the outer diameter of the pipe joints that they connect. There do exist, connections for pipe not having upset ends wherein one end of a joint is threaded externally and the other end is threaded with a mating internal thread such that joints can be screwed together to result in a connection with an outer diameter no larger than the pipe mid-section. However, such joints such as Hydril FJ Premium tubing connections enjoy only 42% axial tension strength as compared to the unthreaded pipe wall, about the same as non-upset API tubing connections. Presently, due to diameter constraints, a typical oilwell pipe program may be: 51/2 OD .times.27/8 OD .times.1.6 OD. To be far more advantageous for use as disclosed in my co-pending application filed herewith and entitled "Method and Means to Pump a Well," a 27/8 OD .times.1.6 OD .times.1.05 OD can often make an installation possible due to clearance or cost reasons that the typical program above could not and in every case, a less expensive and a more efficient installation should result. Many tons of steel per oilwell may therefore be saved from waste. When a pipe having no reduced wall thickness contains fluid pressure, the axial stress within that wall caused by fluid pressure is approximately one-half of the circumferential stress within that wall caused by the same pressure and therefore a like amount of mechanical axial stress may be applied by pipe weight or the like, without the axial stress exceeding the circumferential stress. Reduction of the pipe wall thickness as by a thread formed on a joint of non-upset pipe, will therefore reduce still further, the magnitude of axial stress that may be dedicated to support pipe weight.
There is therefore a substantial need for a flush joint tubular connection having a higher efficiency with no loss of the connection's ability to seal against fluid pressure.


BACKGROUND ART

A flush joint tubular connection has inner and outer diameters substantially the same as the tubing joints which the connection connects.
A flush joint tubular connection made by the Hydril Co., and covered by numerous patents comprise a first straight thread, a second straight thread of sufficient diameter to pass within the bore of the first thread and a tapered mating seal between the two joints of tubing which is a premium joint of high cost and according to published data, enjoys only 42% axial strength with regard to the pipe wall.
Standard A.P.I. non-upset tubing connections comprise couplings having outer diameters considerably larger than the pipe outer diameter but still only enjoy approximately 42% efficiency as above. A.P.I. does list a "turned down" collar outer diameter to increase cleara

REFERENCES:
patent: 1562373 (1925-11-01), Sheldon
patent: 1703232 (1929-02-01), Gray et al.
patent: 1932427 (1933-10-01), Stone
patent: 2094491 (1937-09-01), Janata
patent: 3572771 (1971-03-01), Redwine
patent: 4508375 (1985-04-01), Patterson

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