Seal for a joint or juncture – Process of static sealing – Pipe – conduit – or cable
Reexamination Certificate
1999-07-13
2002-06-25
Knight, Anthony (Department: 3626)
Seal for a joint or juncture
Process of static sealing
Pipe, conduit, or cable
C277S602000, C277S608000, C277S619000, C285S382100, C285S351000, C029S523000
Reexamination Certificate
active
06409175
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to methods and apparatus for connecting tubular bodies. More specifically, the present invention relates to methods and apparatus for effecting a secure mechanical engagement and seal in the connected ends of pipe sections that are expanded radially to form an increased internal diameter pipe string.
2. Description of the Prior Art
A new technique for casing well bores expands the well casing pipe radially after the casing pipe string has been lowered into a well bore. The casing string is enlarged radially by moving an oversized forging tool, or “pig,” through the string, causing the string to expand radially beyond its original radial dimensions. This technique allows subsequent strings of casing to be lowered through the previously enlarged casing string sections and thereafter similarly expanded. The result is a well cased by a series of linked sections of casing having substantially the same internal diameters. The procedure is explained in greater detail in U.S. Pat. No. 5,348,095, assigned to Shell Oil Co.
Conventional casing strings are made up of a series of individual pipe joints secured together at their ends by threaded connections. Typically, a joint of casing is approximately 40 feet in length and has a threaded male “pin” connection at one end of the joint and a threaded female “box” connection at the opposite joint end. The joint may have a pin at each end, with the box connection being formed by a short coupling threaded onto one of the pin connections. Some casing is made with the box connection integrally formed at one end of the casing joint. These integral box connections may be radially larger than the pipe body, or they may be the same size. In the latter case, the connection is called a flush joint connection.
The threaded engagement between a properly secured pin and box connection in a conventional casing joint is effective in maintaining a secure mechanical connection that holds the string together and effectively seals the internal casing area from the formation well bore environment. When the casing string is enlarged radially, a conventional connection changes dimensionally in a way that can prevent the engaged components of the connection from properly engaging and sealing. The radial expansion of a conventional connection may also weaken or otherwise damage the pin and box structure sufficiently to permit mechanical separation.
Threaded connections for oil field use mainly rely on three types of seals: either metal-to-metal shouldering seals or seals formed by engaged threads with high thread interference using thread compound to effect a seal in the void areas, or deformable seal rings entrapped in the thread area. All three seals of the se types are disabled by the radial expansion caused by the pig. In each case, following the expansion of the pin and box, the pin and box members radially separate, causing the seals to fail.
The end of the expanded pin has a natural tendency to spring back into the internal diameter of the pipe when the pig is removed. The separation and distortion following the expansion process compromises the seals located between the pin and box and creates an obstruction in the bore of the pipe. The distortion can be so great that the pin and box threads may also disengage.
A related cause of the failure of expanded connections is that the radial expansion of a conventional casing joint connection produces different degrees of permanent deformation in the pin and box. When the expanding force is removed, the pin tends to return to its original dimensions more so than does the box. The result is an annular separation between the pin and box that may permit leakage or mechanical separation.
Radial expansion of conventional connectors may also permit the connectors to leak. The sealing mechanism in many threaded pipe connections results from the engagement of metal-to-meal sealing surfaces in the pin and box. The engagement of these seal surfaces closes the annular space between the pin and box to provide a pressure seal. Radial expansion of the connection can distort or displace the sealing surfaces to permit leakage through the annular space.
Connectors that employ an elastomeric, annular seal ring between the engaged surfaces of the pin and box are also subject to leakage when the connection expands radially. The annular elastomeric seal of conventional O-ring-sealed connectors is carried in an annular groove formed in either the pin or the box, or both. The seal of such a connection is formed when the annular seal ring is compressed radially between the fully engaged pin and box. Subsequent radial expansion of the engaged connection changes the radial compression of the annular seal ring, which in turn may permit leakage through the expanded connection. The dimensional changes in the groove occurring during the expansion process may also damage the annular seal ring, permitting the seal to leak.
Conventional well pipe connections are also susceptible to splitting along the length of the box when the connections are expanded radially. The expansion process concentrates stresses of expansion in any thin wall sections present at the ends of the connected pipe segments. The acceptable tolerance for wall thickness in conventional connectors is relatively large so that a pin or box may have a non-uniform thickness that includes relatively thin wall areas without being defective. In this conventional connector, however, the concentration of the stresses induced by expansion of the connections may be sufficient to rupture or over-expand the thin section. The probability of a conventional connector having an area with a relatively thin wall section in either the box or the pin is too great to employ such connectors in pipe strings that are to be radially expanded.
SUMMARY OF THE INVENTION
An annular, elastomeric seal is carried in a non-standard annular groove formed within the threaded box of a tubular connector. An annular, spacer ring is positioned adjacent the seal ring within the groove. The dimensions of the groove and the seal ring and spacer ring are functionally related so that the seal ring is compressed axially and radially when the pin of the connection is expanded radially into the box and both the box and pin are then further expanded radially. Radial expansion of the connection causes the groove in the box to contract axially, forcing the spacer ring against the seal ring to compress the seal ring between the spacer and the opposing wall of the groove. The spacer ring assists in retaining the seal ring within the groove and also serves as a compressive wall surface to trap the seal ring and force it to expand within the groove as the groove contracts during the expansion of the connection. The expanded seal ring is extruded into the gap between the pin and box at the groove wall opposite the expansion ring to provide a pressure-tight seal.
A preferred form of the connection of the present invention is equipped with a single-taper thread section having a hooked thread form with no significant radial thread interference between the engaged pin and box components. An internal, reverse angle torque shoulder engages the end of the pin to prevent the pin end from moving radially inwardly away from the expanded box following the expansion of the connection.
The outside diameter of the box adjacent the thin section of the face of the box and the inside diameter of the pin adjacent the thin section end of the pin are machined to limit the variation of the wall thicknesses of the two connection components to prevent concentration of stresses in a thin-walled portion of either of the components during the expansion process.
Where the pig travels from the pin into the box, the pin internal diameter is less than or equal to the box internal diameter. Smooth and gradual transitions between the machined internal diameters and the “as rolled” internal diameters on the pin and box connections are also provided to limit the induced stress
Brock James N.
Costa D. Scott
Evans M. Edward
Browning & Bushman P.C.
Grant Prideco, Inc.
Helmreich Loren G.
Knight Anthony
Patel Vishal
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