Wedgethread pipe connection

Details Wedgethread pipe connection Wedgethread pipe connection

2002-09-25

2004-01-27

Nicholson, Eric K. (Department: 3679)

Pipe joints or couplings

With lubrication

C285S334000, C285S390000

Reexamination Certificate

active

06682101

ABSTRACT:

TECHNICAL FIELD
The use of screw threads to connect joints of pipe together so as to convey fluid, is a very old art that has progressed for hundreds of years in an effort to satisfy periodic needs for stronger and better sealing pipe connections. Performance requirements for pipe connections still vary widely, such as for home piping containing less than 80 psi fluid pressure with virtually no mechanical loads, to Oil Well Pipe that may be required to hold 15,000 psi gas pressure, and simultaneously withstand extreme mechanical loadings and wide temperature fluctuations. The use of pipe threads to connect structural members is also old art.
Due to the historical weakness of threaded pipe connections and their tendency to loosen, leak, and/or break, their use in industrial plants and refineries has been limited by Industrial Codes, to very small pipe sizes and low pressures. However, because there is no reasonable alternative pipe connection for use within the very limited hole sizes drilled for Oil & Gas Wells, threaded pipe connections are still used today in wells, so most research on and development of threaded pipe connections has been directed toward such use. Structural use of conventional pipe threads has been limited by their weakness and their tendency to loosen and/or fracture while in service.
There has been considerable confusion in the industry as to what constitutes a reliable qualification test for threaded pipe connections, which has resulted in too many sales claims reflecting hopes, more than facts. New standard ISO-13679 gives promise to end that problem, in that it allows one to choose the percent efficiency ratings relative to the pipe ratings that a connection is to be tested and qualified for, under combinations of: internal pressure; external pressure; tension; compression; bending; temperature; and the choice of water or gas as the pressurizing fluid. It also specifies test procedures to accurately measure performance capability. Therefore, it is expected that the number of new types of connections offered for sale will decline in face of such stringent standards, but that real progress should accelerate. This application is made with that thought in mind.
BACKGROUND ART
Blose Re. 30,647 discloses Trapped Wedgethreads that suggests a thread seal in Col 2 ln 7-11 but does not teach how to accomplish a thread seal and in fact, cites undefined clearances between roots and crests in Col 3 ln 40-43.
Blose 4,600,224 discloses a trapped wedgethread and cites in Col 1 lines 56-60 that he provides a “controlled clearance between mating roots and crests”. Nowhere does he claim a thread seal as he suggested in Re. 30,647, but provides metal-to-metal seals as at
12
of
FIG. 1
, as at
24
&
26
of
FIG. 2
, and as at
32
and
34
of
FIG. 3
for the three embodiments disclosed.
Blose 4,600,225 adds additional clearance as at
43
between mating threads to further confirm that he was not able to form a wedge thread seal.
Ortloff 4,671,544 further confirms lack of thread sealing attained by the inventions above having a common assignee, in that he provides a resilient seal (
26
) mid-point the mating threads and metal-to-metal seals as at
22
and
24
of FIG.
1
. Col 2 ln 18-20 he mentions that the threads seal but does not teach how. If those threads did seal, then his resilient seal and metal-to-metal seals would not be needed. The embodiment shown in
FIG. 4
does not claim a thread seal, but claims a metal-to-metal seal as at
50
.
Reeves 4,703,959, discloses a trapped wedgethread connection that seals on a soft seal such as polytetrafluoroethylene in Col 2 ln 6-17. Again, he claims a thread seal but does not teach how to accomplish it. If the threads sealed the contained fluid, the soft seal is not needed.
Blose 4,822,081 discloses a trapped wedgethread but nowhere does he claim a thread seal, having no doubt witnessed tests on several of his inventions listed above. Instead, he cites seals as at
51
and
54
.
Mott 5,454,605 depicts a trapped wedgethread described in Col 2 ln 48-61 and illustrated in
FIGS. 3 & 4
. He properly describes the assembly and disassembly problems and the damage susceptibility of dovetail wedge threads in Col 1 ln 51-Col 2 ln 2. In Col 2 ln1 60-65, Col 4 ln 61-Col 5 ln 14, he claims a thread seal but again, does not teach how to seal against even mud. He states, “when made-up, there is no clearance between the threads” so not even thread lubricant is entrapped there between” but unfortunately, such perfect confirmation is and will always be beyond machining capability, and particularly within cost limitations for pipe connections.
Watts 2,766,998 teaches how to form an elastic metallic lip-seal and mating seat so as to effect a high-pressure seal against gas for many years, while under conditions of extreme variations of pressure and temperature.
Watts 5,427,418 teaches the elements that must exist at the position of full makeup for a pipe thread to seal high pressures with thread dope, and depicts a preferred embodiment having a positive included angle. A final judgment has been made that the XLC wedgethread connection made by XL SYSTEMS, INC. infringes '418, and a permanent injunction has been issued. The present application is an improvement over '418 that discloses a workable sealing range ratio for, the radius change to the thread width change, per turn.
Watts PCT Patent Application PCT/US00/28829 teaches that an Open Wedgethread can seal and operate successfully, teaching away from all prior art wedgethread patents cited above. Six of the wedgethread patents cited above have a common assignee and four name a common inventor, which confirms that a long, careful and continuing improvement effort has been focused on wedgethreads for over 25 years. Experience has taught a common characteristic of all Trapped Wedgethreads of other inventors listed above, that the load flanks do not engage but trap dope between them, and that the stab flanks engage and generate a high premature frictional resisting torque, as urged by the pressurized dope in the load flank gap before the ideal position of full makeup is reached, and that the threads do not seal. That premature makeup resisting torque acts to stop rotation short of full makeup, which allows dope in the load flank gap to later leak out when subjected to operational loads and to loosen the connection which in turn, reduces its ability to be driven or to serve as a mechanical support, or to seal. Upon first rotation of such pins into such boxes, both the crest gap (the gap between mating roots and crests) and the load flank gap are very wide, so excess dope flows freely outwardly from the connection. Increased torque begins during the latter stages of makeup when the gap widths between both thread surfaces, are reduced sufficiently that the dope being forced outwardly through the long narrow helical gap begins to seal and thereby, begins to build a progressively increasing back-pressure which in turn, causes frictional resisting torque between mating surfaces on the opposite side of the thread. None of the wedgethread patents by others cited above teach or even mention, the importance of a workable change ratio (CR=the thread diameter change to the crest width change per turn) that is required to result in contact of all mating flanks and a dope thickness in the crest gap so as to: (1) effect a rigid non-loosening connection; (2) effect a thread seal and; (3) maintain both the seal and non-loosening characteristic after being subjected to service forces.
When wedgethreads by others are made up to the Snug Position, the crest gap equals BTD and one flank gap is wider due to the threads' low CR value, and further makeup will cause dope to flow in accord with the laws of hydraulics, radially a fraction of an inch from the crest gap whose long helical path has just then begun to seal, into the wider flank gap and thence helically outwardly from between the mating threads, as the crest gap is reduced to the least thickness (Q), that the threads can compact solids

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