This application is: a C-I-P of prior Canadian Application 2,111,133 filed Dec 10, 1993; which is a Continuation of U.S. Application 855,850 filed March 2, 1992; which is a C-I-P of U.S. Application 705,328 filed May 24, 1991 & issued as Patent 5,143,411; which is a C-I-P of U.S. Application 315,271 filed Feb 24,1989 & issued as Patent 5,018,771; which was a C-I-P of U.S. Application 897,069 filed July 18, 1986 & issued as Patent 4,813,717; which was a Continuation of PCT/US85/0260 filed Feb 19, 1985 now abandoned which was a Continuation of PCT/US84/1936 filed Nov 23, 1984 now abandoned.

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 constzaints are presented oy not normally present in surface piping systems. Each cc.αsecυtive string including ∞ 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 fanned for fluids without causing an unacceptable pressure drop caused by friction in 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 woήc in the presoκe of such constraints. However, such solutions result with the outer diameters of connections being greater than the outside diameter of the pipe joints that they connect There do exist, ∞nnections 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 outside diameter no larger than the pipe mid-section. However, such joints _ni-Λas IfydrilFJPr->oήumtabing c to the unthreaded pipe wall, about the same as non-upset API mbing ccαmections. Presently, due to diameter constraints, a typical oilwell pipe program may be: 5-1/2" OD x 2-7 8" OD" x 1.6" OD. To be far more advantageous, a 2-7/8" OD x 1.6" OD x 1.05" OD can often make an installation psajhlft due in clearance nr coat reasons that the rwΩ ram ahπve c-iiilri not anrf jτι

every case, a less expensive and a more efficient installation should result Many tons of steel per oilwell may be therefore be saved from waste. When a pipe having no reduced waH 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 fbπned on a joint of non-upset pipe, will therefore reduce still further, the magnitude of axial stress that may be dedicated to support the pipe weight There is therefore a substantial need for a non- upset, integral tubular connection having a higher efficiency with no loss of the connections ability to seal against fluid pressure.

For assembly of conventional threaded connections, the external thread must be carefully aligned both axially and angularly, with the with the internal thread before stabbing so as to prevent cross-threading of the connection. It is then moved axially to contact the end thread of the pin with a thread of the box to thereby effect stab position. The length of the pin thread that then projects into the box if any, is known as stab depth. Then, while being careful to maintain said alignment, the pin is rotated into the box by hand to a "hand-tight" position after which, a wrench is used to tighten the pin to a position of full makeup. The accuracy of stabbing often determines the effect of the connection. Connections that have been cross-threaded usualfy leak even after a proper makeup. Connections that are put into service in a cross-threaded condition will not only leak but will rupture at a small fraction of Vjhe rated load. It is therefore dear that a connection designed to prevent cross-threading is highly desirable to eliminate the danger and damage that can be caused by such leakage and rupture.

An upset end is generally understood by the industiy as being a pipe end that has been heated to a temperature above the lower critical temperature for the pipe metal and then formed under - great pressure so as to gather axially, metal of the pipe waU and thereby iικaease substantiaJUy cross-section area of the pipe wall at that end of the pipe. After upsetting the end of a high strength pipe, API Specifications require that the entire joint of pipe be quenched and tempered, all of which can greatly increase the cost of a joint of pipe.

In an effort to improve the radial clearance and cost of a tubular ccαmectiσn and still retain significant strength, "near-flush connections" were introduced whiώcαrrιprise ^u swaged" pipe ends. Swaged pipe ends are formed at temperatures below the lower critical temperature, by moderate radial pressures that increase or decrease the mean pipe diameter of the swaged zone, but do not subβtantialfy-chaoge the cross-section area thereof. The swaged end of a high strength

pipe rieed ot-Lty be stress relieved ai a tern far less costly than a quench and temper. A pipe end n^y be ^u swaged-m ⁿ to a smaller diameter to receive an external thread or may be ^u swaged-c^ thread. Generally, the outermost diameter of swaged-out ends is less than an API Coupling OX). but more than pipe body OD.

A typical family of swaged pipe connections having efficiencies of 65% may seem to be adequate to an engineer while designing a well, if calculations indicate that pipe weight and fluid pressure will generate loads on the connections of only 50% of pipe strength. However, many factors deep in the earth can cause unexpected rupture of a ccβ_4t-4e tion, endangering bo and the environment, when well designs are based on pipe stress. For example: 0.19% strain will yield the body of API J55 pipe; 0.28% strain will yield N80; 0.38% strain will yield PI 10. If a high efficiency connection allows the strain an the pipe body to continue, it wiU usually accept 5% or more strain before rupture. However, if the parting load of a casing connection is less than the load to yield the pipe body, then the connection will part before strain reaches the low limits given above. Strains over 1% are often imposed on the casing of welb that produce from or near, over- pressured and under-compacted reservoirs, of which mere are many. If a connection parting load exceeds slightly, the load that will yield the pipe body, then the casing string will accept several times greater than if connection parting load ώ stighlly below the pipe body yield load. To safely meet strain criteria for well design, connection efficiency should exceed the value = 100 x (pipe yield strength/ pipe ultimate strength). Accordingly, casing connection strengths should exceed by some reasonable margin, the following % efficiencies: 73% for J-55; 80% for N-80 and P-l 10 pipe grades.

Although most non-upset threaded pipe connections have compressive axial strengths in the range of 50% as compared to the pipe body strength, there are needs for plain-end threaded pipe connections having much higher strengths. One such need is for joints of "Drive-Pipe" in pipe sizes of up to 60" and larger, that are hammered into the earth successively after connection with a previous joint driven, to form long strings of pipe driven into the earth. The API 8Rd Connection can not be used for drive-pipe because easy stabbing, low makeup torque and structural rigidity is imperative for such joints. Drive-pipe strings are used as "piling" to support the weight of other -rtructures and are also used as the first string in a deep well. To efficiently and reliably transmit extremely heavy blows from massive hammers, the threaded connection must not allow relative motion between the box and pin members of the connection so as to prevent loosening, leaking, wear and/or compressive failure. The API Buttress Connection is

not used for such service because it allows end-play between box and pin which dissipates the hammers impact and allows leakage of the connection. Such ccαinections must also have high strengm tensira so as being driven. Flush-joint drive-pipe connections offer less ground resistance than collar-type or weld-on connections while being driven and they cost much less however, the best flush-joint connections available for Drive-pipe have only 60% efficiency and are very difficult to stab. When higher strength drive-pipe connections are needed, the user UjiUst now use a weld-on type. Both types seal on rubber which reduces the connections service life.

Therefore, a threaded pipe connection for large pipe sizes is needed that is cost effective; has high axial strength; stabs easily, makes up with low torq'ue; provides a rel bte permanent seal against dangerous fluids; resists handling damage; does not leak or loosen after being driven into the earth.

BACKGROUND ART

A flush-joint tubular connection has inner and outer diametera substaniialfy the same as the tubular joints which the connection connects. A flush-joint tubular connection made by the Hydril Company and covered by numerous patents comprises a first straight thread, a second straight thread of sufficient diameter to pass within the bore of the fi thread, aι i a between the two joints of tubing, which is a premium joint of high cost and according to published data, enjoys only 42% axial strength, relative to the pipe wall.

Standard API non-upset tubing connections comprise couplings having outer diameters considerably larger than the pipe outer diameter but still enjoy only about 42% efficiency as above. API does list a "turned down" collar outer diameter to increase clearance between strings however, the turned down diameter still exceeds substantially, the pipe outer diameter.

No prior art discloses a flush-joint tubular connection having tapered threads, that when properly assembled, effects optimum stresses within the small end of the external thread and within the large end of the internal thread so as to provide a connection of maximum efficiency, Conventional pipe connections have thieads formed wim like tapera and resiilt diametrical interference along the taper between the external and internal threads, thereby causing excessive stresses or requiring increased wall tlήckness at the end of the pipe. Excessive stresses reduce the joint strength and an increased wall thickness rules out a flush-joint connection.

It is therefore clear that a flush-joint connection having a high efficiency as provided by the instant invention is needed for use within oilwells arid other pipe assembties wherein radial clearance is limited.

Standard pipe threads as well as API threaded cαnnectic*ns have such a tendency to cross- thread that "stabbing-guides" are often used at a considerable cost of time and expense. Such threads have an extremely shallow stab depth and a relatively large thread depth, both of which add to the cross-thread problem. Perfect alignment is difficult to attain under normal field conditions and often impossible to attain under difficult conditions. Premium connections such as disclosed by Stone in U.S. Patent 1,932,427 require even closer alignment to stab because of the close fit of straight threads and the "pin-nose" seal 32, which is highly susceptible to damage. To applicants belief, no prior art comprised the combination of a deep stab, thread height and thread diameter as required to provide a tajered threaded cc^ without the possibility of cross-threading. By way of example, a 2-3/8" EU 8Rd API tubing thread has a 2.473" pin end τnaτiτnιιm diameter and a 2.437" box bore at the first thread, which allows no entry of the pin into the box thread when at stab position. The counterbore of the box allows

entry of the pin only 0.446" afibrding at best, axial ahgnment but no angular alignment, so six degrees of angular misalignment will allow it to cross-thread.

About 1940, API changed from ION threads to 8Rd threads and a substantial improvement resulted, because less galling occurred during makeup of the threads. It was then commonly assumed "that any thread finer than 8 threads per inch would gaU and cross-thread", and that myth persists today. However, the improvement resulted almost entirely from the be^ form, eliminating sharp edge N threads. The present inveαticsi with threads as fine as 20 per inch, run last and smooth without cross-threading, and it has omer features as we

Conventional near-flush connections mentioned above, have two-step box straight threads formed within swaged-out ends and pin threads formed on swaged-in ends. Such swaged ends comprise a single tapered zone extending axially lrom the mpe body of crigind pipe diameters having a mean conical angle of taper of approximately two degrees. Typically, such swaged connections are rated by their suppliers as having frcπn 50% to 75% on wall thickness, and with a variety of fluid pressure ratings. Such a swaged connection when compared to a 42% conventional flush-joint connection, has improved strength, but at fte expense o dearance.

To applicants best knowledge and belief, all such swaged connections now on the market are swaged to form only the degree of taper that approximates the lay of the threads to be formed thereto. Typically, before a thread is machined in the tapered zone, a clean-up cut is made to assure there being enough metal to fully form the threads. Unforturately, εroch a cut rec ces the cross-section area of the tapered zone which limits connection efficiency. Additionally, production machining allows for only approximate axial positioning of the pipe in the machine prior to gripping the pipe in the chuck and such approximation can cause further thinning of the tapered zone. Thirdly, if first measurement of a freshly cut thread indicates that a thread recut is required, men the swage must be cut off and the end reswaged before even a 75% thread could be cut at that end. Therefore, in addition to the basic disadvantages of a two-stφ thread having a pin nose seal, it is now even more clear wiry suppliers of pipe threads that are formed on swaged ends cannot provide a family of pipe connections with efficiencies greater than 75%.

Applicants U.S. Patent 4,813,717 which is in the line of priority of the present application, discloses a connection with selective effidency between 75% and 100% for non-upset pipe using a coupling in one embodiment per claims 1-17 and an integral comiectim m another <<^^ per claims 18-19. The present invention is complimentary to said patent and teaches configurations for connections having swaged ends. To applicants best knowledge and belief, no

non-upset integral connection is cuπeirtfyavaihbte that witt meet t^

For users who prefer integral non-upset pipe connections, there is deaify a need for one with an efficiency suffident to meet the strain design criteria defined above.

For purposes of this application, I define as follows: "pin" is an externally threaded end portion of a tubular member, "box" is an internally threaded end portion of a connecting member, "flank angle" is the angle measured between a thread flank profile and the tubular axis; "included angle" is the angle measured between the flanks, in the space between the flanl surfaces; "dope" is a pipe thread compound such as specified in API 5 A2 that has been developed for 8Rd threads over many years to have an optimum combination of selected greases mixed with solid particles of specific dimension and nature so as to provide most desirable characteristics for sealing, lubricating and brushing over a substantial range of service temperatures and pressures. "Gap" is a distance that may exist between mating tliread sur-faces when they are positioned in best mating contact with each other, the distance being measured perpendicular to the surfaces.

The pipe thread form most widely used is the old "sharp-V", having a 60 degree included angle as specified in ANSI B2.1 for AMERICAN NATIONAL STANDARD TAPER PIPE

THREADS and in API SB Table 2.8 for API LINE PIPE THREADS. Although ANSI B2.1 shows thread sizes up to 24" and API 5B shows thread sizes up to 20", sizes above 4-1 2" are seldom used because: their high make-up torque makes field assembly impractical; such threads are very prone to handling damage; they frequently leak, loosen or break and are difficult to stab. Shaip-V threads are restricted to very low pressure services by govemrnent and indu∑rtry codes such as API & ASME, who require the use of other connections such as flanged or welded, when dangerous fluids are to be contained. In addition to problems cited above, Sharp-N threads often tear and gall during makeup which can cause excessive torque and worse, such as dangerous and costly leakage of fluid from within the pipe at some unpredictable time in the future. In an effort to solve such problems and because there is no reasonable alternative to the use of threaded pipe connections for downhole use in oil and gas wells, API adopted about 1940, the 8Rd form shown in API 5B Table 2.9 which has 8 threads per inch and an included angle of 6O degrees, the flanks being connected by rounded roots and crests formed with radii of 0.017" and 0.020" respectively. Although thread tearing and galling 60 degree included angle still allowed axial and bending loads to cause loosening, leakage and IhenpuUout of a connection. For many 8Rd connections, pullout deteπnines the parting load, and leaks may occur at much lesser loads. The δRd thread form without regard to pipe strength is limited to only 5,000 psi service by API 5A due to such weaknesses. Both sharp-N and 8Rd form standards specify

intentional mis-matohes between crest and root radii of mating threads like other conventional threads known to applicant which in turn, acts to increase the root gaps, which within their tolerances, ranges from 0.005" to 0.011" for sharp-N and from 0.003" to 0.008" for 8Rd even after the mating flanks are wedged tcgether at fuUi-αakeυpw ch allows dcpe to leak through gap. As makeup begins, the root gap substantially equals me flank gaps as dictated by the 60 degree included angle whereupon, solid particles in the dope extrude helically from between mating flanks and out of the cc∞ectio as easifyas it fiows fπxntl-βrort Thus, flanks wedge against each other with virtually no solid lubrication retained between them, which greai^ increases galling tendency. The coefficient of friction with just grease is 0.084 vs 0.021 with the solid lubricants, which can increase torque by a factor of four. It is now clear how the root- gap/flank-gap ratio can affect torque.

To reduce thread pullout, API adopted many years ago, the "BUTTRESS THREAD FORM" depicted in API 5B Figs 2.5 & 2.6 for use on casing strings. The 87 degree tension flank angle greatly reduced tendency of pullout and an 80 degree cc pression flank angle reduced to a lesser extent, tendency for axial loads to jump the pin mto or out ofthe box. However, such improvements were traded for a loss of sealing ability, a loss of rigidity and a cost increase as compared to API 8Rd threads. The buttress form has marry more dime∞ions to ccmrol than does the 8Rd form which in turn, increases tolerance stack-up and results in flank gaps of 0.002" to 0.008". Even if a low pressure seal is formed an makeup, exteπial loads imposed on such a , connection cause end play between the mating flanks which extiυdes dope to cause loosening and leakage of the connection, particularly after vlhe dope has had time to dry. Such end-play was felt tobe necessary by the mdustry experts on API Committee 5B, to prevent extreme torque and galling if 'Svεdging" between the 13 degree induded angle was allowed however, not obvious to them were the ill effects on connection rigidity and sealabiliry that they incuπed by the change. As a result, whm good scalability, the operator must use more expensive "pin nose type connections" that do not seal on the threads.

My force vector analysis for flank-wedging mating threads having no ιτx>t-crest contact, shows unit fiictional resisting force: F = f(P)(l/sin T + 1/sin C) / (1 tan T + 1/tan C) where: flank angle. WhenT = C then this equation reduces to F = fζPy∞s C, the conventional fomiulas f^ pages 3-28 and 3-29 of Marks Standard Handbook For Mechanical Engineers, 8th ed, which is correct when dope is allowed to extrude easily from between the load bearing sui-faces. Marie shows "sin" instead of "cos" because that angle is referenced 90 degrees from mine. Since both sharp-N and 8Rd threads have flank angles of 60 degrees, their torque is proportional to F = 2(f)(P) when calculated in accord with conventional practice. API Committee 5B evidently thought that if they allowed flanks of the Buttress form to wedge like the 8Rd fbπn, that torque would be pro torque for the sharp-N or δRdform, and out of range for practical use. However, since API Buttress threads do not wedge, then F = (f)(P) = 0.084 P. .API Bulletin 5C3 entitled FORMULAS AND CALCULAΗONS FOR CASING, TUBING, DRILLPffE AND LINEPIPE PROPERTIES gives many formulas, but does not give a foπnuk for torque because their test results were so erratic. The reason why API 8Rd Connections have erratic torque is because a first connection may have large root gaps that will prematurely extrude dope, resulting in high torque and leakage while the next one may have small root gaps and much lower torque. However, a well may have hundreds of threaded connections and only one leaking connection can result in disaster. Pattersons connection disclosed in US Patent 4,508,375 may have a more consistent torque than 8Rd, but because he does not wedge flanks, end-play will cause it to loosen and leak when it is subjected to repeated service loads. For many years, thread experts all over the world have used API 8Rd, Buttress and Pattersons threads, but none have recognized features and advantages of the present invention. The API Buttress thread for allows <dope to extruαe i-hroughgar^ between the flan a which allow 0.002" to 0.008" end-play after full makeup. Even if Patterson's root gaps are reduced to between 0.002" and 0.004", per US Patent 4,508,375 to Patterson, end-play will still occur when external loadings are imposed to cause loosening, extrusion and leakage at some unknown time later. Patterson also evidently knew that wedging of his threads would cause extreme torque, as evidenced by bis 0.002" m ni um gap allowed between flanks to prevent wedging. Had the API Committee or Patterson recognized advantages of the present invention, they could have solved their loosening, leakage and torque problems.

API Specification 5CT on Tubular Specifications states in Paragraph 5.19(a), "Pipe test pressure shall be held for not less than five seconds" which tests the pipe wall strength but does not test thread sealability because, it may take more than an hour for pipe dope to extrude through the thread gaps to prove a leak whereas, the required s<ervice life is generalfy between five and fifty years. Therefore, many casing connections are now on tlie market claiming high strength, good sealability and or reasonable torque, but they use a separate pin-nose seal in addition to threads for holding the pin-nose seal together, which increases susceptibility to damage and increases cost, which in turn, prohibits their use for most applications. The resulting failures of pipe connections in deep wells increases rework costs, energy loss, danger to the pubhc and damage to the environment

The manufacture and use of large diameter pipe connections presents several problems not encountered with small connections. Handling damage is much more probable and much more costly. Reimert US Patent 4,429,904 discloses a large diameter welded-on connection having special form Buttress threads that neither wedge nor seal. The O-ring 76 and stop shoulder 73 are mounted with a welded-on tubular member of increased diaineter and radial tlnckneas, at a great increase in cost. A reliable connection formed within dimensions of the pipe would save time, energy, cost and the uncertainty of weld quality. Reimert also reduces torque by preventing wedging ofthe thread flanks as shown in Figure 9, but at a very high price. He also provides a seal separate from the threads by means of an O-ring and a pin-nose, but a seal that will degrade with time and that is not retrievable with the pin to the surface ofthe ocean.

Many patents such as US Patent 2,094,492 to Janta and US Patent 2,196,966 to Hammer disclose high angle tension flanks to wedge in cooperation with low angle compression flanks so as to keep torque within useable range. However, low compression flank angles sacrifice compressive strength of the conriecticαi which tends to cause loosening and leakage if subjected to ∞mpressive or bending loads. Others such as

Patterson have high flank angles for both tension and con-φressiσn, but do not allow wedging of the flanks that is necessary to prevent loosening and leakage.

Therefore, industry is dearly in need of a threaded pipe connection having low torque that stabs easily, that will seal reliably and does not loosen when service loads are imposed upon it.

DISCLOSURE OF THE INVENTION

The present invention provides a tubular ∞nnectionl ^joints ofplamerid pipe or the like, having a first tubular member formed with tapered external threads and a second tubular member formed with tapered internal lihreads for sealing cooperation with the extend So as to avoid the thread pullout tendency inherent in a non-upset threaded pipe connection fbr^ conventional 60 degree thread flank angles with resped to the tubular axis, a thread form is provided that has a flank angle of at least 75 degrees w m respect to the tabular axis, tto angle depending on such factors as the pipe diameter, the wall thickness and the material strength

As taught by my series of patents beginning with US Patent 2,766,829 which have enjoyed worldwide commercial success for over thirty nuclear industry, the taper ofthe external thread may be i mied at a lesser angtem taper of the internal thread so as to ensure a maximum primary sealing tendency at the smallest pressure area an an in mmimira the a-rial load i pnβerl nn the cnnrtectinn due in internal fluid pmnmim Th _* ? present invention may utilize this feature in combination with other features. With this feature, initial thread engagement occurs on the external thread at the smaU diameter end only, simultaneously as a radially spaced relationship exists between internal and external threads elsewhere. As the connection is tightened toward fuU makeup, thread conta incaeases progressively from the small diameter end toward the large diameter end of the threads. The threads may be dimensioned such that at mil makeup, the threads at the large diameter end are in contact also.

The use of flank angles that reduce pullout tendency also allows the use of a lesser thread depth than would be practical with the use of conventional 60 degree flanks. In turn, the lesser thread depth allows for a higher connection efficiency because a smaller portion ofthe pipe wall is removed to form the thread and thereby, a higher connection efficiency is possible for a flush or near-flush connection.

Machines to swage pipe sizes over 10" are very expensive and fewer large connections are threaded per run, so the cost usually prevents serious consideration of swaging large pipe connections. Yet the need for swaged ccrmections several feet in diameter exists for such uses as on drive pipe, for pipe lines, etc. Also a less expensive swaged pipe connection than is now available is needed in smaller sizes for some uses.

For these and other reasons, the present mveution discloses a self-swaging co ^ tapered mating threads of desired dimensions that can be formed on plain end pipe where upon make-up, the internally threaded box expands and tlie externalfytlHeaded pin contra

predetermined limits, so as to provide a swaged connection of high efficiency. Before assembly of the connection, the threads are dinjiβnsioned such that: the box wafl ia thinner t^ pin wall by a predetermined amount at the large end of thread engagemem; the box wall is tMckerm wall by a predeteπnined amount at the small diameter end ofthread engagement; tire box and pin walls are substantially equal in strength in a plane intømedkte tit^ large dian-4etereaod and the small diameter end.

Thread dimensions are selected such that upon full make-up ofthe connection: toward the large thread diameter end, the box wall will expand to predetermined dimensions; towari small thread diameter end, the pin wall will coπtra to predetermined dimensions will expand about the same amount that the pin waU contracts at the plane of equd strerigth; to thereby effect sealing engagement ofthe threads along their full length of engagement

By way of example, the outer box diameter may be swaged larger than the original pipe diameter by an amount equal to twice the radial thread depth so as to provide effect a connection effidency of approximately 90%, or by an amount equal to four times the rad thread depth to effect 100% efficiency. Within reasonable design parameters, the ratio of plastic to elastic deformation effected will decrease witk thread depm decrease; pipe diametOT material yield strength increase, hi a connection of 100% effidency, the pin lace bore will contract about the same amount that the box face OD will expand.

After assembly, the threads will lie along a generaJfyste<j$er toper 1han the te machined on The thre s must he dimensioned hefore their assembly such that when the hoτ and pin are assembled to the hand-tight position, there is a predetermined number of turns to the position of full make-up so the angle of taper can effect the desired amount of swaging ofthe box and pin as they are tightened to a position of full-makeup. The threads may be machined with a single taper or on various taper combinations without departing from the spirit of the preε^ invention.

Such desired dimensions may effect: face widths ofthe box and pin sufficient to prevent jumpout of the threads when under axial loads; suffident length oftliread engagement to ensure a fluid seal a cross section wall area at the last engaged thread of the box and of the pin to allow a selective connectiαn efficiency between 50% and 100%. For services that can accept an efficiency less than 100% for instance, the resulting bore through the connective box outermost diameter can be decreased by tightening the connection a lesser riumber of turns past the hand-tight position than is necessary for a 100% connection.

Such self-swaging will usually be mostly plastic and partially elastic. However, for very large diameter pipes with thin walls and high yield strengths, the swage could be fully elastic. Per inch of diameter, all connections will have a an elastic return equal to: the yield strength ofthe material divided by its modulas of elasticity. The remainder ofthe swage will be in the plastic range, and the pipe will not return.

Some services require pipe connections having higl<er bending and or coπ.<jxession strengths than normal service, such as for use with drive-pψe and marine risen used on oflshore provide such strengths, the thread form stab flank angle ofthe present invention may be increased as required and also, the taper angle of the thread cone may be reduced to increase the length of engaged threads within existing diameter constraints.

The present invention provides a high efficiency threaded connection for tubular members for easy assembly with the use of pipe dope at relatively low torque, that seals reliably between the mating threads and provides fiπnstι«ng again-rt repeated mechanical shodc loadings without loosening, leaking or failure. A preferred embodiment is described below: The ccwiection lias a pin and box with noting threads for assembly with pipe dope and is formed wi 83 degree compressicmflaiά angles and 83 degree tension flank angles, the temion and compression root formed with like radii positioned tangent with the flanks they connect, a radial thr^ equal to two-thirds ofthe axial thread pitch, box and pin thread forms being formed sufficiently ccmplementary to each other such that no gaps wider than 0.006" mtiy exist upon makeup ofthe connection, but in no case is a gap allowed having an inscribed circle diameter greater than the quantity: 0.33 (L)/psi where L = inches of helical engaged thread length psi = service pressure.

I have discovered that API dope will readily <Bxtrυde through gaps greater than 0.006" because the solid particles are too small to be clamped by the thread surfaces, so they flow along the helix entrained in the grease. Such flow is in accord with the laws ofRheology and is therefore slow and will often give a short time indication of a seal. However, water pressure may days later, push out the dope and cause a leak. Gas pressure may channel through the dope in a matter of minutes. I have also found that threads having lesser gaps less than 0.006" will clamp the particles and then extrude grease from between the particles while compressing those particles to a thickness range between 0.006" and 0.0007" depending on the specific interface pressure of a connection. Therefore, it is now clear, that to reliably and permanently seal between mating threads with API dope, there must not be a gap greater than 0.006"; and that simultaneously, the

mating thread surfaces must not be required to compact solid particles to less than 0.0007" thickness in order to reduce larger gaps to less than 0.006".

API 8Rd and Buttress threads have erratic torque because they allow gaps greater, and allow gaps less than 0.006". One such connection may extrude dope prematurely and the next may retain dope late enough during makeup such that torque is much less.

All during makeup of a connection of this preferred embodiment, the root gap will be approximately four times as great as the combined flank gaps and therefore, as make-up begins, the dope will slowly flow from between the flanks into e much larger root gaps lea vu^ solid particles gripped between the flanks, as compared to fast helical flow along root gaps that toads to carry solid particles out of the connection. Shαrffy before reaching the position of makeup, such flow will be slowed by reduction in size of the root gap to less than 0.006" but will continue, while exerting 93% of the radial fluid dope pressure against crests and roots and thereby bold flanks out of mating contact, as the widest flank gap is reduced toward 0.0007", makeup being finally stopped by compression of solid particles to a thickness suffident to firmly support and seal between wedged mating flanks. Ifthe axis is positioned vertically during a∑isembly, the mating compression flanks may be held in contact during by weigm of the pm member which may wipe them substantially clear of solid particles, but a layer of solid particles toward 0.0007" thick for example, may trap between tension flanks and such as a 0.003" layer may be trapped in root gaps, as dictated by geometry of the included angle and the precisely cCjQLψlimentary forms of mating threads. Should the axis be positioned horizontally during makeup, then a 0.0007" layer of solid particles may be trapped between all flanks in which case, the layer of dope that is trapped in root gaps may be toward 0.006". either case, the solid particles cannot flow from between the mating threads after makeup because they are squeezed all along the helical length ofthe root gaps and are held in there against fluid pressure. Likewise, no end play can occur between the box ar pmbe∞use the sohd particles are packed fim-fy to a tlύckness sufficient to support loads between wedged mating flanks. No thread wedging can occur during makeup because crests aid axial thread length and they ride against solid lubricants, holding flanks out of wedging contact with each other. Near the final stage of makeup, solid particles are compressed in the root gaps to a thickness between 0.006" and 0.003" as the high angle flanks compress particles toward a

0.0007" thickness. Immediately before wedging of flanks at makeup position, F=0.021(P) which is suprisingly lower than "F" values for 8Rd and buttress threads above. Then, after wedging, F = flP) cos(83) = 0.172CP) .

Makeup progressively reduces the gaps, increasing pressure on the dope which slowly squeezes grease from the small flank gaps to the much larger root gaps and thence along the thread helix. Only at full makeup will the flanks wedge with solid particles therebetween to desirably signal full makeup position by an abrupt increase in torque, without the use of a torque shoulder. This feature is of great advantage for an integral connection cut on non-upset pipe, where no shoulder can be formed thereon without removal of some ofthe pipe waU that greatly reduces connection efficiency.

Although I believe the 83 degree flank angles of the prefeπed embodiment to be good for general use when using API dope, other combinations of flank angles having a fourteen degree included angle may be of advantage for certain uses. For instance, if a compression flank angle of 90 degrees is desired for a particular service, then a tension flank angle of 76 degrees in combination, would effect similar torque and sealability, when using API dope. Should other dope formulations be desirable for specific uses, then the theoretical included angle may be approximated by use of my formula as follows: Angle = 2 x aιcsin( mfn thickness that dope will compact) / (max. gap dope will seal)

The angle calculated by this formula for threads using dope formulated with particles in accord with API 5A2 1982, is 13.4 degrees. To allow for a reasonable tolerance, I chose 14 degrees for the preferred embodiment which results in a reliable high pressure gas seal and a torque of approximately 1 8 that for conventional threads such as 8Rd, were they formed with the same included angle. Selection of an angle just greater than 13.4 provides maximum strength against axial loads. The torque advantage ofthe preferred embodiment over conventional threads reduces as the included angle increases toward 60 degrees. It should be understood that neither API Buttress nor Pattersons thread can effect such favorable characteristics, because flanks do not wedge to prevent relative motion between the box and pin, wluch allows their lc sening and leakage.

So as to hold mating threads ofthe present invention in firm mutual contact against relative movement during service against relative movement that may be urged by service loads, the box and pin should be dimensioned suffidenuy to induce preloaded circumferential stresses in the box and pin that are greater than any such stresses that could be iriduced by any combination of loads within rated capacity. The 83 degree flank angles help to meet this need as explained, without the use of "hook" threads having negative flank angles to reduce pullout tendency. Such hook threads present marry problems in their πianufacture and quality control, that result in poor sealing reliability and excessive costs.

API 8Rd threads wedge on their flanks but the crest length is only 28% of the axial pitch length, and the root gap is too large to retain dope during assembly sufficiently to hold flanks out ofpremature wedging contact. Buttress threads such as API and Patterson forms have small enough root gaps and broad crests but do not wedge at full makeup which allows end-play, which loosens the connection. To operate in accord with the present invention, the axial length ofthe crest must be substantially the same as axial root length, within close limits as defined below: N = the minimum thickness that solid particles in the dope can be compressed by the threads S = maximum thread gap the particles will seal. T = the tension flank angle as measured from the axis. C = the compression flank angle as measured from the axis.

Phis Tolerance = [ (S -N cosT) /tanT] + [(S -N cosQ /tanC] - N (sinT + sinCT) Minus Tolerance = N [sinT - (1 - cosT) /tanT + sinC - (1 - cosC) / tanC] Using API dope, N = 0.0007"; S == 0.006"; T = 87 deg; C = 80 deg; then tolerance far API and Patteraon Buttress threads are: +0.0000"; -0.0012". Thus, another reason is now obvious why API and Patterson Buttress threads will not operate in accord wim the present invent they allow up to 0.008" and 0.004" end play respectively. The length ofthe crest or root, is the axial distance between the tangent points on the flanto they connect, the prefe^^ 33% to 46-1/2% ofthe axial thread pitch.

16

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1. depicts a vertical section of a ccr ectcr in accord with the mvention

Figure 2. iflustrates a thread foπnm accord wim

Figure 3. illustrates a thread form in accord with conventional ∞nnections.

Figure 4. depicts an embodiment of the invention that provides a shoulder abutment on makeup

Figure 5. depicts a fragmentary section of a connection m accord with the present invent when hand-tight

Figure 6. depicts a connection of Figure 5, at a make-up position to effect a high-efficiency connection.

Figure 7. depicts the connection of Figure 5, at a make-up position to effect a full strength connection.

Figure 8. depicts a fragmentary section from Figure 4 of a pin thread ofthe present invention.

Figure 9. depicts the pin thread of Figure 8 upon initial contact with the mating box thread.

Figure 10. depicts the box and pin threads of Figure 8 when partially made up.

Figure ll. depictø fufyniade up threads ofthe presert

Figure 12. depicts a thread foπn having gaps, flank angles and crest lengths, and conformity in accord with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 depicts tubular connection shown ge∞rafy at 20 comprising coupling 2 with tapered external threads 3 formed an an upper portion and having like threads 4 formed on a lower portion, so as to mate in sealing engagement with tapered internal threads 6 and 7 formed within joints of non-upset tubing 8 and 9 respectively, to be connected.

Coupling 2 may comprise inner diameter 10, upper end surface 11 and lower end surface 12, said end surfaces not extending for the full length of intemd threads 6 and 7. Such a connection as limited by the tension area resulting between the root diameter of the last engaged thn^ 12, and the tubing outer diameter, may provide an axial tension straogm m excess ofthree fourths of the pipe wall strength, effecting an efficiency greater than 75%

Should a connection of higher strength be required, coupling 2 n_ay be foπned wi^ diameter as at 13, upper end surface as at 14 and lower end surface as at 15. The coupling thereby extending for substantially the full effective length of the internal threads so as to provide a connection having an axial strength substantialty equal to the pipe waU strength to thereby approach 100% efficiency.

Since typical tubing joints have lengths of sixty times or more the lengths of couplings that connect them, the couplings may be formed of material much stronger than the material the joints are formed of without causing significant increase of cost for the entire string. The use of higher strength material for the coupling 2 provides a ltighβr axial strength for tlie the strength ofthe coupling neck section 16 is increased and because, collapse resistance ofthe pipe end as at 12 is increased to thereby increase the r^out strength also. To further increase the pullout strength ofthe connection, a thread form having a load bearing flank 30 formed at 75 degrees with respect to the tubular axis as depicted in Figure 2, may be used lor the mating threads as opposed to the most common thread fo<mι used on oflweUtubulara, depicted in Figure 3. The form ofFigure 3 has a load bearing flank 25 which effects an angle of 60 degrees with the tubing axis. Assuming an angle of friction of 5 degrees, elementary vector analysis will show that the form depicted in Figure 2 results in a pullout strength 2-1 2 times that ofFigure 3. Reduction of the flank angle still further, can virtually eliminate tendency to pullout.

So as to ensure a seal diameter for the connection of least diameter and therefore the least axial fluid load, the taper ofthe external thread may be made slightly less than the taper of the internal thread. Such a condition also allows maximum radial compression ofthe coupling as at end surface 12 adjacent pipe wall as at 17 which may be formed thicker than the adjacent coupling wall. Thus, upon makeup, end 12 will compress more than wall 17 expands due to the

diifererice in thicknesses, the mo Since coupling 2 may be made of higher strength material than tubing joints 8 or 9, the thicknesses may be dimensioned such that stresses in walls at 12 and 17 are more nearly at the same percentage of the yield strength ofthe materials of which the members are formed. When the taper ofthe external thread is made less than the taper ofthe internal thread, initial ccntectbetv^enthetwo occurs c^atthe srij.all en as at 12 with the internal thread as at 17. Upon continued makeup, thread contact progresses toward the larger end ofthe tapers to cause full engagement ofthe threads as at 18. A slight amount of further makeup may cause a predetermined magnitude of circumferential stress within the end ofthe tubing joint as at 18 and thereby establish a position of full makeup, so as to cause: compressive circumferential stresses within end 12 to be at a first desired value, simultaneously with tension circ tnferential stresses within the tubing joint wall between 17 and 18 being at a second desired value, less in magnitude than said first value. Said values maybe set at the same percentage ofthe unit yield strengths of the respective materials to thereby effect a maximum strength for the connection. Connection 20 may comprise shoulder 18 formed on the end of joint 9 and shoulder 19 formed on coupling 2 intermediate thread 4 and the outer diameter 21 of coupling 2. The mating threads may be dimensi∞ed so as to makeup as shown in Figure 1 or should greater bending and compression strength or greater tortional strength be desired, the mating threads may be dimensioned and given closer tolerances so as to allow shoulders 18 and 19 to abut upon makeup. Figure -t Harriets a preferred bore configuration tor the pin end which can include m inmtm bore diameter extending to the pin neck as at 13 and an outwardly tapering bore extending therefrom to the pin end as at 53 which is sufficiently larger than bore 13 so as not to restrict bore 13 upon contraction of bore 53 upon makeup ofthe connection. This preferred pin configuration may be formed on each end of a coupling and it may also be formed on the end of a pipe joint that has been swaged-down so as to provide for bore 13 be in smaUer than the liominal pipe bore.

Figure 5 depicts a self-swaging tubular connection ofthe present invention in the hand-tight position, comprising pipe joint 60 Jbrmed wi tepered pin thread 62 and piipe joint 61 having tapered box thread 63 formed for sealing cooperation wim pin thread 62 as later described. Box thread root diameter 64 at box face 65 is preferably dimensioned such that the radial with 67 of face 65 is not less than radial thread depth 68 positioned between root diameter 64 and box thread crest diameter 69 to prevent premature "jvπnp-out" of the threads under t<iaιsik loading. Likewise, it is preferred that radial width 70 of pin face 71 not be less than depth 68 for the same reason.

Box thread taper 72, should be slow enough to provide a sufficient length of box thread 63 to prevent thread jumpout, in cooperation with the thread load flank angle depicted in Figure 2.

If the root diameter of the pin thread extends sυbstaritialfy to the outer diameter ofthe pip^ at 73 as is well known in the manufacture of collar type connections, and if me root diameter of the box thread extends to the bore ofthe pipe as at 74 taught by my U.S. Patent 4,813,717 in the line of priority for the present application, then a high strength self-swaging connection is now apparent.

For services where a full-strength connection is not required and a mavimnm bore is desired, the connection may be made-up as depicted in Figure 6. Upon such make-up, box wall 74 toward the large diameter end ofthread engagement at face 65, is thinner than adjacent wall 75 and therefore, box wall 74 is swaged outwardly by pin wall 75 to a predetermined outer box diameter 79. Likewise, pin wall 76 toward the small diameter end ofthread engagement at face 71, is thinner than adjacent box wall 77 and pin wall 76 is swaged in by box waU 77 to bore dimension 78 predetermined by both the box and pin thread dimensiom and the make-up position. At plane of equal strength 80, axially positioned intern_u9diate &ces 65 and 71, the outwardty swaging of box wall portion 81 is substantially equal to tlie iπwardty swaging ofpin wall 82. Because both the box and pin wall are stressed triaxialfy when under tension, it is an important feature ofthe present invention that the degree of swaging in both walls decreases as the axial load transfers from the mating thread. In further explanation, wall 74 has received a greater degree of swaging and therefore more tangential stress than wafl 77 but does not cany as much a-tial stress.

Conversely, wall 77 can carry a higher axial stress because it does not carry as much tangential stress.

Fen: services where a full strength connection is required and a smaller bore is acceptable, the connection may be made up as depicted in Figure 7 whereupon, box outer diameter 90 has been swaged larger than diameter 79 and bore 91 has been swaged smaller than bore 78. It is now apparent that pin wall 92 at the last engaged pin thread and box wall 93 at the last engaged box thread are substantial the same as the nominal pipe wall 94 to thereby effect a full-strength connection.

As taught by the above identified patent, the use of thread forms having minimum thread depths and high load flank angles with respect to the tubular axis, facJli es the Junctions of clearance and efficiency for flush and near-flush connections. Such features may be used in combination with the present invention to add new features such as, reducing tlie d^ree of swaging required to attain a desired face widt

Upon review of these disclosures, it is now apparent that an integral, full strength swaged connection can be formed with plain end pipe without need for upsetting or swaging prior to threading of the pipe ends. The portion ofthe swage that is elastic equals the pipe diameter multiplied by the yield stress, divided by the modulas of elasticity. The rest ofthe swage is plastic. The present invention may be used for a wide range of services arid it may be desirable to varythe amount ofmakeup to suit each service. One API Standard allows for 3% cold work of tubular goods, with regard to cold swaging before threading, so tl t may be a practic limit of this connection for such API services. Anexaπφlewith sucha hnώ is as foUows: A 30" O_D. pipe with a 1" wall and a radial thread depth of 0.133" requires a full strength connection; then 4 x 0.133 = 0.532" = the amount of swage required; 0.532/30 = 0.0177" which is 1.77%; since 1.77% is less than 3% then the connection would be acceptable.

Many tubular connections have only half as much strength under axial compression loads as they have under axial tension loads. A connection that is derated in compression will have approximately that same derating in bending. So as to adapt a connection in accord with the present invention to any desired compression rating up to 100%, the steb flank angle 24 depicted in Figure 2 may be adjusted as required without departing from the spirit of the present invention. The thread form depicted in Figure 2 may be used with the present invention wherein angle 22 formed between load flank 30 and stab flank 24 is at least twice the angle of friction between the box and pin materials, so as to prevent lockup of the box and pin threads with each other due to the high interface pressures generated by the radial during makeup.

Figures 8-11 depict a fragmentary section of a preferred embodiment ofthe thread form ofthe present invention through four stages ofmakeup, enlarged from a connection as at 50 in Figure 4. However, it should be understood that these features may be used to advantage with other embodiments without departing from the spirit of my invention.

Pin member 31 formed with tapered pin threads shown generally in Figure 8 at 32 comprise: tension flanks 33 and compression flanks 34 formed at 83 degrees relative to tubular axis 35; root 36 foπnedwim a radius tangent to flanks 33 ai d 34 as at 29 and 37 respectively; crest 38 formed with a radius of equal dimension to the root radius, tangent to flanks 33 and 34 as at 39 and 40 respectively, induded angle 41 dimensioned as fourteen degrees between the -surfaces of flanks 33 and 34.

Figure 9 depicts first contact of tapered pin threads 32 with tapered box threads 42, formed complimentary to pin threads 32 with no intended root gaps. After pin member 31 has been

axially positioned vertically without rotation into box member 45 such that crests 38 will pass box thread crests 48 as along vertical line 56 no further but will make circumferential contact with crest 48 as at 47, it will thereby establish "stab position" ofthe connectiαn whereafter, weight of the pin member will serve to maintai contact between the mating threads during makeup ofthe connection. Box threads 42 also comprise tension flanks 44 and compression flai 43 connected by roots and crests 46 and 48 respectively. A coating ofAPI thread dope 49 is slrøwn on pin threads 32 so as to lubricate between the threads during makeup and to seal between them as the threads become fully engaged

Figure 10 depicts the threads at an intermediate stage ofmakeup whereupon: pin thread flank 34 has gained an increased area of contact as at 51 with box thread flank 43, the flanks having shd along each other in response to rotation of the tapered pin threads into the tepered box threads; dope having been slowly squeezed radially from between flanks as at 55, to the pin root gap as at 52 and toward the box root gap as at 54, the slow flow allowing retention of solid particles between flanks 33 and 34 as dope flows helically along root gaps 52 and 54. As makeup continues, some ofthe solid particles are carried along root gaps until gaps 52 and 54 are reduced toward 0.006" after which, the flow slows due to a buildup of back-pressure as solid particles are then increasingly gripped between the roots and crests. While grease flowβ momentarily around the particles just before full makeup, the particles are firmly compacted as in Figure 11 to seal the gaps. It should be noted that gap 55 between flanks 33 and 34 is less than one-fourth the width of the root gaps at any stage ofmakeup, dictated by the 14 degree included angle and complimentary thread form.

Figure 11 depicts the position of full makeup of threads in accord with the preferred embodiment with the axis positioned vertically whereupon: the extremely high mechanical advantage afforded by 83 degrees flank angles has compressed solid particles to thicknesses towards 0.0007" in gap 55 to support high end loads and to 0.003" in gaps 52 and 54 to seal against extremely high fluid pressures. Since the mating threads are formed complimentary in each other without large root gaps such as allowed for 8Rd threads, the ratio of root-gaps / flank- gaps will be essentially constant at 4:1 , such that reasonable variations m formulation of the dope may slightly affect final dimensions in the gaps, but will not substantially affect strength, torque nor sealability.

Should the axis ofthe present invention be positioned horizontally during assembly, then toward a 0.0007" thick layer of solid particles may be trapped between both compression and tension mating flanks at full makeup ofthe connection whereupon, the root gaps may compress

solid particles to a thickness such as 0.006" to seal high fluid pressures when a sufficient helica length of threads exist and the threads are held in best mating contact against all service loads. In comparison to the present invention, even if API 8Rd threads had no ixitended root gap, their flank gap would equal the root gap when assembled horinnitalty arid would be twice the root gap when assembled vertically. Such a large flank gap during makeup allows a high rate of helical flow of dope from between the flanks which reduces retention of solid partides that are need for best lubrication between the flanks. Even at full makeup with the 8Rd flanks wedged, the root gaps may be as large as 0.011" which allows a continued iheological flow ofdope out of the connection to cause leakage, because the dope c»ιmot permanently seal such a gap. This explains one reason why 8Rd threads cannot be expected to hold high pressures, and the 60 degree flank angles allow mechanical loosening ofthe connection upon the application of mechanical loads.

My thread form may be combined with features presented earlier in the specification so as to provide low-torque threaded connections for non-upset pipe joints with effidencies as high as 100%, that do not loosen or leak even when heavy shock loadings are imposed, as mtiy occur when they are used for drive-pipe.

Thus, it is now clear that the present invention provides a thread form for high strength tubular connections that: will not loosen in response to external loads; that will effect a reliable long life seal between the threads; that can be easify assembled and madeupwi relatively low torque.

Although this low-torque, high-strength, reliable-sealing thread form is of greatest advantage when used for drive-pipe, it may also be used to advantage on connections depicted in Figures 1,4,5,6,7.and others that may need such advantage.

The exact thread form that must be used for the present invention extends onty to the requirements as stated by my formulas above, and the requirement for relativety complimentary thread forms as specified. The flank angles may be chosen for the service load on the tension flank or the compression flank first, without regard to my formulas, however, the second flank should chosen within limits of my formulas, as should the complimentary fit of mating threads. The crests may be arcuate, flat, or in between, so long as they are paraltel to the mating roots so as to stay within the ranges specified. For instance, Fig 12 depicts a buttress thread form made in accord with the present invention wherein, tl-© crest axial leiigthre tive to the axial root lengώ within limits of my formulas substantially, together with the gaps and complimentary requirements. The numbers are one-hundred higher than similar features shown in Fig 8-11.

Pin compression flank 134 is depicted as being loaded against box compression flank 143 with a first thickness of solid particles compressed therebetween as at 155. Box and pin tension flanks 144 and 133 respectively, compact soUd particles likewise. Pin root 136 cooperating with box crest 138 compress the dope to a thickness sufficient to seal between the threads. Crest length is measured axially between points 139 and 140 at which, the crest is tangent with the adjoining flanks. The root length is measured axially between points 129 and 137 at which, the root is tangent with adjoining flanks 133 and 134 respectively. It is necessary to maintain the crest length and the root length more nearly equal than does API or Patteraon, to gain the benefits of tl∞ present invention. After many years of use, such an importance of these lengths has not been obvious to practitioners all over the world.