CA1103430A - Pin and bell pipe joint and method of forming the same - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Mechanical pipe joints of the pin and bell variety, and methods of forming same, wherein the ends are pre-formed so as to permit a controlled interference fit upon joining and preferably provide a double seal against both internal and external pressure, the joints being particularly adapted for field-grade materials, aluminum members, and internally and externally coated members and being readily disengagable and re-formable without producing galling.

Description

BAC~(~ROUI~D OF THE I~lVE~IOl`T
-1. Field of the Invention ~ he present invention relates generally to methods of forming mechanic'al joints between lengths of pipe and more particularly to pipe of the type and quality typically utilized in oil field applications, such as gathering lines for distribution systems down-hole casing, and the like, and to the joints so formed. It is particularly adapted for joining materials heretofore considered highly difficult if not impossible to join mechanically with consistent reliability, namely, plain aluminum pipe and steel pipe.

2. Description of the Prior Art .
The literature contains many schemes for mechanically joining pipes, tubing and the li~:e, only a few of which have . proved actually'capable:of forming leak-free joints with oil--~ field ~aterials. One ~uch method known to be actually operative ,.
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is that disclosed in U. S. Patent llo. 3,20~,13G. Such patent discloses a pipe joining method consisting essentially of forming a bell on one pipe end, rolling an annular groove in another pipe end, and telescoping the latter into the former. Additionally, one or the other of the two surfaces was typically coated with a liquid lubricant-sealant prior to the joining of the pipes. Related U. S. Patent Mo. 3,210,102 discloses the coupling or joint essentially formed hy the above-described rnethod.
IJ. S. Patent~llo. 3,466,738 discloses a method of '' joining pipe consisting essentially of simply forcing together two pipe ends of like diameter, the only preparatory step being the slight flaring 03c one tip in order to permit the initial entry of the other. The amount of force and the time required to so join two such pi~e ends is many times greater than that required by the method of the present invention, and it is likely that galling of the parts can occur.
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'S'umrnary'of the I'nvention The present invention is directed to the formation o~ high integrity, reliable mechanical jolnts of the pin and bell variety. Although applicable to tubular elements of pre-cision manufacture and/or finishing, it is particularly appli-cable to tubular goods such as field-grade pipe, down-hole cas-ing, and 'che lil.e ~lich are subject to variation iIl dimensions and quality. It is also particularly well sui'ced for joining tubular goods heretofore considered highly difficult if not irnpossible to join mechanically with consistent reliability, namely, aluminum ancl steel pipe, and pipe which llas been coated both internally an~ externally. ~ddi~ionally, it is well suited for forming joints from elements coated with brittle material, and it permits the joining of externally-coated pipe without a subsequent "field joint."

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In accordance wi.th one ~road aspect,,the invention relates to a method of forming a pin end on a tubular member to be inserted in an Lnterference fit ~ithin a bell end of a tubular membe.r having an open end portion with a terminal end which is flared outwardl~ at a first angle with respect to the central axis of the tubular mem~er and with a lubricant sealant for filling the space between a pin end inserted into a bell end, the improvement for forming such a pin end for such a pin and bell interconnection comprising: forming an inwardly tapered portion on the terminal end of a pin end of a tubular mem~er at an angle of ten degrees with res'pect to the central axis of the pin end wheSe said ten degree angle is greater than a first angle of the flared portion of a bell end of a tubular member by at least six degrees; and forming an annular groove in the outer circumferential surface of said pin end as near to said tapered portion as practical so that said groove and inwardly tapered portion are capable of containing a lu~ricant sealant.

.. 20 - 2a -~ he invention involves pre-forming the ends of the pipe to be joined in such a manner as to permit a controlled "minimum interference fit" upon joining. One end is expanded, both elasticall~ and inelastically, into a bell-shaped configura-tion which has, after "snap-back" from expansion, a minir~ura interference dimension with respect to a pin having the rnaxir,1ur,~
.P.I. allowable devia~ions. An annular groove of desired configuration is preferably formed on the pin end as close as possible to the end-of the pin to act as a reservoir for a sealant and provide a secondary seal. The pin end is preferably coated with a lubricant-sealant for lubrication during the joining process. The leading portion of the end of pin is mechanically worked to a tapered configuration such that the bearing pressure between the pin and bell, upon engagement o* the pin with the hell is alwavs insufficient to producing galling.
The portion of the pin bevond the leading portion preferably is not wor};ed because the bell is sized to accornmodate the maximum expected variation in dimension of this portion. In certain other aspects of tlle present invention the location o- interior and exterior coating is controlled.
Alternate ernbodiments of the inven~ion, as well as the preferred form of the invention itself, will be More fully under~tood bv reference to the description below.

Brief Description of the Drawings ... . ... . _ .. ... _ _ _ _ FIG. 1 is an enlarged sectional view of bell and pin ends formed for joining plain or uncoated pipe, the dotted por-tion of which illustrates the position of the pin end after forma-tion of the joint.

FIG. 2 is a similarly enlarged sectional view of bell and pin ends formed for joining coated pipe, and illus-trates a preferred arrangernent for internal coating. FIG. 2a illus-trates the protection afforded the coating material duriny ini-tial contact by a misaligned pin member whereas FIG. 2b illus-trates the completed jolnt with the resultant deposits of sealant. FIG. 3A similarly depic~s the completed joint but illustrates a preferred arrangernent for external coating, and FI~J. 3B illustrates a joint with hoth internal and e~ternal coating.

Description of the Preferred Ernbodlments A preferred ernbodiment for joining plain, uncoated tubular elements, whether of "hard" material such as steel or of "soft" material such as aluminurn, is illustrated in FIG. 1.
In FIG. 1, the pin 10 is ~orced into the open end of the bell 11 to ~orm a joint as illustrated by the pin outlined in dashed line in FIG. 1. rrhe method employed to create the joint illustrated can best be understood by a step by~step explanation for a given siæe tubular element. In the case of American Petroleum Institute "Sc~edule 4~" steel pipe of nominal 4-1~2-inch outside diameter ~.D.), the norninal wall thickness is 0.237 inchr resulting in a nominal inside diameter (I.~.) of 4.026 inches. It is an ob-ject o~ the present invention to o~tain the "minimum interfer-ence ~it~' necessary to provide a strong joint while allowing for the rnaximum dimensional variation permitted by A.P.I. standards.
Maximurn grippirlg force between bell and pin, for rnost rnaterials, is typically obtained at internal stresses near the elastic limit; any amount of interference greater than that which pro~

~luces a practical maximum of gripping strength is not only un-necessary but actually undesirable. Such excess interference is unnecessary in that it produces little or no increase in ~age 4 .~ A.~ ~

grippin~ force, and is undesirable in that it both requires greater force for the subsequent joining operation and can prod1lce galling hetween the Materials being joined. The term "galling" as used herein refers to the effect of gouging a groove ~long the length of the pipe ends. The effect of "galling" is to permit leaks to occur when pressure is applied.
In accord with the present invention, a satisfactory 'Irninimum interference fit" for steel has been determined to be approximately 0.005 inch per inch of outside diameterqper 3p,000 pounds of minimum specified yield. Actually, the precise dimension is 0.002 inch rather than 0.005 but the 0.005l~figure compensates for miscellaneous irregularities which may be found in pipe. For a nominal 4.5-incl1 diameter pipe~, then, the minimum desired interference is 0.0225 inch. A.P.I.
standards on such pipe allow +0.75% variation. A 4.5-inch diarrleter pipe with A.P.I. standards may thus be encountered with outside diameter as small as 4.46625 inches (~.50-[0.0075 x

4.50]). ~hus, to allow for the minimum desired interference of 0.0225 inch~ the bell must be expanded such that its r~a~ximum I.D. after "snap~bac]" is approxirnately 4.~ inches (4.46~25-0.0225).
5uch sizing to obtain a "minimum interference fit" has ~een ound to satisfactorily accom~nodate pin ends of pipe with the maximum positive A.P.I. variation without significantly increasing the force re~uired for joining and while maintaining an adequate gripping force.
The relationship described al~ove may be expressed in restated form as ~ollows:
Max I.D. Bell = Min O.D. pin - 0.005X
where Max I.D. hell = "Snap-back" dimension in inches Min O. D. pin = Smallest pin O.D. in inches X = 11Ominal Pin O.D. in inches ~,r~

For aluminum pipe it is three tirnes the value of steel or 0.~15" because the modulus of elasticity of aluminum is three times that of steel.
The foregoing is usually su~ficient to permit lea~-free, strong joints to be formed between precision-made or pre-cision~formed elements, but such high quality workpieces are not ordinarily encountered in actual practice. ~lsol joints which are onl~7 "usually" leak-free are unacceptable in the pipeline industry, the needs of which demand a lea}~-free join-ing rate of virtually 100%. To consistently achieve the high degree of reliability with tubular elements of typical oil-field quality, it has proved desirable to perform a prelimi-nary forming operation on the pin 10. This is preferably accomplished by forming an annular groove 12 in the end of the pin 1~, preferably as near the terrninal end 13 of said pin 10 as conveniently obtainahl~e. ~he reason for this is that the hydraulic pressure tends to expand the bell and a more effective seal is obtained by bringing the groove as close as possible to the end of the pin. By applying a lubricating sealant to either the inner sur~ace 14 of the bell ll or to the outer surface 15 of the pin 10, the region about the groove 12 will serve as a reservoir for sealant and a secondary seal 16 after make-up of the joint. The sealant in the groove 12 does not significantly contribute to the mechanical strength of the joint hut does interdict any longitudinal interstitial voids whicll might otherwise, either singly or in combination, permit the joint to leak. Liheral application of the lubricating sealant will insure the filling of any macroscopic localized voids, such as between a localized flat spot on the pin end and the surroundinq ~ell. The groove 12 need not indent the inncr wall of the pin as illustrated but can be merely an indentation in the outer wall of the pipe.

In a preferred embodiment, the aforementioned groove 1~ is formed with a heveled annular relief portion 17 acljacent the sides of the groove. I)ependent upon the quality of the tubular goods to he joined it may be desirable to take the edge off the outside diameter of the pin. rrhis can be done hy mechanically working as hy rolling, the extreme edge or lip 18 of the pin in order to remove any upset of material whicll other-wise could initiate deleterious galling in the bell. ~t the same time it is usually desirable to work at least part of the leadin~ portion 1~ of pin 10 such that said portion has a conical shape defined hy an angle and relative to the outer surface of the pin. It has been found that, for "hard" materials such as steel, a nominal declination or angle of ~ degrees is sufficient to reduce the hearing pressure upon insertion below that pressure whicll ordinarily produces galling.
Although alternate means are readily apparent to those skilled in the art, all of the forming operations on the pin e~d rnay be advantageously carried out in essentially one opera-tion. U. S. Patent No. 3,473,359 discloses a grooving device having three rollers spaced roughly circur.lferentially equi-distant; such a grooving device may be readily adapted for performing all of the foregoing pin forming operations by replacing two of said rollers with "nose" and "finishing" }
rollers. The nose roller i9 preferably spaced longitudinally from the grooving roller and i5 adapted (1) to remove any up set of material which may be present at the extreme edge or outer lip 13 of the pin and/or (~) to mechanically work, if desired, at least part of the leading portion 1~ of pin such that said portion 13 is turned down the desired small angle~C.
rrhe finishing roller is adapted to turn down any ridges which mav be present ad~acent the groove. ~dditionally/ the described roll-forminq operation reduces the deviation from a perfect circle or"out-of-roundlless" of the pin end, and cloes so witl no possibility oE ~alling the pin as may occur witl- other forming procedures such as swaging.
The desired pre-forming operations may be carried out most advantageously in a steel mill, pipe yard, or other locale prior to distribution of the material to the job site.
In actual fielcl tests of pipe to be joined to form a pipeline, several sections of pre-formed pipe were pre distributed at various points along the pipeline right-of-way. An irn-provecl device of the yeneral type as shown and described in U. S. Patent l~lo. 3,503,2~4 was set up at one such point and the pipe was then, seriatim, swabbed with lubricating sealant, sta~bed, made-up, and pulled through the joining device by a tractor. In this ~anner, an ine~perienced crew of only three, including the tractor operator, was able to achieve a "produc-tion" joining rate of one forty foot joint of pipe per sixty seconds.
Heretofore it has been considered highly diffirult if not in~possible to join all~ninum pipe with consistent reliahilit~v and economy. ~luminurn has heretofore presente special difficulties because of certain of its unusual charac-teristics, two of which are (1) the extrernely low bearing pressure at which a cold pressure-weld occurs, and (2) the extremely high coefficient of friction between two smooth alurninurn parts.
~epending u~on the quality of the workpieces, the present in-vention as rlescribed above overcomes these difficulties and satisfactoril~ accornplishes the objects of the present invention.
To insure reliable joints to the degree required in the pipeline industr~ it is preferred to use a high-film-strength luhricant-sealant in the formation of the joint as above described~

Page The application of the present invention for joining pipe or other tubular goods which are internally coated may be best understood by reference to FI~. 2, 2A and 2B. For this application, it is preferred to turn down or taper the leading portion or nose 20 of the pin 21 to typical values of a declination or inward angle on the order of 10 with respect to the wall surface of the pin. As will be seen, the present inven-tion perraits a complete overlapping of the internal coating of a pin and bell while simultaneously permitting greater tolerance on the joint makeup length or insertion depth.
In the embodiment illustrated, the internal coating 22 of the pin 21 does not terrninate at edge 23 but continues around the end of the pipe and up the outside of the turned down portion 20 of the pin, up to a point near but short of outer diameter of the pin. The internal coating 25 of the bell end 26 preferably extends a convenient distance past the junction of expansion shoulder 27 and the expanded straight portion 28 of hell 26, but need not extend to the outer flare 29 at the end of the bell. The inclination or outward angleJ~ of flare 29 or outwardly extending taper may be any convenient small angle of lesser rnagnitude than the declination angle 13 of taper on the end of pin 21. Satisfactory results have been obtained~with inclination and declination angles of 4 and 10, respectively. ~s shown in FIG. 2~, such an angular difference has been found adecluate to protect the coating on the outer part 20 of the pin from contacting the inside surface of the flare 29 during the "stabbing" or initial-insertion of the pin into the flarecl end of the bell of the joining pro-cedure, even though the rn~rnbers prior to stabbing be initially somewhat misaligned. Subsequent to stabbing, the raembers to be joined are in alignment, and the coating on the exterior ~lose portion 20 of the pin cannot corne into contact with the bell 26 during the remaincler of the joining process. Insertion is nominally halted at the depth at which the pin and bell coatings overlap (See FIG. 2B), but a slight overrun in insertion depth can be tolerated without adverse consequences.
As illustrated by FIG. 2s, the completed joint is seen to be "holiday free" (no bare spots) in that the internal coatings 27 and 22 of the bell and pin overlap in such a manner that no bare -metal is exposed on the interior portion of the joint. Additionally, the wiping action of the joining process insures that a wedge 30 of sealant occupies what otherwise woulcl be the void between the coated inner portion o~ the bell member and the coated turned-down portion of the pin thereby providing additional pro~
tection against the subse~uent development of "holidays" as we~l as providing a pressure seal.
~ double seal is provide~ against internal pressure in the pipe by the wed~e 3~ and the sealant 31 contained within the groove 2A. With respect to pressure external of the pipe, a double seal is provided by sealant wedge 32 between the flare 29 and pin 21 and by the sealant 31 in the yroove 2~.
The present invention as ~escribed for application to internally coated rnembers provides several advantages over previous means for joining internally coated pipe. EIereto-fore, such coatings had to be ~lexible, tapered at the end on the inside of the ~ell, and coated on the edge of the pin end up to the outer surface of the pipe. The first requirement eliminated the man~ applications which required a harder but more brittle coating, and the latter two were extremely diffi-cult if not impossible to achieve consistently. Additionally, extremely precise make up of the pipe ends was required (to within 1/6~ of an inch). E~en such precision on insertion depth clid not always produce satisfactory results; the bevel dimension on the pin end could vary sufficiently even within A.P.I. standards that the coating was fre~uently sheared of~ the bell and pin during ~oining. Also, since there was alrnost no overlap of coating upon even successful joining, the single-thickness seal was not reliable and occasional "holldays" resulted.
With the joint disclosed, the coating can be either flexible or brittle, there is no requirernent for tapering inside the bell, and the di~ficult task of coating the edge of the pin end up to its outside diameter is eliminated.
For the reasons explained earlier, the coating is not damaged during stabbing or makeup, and a substantially overlapping seal is easil~ ef~ected. Additlon~allv, considerably greater tolerance of makeup depth is obtained, thereby eliminating the need for precision control of insertion depth. An~additional protection against "holidays" lS provlde~d by the substantial sealant wedge hetween nose and bell whicll always provides a coating to-coating seal.
It has been found that the normal joining method allows the bell to expand to a degree which sometimes perrnits brittle interior coatings 25 to crack. rrhis disadvantageous feature is eliminatecl by the use of exterior slips 50 designecl to grip and contain the outside of the bell rather than the pipe behind the bell. When the bell slips are used, the bell is preventecl from substantially deforming, outwardly, and such deforrnation as does occur is in compression of the pin member.
Since such linings can withstand greater deformation in corn-pression than in tension, the internal lining of the pin memher does not crack during compression of the pin. As the pin rnemher is compressed to accornmodate the necessary deforrnation, the member becomes progressively stronger and provides greater resistance to compression. Thus it is possible for quite high ine'lastic stresses to be created in the pin member, which stresses, while high enough to expand the bell sliyhtly upon its release from the slips, or other pipe grippi.ng devices, are not la.rge enough to overcome the greater resistance of the pin member and he dissipated in further deformation of said pin memher. The suhsequent expansion of the bell, however, is always small enough so that its brittle lininy does not brea}~ upon release of the bell slips The bell slips 50, of course, may be used in con-junction with any of the described joints, and are especially valuable in the prevention of splits in the bells of pipe of lesser ~uality.
Still another embodiment permits the mechanical joining of externally-coated pipe or~ upon comhination with the joint as described immediately above, of pipe which is coated both internally and externally. ~o avoid marring or destroying the external coating, it is preferred to use external pipe gripping device or slips 51 coated with an elastomer 52 of lower durometer than the external coating~
A particularly attractive advantage of this joint compared to those produced by conventional methods i5 that it permits the joining of externally-coated pipe without the necessity of a "field joint"; i~e., without the application of coating material to the exposed ends in the field after the completion of the joint.
Several variations of the externally~coated joint are possihle. The joining procedure is essentially the same in all instances, the differences being primarily in the pre-paration of the ends prior to joining. In one, the external coating on the bell end i.s conkinued around the edge, down tlle inside of the flared portion of the bell, and into the straight portion of the bell for a short distance; the external coating on the pin end is not continued to the groove region hut is 'cerminated a short distance past the point of over-lapping of bell and pin. In another, the external coatiny 35 on the bell is continued around the edge of the flared portion and terminated; the external coating on the pin continues up to the groove regiorl. In still another, as illustrated in FIG. 3~, the external coating 35 on the bell 36 is continued arolmd the edge of the flared portion 37 and down the inside of said flared portion, and terminated near the point of transition 40 from the flared portion of the bell to the essen-tially straight portion 41 of the bell. When the bell 36 is so coated, it is necessary that the pin 39 be coated only to a distance which will permit the exterior coating 3~ of the pin to engage the extended exterior coating of the bell 36 upon ma]~e-up. Lubricating sealant A2--either conventional or of high film strength--is applied to the pin, frorn the edqe to just past the groove 43, and in an amount which will insure filling of the void ~4 between pin and hell caused by the turndown of the pinO Sealant ~2 is also preferably applied on the internal portion of the bell/ in a circumferentia]
ring of about 1/2" to l" in width, beginning at the point at which the flared portion of the bell changes into the straight portion. The joint rnay then be rnade up in the normal manner, during ~lhich the space between the flared portion and the pin becomes filled with sealantO
In FIG. 3s, the pin 3~ is provided Wit}l an internal coating ~6 which laps around the tapered end of the pin and extends to the outer diameter. Thus, a holiday free joint can he formed.
It will be recognized by those shilled in the art that two of the foregoing will provide a coating-to-coating seal when properly made up, and that the other will provide a coating-to-sealant-to-coating seal; it will also be recog-nized ~hat overrunning or un(lerrunning the nominal insertion depth will not leave an exposed area or "holiday" on the joint, the sealant occupying any voids between bell and pin an~ pro-viding the necessary coverage. It will also be recognized that such joints as contain a groovecl region will provide a double seal against internal pressure and at least a double seal against external pressure.
It will be apparent that the embodiments herein shown and clescribed are exemplary only, and various modifi-cat:ions may be rnade in construction, materials and arrangement yet be within the scope of the invention as defined by the following claims:

Claims (4)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a method of forming a pin end on a tubular member to be inserted in an interference fit within a bell end of a tubular member having an open end portion with a terminal end which is flared outwardly at a first angle with respect to the central axis of the tubular member and with a lubricant sealant for filling the space between a pin end inserted into a bell end, the improvement for forming such a pin end for such a pin and bell interconnection comprising:
forming an inwardly tapered portion on the terminal end of a pin end of a tubular member at an angle of ten degrees with respect to the central axis of the pin end where said ten degree angle is greater than a first angle of the flared portion of a bell end of a tubular member by at least six degrees; and forming an annular groove in the outer circumferential surface of said pin end as near to said tapered portion as practical so that said groove and inwardly tapered portion are capable of containing a lubricant sealant.

2. In a method of forming a pin end on a tubular member to be inserted in an interference fit within a bell end of a tubular member having an open end portion which has a terminal end portion which is flared outwardly at an angle with respect to the central axis of the bell end and using a lubricant-sealant for filling the space between a pin end inserted into a bell end, the improvement for forming such a pin end for a pin and bell interference fitting comprising:
forming an annular groove in the outer circumferential surface of a pin end of a tubular member at a location spaced from the terminal end of said pin end so that, upon insertion of said pin end into the bell end of a tubular member, the groove would be disposed within such a bell end;

providing a tapered relief portion on each edge surface of said groove thereby to eliminate sharp edges; and deforming the outer edge of the terminal end of said pin end to provide an inwardly tapered portion at an angle of ten degrees with respect to the central axis for said pin and thereby to minimize galling of the interior surface of a bell end upon insertion of said pin end.

3. In a method of forming a pin end on a tubular member to be inserted in an interference fit within a bell end of a tubular member having an open end portion with a terminal end which is flared outwardly at a first angle with respect to the central axis of the tubular member and with a lubricant sealant for filling the space between a pin end inserted into a bell end, the improvement for forming such a pin end for such a pin and bell interconnection comprising:
forming an inwardly tapered portion on the terminal end of a pin end of a tubular member at an angle of ten degrees with respect to the central axis of the pin end where said ten degree angle is greater than a first angle of the flared portion of a bell end of a tubular member by at least six degrees; and forming an annular groove in the outer circumferential surface of said pin end as near to said tapered portion as practical so that said groove and inwardly tapered portion are capable of containing a lubricant sealant.

4. In a method of forming a pin end on a tubular member to be inserted in an interference fit within a bell end of a tubular member having an open end portion which has a terminal end portion which is flared outwardly at an angle with respect to the central axis of the bell end and using a lubricant-sealant for filling the space between a pin end inserted into a bell end, the improvement for forming such a pin end for a pin and bell interference fitting comprising:
forming an annular groove in the outer circumferential surface of a pin end of a tubular member at a location spaced from the terminal end of said pin end so that, upon insertion of said pin end into the bell end of a tubular member, the groove would be disposed within such a bell end;
providing a tapered relief portion on each edge surface of said groove thereby to eliminate sharp edges; and deforming the outer edge of the terminal end of said pin end to provide an inwardly tapered portion at an angle of ten degrees with respect to the central axis for said pin and thereby to minimize galling of the interior surface of a hell end upon insertion of said pin end.