Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF THE INVENTION
ln Field of the Invention ':`
The present invention relates generally to methods of ` ~.
forming mechanical 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 consicLered highly difficult if not impossible to
join mechanically with consistent reliability, namely, plain
aluminum pipe ancl steel pipe.
2. Description of the Prior Art
~ ', '.
The literature contains many schemes for machanically
joining pipes, tubing and the like, only a few of which have ~ .
proved actually capable of forming leak-free joints with oil-
field materials. One such method known to be actually operative ~:~
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is that disclosed in U. S. Paten-t No, 3~208,136. 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 li~uid lubricant-sealant prior to the joining of the
pipes. Related U. S. Patent No. 3,210,102 discloses the coupling
or joint essentially formed by the above-described method.
U. S. Patent No. 3,~66,738 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 of 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 pipe 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.
Summary of the Invention
_ _
The present invention is directed to the -Eormation
of high integrity, reliable mechanical joints of the pin and
hell 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 the like which are subject to variation in dimensions
and quality. It is also particularly well suited for joining
tubular goods heretofore considered highly difficult if not
impossible to join mechanically with consistent reliability,
namely, aluminum and steel pipe, and pipe which has been coated
both internally and externally. Additionally, it is well suited
for forming joints from elements coated with brittle material,
and it permits the joining of externally-coatedpipe without
a subsequent "field joint."
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In accordance with one bxoad aspect, the invention
relates to a method of forming mechanlcal joints between
tubular elemen-ts, of the type wherein a bell is formed in an
end portion of one such element for receiving a pin end of the
other element, the improvement comprising: tapering inwardly
one end of tubular member to form a pin end and enlarging one
end of another tubular member to form a bell end sized to
receive a pin end with an interference fit, forming an annulax
groove on the exterior on a cylindrical wall portion of said
pin end as near to said tapered end as practicable, and
applying a lubricant-sealant to one of said ends so as to
fill the angular space between said tapered end and said annular
groove upon formation of said joint, and inserting said pin end
in said bellend in interference fit.
In accordance with another aspect, the invention
relates to a method of forming a pin end on a tubular member
and a bell end on a tubular member wherein such pin end is
inserted into such bell end and a lubricant-sealant is used
for filling the space between the pin end inserted into a bell
end, the improvement for forming such pin and bell ends to
provide a minimum interference fit therebetween comprising:
expanding one end of a tubular member to form a receiving bell
end and controlling the expansion of said one end so that
the inner diameter of the expanded end of the tubular member
is a dimension not less than the minimum outer diameter of pin
end on a tubular member less the product of 0.005 times the
n~minal outer diameter of the pin end on a tubular member;
applying a deforming force to the pin end of the tubular
member to deform the terminal end of said pin end inwardly
at an angle of ten degrees with respect to the central axis
for said pin end thereby eliminating sharp edges which could
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cau~e galling upon inse~tion of such pin end into a bell end,
and inserting the pin end into the be:Ll end with such minimum
interference fit therebetween while filling the space between
the pin end and the ~ell end with a lubricant-sealer~
In accordance with a further aspect, the invention
relates to a method of forming a pin end on a tubular member
and a bell end on a tubular member wherein such pin end is
inserted into such bell end and a lubricant-sealant is
used for filling the space between the pin end inserted into
a bell end, the improvement for forming such pin and bell ends
to provide a minimum interference fit therebetween comprising:
expanding one end of a tubular member to form a receiving bell
end and controlling the expansion of said one end so that the
inner diameter of the expanded end of the tubular member is a
dimension not less than the minimum outer diameter of pin end
on a tubular member less the product of 0~005 times the nominal
outer diameter of the pin end on a tubular member; applying
a deforming force to the pin end of the tubular member to
deform the terminal end of said pin end inwardly at an angle
o~ ten degrees with respect to the central axis for said pin
end thereby eliminating sharp edges which could cause galling :
upon insertion of such pin end into a bell end, and inserting
the pin end into the bell end with such minimum interference :
fit therebetween while filling the space between the pin end
and the bell end with a lubricant-sealant.
The 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 elastically and inelastically, into a bell-shaped configura-
tion which has, after "snap-back" from expansion, a minimum
interference dimension with respect to a pin having the maximum
A.P.I. allowable deviations. An annular groove of desired
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con~iguration is preEerably Eorme~ on the pin end as close as
~,ossible -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 of the
pin with the bell is always insufficient to producing galling.
The portion of the pin beyond the leading portion preferably
is not worked because the bell is sized to accommodate the
maximum expected variation in dimension of this portion. In
certain other aspects of the present invention the location
of interior and exterior coating is controlled.
Alternate embodiments of the invention, as well as
the preferred form o the invention itself, will be more
fully understood by 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 afterformation of the joint.
FIG. 2 is a similarly enlarged sectional view of bell
and pin ends formed for joining coated pipe, and illustrates a ,~
preferred arrangement for internal coating. FIG. 2a illustrates
the protection afforded the coating material during initial
contact by a misaligned pin member whereas FIG. 2b illustrates
the completed joint with the resultant deposits of sealant.
FIG. 3A similarly depicts the completed joint but illustrates
a preferred arrangement for external coating, and FIG. 3B illus-
trates a joint with both internal and external coating.
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Descri~ion o~ the Preferred Embodiments
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A preferred emhodiment for joining plain, uncoated
~ubular elements, ~hether of "hard" material such as steel or -
of "soft" material such as aluminum, is illustrated in FIG. 1.
In FIG. 1, -the pin 10 is forced into the open end of the bell
11 to form a joint as illustrated by the pin outlined in dashed
line in FIG. 1. The method employed to create the iintillustrated
can best be understood by a step-by-step explanation for a given
size tubular element. In the case of American Petroleum Institute
'ISchedule 401l steel pipe of nominal 4-1/~-inch outside diameter
(O.D.), the nominal wall thickness is 0.237 inch, resulting in
a nominal inside diameter (I.D.) of 4.026 inches. It is an ob-
ject o~ the present invention to obtain the "mînimum interfer-
ence fitll necessary to provide a strong joint while allowing for
the maximum dimensional variation permitted by A.P.I. standards.
Maximum gripping force between bell and pin, for most materials,
is typically obtained at internal stresses near the elastic
limit; any amount of interference greater than that which pro-
duces 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
gripping force, and is undesirable in that it both requires
greater force for the subsequent joining operation and can
produce galling between the materials being joined. The term
I'galling" as used herein refers to the effect of gouging a groove
along 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
"minimum interference fit" for steel has been determined to be
approximately 0.005 inch p~r inch of outside diameter per
30,000 pounds of minimum specified yield. Actually, the precise
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climension is 0.002 Lnch rather than 0,005 ~ut the 0.005 figure
compensates for miscellaneous irregularities which may be
found in pipe. ~or a nominal 4.5-inch 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
diameter pipe with A.P.I. standards may thus be encountered
with outside diameter as small as 4.46625 inches (4.50-[0.0075 x
~.50]). Thus, to allow for the minimum desired interference
of 0.0225 inch, the bell must be expanded such that its maximum
I.D. after "snap-back" i5 approximately 4.44 inches (;4.46625-0-.0225~.
Such sizing to obtain a "minimum interference fit" has been
found to satisfactorily accommodate pin ends of pipe with
the maximum positive A.P.I. variation without significantly ~`
increasing the force required for joining and while maintaining
an adequate gripping force.
The relationship described above may be expressed
in restated form as follows:
Max I.D. Bell = Min O.D. pin - 0.005X
Where Max I.D. bell = "Snap-back" dimension in inches
Min O. D. pin - Smallest pin O.D. in inches
X = Nominal Pin O.D. in inches
For aluminum pipe it is three times the value of
steel or 0.015" because the modulus of elasticity of aluminum
is three times that of steel.
The foregoing is usually sufficient to permit leak-
free, strong joints to be formed between precision-made or pre-
precision-formed elements, but such high quality workpieces are
not ordinarily encountered in actual practice. ~lso, joints
which are only "usually" leak-free are unacceptable in the
pipeline industry, the needs of which demand a leak-free join-
ing rate of virtually 100%. To consistently achieve the high
degree of reliability with tubular elements of typical oil
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field quality, i-t has proved desirable to perform a prelimi-
n~ry forminq operation on the pin 10, Thi~ is prefexably
accomplished by -Eorming an annular groove 12 in the end of the
pin 10, preferably as near the terminal end 13 of said pin 10
as conveniently obtainable. The 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. ~y applying a lubricating sealant
to either the inner surEace 14 of the bell 11 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 but does interdict any longitudinal interstitial
voids which might otherwise, either singly or in combination,
permit the joint to leak. Liberal 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
surrounding bell. The groove 12 need not indent the inner
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
12 is formed with a beveled annular relief portion 17
adjacent the sides of the groove, Dependent upon the quality
of the tubular goods to be joined it may be desirable to take
the edge off the outside diameter of the pin, This can be done
by mechanically working as by rolling, the extreme edge or lip 18
of the pin in order to remove any upset of material which other-
wise could initiate deleterious galling in the bell. At the
same time it is usually desirable to work at least part of the
leading portion 18 of pin 10 such that said portion has a conical
shape defined by an angle and relative to the outer surface
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234
of the pin. It has been found -that, for "hard" material$ such
as s-teel, a nomin~l declination or angle of 4 degrees is suf-
~iciPnt lo reduce the bearing pressure upon insertion below that
pressure which ordinarily produces galling.
Although al-ternate means are readily apparent to those
skilled in the art, all of the forming operations on the pin
end may 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 circumferentially equi-
distant; such a grooving device may be readily adapted forperforming all of the foregoing pin forming operations by
replacing two of said rollers with "nose" and "finishing"
rollers. The nose roller is prererably spaced longitudinally
from the grooving roller and is 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 (2) to mechanically work, if
desired, at least part o~ the leading portion 18 of pin such
that said portion 18 is turned down the desired small angle ~ .
The finishing roller is adapted to turn down any ridges which `
may be present adjacent the groove. Additionally, the described
roll-forming operation reduces the deviation from a perfect
circle or "out-of-roundness" of the pin end, and does so with
no possibility of galling the pin as may occur with other
forming pro~edures 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 field 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 im-
proved device of the general type as shown and described in
U. S. Patent No. 3,503,24~ was set up at one such point and
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th~ pipe was then, se~iatim, swabbed with lubric~-ting sealant
s-tabbed, made~up, and pulled throu~h the joining device by a
trac-tor. In this manner, an inexperienced 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 difficult if
not impossible to join aluminum pipe with consistent reliability
and economy~ Aluminum has heretofore presented special difficul-
ties because of certain of its unusual characteristics, two of
which are (l) the extremely low bearing pressure at which a cold
pressure-weld occurs, and (2) the extremely high coefficient of
friction between two smooth aluminum parts.
Depending upon the quality of the workpieces, the present
invention as described above overcomes these difficulties and
satisfactorily accomplishes the objects of the present invention.
~o insure reliable joints to the degree required in the pipeline
industry i.t is preferred to use a high-film-strength lubricant-
sealant in the formatioll of the joint as above described.
The application of the present invention for joining pipe
or other tubular goods which are internally coated may be best
understood by reference to FIG. 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 invention;~permits 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 terminate at edge 23 but continues around
the end of the pipe and up the outside of the turned down
239~
portion 20 o;E the pin, up to ~ point near but short of oute~
diameter of the pin. The internal coating 25 of the bell end
26 preferabl~ extends a convenient distance past the junction
of expansion shoulder 27 and the expanded straight portion 28
of bell 26, but need not extend to the outer flare 29 at the
end of the bell. The inclination or outward angle ~ of flare
29 or outwardly extending taper may be any convenient small
angle of lesser magnitude than the declination angle B of
taper on the end o~ pin 21. Satisfactory results have been
obtained with inclination and declination angles of 4 and
lO , respectively. As shown in FIG. 2A, such an angular
difference has been found adequate 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 flared end o the bell of the joining pro- ~`
cedure, even though the members prior to stabbing be initially
somewhat misaligned. Subsequent to stabbing, the members to be
joined are in alignment, and the coating on the exterior
Nose portion 20 of the pin cannot come into contact with the
bell 26 during the remainder 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 conse~uences.
As illustrated by FIG. 2B, 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. ~d~it~onally
the wiping action of the joining process insures that a wedge
30 of sealant occupies what otherwise would be the void between
the coated inner portion of the bell member and the coated
turned~down portion of the pin thereby providing additional pro-
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-~ection agclinst -the subsequen~ development of '`holidays~' as
well as providing a pressure seal.
A double seal is provided against internal pressure
in the pipe by the wedge 30 and the sealant 31 contained within
the groove 24. 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 groove 24.
The present invention as described for application
to internally coated members provides several advantages over
previous means Eor joining internally coated pipe. Hereto~
fore, such coatings had to be flexi~le, tapered at the end on
the inside of the bell, and coated on the edge of the pin end
up to the outer surface of the pipe. The first requirement ~-~
eliminated the many 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 1/64 of an inch). Even such precision on insertion depth
did not always produce satisfactory results; the bevel dimension
on the pin end could vary suficiently even within A.P.I. standards
that the coating was frequently sheared off the bell and pin
during joining. Also, since there was almost no overlap of
coating upon even successful joining, the single-thickness seal
was not reliable and occasional "holidays" resulted.
With the joint disclosed, the coating can be either
flexible or bri~tle, there is no requirement for tapering
inside the bell, and the difficult 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
easily effected. Additionally, considerably greater tolerance
of makeup depth is obtained, thereby eliminating the need for
precision control of insertion depth. An additional protection
~L~23~
~y~ins~ "holidays~' is provided by the su~stantial sealan-t wedge
between nose and bell which always provides a coatin~-to~coating
se~l.
It has been ~ound that the normal joininy method allows
the bell to expand to a degree which sometimes permits brittle
interior coatings 25 to crack. This disadvantageous feature
is eliminated by the use oE exterior slips 50 designed to grip
and con~ain the outside of the bell rather than the pipe behind
the bell. When -the bell slips are used, the bell is prevented
from substantially deforming, outwardly, and such deformation
as does occur is in compression of the pin member. Since such
linings can withstand greater deformation in compression than
in tension, the internal lining of the pin member does not crack
during compression of the pin. As the pin member is compressed
to accommodate the necessary de~ormation, the member becomes
progressively stronger and provides ~reater resistance to com-
pression. Thus it is possible or quite high inelastic stresses
to be created in the pin member, whic:h stresses, while high
enough to expand the bell slightly uE~on its release from the
slips, or other pipe gripping devices, are not large enough to
overcome the greater resistance of the pin member and be dissipated
in further deformation of said pin member. The subsequent
expansion of the bell, however, is always small enough so that its
brittle lining does not break upon release of the bell slips.
The bell slips 50, of course, may be used in conjunction
with any of the described joints, and are especially valuable in
the prevention of splits in the bells of pipe of lesser quality.
Still another embodiment permits the mechanical joining
of externally-coated pipe or, upon combination with the joint as
described immediately abo~e, of pipe which is coated both exter-
nally. To avoid marring or destroying the external coating, it
is preferred to use external pipe gripping device or slips 51
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coated with ~n elastomer 52 oe lower durometer than the external
coating~ A particularly attract~ve advantage of this joint
compared to those produced by conventional methods is 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
possible. The joining procedure is essentially the same in all
instances, the differences being primarily in the preparation
of the ends prior to joining. In one, the external coating on ;~
the bell end is continued around the edge, down the 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 but is terminated
a short distance past the point of over-apping of bell and pin.
In another, the external coating 35 on the bell is continued
around the edge of the flared portion and terminated; the external
coatlng on the pin continues up to the groove region. In still
another, as illustrated in FIG. 3A, the external coating 35 on
the bell 36 is continued around 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 essentially 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
38 of the pin to engage the extended exterior coating of the bell
36 upon make-up. Lubricating sealant 42--either conventional
or of high film strength~is applied to the pin, from the
edge to just past the groove 43, and in an amount which will
insure filling of the void 44 between pin and bell caused by
the turndown of the pin. S~alant 42 is also preferably applied
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on the ii~ternal ~ortion o~ the bell, in a circumferential ring
of about ~/2 to 1" in width, beginn:in~ at the point at which
the flared portion of the bell changes into the stralght portion.
The join-t may -then be made up in the normal manner, during which
the space between the flared portion and the pin becomes filled
with sealant.
In FIG. 3B, the pin 39 is provided with an internal
coating 46 which laps around the tapered end of the pin and
extends to the outer diameter. Thus, a holiday free joint can
be formed.
It will be recognized by those skilled 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 recognized that
overrunning or underrunning the nominal insertion depth will not
leave an exposed area or "holiday" on the joint, the sealant
occupying any voids between bell and pin and providing the
necessary coverage. It will also be recognized that such joints
as contain a grooved 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 described are exemplary only, and various modifications may
be made in construction, materials and arrangements yet be within
the scope of the invention as defined by the following claims:
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