Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1 ! BACKGROUND OF THE INVE~ION
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! 1. FIELD OF TH~ INVE~TION: This invention generally
~relates to an insulated conduit having particular utility in
subterranean wells and more particularly to a concentric walled
insulated conduit having an annular space between the walls
within which an insulating material is deposited and sealed
! therein.
,l 2. DESCRIPTION OF THE PRIOR ART: In producing some subter-
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,'ranean wells, steam is injected into an injection well to increase
'recovery of hydrocarbons by reducing high viscosity crude oil,
! otherwise know,n as "heavy crude". The lower viscosity makes the
oil more readily pumpable. One ~echnique for doing this is to
inject a high quantity of steam into the production zone contain-
¦¦ing "heavy crude" for an extended period of time, such as from
,labout three to about five weeks. At that point, the viscosity of
,l ~he heated crude will be reduced and will be readily pumpable,I through a production well in communication with the produe~ion
'i zone. The injection well may also be modified for production. A ;
I steam 'Iflood" may also be provided by known techniques, generally
~ ; through an injection well, to drive the flood and the produced
hydrocarbons into a nearby production well.
! One of the major problems in injecting steam into a subter-
ranean production zone through conventional well production
1! tubing is that the steam loses a large quantity of its heat to
~I the ~ell bore casing and surrounding formation as i~ travels
! downwardly to the production zone. Attempts have been made in
i the past to reduee the heat loss of steam introduced into sub-
.¦ terranean formations. One such attempt is disclosed in U. S.
¦¦ Patent Mo. 3,511,282, issued on May 12, 1970. This paten~
J discloses a dual-wall tube structure ha~ing insulation sealed in
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he annulus between the inner and outer walls by bushings respec^
i tively welded at each end between the inner wall and the outer
wall. The inner wall is prestressed in tension prior to being
li welded to the outer wall. The space defined between the inner
'I and outer walls is filled with a conventional in~ulating material,
! such as calcium silicate. Althou~h this technique mav be satis-
~i! factory in some oil field installa~ions, it is not satisfactory
Il for all oil field installations where large temperature differen-
11 tials are encountered between the inner and outer wal]s. In this
~I case, even though the inner wall is prestressed in tension, the
inner wall, as it is heated, will elDn~ate with respect to the
outer wall so that the inner wall may even change from a tensi~n
l! to a compression condi~ion with the attendant danger of buckling.
¦~ The magnitudes of the rorces generated are such that localized
i5 !¦ s~res~es are created in the weld areas causing cracks which
permit exposure of the insulation to well fluids and eventually
causing failure or degradation of the insulating s~ructure.
!I Centralizers are incorporated to reduce buckling~ but may also,
Il in turn, contribute to a loss of heat because of the generally
1 durable nature of such devices.
Another known technique of handling the aforedescribed
temperature differential and resulting elongation between the
inner and outer walls of an insulating tube is to place a thin
walled bellows betT~een the two walls a~ each end of the assembly,
~5 one end of each of the bellows being rigidly attached to the
il inner wall, and the other end of the bellows being rigidly
¦ at~ached to the outer wall. This technique, of course, relieves
the strain on the welds and joining structure between ~he walls
! due ~o the relative movement between the inner and outer walls.
However, the bellows introduce other problems; namely, the bel-
¦¦ lows are comparatively thin walled and delicate, being ~ypically
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formed from a heat resistant, springy material, which cannot
withstand the rough handling normally encountered in the oil
patch.
Also known is a concentric walled thermal insulating
conduit which comprises concentric tubular members in which
the inner tubular member is corrugated and has flared ends
welded to the outer tubular member adjacent each end. Insul-
ation is provided within the annular area between the -~wo
tubular members for reducing heat loss during steam injection.
1~ SUMMARY OF THE INVENTION
A concentric walled insulating tubular conduit for forming a
tubular string in a subterranean well has an inner tubing member
with flared endsO The flared ends of the tubing, with a thic~-
ness at least equal to the nominal thickness of the inner tubing
intermediate the ends, is welded to the outer tubing. Only two
welds per individual conduit are necessary. The flared inner
ends are fabricated by forging the ends of a tubular member
having upset or enlarged ends. Although the thickness of the
ends will be reduced by the forging operation, the flared ends
will remain relatively ~hick, thus adding to ~he integrity of the
weld. The inner tubing member is preferably prPstressed in
tension relative to the outer tubular member.
An exterior coupling joins adjacent members by oonventional
threaded engagement with the outer tubing and an inner coupling
member extends between flared sections of the inner tubing ends.
Insulation may be incorporated between the interior and exterior
li :
1 ,coupling and in the annular cavity between the inner and outer
~,ltubing. Blanket insulation, rigid load-bearing insu~ating
,l~embers, and a shield having a low thermal emmissivity are pro-
i! v~ded in the axially extending cavlty.
The concen~ric walled conduit is preferably fabricated by
using standard tubular members used in oil and gas wells, the
Ij inner tubing originally having upset ends. Fabrication utilizing
~lthese standard tubular members yields a concentric walled tubular
limember in which only L~O welds would be necessary on each conduit
0 ¦Isection for joining the flared end sections of at least nominal
I tubing thickness to the outer tubing. These flared end sections,
¦ however, remain relatively long and thin, thus reducing the path
! available for conductive heat transfer.
I . ,
¦ BRIEF DESCRIPTION OF THE DRAWINGS
¦ Fig. 1 is a schematic illustrating the in~ection of steam
through a tubing string formed of individual conduit members
Il constructed in accordance with this invention.
,¦ Fig. 2 shows two conduits coupled at ~heir ends and this
¦I section view depicts the components of the preferred embodiment
of this invention.
Fig. 3 illustrates the forging operation in which a conven-
I tional upset tubular is 1ared by use of a swage to form theinner tubing of the concentric insulating member.
Fig. 4 shows the profile of an upset tubular after the ends
l have been flared for use as the inner conduit of the concentric
l¦ walled tubular assembly.
Fig. 5 depicts the means of forming a vacuu~ within the
annular insulating cavity in this invention.
Fig. 6 is a view of an alternate embodiment.
DESCRIPTIO~ OF THE PRE~L~ Y~_DlMFNT
Fig. 1 illustrates, in sche~atic form, the use ~f a plurali~y
of seccions comprising ~oncen~ric walled insulating tubing members
ormed in accordanee with this invention, t~ cons~ruc~ an insula-
5 ting tubing string. The tubing st;lng T, sho~l in Fig. 1, per~itsthe injection of steam at the surface of the well through the
` tubing to the formation therebelow. The ins~lating tubing string
" ensures that the heat loss between the surface and the forma~ion
Il will not be so excessive as to defeat the function of steam
3~ il injection. The tubing string ~, comprising a plurality of
individual insulating tubing conduits 2, is positioned within the
well and within the well casing C in much the same ~anner as a
conventional tubing string.
Il Fig. 2 shows the components of each individual conduit and
,, the interconnec~ion betwee~ adjacent abu~ting tubular conduits.
' It will be understood ~hat the opposite ends of each individual
i conduit i5 of generally the same configuration as is shown in
Fig. 2. Eaeh individual concen~ric insulating ~ember 2 comprises
~ an outer tubing 4 and an inner tubing 6. The outer tubing 2
1 comprises astraight cylindrical member having conventional
1 threads lO a~ each end. A conventional external coupling 8,
" engaging threads lO, can be used to join adjacent concentric
! members. In order to reduce the number of welds needed to secure
,1 inner tubing 6 ~o outer tubing 4, ~he end of inner tubirlg 6 is
,, outwardly flared, as shown in Fig. ~. A single circular face
!i weld 30 can then be made between inner tubular 6 and outer
! tubular 4. The refonming of inner tubing 6 results in flared
ends having substantially three sections, First ou~er section 32
i generally comprises a radiused portion having an efec~ive radius '
3D I of cur~ature approximately e~ual to or on the order of ~he
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,' separation between the inner and outer tubing. The radius of
! curva~ure need not be limited ~o this separation distance, but a
,, desirable structure can be constructed by e~loying a radius of
i' curvature of that order of magnitude. As shown in Fig. 2, the
l! i
S l thickness of this radiused portion would be generally equal to a
value, D3. Adjacent the outer radiused section 32 on each end of
i' inner tubing 6, is a tapered section 34. The degree of taper in
Il this section need not be large and, in the preferred embodiment
Il ;
Il of this invention, a radially outward taper of 1 is employed in
section 34. In the preferred em~odiment of this invention, a
I¦ second more significantly tapered section 36 is employed to form
¦i, a transition between the 1 tapered section 34 and the central
i! portion of the inner tubing 6. This ~ransition section 36, in
¦~ the prefPrred embodimen~ of ~his inven~ion, has a taper equal to
~5 il approximately 5 .
In the assembled configuration of a single insulating tubing
¦I conduit, as shown in Fig. 2, an annular cavity 13 is formed
Il between outer tubing 4 and inner tubing 6. This annular cavity
Il 13 may be filled wi~h thermal insulation. In the preferred
1! embodiment of this invention, this thermal insulation comprises a
combination of a blanket insulation 12 having ceramic fibers, at
,l least one rigid insulating member 14, and a re1ective heat
¦¦ shield 18. At least one rigid cylindrical insulating member 14
!l
1 is located within annular cavity 13 between the welded ends
1! joining outer tubing 4 to inner tubing 6. In the preferred
embodiment of this invention, this rigid insula~ing me~ber
comprises a molded, high temperature pipe and block insulating
¦ composed by hydrous calcium silicate. This molded calcium
!¦ silica~e m~mber 14 provides structural support between inner
1I tubing member 6 and outer tubing ~ember 4 between the ends of
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;~ annular cavity 13. In the preferred embodiment of this invention,
insulating member 14 omprises a conventional pipe and block
insul~ting member which is commercially available. One molded
Il calcium silicate pipe and block insulation mem~er that can be
1~ used in this invention is manufactured by Johns-Manville and is
co~monly reffered to under the trademark "Thermo-12". These
standar~ pipe and block insulation members are available in half- ;
!j sections which can be positioned in surrounding relationship with '
I¦ respect to inner tubing 6. Metal bands 16 can then be attached
,¦ around the peripher~ of the t~o half-sections to form a single
j annular insulating me~ber structurally supporting the outer
tubin~ 4 relative to the inner tubing 6.
¦¦ The remalnder o annular cavity 13 contains a blanket
i insulation 12, which is also commercially available. Thermal
5 ¦1 insulating blankets, composed of long mechanically bonded refrac- i
Il tory fibers pr~viding a co~bination of high blankPt strength,
¦¦ flexibility and high thermal performance, are commercially
i! available. In the preferred embodiment ~f this invention, a
~¦ thermal insulating blanket of the type manufactured by Johns-
20 1l Manville under the trade~arks "Thermo-Mat'i or l'Ceratex", has been
j employed to form a convective insulating barrier within annular
cavity 13. This insulating blanket can be secured to the inner
1 tubing between calcium silicate insulating members 14 and the
¦¦ ends of annular cavity 13~ This insulating blanket 1~ can be
secured to inner tubing ~ by wrapping a conventional glass fiber
i tape aro~nd the exterior of the insulating blanket 14. When
¦¦ employed in ~ombination, blanket insulation 12 and the rigid
¦ calcium silicate insulating member 14 should substantially fill
¦ annular cavity 13 between ~he inner and outer tubings. In the
j preferred embodiment of this invention, at least a partial vacuum
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is established in annular cavity 13 to prevent moisture from
de~rading t~e performance of the convective insulation.
In addition to the convective insulating barriers provided
by blanket insulation 12 and rigid insulatin~ member 14, a
,~ radiant reflective heat shield member 18 can be provided. In the
preferred embodiment of this invention, this reflective heat
shield is incorporated on the outer surface of inner tubing 6,
and comprises a material having a relatively low thermal emis-
1 sivity. In this embodiment, aluminum foil has been applied
1~ 1 around inner tubing 6. This aluminum foil comprises a reflective
! surface which will further reduce the heat transfer of this
! tubing assembly.
Annular cavity 13 provides sufficient space to contain
Il insulation for maintaining appropriate heat transfer character-
lj , istics over most of the length of this tubing. There does,
j however~ remain a space between interior flared ends on adjacent
' tubing mem~ers. An interior coupling or cylindrical spacer
member 20 can be employed to completely isolate the area other-
I wise bounded by the flared inner tubing ends of adjacent conduits
. and the outer coupling 8. This interior coupling 20 comprises acylindrical member having outer sections 24 and 26 having a
, thickness which is less than the thickness of the central section
28 of the interior coupling member. As shown in Fig. 2, the ends
,1 24 and 26 can be wedged into engagement with the tapered section
34 of each inner tubing member 6. Insulation can then be posi-
I tione~ around the exterior of interior coupling 20 to reduce heat
', loss in the vicinity o the coupling. In the preferred embodi-
ment of this invention, blanket insulation of the same type as
! blanket insulation 12 used within annular cavity 13 can be
: affixed around interior coupling central section 28 in a donut
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1 fashion~ The blan~et insulation ~hen fills the cavity bounded by
the radiused ends of adjacent interior tubing members and the
interior and exterior coupling members. An assembled tubing
string or conduit comprising a plurality of individual insulating
tubing conduits 2 would then have insulating material positioned
within the annular space between inner tubing 6 and outer tubing
4 along substantially the entire length of the insulating tubing
conduit 2. Finally, a second low emissivity barrier or radiant
heat shield is provided on the exterior of the outer tubing. The
~0 outer tubiny can be painted along its entire length to provide
this barxier. Two low emissivity barriers will then act to
reduce heat transfer over most of the tubing.
The flared ends of inner tubing 6 not only provide an
effective means of increasing the performance of ~he welds, both
by reducing their number and by increa~ing the welded area, but
they should also provide for low heat loss by means of conduction
through the welded joint. The only heat conductivity path
between the junction of the interior coupling 20 and the tapered
portion 34 of inner tubing 6 is along the relatively long thin
flared tubing itselP. No relatively wide bushing rnember with its
inherently greater hea' conductivity is necessary. Still, the
flared portion of the tubing is thick enough to provide a weld of
high integrity.
The alternate embodiment of Fig. 6 employs a corrugated inner
tubular member 72 with a wall thickness on the same order as
conventional well tubing of the same diameter, thus proYiding a
structurally rugged element but having axial springness. It is
seen that the ends of the inner tubular member 72 are respectively
provided with straight portions 74 and 74' and flared portions 76
and 75' with the end of each flared portion 76 and 76' being
OO
1 ¦ respectively ~ecured to ~he inner surface of the outer tubular
I member 80 b~ welds 78 and 78'. Also, it will be noted that the
¦ flared portions 76 and ~6' define the annular space 84 in this
embodiment of the invention for receiving the insulation 86. In
3 this case, the straight portions 74 and 74' conveniently provide
transi~ion surfaces between the flared ends and the corrugated
portions of the corrugated inner -tubular member 11. It should be
noted that the flared portions 76 and 76' are radially spaced from
the corrugations on inner tubular member 72. In order to preven-t
~¦ heat loss it is essential that the corrugations, whether sinusoida
or helical, not come into contact with the outer tubular member.
As with the other embodiments, the "flared portions" 76 and 76',
located only a~ the ends of inner tubular member 72, are provided
l to establish contact with the outer tubular member 80 while at
1~ ¦ ~he same time reducing the number of welds.
l FABRICATION
l ..
One very significant feature of the preferred embodiment of
l this invention is that it can be fabricated using only conven-
tional and commercially available components. While the concen
tric conduit 2 can be fabricated by using a wide variety of
cylindrical members, the preferred embodiment of this invention
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I `can be fabricated by using standard American Petroleum Institute
tubulars. In one size, this invention may utilize a standard
,12-318ths inch O.D. A.P.I. J-55 tubing havin~ ùpset or enlarged
,¦ends to allow fabrication of the flared inner ~ubing 6. In ~he
~5 '~same configuration, a 4-1/2 inch A.P.I. J-55 casing h2ving non-
llupset ends can be employed for outer tubing 4. The standard
!i tubîng shown in Fig. 3, such as 2-3/8ths inch O.D. J-55 tubing
¦Ihas a nominal thickness Dl along most of the tubing. This
¦Inominal thickness Dl is less than the thickness D2 of the upset
¦¦ends. The ends of the standard J-55 tubing can be flared to
!!their final configuration by utilizing a forging operation
¦¦employing a swage 42, shown in Fig. 3. The swage has a beveled
l¦portion 44 at its end. Adjacent this beveled entry surface 44 is
¦!a cylindrical or guide portion 46 which serves to align the
~5 ¦itubing during the forging operation. A swage transition profile
jl48, havin~ a radially outward taper extends from the lower end of
guide section 46. This transition profile constitutes a mirror
i~age of the transition section 36 of the fabricated inner tubing
,! member 6. In the preferred embodiment of -this invention, the
20 il taper of this transition section would be on the order of 5.
Adjacent the transition section 48 is a swage taper~d profile 50
which corresponds to the tapered section 34 of the fabricated
inner tubing 6. Tapered proile 50 has a ~aper which is less
than the taper of transition profile 48, and in the preferred
¦ embodiment this swage profile has a taper of approximately 1 to
match the ~aper of the transition section 34. At the lower end
of the swage is a radiused profile 52. As with profile sections
48 and 50, the radiused profile 52 is intended to match the
cooperating section on the final inner tubing member 6. Radiused
I section 32 of inner tubing 6 will be formed as the outer end o a
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I ,IstandaTd upse~ J-55 tubing is forged by radiused profile 52. It
" should be understood that although profile 52 is herein referred
to as a radiused profile, it need not be generated by a constant
llradius of curvature. The term "radiused profile" is merely
l intended to indicate t~at the outward flaring of tapered section
~136 generated by profile 52 is significantly greater ~han that of
adjacent sections 32 and 34 in inner tubing 6. It is believed
lthat the term "radiused pro~ile" is appropriate, howcver, since
¦the actual profile would at least closely approximate a surface
having a constant radius of curvature. Since the principal
¦Ipurpose o~ this radiused section is to provide radially ~raverse
¦the separation between inner tubing 6 and outer tubing 4, an
¦¦effecti~e radius of curva~ure on the order of magniture of the
l¦spacing between outer tubing 4 and inner tubing 6 should be
~ ef~ective to for~ this profile. As can be seen in Fig. 3, the
final shape of inner tubing 6 can be fabricated by driving swage
42 into a standard tubular 38 havlng enlarged or upset ends 40,
~Preferably, the portion of a standard tubular 38 adjacent ~he
upset ends 40 would be heated prior to this forging process.
I~When the swage is driven into the end of the tubular, the tubular
radially expands to form the flared end proiles desired for the
¦Ipreferred embodiment of this invention. During the course of
l this forging process ~ the ends of the standard tubular 38 would
25 j not only be radially flared but they would be stretched by the
¦forging process. As the end is stretched the thickness of each
¦tubular would be reduced. The flared inner tubing 6 would have a
¦ radiused section 32 having a thickness D3, a tapered section 34
ha~ing a thickness D4, and a transition section 36 having a
thickness Ds. Xf the flaring and stretching of the material of
the standard tubular is confined to the upset ends 40, the
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~' thicknesses, D3, D4 and D5 can be greater than or at leas~ equal
I to the nominal thickness Dl of a standard tubular. Even if the
i final thickness is slightly less than the nominal wall thickness
¦~ of the tubing, the use of tubing initially having upset or
1l enlarged ends should promote greater structural in~egrity in the
,l flared ends of the ~ubing. The stretching will, however, reduce
the thicknesses D3, D4 and D5 to a value less than the original
¦ thickness D2 of the upset tubular ends 40. A significant advan-
¦l tage to forming the inner tubing 6 from a standard tubular having
~ ¦l upset ends can be seen in that evPn though the thickness of the
¦~ standard upset ends is reduce~, the thickness D3 of radiused
¦¦ section 32 can still be larger than the nominal thickness Dl of
¦¦ ~he inner tubing member. This increased thickness should enhance
the structural integrity of the welds 30A and 30B along the
~5 ,! radiused sections 32 to the outer tubular member 4. The welds
,j will extend over a larger surface area and the thickness of the
!1 inner tubing adjacent the welds, including radiused section 32,
¦I tapered section 34; and transition section 36, wi 1 not be
l! reduced below the nominal thickness of ~he tubing. This improved
20 li weld integrity would, in addition to the weld reliability improve-
iii ment, be gained by reducing ~he number of welds at each end,
After both ends OI a single inner tubing member 6 have been
I 1ared by the forging process depicted in Fig. 3, the final
i configuration of inner tubing 6 will be that shown in Fig. 4. At
¦ this point, the reflective heat shield or low emissi~ity barrier
~ can be applied to the outer surface of inner tubing 6. In the
¦! preferred embodiment, aluminum foil would be wrapped around the
inner tubing. The rigid insulation members 14 may then be
attached at appropriate positions along the exterior of the inner
! tubing by placing two half sections around the tubing with me~al
1 llbands securing the calcium silicate members to~ether. Blanket
insul~tion 12 can then be attached over the remaining portion of
inner tubing 6.
~i The next step in the fabrication of the final insulating
1I tubing conduit 2 would be the insertion of the inner tubing-
il insulation assembly into outer tubing 4. Upon insertion, the
l continuous clrcumferential surface formed at each free end of the
Il flared inner tubing is positioned adjacent to the interior of
Il the out~r tubing around its complete inner circumference and is
]~ 1¦ in position to be attached to the outer tubing. The radiused end I
l of inner tubing 6 can then be welded to outer tubing 4 along one
end of the eoncentric tubing assembly. This first weld 30A
I extends completely around the junction between inner tubing
¦, radius section 32 and the ou~er tubing 4. Multiple passes may be
il used to ensure ~hat this weld is structurally sound and completely
¦I seals the juncture between inner and outer tubing.
l In the preferred embodiment of this invention, it is desired
li to prestres5 the tubing assembly by placing the nner tubing 6 in
! ~ension and the outer tubing 4 in compression. This prestress is
ii Lmportant because of the loads which will be imparted to the
ji conduit during high temperature operation. The outer tubing,
although in compression, would serve to maintain the inner tubing
¦ member 6 substantially in its prestressed or preexpanded configura-
¦¦ tion. The length of the concentric tubing assembly should there-
¦¦ fore be substantially the same in both the cooled and heated
¦l configuration. In addition, the stresses in the concentric
tubing assembly should be reduced during operation at elevated
~¦ temperatures. After the first weld 30A has secured one end of
¦¦ inner tubing to outer tubing, the desired prestress may be
¦1 imparted by stretching the inner tubing 6 at the opposite end of
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1 the concentric tubing assembly. This stretchir-g operation can be
~aecomplished by mechanic211y pulling the inner tubing while
holding the outer tubing fixed, or by heating the inner tubing
'rela~ive to the outer tubing. In the preferred embodiment of
this invention, the inneT tubular member 6 would not be initially
!prestressed beyond its yield point. After the desired amoun~ of
'prestress is imparted to the inner tubing, a second weld 30B
:extending completely around the junction between inner tubing and
outer tubing is made. Again, this weld m~y consist of multiple
" passes to ensure the integrity of the weld.
i Welds 30A an 30B ha~e not only secured inner tubing member 6
!lto outer tubing member 4, but have sealed ~he annular insulating
cavity 13 between the inner and outer tubing. In the preferred
il embodLment o this inven,ion, it is desirable to increase the
'' insulating capacity of the material in annular cavity 13 by
,withdrawing the gasses in annular cavity 13 to establish a
vacuum. This vacuum may be established by initially drilling a
hole in, or otherwise piercing, the outer tubing 4 to form an
~opening in the annular cavity 13.
A fi~ure 54, sho~n in Fig. 5, can be used for drilling a
hole into the outer tubing 6 and for evacuating the ~ases from
~annular cavity 13 This fixture comprises a clamp 56 extending
l around Lhe exterior of outer tubing 6. A passage 68 extends
;ithrough fixture 54 ~adially to the outer surface of tubing 6. A
drill bushing, not shown, can be inserted into passage 68 and
' an opening or hole 60 can be drilled into the outer tubing 6 in
! alignment with radially extending passage 68. The same fix~ure
. can then be used to establish at leas~ a partial vaeuum in
annular cavity 13 without losing alignment ~ith the drilled hole
, 60. ~he drill bushing can be removed and a plug, such as a
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Itapered pin, surrounded by an annular seal 62 can be inserted
, into passage 68, as shown in Fig. 5. A vacuum hos~ 58 can then
be attached between fixture 54 and a vacuum pump (not shown).
! Vacuum hose 58 communicates through passage 68 to the interior
5annular cavity 13. An O-ring seal 66, between vacuum fix~ure 54
and the exterior of concentric insulating conduit 2, prevents
leakage during evacua~ion of annular chamber 13. The tapered pin
64 extending into passage 68 and the circumferential seal 62
il eY.tending around t2pered pin 64 prevent leakage through passage
,~ 68 past tapered pin 64. After a suitable vacuum has been estab-
' lished within annular cavity 13, tapered pin 64 may then be
driven into drill hole 60 to close ~hat hole. The ou~er portion
of pin 64 extending beyond the surface of outer tubing 4 c~n then
Il be removed, an~, if necessary, a weld could be employed to seal
ll this pin.
! After fabrication of ~he individual conduits, a plurality of
,I conduits may be assembled to form an insulated tubing strlng by
i~ first inserting an internal coupling 20 in one end of each
separate tubular members. The interior co.upling is wedged into
the flared end of inner tubular member 6. Preferably, each
interior coupling member 20 would be inserted farther into one
conduit than into the adjacent conduit. If the interior coupling
member 20 is wedKed into the tapered section 34 of one member
, farther than into the other, the interior coupling would remain
~l affixed to a designated me~ber upon disassembly. Field disassem-
1l bly could then be simplified.
i! The preferred embodiment of this invention thus comprises a
il prestrPssed concentri.c tubing member having thermal insulation
Il along substantially its entire length. Convective, as well as
3~ radiant insulation, is provided and the evacuation of the annular
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cavity between the two concentric tubing members re~oves residual
jmoisture and reduces the heat transfer through the insulation.
The preferred embodiment -~lso employs onl~ two welds for each
individual conduit. The integrity of the welds employed in this
! invention is increased bv both reducing their numbPr and by
employing flared inner tubing sections in which the t~ickness of
the flared ends is not reduced below the nominal thickness of the
intermediate sections of the inner tubing member. Furthermore,
I¦ individual concentric insulating tubing members 2 have been
ll fabricated using conventional ~ubing members.
Il Although the inven~ion has been described in terms of the
il specified embodiment which is set forth in detail, it should be
¦Ij understood that this is by illustration only and that the inven-
!~ tion is not necessarily limited there~o, since alternative
il embodiments and operating ~echniques will become apparent to
¦l ~hose skilled in the art in view of the disclosure. Accordingly,
modifications are contemplated which can be made without departing
Il from the spirit of the described invention.
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