Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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MULTI-WALLED TUBULAR MEMBER AND METHOD OF FORMING
Background Of The Present Invention
, This invention relates to the method of
fabricating a multi-wall tubular member and
particularly to such a multi-wall tubular member ha~ing
a hardened inner wall and a high strength outer wall.
In various fluid systems, the piping and
other tubular members may require an inner surface or
wall having special specifications and requirements
which are different than that of the surrounding outer
wall. In such applications, a dual or multi-wall
tubular member can be formed from two separate
telescoped tubular members. Concrete pumping
represents one application in which a dual wall
specification is encountered. The abrasive
characteristic of the concrete being pumped requires
that the inner surface of the piping having a highly
abrasive resistance characteristic. Generally, where
metal piping is used, this requires an inner wall of a
very hardened metal. Concrete pumping however also
involves relatively high pressures, particularly
pressure surges. This requires a pipe having a very
high tensile strength to operate satisfactorily over
long periods of time under normal pumping pressures.
For example, pipe units which would advantageously be
constructed as in such a composite pipe are truck
mounted elongated pipe section for pumping concrete,
such as shown in V. S. Patent 3,860,175 which issued on
January 14, 1975 and is assigned to a common assignee
with the present application. Various other
applications encounter similar differential
characteristic requirements. Oil well piping systems,
nuclear power plants and various chemical flow systems
require various special specifications for interior of
the piping and contrast to a normally high strength
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requirement for the piping generally. Thus, one
solution which has been disclosed and used commercially
involves forming a composite multi-wall pipe from
individual pipes or tubular members mounted in
telescoped relation and specially processed to
establish a firm interfaced engagement and connection
between the two pipes. The inner pipe can then be
formed with the necessary characteristics demanded by
the particular product being tfansported. The outer
pipe can be formed as a high strength member such that
the pipe unit can withstand the pressures encountered
under operating conditions.
United States patent 4,497,673 which issued
February 5, 1985 discloses a multi-wall pipe for
applications in those systems requiring a hardened
inner liner or wall. In accordance with the teaching
of that patent, the tubular members are originally
constructed to permit telescoping of the tubular
members. After assembly, the inner liner is flame
hardened causing the expansion of the inner liner into
engagement with the outer liner or shell to form a
composite member. The pa'ent specifically teaches that
the inner liner is provided with sequential heating and
hardening to progressively expand the pipe and provide
the desired interface interconnection. The flame
hardening requires entry into the pipe with an
appropriate torch unit for heating of the inner pipe to
the necessary degree for hardening. U.S. Patent
4,449,281 which issued May 22, 1984 discloses a
alternate system. In this system or disclosure, cold
water is introduced into the pipe, with the ends of the
inner pipe sealed. The water is pressurized to expand
the inner pipe. Thereafter, an induction heating unit
is moved over the pipe unit and specially arranged to
heat only the exterior pipe of the two telescoped
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pipes. The inner water chambers are further
pressurized to expand and produce a bond therebetween
or the firm engagement therebetween. A similar system
is disclosed in U.S. patent 4,598,857 which issued on
July 8, 1986. In this disclosure, after the induction
heating, a mechanical working device is applied within
the expanded exterior pipe and inner pipe to collapse
the pipes to form a composite pipe. U. S. Patent
3,579,805 which issued on May 25, 1971 discloses a
system using freezing of the pipe unit to effect
interengagement between the pipes of a multiple layered
pipe unit. Other methods of forming composite dual
walled pipes or multiple wall pipes are disclosed in
the following ~nited States patents:
Patent No. Issue Date Inventor
3,579,805 05-25-1971 Kast
4,030,711 06-21-1977 Siller
4,322,894 06-01-1982 Whistler
4,332,073 06-01-1982 Yoshida
Nothwithstanding, the activity and the
efforts in the prior art in developing a multi-wall
tubular member and pipe unit, the present systems are
relatively costly and also have certain limitations
which prevent long life operation.
Summary Of The Present Invention
The present invention is particularly
directed to the method of forming and fabricating a
multi-wall composite tubular member particularly a dual
wall pipe unit which has a long reliable life and is
particularly adapted for commercial implementation.
The present invention has been particularly developed
in connection with concrete pumping systems and is
correspondingly described in connection therewith for
convenience and clarity of description, but is not
limited in application thereby. Thus, the multiple
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wall piping method and the resulting product made in
accordance with the present invention can be used in any
other application requiring a hardened inner surface in
combination with a high strength outer wall. Generally, in
accordance with the present invention, the pipe or other
tubular members are constructed or processed for relatively
free and ready assembly of the member in superimposed
relation. The inner and outer members are then forced into a
reasonably tight engagement with one another. Although
various means of accomplishing such engagement will be
apparent to those skilled in the art, especially having
regard to the prior art exemplified by the aforementioned
patents, forcibly expanding outwardly the inner member a
distance in excess of the interface gap to engage and
simultaneously deform and expand the outer tubular member,
thereby further expanding the outer walls prior to heating,
provides a particularly satisfactory and unique procedure to
form a close and reasonably tight fit between the pipe or the
members. An induction heating unit operating at a low
frequency in contrast to the conventional high frequency is
coupled to and moved relative to the expanded pipe
subassembly and provides for progressive heating of
relatively small lengths of the expanded pipe unit.
Immediately aftçr the heating, the expanded pipe unit is
quenched with a suitable quenching liquid, and preferably a
chilled brine solution applied to both surfaces.
As will hereinafter become apparent, the
application of the quenching liquid fully and rapidly
quenches the high temperature of the inner pipe heated areas,
resulting in an ultra hardening of such areas. On the other
hand, the induction heating process allows the restriction of
the significant heating to the inner pipe with the result
that the outer pipe is only slightly hardened. This means
that it essentially retains a ductile state and maintains the
necessary high tensile strength of the composite member for
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operation in high pressure applications. This is the essence
of the present invention.
More particularly, in a preferred and practical
application of the present invention in the forming of
concrete pumping line members, the induction heating
apparatus is specially constructed as a low frequency
induction heating source. Generally, the unit operates in
the range of low hundreds hertz in contrast to the
conventional high frequency induction heating unit operating
in thousands of hertz frequency
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such as heretofore suggested for use in forming of dual wall
piping. With the unit operating at a low frequency, the
induction unit can be mounted to the exterior of the
multi-wall pipe and effectively progressively heat both the
inner tubular member or pipe wall to the necessary
temperature for quenching while effectively heating of the
outer wall. The low frequency source also may be adapted to
internal mounting and direct heating of the inner tubular
member. The effectiveness of the internally located heating
unit however is significantly affected by the length of the
leads and thus is severely limited as to the length of the
piping or tubular member formed and the frequency which can
be used.
More particularly in a preferred construction of
the present invention for commercial production of concrete
pumping composite pipe sections and the like, outer and inner
pipes of essentially corresponding lengths are constructed,
with the inner pipe of a significantly smaller outside
diameter than the inside diameter of the outer pipe to permit
the free assembly of the tube into alignment. The pipes are
then forced into engagement by outward expansion of same and
in a particularly preferred embodiment, this is accomplished
by forcing a mechanical working mandrel through the aligned
pipes while maintaining the longitudinal alignment. The
working mandrel has the outer round diameter corresponding to
the desired final diameter of the composite pipe section and
serves to expand the inner pipe outwardly into tight
engagement with the outer pipe, also expanding of the
abutting pipes outwardly a further distance. The expansion
of the pipes establishes a very firm and tight engagement
between the interface surfaces which is essentially free of
air gaps. The diameter of the member corresponding to the
final desired diameter also provides the final sizing of the
composite pipe section and establishes a true round
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inner passage. The expanded subassembly is then moved
relative to an encircling heating coil to rapidly
increase a short circumferential annular portion of
only the inner pipe to the quenching temperature. The
pipe section and coil unit are moved relative to each
other in a continuous manner to progressively heat the
pipe section over the axial length thereof.
Immediately upon leaving of the coil unit at the
quenching temperature, the inner and outer surfaces of
the heat subassembly are subjected to the quenching
liquid over the high temperature area on both the inner
and outer surfaces of the heated pipe section. The
quenched hardening of the inner pipe using the
induction heating provides a greater hardness than that
normally obtainable with a conventional furnace
hardening system. The present invention also permits
forming of the dual pipe in a single pass in contrast
to sequential multi-step flame hardening and the like,
avoiding the distortion which may occur on each of a
plurality of heating passes. The single pass
processing also creates an improved grain growth and
minimizes cracking, as well as reducing the energy
consumption and cost. Further, the present invention
providing a continuous process permits rapid and
effective forming of a composite tubular member with a
hard inner lining or wall and high strength ductile
outer wall.
The present invention provides a low cost
method of forming a dual wall tubular member
particularly adapted to high pressure applications such
as encountered in concrete pumping and other similar
high pressure applications. The process and product
use conventional and readily available technology
thereby providing a highly cost efficient process and
product which particularly adapts the present invention
for commercial implementation.
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Brief Description Of The Drawings
The drawings furnished herewith illustrate
the best mode presently contemplated for carrying out
the invention and are described hereinafter.
In the drawings:
Fig. 1 is side elevational view of a
composite pipe unit constructed in accordance with the
present invention and connected in a concrete pumping
system, and with parts of the pipe unit broken away to
more clearly illustrate the composite pipe unit
constructed in accordance with the present invention;
Fig. 2 is an enlarged fragmentary view of a
composite pipe unit of Fig. l;
Fig. 3 is a side elevational view
illustrating an initial step in assembly of the
composite pipe unit with respect to a composite pipe
forming apparatus;
Fig. 3a is an enlarged longitudinal section
of the apparatus shown in Fig. 3 with the pipe unit
located and being subjected to the first step in the
composite pipe forming process;
Fig. 4 is a view, similar to Fig. 3
illustrating a subsequent processing of the composite
pipe unit to finalize and complete the forming of the
composite pipe unit; and
Fig. 5 is a view similar to Fig. 4
illustrating an alternate mode of carrying out the
present invention.
Description Of The Illustrated Embodiment
Referring to the drawing and particularly to
Fig. 1, composite dual wall pipe units 1 are
illustrated connected in a concrete pumping system such
as shown in the previously identified U.S. Patent
3,860,175. A high pressure pump source 2 of concrete
is mounted on the bed of a vehicle 2a for transport
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through a series of composite pipe units l and
discharged at a discharged nozzle unit as at 3. The
concrete source 2 introduces the concrete into the
composite pipe units l under high pressure conditions
and establish the high pressure flow through the pipe
unit to the discharge end. In actual practice, the
plurality of pipe units l are interconnected to each
other and/or to other components with releasable
couplings for pipe replacement. Such replacement is
time consuming and costly, the pipe is costly and the
demand for pipe sections and this and other concrete
pumping systems having a long life is significant.
Generally as shown in Figs. 2 and 3, each
pipe unit l, constructed in accordance with the present
invention, includes an inner pipe 4 to form a liner
which is abrasive resistant and an outer pipe 5 having
a high strength. The pipes 4 and 5 are formed as a
composite pipe unit with a tight and effective
contiguous interface 6 between the pipes 4 and S. The
pipes are shown non-bonded in that there is no bonding
element interposed within the interface. As more fully
developed hereinafter, the inner pipe 4 is a hardened
metal member to maintain high abrasive resistance to
the effects of the flowing concrete and particularly
its highly abrasive characteristic. The outer pipe 5
is a ductile steel member to maintain the necessary
strength in the pipe unit l. In a concrete pumping
system, suitable carbon steels of slightiy different
carbon content have been used for t-he pipe units but
any other material may obviously be used which will
permit the forming of a hardened inner liner in
combination with an appropriate characteristic outer
- shell.
Figs. 2-4 inclusive particularly illustrate
one preferred mode and embodiment of carrying out the
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present invention, and which has been particularly
found to produce an effective and reliable concrete
pumping pipe unit 1.
Referring particularly to Fig. 3a, the initial
assembly of the pipes 4 and 5 for forming of the pipe
unit 1 is illustrated. The pipes 4 and 5 are initially
formed as standard ductile steel pipe, or of any other
metal which can provide the required specification in
the composite pipe unit and with the internal diameter
of the outer pipe 5 slightly greater than the exterior
diameter of the inner pipe 4, such that the inner pipe
is conveniently and readily introduced and passed intc
alignment with the outer pipe. A small gap 8 exists
between the assembled pipes. The loose sub-assembly 7
is supported within an expanding machine or apparatus 9
and positively held against axial or longitudinal pipe
movement in the illustrated embodiment. The assembled
pipes 4 and 5 are shown in a suitable rigid support 10
having an axial end abutment unit 11 for axially and
~0 longitudinally supporting the pipes in fixed
position.
A mandrel 13 is located in coaxial alignment
with the sub-assembly 7 within the expander apparatus
9. The mandrel 13 has a precisely formed cylindrical
wall 14 corresponding to the desired final internal
diameter of the composite pipe unit 1 and a tapered
lead-in section 14a. ~ hydraulic positioner 15 is
mounted to the machine support 10 to one end of pipe
subassembly 7. The cylinder 16 of ~the actuator is
fixedly mounted, with the piston rod 17 extending
outwardly and rigidly affixed to the mandrel 13. The
piston rod is movably axially through the location of
the pipe sub-assembly 7 and is releasably connected to
the mandrel 13 for assembly of the sub-assembly 7
within the support 10 and with mandrel 13. In the
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assembled position as shown in Fig. 3, the expanding machine 9 is
in the extended position with the mandrel 13 located
immediately adjacent the one end of the sub-assembly 7
which is rigidly held in position. The hydraulic
cylinder unit 15 is then actuated to retract the piston
rod, thereby pulling the mandrel 13 through the pipe
sub-assembly 7, as shown in Fig. 3a. The mandrel 13
mechanically works and forces the inner pipe 4
outwardly into inner engagement with the outer pipe
5. The mandrel has a diameter to work and deform both
of the inner and outer pipes outwardly into an enlarged
cylindrical configuration and preferably with a true
constant diameter corresponding to the specified final
configuration of the composite pipe unit 1. The
mandrel 13 can readily work both of the metal pipes 4
and 5 in the ductile state of the pipes 4 and 5. The
mandrel thus moves completely through the assembly to
completely deform and shape the sub-assembly 7 to the
desired final diameter configuration. The interaction
of mechanically working and expanding both the inne~
and the outer pipe establishes an extreme tight
interfit at the interface bet~een the two pipes which
is essentially void of air gaps and the like.
The expanded sub-assembly 7 is placed in a
suitable heat treating apparatus as shown in Fig. 4,
which can be a separate machine as shown or
incorporated into the expanding apparatus. The heat
treatin~ apparatus includes an ind~ction heating unit
18 including an outer annular housing 18a. A heating
coil 19, appropriately mounted within the cylindrical
h~using, establishes an annular alternating magnetic
field within the opening of the housing. A low
frequency power supply 20 is connected to the heating
coil unit 19 to establish a low frequency field, as
diagramatically shown at 21, within the opening of the
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cylindrical housing. In forming a composite pipe unit
1 for concrete pumping a frequency of about 180 hertz
was used, as hereinafter described, Although the
particular requency used is not critical, the
frequency must be low and significantly less than 1000
hertz such has heretofore been used in heating of
similar tubing for composite pipe. The low frequency
allows the penetration to the inner pipe 4 for
effective concentration of the heating effect.
A supporting track 22 of any suitable
construction is located in alignment with the
cylindrical housing. The supporting track 22 may
include a series of supporting rollers 22a for proper
pipe support. In a practical structure, eight rollers
of a substantially larger diameter than shown supported
a forty foot length of pipe. The expanded sub-assembly
7 is mounted on the track in co-axial alignment with
the housing opening and thus centrally of the low
frequency magnetic field generated by the induction
heating unit 17. The length of the heating coil unit
19 is relatively shore and thus provides alignment with
a short portion of the sub-assembly 7. Energization of
the coil unit l9 provides rapid heating of the small
aligned area 23 of the inner pipe 4, corresponding
generally to the axial lenqth of the coil.
A drive unit 23a is coupled to the heating
unit and the supporting track to establishing relative
movement of the expanded sub-assembly 7 unit through
the center of the heating unit 18 and therefor through
the magnetic field created by the energization of the
induction heating coil 19. The relative movement
provides for a continuous progressive heating of small
areas 23 of the inner pipe 4 of the sub-assembly 7.
The low frequency field created by the coil unit 19 is
such that the inner pipe 4 of the sub-as~embly 7 is
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rapidly heated to the necessary hardening temperature
such as 1600 degrees Fahrenheit ~F).
Immediately downstream of the induction
heating unit 18, a quenching unit 24 is mounted. The
quenching unit incl~des an inner solution nozzle 25 and
an outer solution nozzle 26. Both nozzles are
generally cylindrical ring members of a diameter
respectively related to the internal diameter of the
inner pipe 4 and the external diameter of the outer
pipe 5 of the expanded sub-assembly 7 and therefore the
composite pipe unit 1. The diameters are selected to
space the respective nozzles 25 and 26 slightly from
the inner and outer sut-faces of the expanded pipe sub-
assembly 7.
A quenching solution source 27 is mounted to
the end of the machine support and connected by
suitable flow lines 28 to the respective nozzles 25 and
26.
As the expanded pipe unit moves through the
magnetic field 21, the heated area 23 is created and
then passes directly from the induction heating unit 18
into alignment with the nozzles 25 and 26. The nozzles
have similar radial discharge openings 29 extending
inwardly and outwardly respectively. A quenching
solution 30 is ejected ~rom the nozzles 25 and 26 onto
the heated area 23 to fully and rapidly ~uench the high
temperature of the inner pipe heated areas 23,
resulting in an ultra-hardening of the area 23. The
inner pipe 4 is thereby fully hardened to develop the
desired abrasive resistent inner wall of the composite
pipe unit 1. The outer pipe 5 will be slightly
hardened. It will however essentially retain a ductile
state and maintain the necessary high tensile strength
of composite unit 1 for operation in various high
pressure applications. In accordance with known
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phenomena, the induction heated and quenched inner wall
provides a hardness significantly greater than that
obtained with a conventional furnace type or flame
hardening. This results from the various factors such
as residual stresses in the metal, a less retained
austenite as well as appropriate carbon segregation.
More particularly, in forming a pipe unit 1,
particularly adapted for and used in a truck mounted
concrete pumping unit, the pipe sections consisted of
an inner pipe of a 1040 carbon steel. The external
diameter of the pipe in the original state was five
inches with a wall thickness of .095 inches. The outer
pipe 5 was formed of a 1020 carbon steel, and having an
- original outer diameter of 5.25 inches and a wall
thickness of .095 inches. In the assembled state, it
therefore developed a gap of approximately .155
inches. Such a gap permits the very simple and ready
telescoped assembly of the inner and outer pipes to
form sub-assembly 7. The mandrel had a forming
diameter or cylinder wall of 4.92 inches corresponding
to the internal diameter of the composite pipe unit
1. In one practical structure, the mandrel 13 had a
constant diameter length 14 of about four inches with a
gradual or inclined lead in portions 14a. The relative
movement of the mandrel and the pipe sub-assembly 7
expands the sub-assembly 7, with the inner diameter of
the inner pipe 4 expanding outwardly substantially
0.125 and the outer pipe .065 inches. Such expansion
stretches the inner pipe 4 closing the gap, with the
ductile outer pipe 5 stretched. The expanded ductile
pipe sub-assembly 7 are then moved relatively through
the short heating unit 18 and the immediately adjacent
quenching unit 24. Energization of the heating coil 19
rapidly raises the inner carbon steel pipe to the 1600
degree Fahrenheit quenching temperature. As heated
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pipe unit moves from the heating unit, it is
immediately subjected to the quenching solution 30. A
brine solution is preferably used to establish a rapid
heat transfer from the heated metal resulting in
creation of an ultra hard inner wall located in
effective integrated engagement with the outer high
strength ductile pipe 5 for use in concrete pumping or
other applications having similar strength and abrasive
specifications. The present invention permits
completing of the dual wall pipe in a single pass which
produces an improved hardened pipe assembly as a result
of minimizing of distortion, cracking and the like as
well as minimizing the cost of ma,nufacture. In
addition, the induction heating enhance the physical
engagement at the abutting interfaces of the two pipes
4 and 5. Thus, the inner pipe 4 grows more than the
outer pipe 5 to create such improved interface
engagement.
Although the illustrated embodiment of the
invention provides a practical and effective method for
forming of the composite tubular unit, other apparatus
including means for a mechanically working of the
loosely assembled tubular members to establish an
initial tight fit in combination with an induction
heating unit for induction heating of only the inner
pipe or wall tubular member may of course be used
within the broad teaching of the present invention.
Thus, as shown in Fig. 5 for example, an induction
heatinq unit 31 can be mounted internally of a sub-
assembly 32 with relative movement of the sub-assembly
providing for progressive heating of successive short
areas 33 of the pipe sub-assembly 32. Generally as in
the previous embodiment, appropriate quenching nozzles
34 are located again immediately adjacent to the
heating unit to provide the desired immediate quenching
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of the heated area 33. Inner and outer nozzles are
preferably provided to produce the maximum hardness of
the inner wall. Where the hardness specifications of
the inner wall are of a lesser nature, only the inner
nozzle could be used for purposes of quenching of the
high temperature inner pipe. In this embodiment, a low
frequency is also preferably used. The length of the
power leads 35 to the induction heating unit 31 would
have to be equal to the total length of the pipe sub-
assembly. In high frequency systems, the leads cannotbe practically extended. Thus, the length of the pipe
section which could be hardened even using the low
frequency of the present invention would limit pipe
length which could be made. If a high frequency power
lS supply could be made of a sufficiently small diameter
to permit relative movement of the pipe and power
supply with the power supply relatively moving through
the internal diameter of the pipe, obviously, a high
frequency supply could be used. As a practical matter,
such power supplies are not presently available.
The present invention with present day
technology is generally practically applied to smaller
diameter tubular members. Thus, as described, the
present invention is readily applied with great success
in forming of pipes on the order of five inch
diameters. Although larger diameter pipe units can be
formed, special equipment would generally be necessary
for tubular member having a diameter significantly
above 10 inches or having a relatively heavy wall
thickness because of the difficulty in effectively
mechanically expanding such members. Thus, a 12 inch
pipe with a wall thickness of .5 inches would require
special equipment to process and form an expanded sub-
assembly.
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The present invention provides high strength
tubular members having a hardened inner wall and a
ductile high strength outer wall which can be
commercially mass produced for high pressure
applications requiring substantial flow such as in
concrete pumping as well as other applications
requiring a hardened inner steel wall.
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Various modes o carrying out the invention
are contemplated as being within the scope of the
following claims and particularly pointing out and
distinctly claiming the subject matter which is
regarded as the invention.
