Note: Descriptions are shown in the official language in which they were submitted.
1 ~ZE~33~ ,
CORRUGATED PIPE
BACKGROUND OF THE INVENTION
The present invention relates to a pipe of sheet steel or
the like, fabricated of a single strip of metal, and which is
provided with spirally extending corrugations.
It has long been recognized that pipes such as are used for
conduits, drainage and the like are subject to substantial
compressive loads, and that they have greater strength if they
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are corrugated, instead of being of purely cylindrical
construction. For example, Pratt et al. U.S. Patent No. 365,630
discloses the provision of a tube of a suitable metal which is
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~ corrugated spirally with a single rib and which extends from one
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~; end of the tube to the other. The tube;is produced by placing a
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; plain tube upon a spirally corrugated mandrel, which is placed
between the centers of a lathe, and a roll of angular
corrugations is then f;orced lnto the tube, so as to cause it to
take the form of the corrugated mandrel. This corrugated tubing
had an exterior~ sinusoidal profile formed by convex portions
connected directly to~concave portions. Such tubing is disclosed
~as being used in connection with boilers, radiators, and the
like.
Silk U.S. Patent No. 1~,263,340 discloses a spiral sheet
~ ~ metaI pipe which is intended to be used for culverts, sewers, and
; the like, being formed with~ continuous spirally extending
corrugations, with an upstanding spiral seam provided by flanges
extending outwardly from the pipe. The disclosed pipe is formed
of;a single strip of sheet metal which is wound or coiled into
spiral form, and having the lateral edges interlocked by the
~ above noted outstanding flange and seam construction. It has a
; 30 sinusoidal pro~ile.
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Hartman U.S. Patent No. 1,259,233 provides a drain pipe of
sheet metal, for roadways, gutters, and the like, made of a strip
having circular corrugations, and which is formed into a circle
and welded in the circular form~ with plural strips being axially
joined. The disclosed pipe has a sinusoidaL profile.
Nemer U.S. Patent No. 3,094,147 provides helically wound
strip material formed lnto bendable tubing, useful, for example,
as part of an automobile exhaust system. The edges of the strip
of which the tubing i5 formed with rolled edges which are joined
1nto a four-thickness locked seam. The profile is sinusoidal,
~ interspersed with flat portions formed at the four-thickness
seams.
, Lupke et al. Defensive Publication T103,901 discloses a
stiff thin walled plastic pipe of thermoplastic material, the
lS longitudinal cross section profile of the wall comprising a wave
form.
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Spirally wound steel pipe is widely used for culverts,~storm
sewers, subdrains, spillways~ underpasses and service tunnels.
Accordlng to Handbook of Steel Drainage and Highway Construction
Products~, publ~ished by American Iron and Steel Institute (Second
Edition, 1971), round or clrcular corrugated steel conduits are
n common use for such purposes for medium and high fills, or
trenches, and range in diameter from six inches to 21 feet. The
corrugations are stated to be "circular arcs connected by
tangents" and are described by pitch, depth and inside forming
radius. Riveted and resistance spot-welded pipe are noted,
having circumferential seams, with the corrugations being of two
and two-thirds inch pitch by one and one-half inch depth and
three inch pitch by one inch depth. There is also noted lock
seam pipes, with the seams and corrugations running helically (or
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spirally) around the pipe. Small diameters of six, eight, ten
inches, etc., have a pitch of one and one-half inches by
one-quarter inch depth, while larger sizes, with diameters up to
twelve feet, have a two inch pitch by one-half inch depth, two
and two-thirds inch pitch by one and one-half inch depth and
three inch pitch by one inch depth. Tables are provided for the
configurations of the various pipes, with the pipes being of
convex and concave circular arcs connected by inclined flat
tangential portions. This publication provides tables setting
forth the maximum cover of fill material for corrugated steel
pipe, taking into account pipe diameter and thickness of the
sheet steel material of which the corrugated pipe is made. For
example, Table HC-l provides that with a corrugated pipe having a
two and two-thirds inch pitch and one-half inch depth
: 15 corrugations, for an H 20 Live Load, where the pipe diameter is
eighteen inches, and the pipe wall thickness is .052 inches, the
maximum cover is 132 feet. With other factors being the same,
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and the thickness increased to .079 inches, the maximum cover is
:207: feet. With the use of these tables, engineers designing
; 20 culverts, dra~n pipes, etc., are able to determine the required
size of pipe, based upon such variable factors as the type of
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load,~ depth of fill, and type of soil.
As indicated by the above noted Handbook, the corrugated
steel pipe which has been produced has been engineered for the
maximum fill which pipe of a particular configuration is capable
; of safely supporting. To this end, the thickness and the shapes
of the corrugations have been standardized, the corrugations
having, as above noted, circular arcs connected by tangents which
were inclined. Such pipes have been sufficiently strong to
sustain the design loads as set forth in the above noted
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Handbook.
Consequently, an engineer, under present practices, has a
llmited number of available plpe sizes and dimensions. For
example, where the engineer is to specify a corrugated steel pipe
for an H 20 Live Load, the pipe having an eighteen inch diameter,
such pipe is available in thicknesses of .052 inches, .064
inches, and .079 inches, which are specified for maximum cover in
feet of 132 feet, 166 feet and 207 feet, respectively. If the
engineer is faced with a project which requires such an eighteen
inch diameter corrugated steel pipe, with a rated H 20 Live Load,
and he is aware that his maximum cover will be, for example, 30
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feet, then he is faced with specifying a pipe having a capability
of withstanding more than four times the actual cover of that
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project. Nevertheless, there is available only a very
~; 15 substantial over-strength pipe for the particular requirement,
and therefore the engineer is forced to specify an unnecessarily
expensive product.
While the above noted publication refers to lock seam pipe,
with~ helical corrugations, and to resistance spot-weldcd pipe
with circumferential seams, there has recently been introduced
equipment for produclng spiral wound butt-welded pipes. This
equipment is manufactured by Armco Steel Company. By avoiding
the rolled edges which produce a locX seam, and utilizing the
butt-welded seam, a reduction of metal cost of approximately five
percent is achieved. The equipment required to produce the
butt-welded seam of the corrugated helical steel pipe is
expensive, and therefore, although there is a saving in direct
~; metal cost, there is a substantial addition in overall cost due
to the noted welding equipment.
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SUMMARY OF THE INVENTION
A corrugated spiral pipe of strong material, such as steel
sheet, has spaced, spirally extending corrugations. Between the
corrugations are flat portions, which are closer to the axis of
the pipe than are the crests of the corrugations. Each
corrugation comprises a clrcular arc, and an inclined tangential
portion, the tangential portions each being connected by a
concave circular arc with a flat portion which lies closer to the
axis of the pipe than the crests of the corrugations.
In preferred embodiments, the pitch between corrugations may
be five inches, with a depth of one-half inch. In an alternate
embodiment, the pitch may be six inches, with a depth of one
inch.
~; ~ Preferably, the edges of the strip which is corrugated to
form the corrugated pipe of the present invention are folded
over, so as to provide a lock seam. However, if desired the
edges may be secured by other techniques, including butt-welding.
Among the objects of the present invention is the provision
of corrugated pipe which will utilize less material than is
20~ required for the production of known pipes of the same thickness,
diameter and length; another object of the present invention
being the~ provision of corrugated steel pipe which can be
fdbricated at a significantly lower cost than the pipe now made,
and which is of comparable thickness, diameter and size.
Other objects and many of the attendant advantages of the
present invention will be readily understood from a consideration
of the following specifications, claims and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is an elevational view, with parts broken away, of a
conventional corrugated steel pipe.
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Fig. lA is an enlarged cross-sectional view taken on the
line lA-lA of Fig. 1.
Fig. 2 is an elevational view, with parts broken away, of a
;; corrugated pipe in accordance with the present invention.
Fig. 2A is a cross-sectional view taken on the line 2A-2A of
Fig. 2.
Fig. 3 is a cross-sectional view similar to Fig. 2A, and
showing an alternate embodiment of a corrugated pipe in
accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMEMTS
Referring now to the drawings, wherein like or corresponding
~; reference numerals are used for like or corresponding parts
throughout the several vlews, there is shown in Fig. lA a prior
art corrugated pipe designated 10, and being provided with
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helically extending corrugations 12. In practice, a single sheet
of steel of the deslred width and thickness is subjeoted to a
plurality of corrugating roIlers, which provide~a plurality of
corrugations across~the width of the steel sheet, and then the
cor}ugated steel strip is~ helicallY formed, with provision for
]oining of the edges at helical joints J so as to form a
continuous pipe. As above noted, the joining of the edyes may be
either by rolling the edges, so as to provide the structure for
the formation of a~ l:ock seam, or the edges may be butt-welded.
The length of pipe 10 which is produced is limited only by the
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length of the original steel strip stock material, the handling
facilities of the production plant, and transportation equipment.
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In practice, a saw is provided to saw the completed pipe into
suitable lengths for handling and transportation.
Fig. lA shows the shape of the wall of the corrugated pipe
10. This illustrates the standard shape of the corrugations,
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known as "circular arcs connected by tangents". Here, there are
convex circular arcs 14, the arcs 14 being arranged in a spaced
series. There are also provided concave circular arcs 16
intermediate the convex circular arcs 14. Intermediate adjacent
circular arcs 14 and 16 there are inclined flat tangent portions
18, these being tangent to both the convex circular arcs 14 and
concave circular arcs 16.
The depth of the corrugations of the typical prior art
corrugated spiral pipe 10 is measured from the bottom of the
concave circular arc 16 to the top of the convex circular arc 14,
and is one-half inch in the pipe 10. The pitch of the
corrugations of the pipe 10 is two and two-thirds inches, as
measured at right angles to the corrugations from crest to crest.
Referring now to Fig. 2, there is shown a helically wound
corrugated pipe 20 in accordance with the present invention.
Pipe 20 is produced by equipment similar to that described in
connection with the production of pipe 10 of Fig. lA, except that
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the rolls or dies include not only dies for forming corrugations,
but dies for maintalning portions of the stock steel strip in
flat condition. Thus, there will be seen helical corrugations
22, and between them there are flat portions 24. Helical joints
J join the edges of adjacent strips to form the ipe 20. It will
be noted, further, that while th~e thickness of the sheet steel of
~the pipe 20 in accordance with the present invention may be of
~ ; 25 standard thiclsnesses as used in the art to produce conventional
;~ pipe 10, and while the diameters of pipes 20 may be the same as
the diameters of conventional pipe 10, the angle of the
corrugations 22 may be significantly different from the angles of
the corrugations 12. The angles of the corrugations for pipes 20
of various diameters are given as follows:
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TAsLE A
PIPE DIAMETER ANGLE
(Inches) (Degrees)
12 38
18 25
2I 20
24 19
14
36 13
42 10
48 9
54 8
Referring now to Fig. 2A, the corrugation 22 of pipe 20, as
viewed from the exterior thereof, comprises a convex circular arc
26, on either side of which is an inclined flat tangent portion
28. Adjacent each of the inclined flat tangential portions 28 is
a concave circular arc portion 32 which is tangent to both the
inclined flat portion 28 and the adjacent horizontal flat portion
24. There is thereby~provided a smooth transition of the sheet
steel from each horizontal flat portion 24 to the adjacent
corrugations 22.
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The horizontal flat portion 24 has substantial length, or
25~ distance~between ~adjacent concave arc portions 32. The pitch of
the pipe 20, as measured perpendicularly between crests of
successive corrugations 22, is five inches, and the depth is one-
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half lnch,~as measured from the~crest of a corrug~tion 22 to the
flat portlon 24.
A pipe 20 in accordance with the present invan~ion may be
made with a reduction in cost of sheet steel stock, and using
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standard lock seams, which is ~approximately six and one-half
percent less than a pipe 10, based on equal thicknesses,
diameters and lengths of the pipes. This results in an overall
cost reduction of a pipe 20 of approximately fourteen percent, in
comparison with the pipe 10 of the same wall thickness, length
and diameter.
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Referring now to Fig. 3, there is shown a pipe 40 in
accordance with the present invention, comprising helical
corrugations 42, having the same general characteristics as
corrugations 22; that is, there is provided a convex circular arc
portion 46, a pair of inclined flat portions 48 tangential
thereto, a pair of concave circular arc portions 52, and flat
portions 44 between arc portions 52. The pitch between
corrugations 42 of the pipe 40 shown on Fig. 3 is six inches, and
the depth of the corrugations, measured from the flat portion 44
to the crest of the corrugations 42 is one inch. As is apparent,
the pipes 20 and 40 have in longitudinal cross-section repeated
successions of flat portions and corrugations, the helically
extending and longitudinally spaced corrugations 22 and 42 having
,~ flat portions 24 and 44 intermediate the corrugations 22 and 42.
The flat portions 24 and 44 are parallel to the axis of the pipe
; ~ 20, 40, respectively. As is apparent from Figs. 2A and 3, the
crest of the corrugations 22 and 42 are at a greater radius than
are~the flat portions 24 and 44, respectively.
The angle of the corrugations of the pipe 30 are those set
forth in the following table:
TABLE B
PIPE DIAMETER ANGLE
(Inches) (Degrees)
48 7
- 25 54 6
66 5
72 5
78
96 3
102 3
108 3
g
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The pipes 20 and 40 are illustrative of pipes made in
accordance with the present invention. The herein disclosed
pipes are significantly less expensive than are standard pipes
currently manufactured, as exemplified in the above noted
Handbook of Steel Drainage & }Iighway Construction Products. The
pipes in accordance with the present invention are entirely
; suitable for many installations, particularly wher~ the
anticipated fill height and load factors are significantly less
than the maximum for which the standard corruguated steel pipes
~; 10 are suitable.
The claims and the specification describe the invention
herein presented and the terms that are employed in the claims
draw their meaning from the use of such terms in the
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specification. Some terms employed in the prior art may be
broader in meaning than specifically employed herein. Whenever
there is a question between the broader definition of such terms
as used in the prior art and the more specific use of the terms
; herein, the more specific meaning is meant.
It will be obvious to those skilled in the art that various
changes may be made~in the herein disclosed apparatus. However,
the invention is not limited to what is set forth in the
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~ specification or described in the drawing, but only as defined in
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~ ~ ~ the claims attended hereto.
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