Reinforced smooth flow pipe

A reinforced, spirally wound tube or pipe product shaped from an elongated sheet of ductile material formed into adjacent, helical convolutions. The pipe is impressed with at least one longitudinal impression which is trapezoidal in cross-section and formed at the same helix angle as the convolutions so that it is parallel to the juncture of adjacent convolutions. A conforming reinforcement element is located in the impression to strengthen the impression and form a closure of the mouth of the impression. The impression protrudes from the outer wall of the pipe, leaving the inner wall surface of the pipe generally smooth. Adjacent edges of the spiralled sheet are either welded or joined by a continuous lock seam.

SUMMARY OF THE INVENTION 
The Background 
This invention relates to spirally wound pipe products, and more 
particularly to a helical pipe having one or more strengthening ribs or 
impressions integrally formed in the outer wall of the pipe. 
It is well known to form spiral pipe from an elongated sheet of metal or 
other ductile material. Such pipe products are illustrated, for example, 
in U.S. Pat. Nos. 1,179,577; 2,337,374; 3,106,177 and 3,132,616. 
In the conventional apparatus for producing a helical pipe product, an 
elongated sheet of metal is impressed with longitudinal corrugations, ribs 
or the like, and then spiralled into adjacent, helical convolutions which 
are joined either by welding or by formation of a continuous lock seam. 
One apparatus for forming a reinforced, spirally wound pipe product of the 
present invention is disclosed in applicant's co-pending United States 
patent application entitled "Method and Apparatus For The Manufacture Of 
Reinforced Smooth Flow Pipe" filed on the same date as the present patent 
application. 
Many pipe products of the prior art, although exhibiting sufficient load 
bearing capacity to be used as drainage culvert for highways and the like, 
suffer the disadvantage of having a non-smooth inner wall. For example, 
helically corrugated pipe produced by the apparatus of Freeze U.S. Pat. 
No. 2,136,943 has helical corrugations in the inner wall as well. The 
result of a non-smooth inner wall is inhibition to flow of liquids through 
the pipe, forcing the pipe user to select a larger diameter pipe than 
would be needed were the inner wall of the pipe smooth. 
The prior art has recognized that the strength of corrugated pipe in 
combination with a smooth pipe inner wall is a favorable material 
combination. For example, Lombardi U.S. Pat. No. 3,340,901 has disclosed a 
pipe product formed from at least two layers of metal including a 
corrugated pipe outer shell and a smooth pipe inner shell. 
However, pipe of this nature is often non-competitive with single-thickness 
corrugated pipe. The pipe, being formed of two thicknesses of material, 
often is substantially more expensive than single-thickness corrugated 
pipe. Furthermore, double thickness pipe such as that of Lombardi is 
difficult to form, and often the inner surface of the pipe product is 
dimpled or crimped due to stressive forces inherent in the spiralling 
operation for formation of the pipe. In addition, formation of a double 
lock seam as disclosed by Lombardi can be a tedious procedure if the edges 
of the corrugated and uncorrugated sheets do not exactly align during 
formation of the lock seam elements and final spiralling of the doubled 
sheets of material into a pipe. 
THE INVENTION 
The above disadvantages of the prior art and others are overcome by the 
present invention which provides a reinforced, spirally wound pipe of a 
single wall thickness and smooth inner wall having greater strength than 
the same size and gauge spirally corrugated pipe. 
The pipe is formed from an elongated sheet of ductile material, such as 
galvanized sheet metal, which is curled into adjacent, helical 
convolutions. The pipe has at least one helical impression shaped therein, 
the impression forming a rib protruding outwardly from the outer wall of 
the pipe. The impression is formed as a divergent depression in the inner 
wall of the pipe, so that it always has a greater inner cross-sectional 
dimension than the width of the aperture forming the mouth of the helical 
impression. 
To strengthen the formed pipe product, a helical reinforcement element is 
lodged in each of the impressions. Each element conforms generally to the 
internal shape of the impression and has a first portion of approximately 
the same width as the mouth of the impression, the first portion being 
located parallel to the inner wall of the pipe. A second portion of the 
reinforcement element extends into the impression. 
Adjacent edges of the helical convolutions may be joined by any means, such 
as welding, or, as preferred, by a double lock seam so formed that it does 
not protrude into the interior of the pipe. The lock seam may be 
strengthened by a shallow, helical impression formed in the inner wall of 
the pipe, constituting a heel against which the metal lock seam bears. 
The impressions preferably are trapezoidal in cross-section, with the base 
of each impression lying generally parallel to, but spaced outwardly from, 
the outer wall of the pipe, and being of a greater width than the width of 
the aperture formed by the impression in the pipe wall. The reinforcement 
element corresponds to the inner dimensions of the impression, with a pair 
of opposed legs extending from the first portion of the element and lying 
adjacent and coextensive with the sides of the impression. 
Normally, the trapezoidal impression is isosceles in cross-section. The 
first portion of the reinforcement element lies in the same plane as the 
wall of the pipe so that the inner wall of the pipe is generally smooth. 
The distance between adjacent helical impressions may vary depending on the 
strength and gauge of the pipe material, and the desired load-bearing 
capabilities of the formed pipe product. The wall of the pipe between such 
impressions is normally smooth, so that the inner pipe wall, with 
reinforcements lodged in the impressions, presents a smooth surface to 
liquids and reduces turbulent flow characteristics to the least possible 
minimum.

DETAILED DESCRIPTION OF THE INVENTION 
Turning now to the drawing, a tube or pipe according to the invention is 
generally designated 10. The pipe is composed of an elongated sheet of 
ductile material, such as galvanized steel, which is formed into adjacent, 
helical convolutions. As illustrated, convolutions are joined by a 
conventional double lock seam 12, although, if desired, adjacent 
convolutions can be joined by other means, such as welding. 
The pipe 10 has at least one continuous helical impression 14 formed 
therein in order to strengthen the wall of the pipe. Two such impressions 
are illustrated in FIG. 1. The impressions 14 are formed from the inner 
wall 16 of the pipe, protruding through the outer wall 18 at preselected 
intervals spaced from the double lock seam 12 and from each other. The 
inner wall 16 of the pipe between impressions 14 remains smooth so that 
the inner surface of the pipe 10 is smooth. Each impression is formed at 
the same helix angle as the convolutions so that it is parallel to the 
juncture (lock seam 12) of adjacent convolutions. 
FIG. 2 illustrates each impression with a trapezoidal cross-section, and 
clearly shows the diverging nature of the impression as it protrudes from 
the outer wall 18 of the pipe 10. The base 20 of each trapezoidal 
impression 14 lies generally parallel to, but spaced outwardly from, the 
outer wall 18. The base 20 is of greater width than the elongated aperture 
22 forming the mouth of the impression in order to immobily grip a 
conforming reinforcement element 24 lodged in the impression. 
Each helical trapezoidal impression 14 is preferably isosceles. Opposed 
sides 26 and 28 converge from the base 20 of each impression to the 
aperture 22 and sandwich the reinforcement element 24 between them. 
Although the isosceles cross-sectional configuration is preferred, other 
trapezoidal configurations, non-isosceles, may be used. Additionally, 
non-trapezoidal impressions may be employed, so long as the aperture 22 is 
of lesser width than the inner cross-sectional dimension of the 
impression, lodging the reinforcement element therein. 
Each reinforcement element 24 is utilized to strengthen its corresponding 
trapezoidal impression 14, and also close the impression so that the inner 
wall 16 of the pipe 10 is generally smooth. A first portion 30 of the 
reinforcement element is formed having the same width as the aperture 22 
to provide a closure for the mouth of the trapezoidal impression. A pair 
of legs 32 and 34 divergingly extend from the first portion 30, abutting 
respective sides 26 and 28 of the trapezoidal impression. The legs 32 and 
34 are of sufficient length so that when the element 24 is inserted in 
each impression 14, the first portion 30 lies generally in the same plane 
as the wall of the pipe 10 and the legs are bottomed against the base 20. 
As illustrated in greater detail in FIG. 2, the double lock seam 12 joining 
adjacent convolutions of the pipe is formed so that it protrudes from the 
outer wall 18 of the pipe, leaving the inner wall 16 of the pipe generally 
smooth. The lock seam is formed from closing a partial lock seam element 
36 formed in the edge of one convolution about a corresponding partial 
lock seam element 38 formed in the adjacent convolution of the pipe in a 
conventional "stove pipe" or "Pittsburgh" lock seam not further described 
herein. 
In order to assure that the lock seam 12 protrudes from only the outer wall 
of the pipe 10, the lock seam element 36 is formed with a heel 40. The 
heel 40 also aids in retaining the lock seam 12 securely together. In 
addition, during formation of the lock seam element 38, a shallow 
depression 42 may be formed in the inner wall of the pipe to aid in 
maintaining the lock seam 12 after the lock seam elements 36 and 38 are 
engaged as illustrated in FIG. 2. 
If a welded seam is used in place of the lock seam 12, to assure that the 
pipe wall is of sufficient load-bearing strength, an impression 14 
normally should be located adjacent the seam. Alternatively, impressions 
14 could be spaced on either side of the seam so that the total distance 
across the lock seam between impressions would be about the same as the 
normal distance between impressions when a lock seam joint is employed. 
The pipe 10 may be formed by many methods. One method, and that preferred 
in formation of helically wound pipe having trapezoidal impressions, is 
disclosed in applicant's co-pending application identified above. The pipe 
is formed from an elongated sheet of material which, prior to spiralling 
into a helical tube, is impressed with the trapezoidal impressions 14, the 
reinforcement elements 24 inserted into the impressions, and the lock seam 
elements 36 and 38 partially formed in opposed edges of the sheet. The 
sheet is then curled into adjacent, helical convolutions and the lock seam 
elements 36 and 38 engaged and closed to form the pipe. The pipe may then 
be severed into discrete lengths by conventional apparatus such as that 
disclosed in applicant's U.S. Pat. No. 3,815,455. 
Various changes may be made to the invention as illustrated and described 
without departing from the true spirit of the invention or scope of the 
following claims.