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BACKGROUND OF THE INVENTION
1. FIELD OF THE INVENTION
This invention relates to a pig for cleaning a pipe or pipeline.
For the sake of simplicity, in the following, the term "pipeline" is used
to describe a conventional pipeline or pipes used to convey fluids, e.g.
in industrial heaters or cooling systems.
2. DISCUSSIONS OF THE PRIOR ART
Pipelines are commonly used to transport, inter alia, crude oil, gas,
slurries or water. During use, the interior of a pipeline becomes coated
which decreases flow through the pipeline. Typical coatings include
paraffin, asphaltene, sediments, silica, coke, calcium or other salts and
corrosion products which are often difficult or almost impossible to
remove. The standard method of cleaning a pipeline is to drive a so-called
pig through the pipeline using fluid pressure as the driving force. Pigs
can also be used as dividers when transporting different materials through
the pipeline, the pig simultaneously cleaning the interior of the
pipeline.
Examples of pipeline cleaning pigs are described in U.S. Pat. Nos.
2,447,966, issued to D. K. Stephens on Aug. 24, 1948; 3,204,274, issued to
M. M. Knapp on Sep. 7, 1965; 3,277,508, issued to M. M. Knapp et al on
Oct. 1, 1968; 3,389,417, issued to M. M. Knapp et al on Jun. 25, 1968;
3,538,531, issued to M. M. Knapp et al on Nov. 10, 1970; 3,605,159, issued
to H. J. Girard on Sep. 20, 1971; 3,659,305, issued to M. D. Powers on May
2, 1972; 3,725,968, issued to M. M. Knapp et al on Apr. 10, 1973;
3,863,287, issued to K. M. Knapp et al on Feb. 4, 1975; 4,077,079, issued
to M. M. Knapp on Mar. 7, 1978; 4,244,073, issued to S. Sagawa on Jan. 13,
1981; 4,509,222, issued to K. M. Knapp on Apr. 9, 1985 and 4,603,449,
issued to K. M. Knapp on Aug. 5, 1986.
In general, many existing pipeline pigs are incapable of cleaning deposits
much harder than candle wax. Those pigs which are adapted to clean hard
deposits such as sediment and scale are not able to maintain a seal
between separate products in a pipeline, and are prone to tearing on welds
or other irregularities on the interior of the pipeline.
GENERAL DESCRIPTION OF THE INVENTION
An object of the present invention is to solve the above problems by
providing a relatively simple pipe or pipeline pig, which can remove hard
deposits from the interior of a pipeline.
Another object of the invention is to provide a pipeline pig which can
maintain a seal between different products in a pipeline, i.e. the pig can
be used to clean only or to clean a pipeline and simultaneously separate
products in the pipeline.
Accordingly, the invention relates to a pig for use in a pipeline
comprising one-piece, elongated, flexible, cylindrical body means; a
plurality of annular rib means integral with said body means; longitudinal
rib means integral with said body means extending between adjacent said
annular rib means; and defining recesses with said annular rib means and
tooth means extending out of said body means in each said recess, said
tooth means and said rib means simultaneously engaging the interior of a
pipeline when the pig is moved through the pipeline by a pressure
differential in the pipeline.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described in greater detail with reference to the
accompanying drawings, which illustrate a preferred embodiment of the
invention, and wherein:
FIG. 1 is a side elevational view of a pig in accordance with the present
invention in a section of pipeline;
FIG. 2 is a longitudinal sectional view of the pig taken generally along
line II--II of FIG. 1;
FIG. 3 is a cross section of the pig taken generally along line III--III of
FIG. 1;
FIG. 4 is an isometric view of a tooth used in the pig of FIGS. 1 to 3;
FIG. 5 is an exploded, isometric view of the tooth of FIG. 4; and
FIG. 6 is a cross-sectional view of a portion of a mold used to produce the
pig of FIGS. 1 to 3.
DESCRIPTION OF PREFERRED EMBODIMENT
Referring to FIGS. 1 to 3, the pig of the present invention which is
generally indicated at 1 is intended for use in a pipeline, a section 2 of
which is shown in FIG. 1 for cleaning the interior 3 thereof. The pig 1
includes a onepiece elongated, flexible, cylindrical body 4 with
hemispherical ends 5. The body is symmetrical, permitting travel in both
directions which is important when using the pig in industrial heaters and
similar pipelines. The body 4 is formed, e.g. of polyethylene,
polypropylene, rubber or polyurethane. The flexibility and hardness of the
body 4 are adapted to the intended use.
A wide annular rib 7 is provided at the center of the body 4, and two
narrower annular ribs 8 are provided nearer to the ends 5 of the body.
Thin, longitudinal ribs 10 extend between the ribs 7 and 8. The annular
ribs 7 and 8, and the longitudinal ribs 10 define the sides and ends of
square recesses 11, each of which contains a tooth 12. Another
circumferential row of recesses 13 is provided on each side of the central
ribs 7 (only one row shown). Each of the recesses 13 also contains a tooth
12. Additional ribs or fingers 14 extend outwardly from the outer side
edge of each end rib 8. The fingers 14 are spaced equidistant apart around
the periphery of the body 4, and taper outwardly from a wide inner end
having the same thickness as the ribs 7 and 8 to a narrow outer end 16
(FIG. 1). The fingers 14 lend strength to the ribs 8 in the longitudinal
direction. The dimensions and numbers of ribs 7, 8 and 10 and fingers 14
may vary depending upon the use of the pig, e.g. the seal required for pig
travel through the pipeline. Moreover, the ribs and fingers can be formed
of different material and have a different hardness from each other and
from the remainder of the body 4. For example, the use of harder end ribs
8 may be required because of the fact that the end ribs define the leading
ribs in the direction of pig travel, and thus are subjected to higher
forces than the rib 7.
Each tooth 12 includes an internally threaded anchor or sleeve 17 for
mounting in the body 4, and a separate threaded shank 18 (FIG. 5) carrying
a head 19 for mounting in the sleeve 17. The plates 21 and 22 may also be
circular. Hexagonal flanges or plates 21 and 22 are provided on the bottom
and top ends, respectively of the sleeve 17. The plate 21 anchors the
sleeve 17 in the body 4, and the plate 22 limits movement of the sleeve
into the body 4. The head 19 has a hexagonal base and a pyramidal pointed
end 24. The sleeve 17, and the shank 18 and head 19 are formed of metal,
but depending upon the intended use, can also be formed of plastic.
With reference to FIG. 6, the sleeves 17 are molded into the body using a
mold (not shown), each half 25 of which contains threaded holes for
receiving threaded sleeve holders 26. The sleeves 17 are mounted on the
holders 26 in the mold cavity before the mold is closed. The mold is
closed, and the body 4 is molded. The mold is opened, the holders 26 are
removed and the body 4 is removed from the mold. The shanks 18 are
threaded into the sleeves 17 to complete the pig.
In use, the pig is inserted into a pipe, and is propelled therethrough by a
fluid (gas or liquid) pressure gradient within the pipe. Pressure acting
on one end of the pig body 4 causes expansion of the pig against the
internal surface of the pipe, so that the teeth 12 are caused to scrape
the interior surface of the pipe to dislodge material therefrom. Although
it is not shown in FIG. 1, the outer diameter of the pig is normally equal
to or slightly larger than the interior diameter of the pipe, so that the
outer surface of the pig body 4 is forced against the internal surface of
the pipe. As they become worn, the heads 19 of the teeth 12 can be
replaced. The plates 21 and 22 resist removal of the teeth 12 from the
body 4, and prevent driving of the head 19 into the body 4.
Because the body 4 of the pig is symmetrical, the pig can be caused to
reciprocate in a pipe for removing scale from an area with large
accumulations. In cases where the pig is used to separate different
materials in a pipeline, the teeth 12 can be omitted.
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