Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a pig for cleaning a pipe
or pipeline, and to a method of cleaning a pipe.
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.
Pipelines are commonly used to transport,
inter alia, a 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
United States Patents Nos. 2,447,966, issued to D.K. Stephens
on August 24, 1948; 3,204,274, issued to M.M. Knapp on
September 7, 1965; 3,277,508, issued to M.M. Knapp et al on
October 1, 1968; 3,389,417, issued to M.M. Knapp et al on June
25, 1968; 3,538,531, issued to M.M. Knapp et al on November
10, 1970; 3,605,159, issued to H.J. Girard on September 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 April 10, 1973;
3,863,287, issued to K.M. Knapp et al on February 4, 1975;
~.
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4,077,079, issued to M.M. Knapp on March 7, 1978; 4,244,073,
issued to S. Sagawa on January 13, 1981; 4,509,222, issued to
K.M. Knapp on April 9, 1985 and 4,603,449, issued to K.M.
Knapp on August 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.
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.
Another object is to provide an efficient method of
cleaning a pipe.
According to one aspect of the invention, 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
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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.
According to a still further aspect of the invention
there is provided a pipeline pig comprising a generally
cylindrical body made of elastic material and having first and
second ends and a central portion; a plurality of teeth
disposed about and extending radially outward from the body;
and means to extend the teeth radially outward to different
heights in relation to the body.
According to a still further aspect of the
invention, there is provided a detachable tooth assembly in
combination with a cylindrical pipeline pig having a central
portion, the detachable tooth being attached to the central
portion of the pipeline pig, for use in scraping scale from
the inside of pipelines, the detachable tooth assembly
comprising a detachable tooth having a shank portion and a
head portion; a sleeve secured in the central portion of the
pig and having means to prevent the sleeve from being removed
from the body of the pipeline pig, the sleeve being oriented
radially in relation to the pipeline pig; and the detachable
tooth and the sleeve each having means cooperating with each
other to detachably secure the detachable tooth within the
sleeve.
According to one aspect of the invention, the means
to extend the teeth radially outward in relation to the body
includes threaded sleeves secured to the body and in which the
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teeth are secured to the body by being threaded into the
threaded sleeves. The sleeves may thus be detachably secured
to the body, and may be secured in recesses in the body.
The means to prevent the sleeve from being removed
from the body of the pipeline pig may include a laterally
extending flange.
According to a still further aspect of the
invention, there is provided a method of cleaning a pipeline,
in which the interior of the pipeline is coated with
contaminant, the method comprising inserting a symmetrical
pipeline pig into the pipeline, propelling the pipeline pig
through the pipeline with a fluid; and reciprocating the
pipeline pig within the pipeline through an area with large
accumulations of contaminant. The method has particular
applicability to industrial heaters. The pig of the invention
is preferably used to carry out the method, and the teeth
replaced as they become warm.
The invention will be described in greater detail
with reference to the accompanying drawings, which illustrate
a preferred embodiment of the invention, and wherein:
Figure 1 is a side elevational view of a pig in
accordance with the present invention in a section of
pipeline;
Figure 2 is a longitudinal sectional view of the pig
taken generally along line II-II of Fig. 1;
Figure 3 is a cross section of the pig taken
generally along line III-III of Fig. 1;
g 3a
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Figure 4 is an isometric view of a tooth used in the
pig of Figs. 1 to 3;
Figure 5 is an exploded, isometric view of the tooth
of Fig. 4; and
Figure 6 is a cross-sectional view of a portion of a
mold used to produce the pig of Figs. 1 to 3.
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 one-
D 3b
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piece elongated, flexible, cylindrical body 4 withhemispherical 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
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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.
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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 moved outwardly by rotating the shank 18 in
the sleeve 17, or removed and 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.
It will be appreciated that the recesses in the body
of the pig can be circular rather than square or rectangular.
Moreover, the top plate on the tooth sleeve can be cup shaped
or concavo/convex, so that it is recessed in the body for
certain uses. The geometry of the head 19 of each tooth can
also be different from that described above.
