Note: Descriptions are shown in the official language in which they were submitted.
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PIPELINE PIG WITH FINS
TECHNICAL FIELD
[001] This relates to a pig for cleaning a pipe or a pipeline, and method of
making a pig.
BACKGROUND
[002] The interior of a pipeline may become covered with various substances
that may be
difficult to remove. A pipeline pig may be useful in cleaning the pipe or
pipeline. A variety
of pigs are known such as those disclosed in US patents 1683429, 3460180,
6170493,
6391121 and 6569255.
SUMMARY
[003] In one embodiment there is a pipeline pig, comprising a nose, a central
section
having a central axis, a plurality of fins extending rearwardly from the
central section, each
of the plurality of fins having a pressure responsive scraping end; the
scraping ends of the
plurality of fins collectively define a circular scraping surface extending
radially outwardly
from the central axis of the central section; each of the fins having inward
facing pressure
bearing surfaces; and at least a flow-through passage extending between the
fins.
[004] In one embodiment there is a method of constructing a pipeline pig,
comprising:
making a plurality of slots in a sheet of metal; rolling the slotted sheet of
metal to form a
plurality of fins; and connecting the plurality of fins to a nose and central
section of a
pipeline pig.
[005] These and other aspects of the device and method are set out in the
claims, which are
incorporated here by reference.
BRIEF DESCRIPTION OF THE FIGURES
[006] Embodiments will now be described with reference to the figures, in
which like
reference characters denote like elements, by way of example, and in which:
[007] Fig. 1 is a perspective view of an embodiment of a pipeline pig with
fins;
[008] Fig. 2 is a side view of an embodiment of a pipeline pig with fins;
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[009] Fig. 3 is a perspective view of a plurality of fins of the pipeline pig
of Fig. 1;
[0010] Fig. 4 is an end view of a pipeline pig of Fig. 1;
[0011] Fig. 5 is a perspective view of a fin for a pipeline pig; and
[0012] Fig. 6 is an embodiment of a pipeline pig with fins.
DETAILED DESCRIPTION
[0013] Figs. 1, 3 and 4 show a pipeline pig 10 having a nose 12, a central
section 14
having a central axis A. A plurality of fins 16 extend rearwardly from the
central section 14.
Each of the plurality of fins 16 has a pressure responsive scraping end 18.
The nose may
protrude forwardly in the direction of the pipeline pig's travel from the
central section, the
nose having decreasing diameter with increasing distance from the central
section.
[0014] The scraping ends 18 of the plurality of fins 16 collectively define
a circular
scraping surface 20 extending radially outwardly from the central axis A of
the central
section 14. The circular scraping surface can be seen in Fig. 1 and in the end
view shown in
Fig. 4. Each of the fins 16 having inward facing pressure bearing surfaces 22
(Fig. 5). There
is at least a flow-through passage extending between the fins 16. The flow
through passage
includes,as shown in Fig. 1, an opening 24 at the front end of the nose 12,
the size of which
opening is flow limiting. The flow-through passage may be placed anywhere on
the nose 12
or the central section 14 as long as fluid is allowed to pass through the
pipeline pig. The flow
through passage may be made with different flow limiting diameters. In
embodiments with a
large diameter of the flow through passage, the pipeline pig moves more slowly
and allows
for a greater flow rate of fluid through the pipeline pig. Conversely, in
embodiments with a
smaller diameter, the pipeline pig moves more quickly and allows for a lesser
volume of
fluid flow through. The opening could be made of variable size, but this is
not preferred due
to weight preferences. For example, all 4 inch pigs (intended for cleaning 4
inch lines) are
less than 8 ounces. The use of the nose and selection of the size of the flow
limiting opening
helps eliminate minor scraping on the tube wall in 180 degree short radius U
bends. The
opening is decided by fluid speed of each different heater. No heaters have
the same feed
stock and same heater temperatures. The pig travels in the heater fluid
stream, disrupting the
precursors of coke that adhere to the tube wall. Tubes are made of CR 5, CR 9
and various
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Stainless steels. Depending on flow speed the opening and fin stiffness are
designed to
touch, not gouge or scrape hard the tube wall. The faster the pig speed the
more exerted side
wall pressure is required. The opening size and fin stiffness are thus a
design choice for the
engineer based on experiment and calculations suited to the particular heater
being treated.
[0015] In Fig. 1, each of the scraping ends 18 of the plurality of fins 16
further
comprise flat scraping ends 26. The nose 12, central action 14 and the
plurality of fins 16
may be formed of a unitary piece of metal or alloy.
[0016] In the embodiment shown in Fig. 2, the nose 12 of the pipeline pig
10 has a
conical shape. In other embodiments the nose 12 may have different shapes such
as
parabolic. The nose may have a first section and a second section, the first
section being a
segment of a cone and the second section having a conical shape, such that
both are frusto-
conical and the first section tapers more gradually than the second section,
with the second
section extending most forwardly. The nose may assist in guiding the pipeline
pig through
bends in the pipe. In one embodiment, the nose assists in guiding the pipeline
pig through
90 U-bends. Rivets 28 may be used to connect the central section 14 to the
fins 16. The
central section 14 may also be connected to the fins 16 by other methods, such
as welding.
As shown in Fig. 2, each of the plurality of fins 16 are cantilevered from the
central section
14.
[0017] As shown in Fig. 4, the nose 12 and central section 14 of the
pipeline pig may
be hollow. Fluid may flow through the hollow passage within the nose and
central section of
the pipeline pig.
[0018] As shown in Fig. 5, each of the plurality of fins has a longitudinal
section 30
connected to and extending rearwardly from the central section 14 (Fig. 2) and
a radial
section 32 extending away from and radially outward from the longitudinal
section 30 of the
fin 16, in which the radial section 32 of the fin 16 further comprises a flat
scraping end 26.
The radial section 32 of the fin 16 may be formed at various angles from the
longitudinal
section 30 and may bend, for example, 90 degrees or less, with the radial
section having a
length for example of 3/4 inches or less.
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[0019] In the embodiment of Fig. 6, the nose 12 of the pipeline pig has a
circular
cross-section with a maximal radius denoted by M and in which the central
section 14 has a
cross-section smaller than the maximal radius M of the cross-section of the
nose 12.
[0020] The pipeline pig 10 may be constructed using niconel alloy. The
pipeline pig
may also be constructed from any oxidation and corrosion resistant materials
that is suited
for service in extreme environments.
[0021] The plurality of fins 16 may be formed from a sheet of metal or
alloy that has
been slotted and rolled.
[0022] The pipeline pig may be constructed by making a plurality of slots
in a sheet
of metal, rolling the slotted sheet of metal to form a plurality of fins and
connecting the
plurality of fins to a nose and central section of a pipeline pig. The slotted
sheet may also be
bent to form the scraping ends on the plurality of fins which define the
circular scraping
surface.
[0023] In operation of the pipeline pig 10, fluid flows through the
pipeline pig from
the end of the pig having the plurality of fins 16 towards the end of the pig
having a nose 12.
The pipeline pig is placed within the pipeline to clean the interior surfaces
of the pipeline.
The pressure of moving fluid pushes against the inward facing pressure bearing
surfaces 22
(Fig. 5) of the plurality of fins 16 and causes the pressure responsive
scraping ends 18 to
scrape against the inner surface of the pipe or pipeline. Although the opening
24 is shown in
the center of the nose 12, the opening may be anywhere on the nose 12 or the
central section
14 that allows fluid flow through the pipeline pig.
[0024] The opening size and fin stiffness are thus a design choice for the
engineer
based on experiment and calculations suited to the particular heater being
treated.
Exemplary flow speeds may be as low as two meters per second for a heavy feed
stock and
as fast as 70 meters per second in a vacuum heater with large tube size, where
the fluid in the
tube is a gas, as for example an ethane cracker. Exemplary pig material is
Niconel or
Inconell. Fin length may be for example 4 inches for a pig that fits in a 4
inch tube. Wall
thickness of the pig may be greater in the nose than in the middle section
between the nose
and fins, and thinnest in the fins. Thus for example, wall thickness may be
0.030 inches in
nose, 0.025 inches between the nose and fins, and 0.010 inches or more in the
fins. For a 4
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inch pig, the opening in the nose may be from 6 mm to 30 mm depending on fluid
or gas
speed. These measurements give guidance in making an exemplary pig but are not
intended
to be limiting of all embodiments of the claimed invention. The drawings are
schematic. In a
practical embodiment, the fins would terminate at the same length and/or the
same distance
radially outward, the body of the pig would be in section as close to circular
as the
manufacturing techniques allow and the scraping edges of the fins would form
right angles
or close to right angles with the side edges of the fins.
[0025] Immaterial modifications may be made to the embodiments described
here
without departing from what is covered by the claims. In the claims, the word
"comprising"
is used in its inclusive sense and does not exclude other elements being
present. The
indefinite article "a" before a claim feature does not exclude more than one
of the feature
being present. Each one of the individual features described here may be used
in one or more
embodiments and is not, by virtue only of being described here, to be
construed as essential
to all embodiments as defined by the claims.
