Note: Descriptions are shown in the official language in which they were submitted.
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INTERNAL WELD BLASTING
TECHNICAL FIELD
[0001] The present disclosure relates to an internal weld blasting
system for
the internal surface of pipes and the method of use thereof. The pipes may be
used
for oil, gas and water pipelines.
BACKGROUND OF THE INVENTION
[0002] Many pipes used for pipelines are manufactured by a welding
process.
The welds are usually girth welds or spiral welds. The pipes made this way
have
weld beads along the weld that protrude from the rest of the pipe surface. The
internal surfaces of the pipes may also have corrosions. It is often necessary
to
prepare and clean the internal surfaces for subsequent coatings applications
or to
remove the corrosions.
[0003] Internal blasting is a method commonly used to prepare or clean the
internal surfaces of the pipes. During internal blasting, abrasives are
blasted toward
the internal surface either by a mechanical turbine wheel or in a compressed
air
stream under high pressure. Commonly used abrasives include grit and shot
blast
media of various shapes and sizes, depending on the desired cleanliness and/or
anchor profile necessary for satisfactory coating.
[0004] Conventional internal weld blasting systems normally blast at
an
impingement angle intended to facilitate blast efficiency and removal of
residual
abrasives from the target surface. Common conventional system uses a control
cage with a single 70deg opening, resulting in the abrasives spraying from the
turbine wheel at a 70deg angle which is directed so that the center of mass of
the
sprayed abrasives is slightly ahead of the blast wheel, wherein the center of
mass
impacts the weld, which provides adequate cleaning of the front side and top
section of the weld but fails to clean the back side of the weld leaving an un
blasted
shadow. When a pipe contains a raised weld seam, a "shadow" is created on the
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leeward side of the weld that receives reduced blast exposure and as a result
does
not achieve the intended surface condition. This can result in failure to meet
regulatory or client specification, and/or result in inadequate coating
adhesion.
BRIEF SUMMARY OF THE INVENTION
[0005] According to one aspect of the invention, an internal weld
blasting
system is provided with a modified design of the control cage. The modified
control
cage is modified from a single, wide opening with an average angle of
impingement
of about 70 degrees, to two restricted openings having smaller angle of
impingement. It is understood that there may be more openings depending on the
requirements of blasting.
[0006] In some embodiments, the pipe is rotated at a high rate that
is less
than the centrifugal critical rotation speed for the diameter of the pipe
being
processed for internal blasting.
[0007] In some embodiments, ventilation air flow is provided to clear the
target area of residual blast media.
[0008] According to another aspect of the invention, wear/protection
guards
may be added in the system to avoid damage/wear of blast boom components
exposed to the blast media with the adjusted angle.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Reference will now be made, by way of example, to the
accompanying
drawings which show example embodiments of the present application, and in
which:
[0010] Figure 1 is a top view of a conventional internal weld
blasting system;
[0011] Figure 2A is a section view of the weld of pipes of set 1;
[0012] Figure 2B is a section view of the weld of pipes of set 2;
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[0013] Figure 3 is top view of the conventional internal weld
blasting system
blasting on a pipe, with the middle of the control cage opening between the 7
and 8
o'clock positions.
[0014] Figure 4 is a top view of the conventional internal weld
blasting system
blasting on a pipe, with the middle of the control cage opening at 9 o'clock
position.
[0015] Figure 5 is a top view of an embodiment of the internal weld
blasting
system of this invention blasting on a pipe;
[0016] Figure 6 is a top view of an embodiment of this invention
blasting on a
pipe, which also shows the trajectories of the abrasives hitting the blaster
head;
[0017] Figure 7 is a top view of an embodiment of this invention with a
blast
shield installed;
[0018] Figure 8 is a front view of the embodiment of Figure 7, viewed
from
the roller ring end; and
[0019] Figure 9 is a perspective view of the blast shield.
DESCRIPTION OF EXAMPLE EMBODIMENTS
[0020] In various examples, the present disclosure describes an
internal weld
blasting system. The system and the components therein may be of various sizes
suitable for different pipes.
[0021] A BauhuisTM Internal Blaster (Bauhuis Group B.V., The
Netherlands), a
conventional, prior art, internal hydraulic powered turbine wheel weld
blasting
system, is shown in Figure 1. It was used to clean two set of target pipes,
using
conventional methodology, as follows. The system was fitted with a 24 to 48
inch
blast head. A blast wheel rotates in an anti-clockwise direction at
approximately
2600 rpm. Abrasives was fed through a 70 degree control cage 101, resulting in
a
70 degree abrasives blast spray pattern. The middle of the 70 degree opening
101
is set at between 7 and 8 o'clock positions. Figure 1 shows a conventional,
prior art,
internal hydraulic powered turbine wheel weld blasting system.
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[0022] Each target pipe was prepared with a weld having a width of
approximately 15 mm and a height of approximately 2 to 2.5 mm. The weld of
Pipe
set 1 had a profile approximately as illustrated in Figure 2A, wherein both
sides of
the weld are almost perpendicular to the pipe surface. The weld of Pipe set 2
had a
profile approximately as illustrated in Figure 2B, wherein the large toe
overlap on
both sides of weld.
[0023] The internal weld blasting system of Figure 1 was used to
clean a pipe
of set 1, with the abrasives sprayed from the left side of the weld, as shown
in
Figure 3. During operation, the blaster produced an abrasives spray angle of
approximately 45 degrees from the centerline of the pipe to the center of mass
302
of the sprayed abrasives, which is slightly ahead of the blast wheel. The
blasting
produced a clear un-blasted shadow on the back side of the weld equal to the
height of the weld from the toe to the crown approximately 2mm. The front side
of
the weld was completely cleaned except for a very fine line at the toe of the
weld
that was hardly visible to the naked eye and could likely be removed or
reduced by
varying the blast media particle size.
[0024] The same internal weld blasting system was used to clean a
pipe of set
2, except that the 70 degree control cage 101 was rotated 45 deg clockwise so
that
the middle of the opening was at 9 o'clock position, producing an abrasives
spray
angle approximately 90 degrees measured from the center of mass 402 of the
sprayed abrasives to the centerline of the pipe, as shown in Figure 4
(meaning,
since the control cage was set at 70 degrees, an abrasives blast spray angle
of
approximately 55 to 125 degrees). The result showed that blasting this way was
very effective at cleaning the whole weld profile except for the toe, where a
clear
un-blasted line about 0.25mm thick was left along the length of the toe on
both
sides of the weld.
[0025] The internal weld blasting system of Figure 4 was used to
clean a pipe
of set 1 that had already been blasted using the internal weld blasting system
of
Figure 3. As a result, the weld shadow was completely removed but left a thin
un-
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blasted line along the length of the backside toe that could clearly be seen
by the
naked eye.
[0026] The internal weld blasting system of Figure 4 was used to
clean a pipe
of set 1. The result confirmed that blasting at 90 deg to the pipe surface
will clean
both sides of the weld even if the weld has steep sides but will always leave
an un-
blasted line along the length of the toes on both sides.
[0027] The internal weld blasting system of Figure 3 was used to
clean a pipe
of set 2. This resulted in a clear weld shadow on the back side of the weld as
could
be expected. The front side showed very thin lines of contamination especially
in
the overlapping areas.
[0028] Thus, the conventional internal weld blasting system was shown
as
less than ideal for completely removing the contamination from both sides of
the
weld when cleaning the internal surfaces of the pipes.
[0029] Figure 5 shows one embodiment of the internal weld blasting
system
of the present invention. The blast head 2 of the internal weld blasting
system is
disposed within a pipe 1. The blast head 2 has a control cage 3. The control
cage 3
is provided with two openings 4. Each opening may be less than 70 degrees. In
some embodiments, each opening is 50 degrees. In some embodiments, each
opening is 30 degrees. In some embodiments, the two openings are of different
angles. The angle of the spray pattern 8 or 9 measured between the leading
edge
12 and the lagging edge 11 is the same as the angle of the control cage
opening
each spray pattern 8 or 9 originates from. The two openings may be disposed
anywhere around the control cage 3 depending on the particular application.
[0030] In preferred embodiments, the centers of the two openings are
disposed at 2 and 8 o'clock positions, i.e., the centerlines of the two
openings are
each 50 degrees from the centerline of the pipe, and the centerlines of the
two
openings are 180 degrees apart. It is understood that the control cage may be
made of any suitable material known in the field and manufactured with any
suitable methods known in the field.
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[0031] The internal weld blasting system may also comprise roller
rings 5 to
assist movement of the internal weld blasting system within the pipe 1.
[0032] The internal weld blasting system further comprises an
impeller 10 and
a blast wheel 7. In preferred embodiments, the impeller 10 and the blast wheel
7
are fixed together and rotating at the same speed. The impeller 10 is
configured to
receive abrasives and distribute the abrasives onto the blast wheel 7. In some
embodiments, the abrasive is fed into the impeller 10 via a belt feed
conveyor.
[0033] It is understood that abrasives of various characteristics may
be
chosen for blasting based on the characteristics of the surfaces to be blasted
and
the technical specification to be achieved. The abrasives may be grit, shot
blast
media, their mixture thereof or any other suitable abrasives known in the
field.
[0034] In operation, the abrasives are fed into the impeller 10,
which may be
rotating while receiving the abrasives. The abrasives then exit from the two
openings 4 by centrifugal force of the impeller 10 within the control cage 3
and
enter the blast wheel 7. During blasting, the blast wheel 7 rotates at a rate
of
rotation suitable for the characteristics of the surface and the abrasives and
the
abrasives are accelerated on the blast wheel 7. It is understood that the
blast wheel
may rotate clockwise or anti-clockwise. In preferred embodiments, the blast
wheel
rotates at approximately 2600 rpm. Finally, the abrasives exit from the blast
wheel
7 by centrifugal force and sprays onto two areas of the internal surface of
the pipe.
[0035] In Figure 5, the abrasives exit at 6 and 12 o'clock positions
from the
blast wheel. It is understood that the abrasives may be sprayed from any other
suitable positions from the blast wheel 7, which may be changed by changing
the
position of the control cage openings 4. In some embodiments, the abrasives
exit
the blast wheel 7 at about 180 degrees after the abrasives exits the control
cage
openings. In preferred embodiments, the abrasives exit the blast wheel 7 at
about
150 degrees after the abrasives exit the control cage openings.
[0036] The result of a 10-second blast on a stationary pipe shows
that the
blast patterns and blast effectiveness are equal on both sides. With the two
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openings 4 at 8 and 2 o'clock positions, respectively, the blast sprays 8 and
9 hit
the welds at about 50 degrees, measured from the center of mass 6 of the
abrasives sprayed from the center line of the pipe 1. In preferred
embodiments, the
center of mass 6 overlaps with the weld to be blasted.
[0037] It is understood that abrasives of various characteristics may be
chosen for blasting based on the characteristics of the surfaces to be blasted
and
the technical specification to be achieved. The abrasives may be grit, shot
blast
media, their mixture thereof or any other suitable abrasives known in the
field.
[0038] It is understood that the internal weld blasting system may be
adapted
to be used on pipes of different lengths and internal diameters.
[0039] However, as shown in Figure 6, the blast spray 609 produces a
much
longer spray pattern on the lagging side 611, which is caused by abrasives
rebounding off the side of the blast head.
[0040] In this blast, the side of the blast head 2 that the abrasives
rebounds
onto and the roller ring 5 thereon are covered with masking tape to evaluate
the
impact of the blast abrasives bouncing back from the surface of the pipe 1.
The
spray pattern 609 shows the trajectory of the abrasives bouncing onto and off
the
surface of the pipe 1 and the blast head 2.
[0041] The result of a 90-second blast on a 12-foot long section of a
pipe with
an internal diameter of 36" shows that the embodiment is very effective at
cleaning
the whole weld profile right down to the toes on both sides of the weld.
However,
there is abrasion on the blast head 2 and the roller ring 5.
[0042] The results of the blasts shown in Figures 5 and 6 also shows
that the
welds are cleaned effectively regardless of which side the abrasives hit the
weld
from.
[0043] In some embodiments, a wear/protection guard may be attached
to
the internal weld blasting system to prevent the abrasives from bouncing onto
the
blast head 2 and the roller ring 5. In some embodiments, the wear/protection
guard
may be a blast shield.
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[0044] Figure 7 shows a blast shield 710 attached to the internal
weld blasting
system to avoid abrasion on the blast head 2 and the roller ring 5. The blast
shield
710 may be removably or fixedly attached to the blast head 2.
[0045] In some embodiments, the blast shield 710 may comprise two
plates
711 and 712, and the plates 711 and 712 may be disposed at any suitable angle
relative to the internal surface of the pipe. In preferred embodiments, each
of the
plates being substantially perpendicular to the center line of the blast head
2. In
some embodiments, plate 712 may be positioned further away from the blast
wheel
7 than plate 711. There may be gaps between the two plates 711 and 712 and the
internal surface of the pipe 1. The width of the gap between the two plates
711 and
712 may be adjusted depending on the application. It is understood that the
distances between the edges of plates 711 and 712 to the internal surface of
the
pipe 1 may be adjusted depending on the application.
[0046] The blast shield 710 may be made of any suitable material
known in
the field. In preferred embodiments, the blast shield 710 may be made of
carbon
steel. In more preferred embodiments, the blast shield 710 may be made of 14%
manganese steel.
[0047] In some embodiments, the blast shield 710 may be fitted with
removable liners on the surfaces. In preferred embodiments, the removable
liners
are fitted on the surfaces of the blast shield that receive the rebounded
abrasives.
[0048] In some embodiments, a plate extension 713 may be attached to
plate
712 to close the gap between plate 712 and the internal surface of the pipe 1.
The
plate extension 713 may be removably or fixedly attached to plate 12.
[0049] The plate extension 713 may be made of any material that does
not
affect the relative movement of the internal weld blasting system and the
pipe. In
some embodiments, the plate extension 713 may be a piece of rubber, silicone,
reinforced rubber, or reinforced silicone, formed to fit snugly the internal
surface of
the pipe 1. In some embodiments, the plate extension 713 may be a brush formed
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to fit snugly the internal surface of the pipe 1. The plate extension 713 may
be
made of any other suitable material and/or of any suitable shape known in the
field.
[0050] The blast shield 710 may be of different sizes to best fit the
internal
surfaces of the pipes to protect the blast head 2 and the roller ring 5.
[0051] The internal weld blasting system shown in Figure 7 was used to
blast
the internal surfaces of two eighty-foot long pipes. The result shows that the
welds
can be completely cleaned down to the toes of the welds. At the same time, no
abrasion was observed on the blast head 2 and the roller ring 5.
[0052] The method for using the internal weld blasting system of this
invention includes several steps:
a. dispose the internal weld blasting system inside a pipe;
b. transport abrasives into the internal weld blasting system; and
c. spray the abrasives onto the internal surface of the pipe.
The abrasives may be sprayed onto the internal surface of the pipe using any
suitable spray pattern known in the field. In preferred embodiments, the
centerline
of the spray pattern is 50 degrees from the centerline of the pipe.
[0053] In some embodiments, the pipe may be rotated while the
abrasives
are being sprayed. In preferred embodiments, the pipe rotates at a speed just
below centrifugal critical speed corresponding to the internal diameter of the
pipes.
For example, the rotating speed is about 36RPM for a pipe with an internal
diameter
of 36". In preferred embodiment, when the pipe rotates, the abrasives from the
two
openings blast on the front and back side of the weld, respectively. Rotating
the
pipe while it is being blasted may be advantageous when there are multiple
welds,
girth or spiral welds to be blasted.
[0054] In some embodiments, the internal weld blasting system moves
through the pipe as the pipe rotates so that the full length of the internal
surface of
the pipe may be blasted.
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[0055] In the blasting process, ventilation air flow may be provided
to remove
abrasives and pieces of welds and other contaminations blasted off the
internal
surfaces of the pipes from the interiors of the pipes. The rotation of the
pipes may
assist the removal.
[0056] The embodiments of the present disclosure described above are
intended to be examples only. The present disclosure may be embodied in other
specific forms. Alterations, modifications and variations to the disclosure
may be
made without departing from the intended scope of the present disclosure.
While
the system, devices and processes disclosed and shown herein may comprise a
specific number of elements/components, the systems, devices and assemblies
could be modified to include addition or fewer of such elements/components.
For
example, while any of the elements/components disclosed may be referenced as
being singular, the embodiments disclosed herein could be modified to include
a
plurality of such elements/components. Selected features from one or more of
the
above-described embodiments may be combined to create alternative embodiments
not explicitly described. All values and sub-ranges within disclosed ranges
are also
disclosed. The subject matter described herein intends to cover and embrace
all
suitable changes in technology. All references mentioned are hereby
incorporated
by reference in their entirety.
