Note: Descriptions are shown in the official language in which they were submitted.
2031343
FIELD OF THE lNv~N-lION
This invention relates to a method and
apparatus for the repair of tubes such as are found in
condensers and heat exchangers.
BACRGROUND AND SUMMARY OF THE lNV~ ION
The inlet ends of tubes in condensers and heat
exchangers tend to wear out from corrosion in the
first 12" of the tube. Numerous methods have been
proposed to correct this problem, the most recent
known to the inventor being that of McParland (sic),
United States patent no. 4,941,512. McParland proposes
a method of repairing the inlet end of a damaged tube
(referred to as the parent tube) that includes
inspecting and cleaning the inlet end of the damaged
parent tube, installing a metallurgically compatible
insert in the damaged inlet end of the parent tube,
and securing the insert in the parent tube by
controllably roller expanding the insert along its
entire length within the parent tube to substantially
minimize any end step erosion. McParland states that
"The thin wall design of the insert 26 ensures
elimination of end step erosion along end 28 which
might occur if any gap occurs between the end 28 of
the insert 26 and the inside diameter 16 of the tube
10. Roller expanding the insert 26...further
eliminates any end step erosion." (Column 4, lines 7 -
14).
However, the problem of end step erosion and
other problems resulting from inaccurately expanding
the insert has, before the inventor's invention, been
poorly understood. Thus it is stated in United Kingdom
patent no. 1,588,971 that "Small differences in cross-
section of the lined tube may however not be that
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serious". The inventor has discovered that small
differences in cross-section between the tube and the
insert can be serious and that the solution proposed
by McParland, while it works to some extent, does not
sufficiently eliminate end step erosion to extend the
life of the insert and the parent tube appreciably.
McParland discusses the need for "controllably
roller expanding" the insert using "conventional
roller expanders" (column 4, lines 21 - 23). In
conventional roller expanders, a tapered rod is forced
into a mandrel having pins disposed circumferentially
around the mandrel. The "controllably" refers to the
amount of torque applied to the tapered rod.
Frequently, this torque is applied by an air gun,
since electrical equipment cannot be used in the
environment in which many of these damaged parent
tubes can be found.
The inventor has discovered that it is
difficult to control the amount of torque. In the
common case where the control is pneumatic, it is
subject to error resulting from changes in atmospheric
pressure, air temperature or water in the pressure
lines. The consequence of this error in the torque is
that the insert can be too easily over or under
expanded. Over expansion results in the stressing of
the parent tube. Since the parent tube is frequently
stress relieved, this can cause a situation in which
the parent tube becomes stressed, with the result that
the stressed parent tube is easily corroded. Over
expansion can also break the parent tube being
repaired, or enlarge it to such a degree that it
cannot be removed from the tube sheet in which it is
held. Under expansion results in the formation of an
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undesirable end step, which can again cause
undesirable erosion of the parent tube.
Having identified a problem not properly
understood by the prior art, the inventor has proposed
and is using a method and apparatus that gives
reliable control to the expansion of the insert. Thus
the invention in one embodiment may be stated as being
as follows: In a method of repairing a damaged inlet
end of a parent tube, by controllably roller expanding
an insert having a known thickness inside the parent
tube using a roller expander, the roller expander
having a tapered rod slidable within a fixed mandrel
defining a bore, the mandrel having a first stop at
one end of the mandrel and an expansion device at the
other end of the mandrel, the tapered rod having a
thick end and a thin end and having a second stop
adjacent the thick end, the improvement comprising the
steps of: determining the inside diameter of the
parent tube at an undamaged part adjacent the inlet
end; determining the outside diameter of the insert;
selecting a roller expander capable of expanding the
insert larger than the inside diameter of the parent
tube; adjusting the relative stopping positions of the
first stop and the second stop such that the tapered
rod is slidable into the mandrel no further than is
required to expand the insert to an outside diameter
substantially equal to the inside diameter of the
parent tube less the thickness of the insert, thereby
eliminating any end step between insert and parent
tube; and forcing the tapered rod into the bore of the
mandrel until the first stop is stopped by the second
stop.
Preferably, adjusting the relative stopping
positions of the first and second stops includes:
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expanding a test insert to an outside
diameter under the inside diameter of the parent tube
less the thickness of the test insert; and
further adjusting the relative stopping
positions of the first and second stops if required.
Also, preferably, the relative stopping
positions of the first stop and the second stop are
adjusted by placing spacers between them, and the
first stop is a collar and the second stop is a chuck.
The apparatus for carrying out the invention
may be described in one embodiment as follows: In a
roller expander for repairing a damaged inlet end of
a parent tube, by controllably roller expanding an
insert having a known thickness inside the parent tube
using a roller expander, the roller expander including
a fixed mandrel defining a bore, a tapered rod
slidable within the bore of the fixed mandrel, the
mandrel having a first stop at one end of the mandrel
and an expansion device at the other end of the
mandrel, the tapered rod having a thick end and a thin
end and having a second stop adjacent the thick end,
the improvement comprising:
a spacer for adjusting the relative stopping
positions of the first stop and the second stop such
that the tapered rod is slidable into the expansion
device no further than is required to expand the
insert to an outside diameter substantially equal to
the inside diameter of the parent tube less the
thickness of the insert, thereby eliminating any end
step between insert and parent tube.
There may be a plurality of spacers disposed
between the first and second stops.
.
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20343~3
BRIEF DESCRIPTION OF THE DRAWINGS
There will now be described a preferred
embodiment of the invention, with reference to the
drawings, by way of illustration, in which like
numerals denote like elements and in which:
Figure 1 is a side view, partially in
longitudinal section, showing a damaged inlet end of
a parent tube;
Figure 2 is a longitudinal section of an
insert installed according to the invention in the
damaged parent tube of Figure 1;
Figure 3 is a longitudinal section of an
insert with an end collar installed in accordance with
the invention in the damaged parent tube of Figure 1;
Figure 4A is an exploded view of a roller
expander modified according to the invention showing
a spacer section;
Figure 4B is a blow up of the spacer section;
Figure 5 is a longitudinal section showing a
damaged parent tube, with a side view of a roller
expander in the final expanded position installed in
the damaged parent tube according to the invention;
Figure 6 is a cross-section of a spacer
according to the invention; and
Figure 7 is a top view of a spacer according
to the invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
Physical Confiquration
Referring to Figure 1, there is shown a
damaged inlet end 10 of a parent tube 12, with a
corroded interior surface 14. The parent tube 12 is
installed in a tube sheet 18. The inside diameter of
2 1) e$ ~ 3 ~ 3
the parent tube 12 is indicated at 16. Referring to
Figure 2, there is shown an insert 20 installed in the
damaged inlet end. The insert 20 has a chamfered end
22, a thickness 24, an inside diameter 26 and an
outside diameter that as shown is essentially the same
as the inside diameter of the parent tube 12 after the
expansion of the insert (which might include a slight
expansion of the parent tube 12 as set out below).
Figure 3 shows the same features as Figure 2, but
includes a collar 30 mounted in the more severely
corroded part of the inlet end 10. The collar 30
ensures a total metal to metal fit for severely
corroded parent tubes.
Referring to Figure 4A, there is shown a
modified roller expander 40 as an example of an
embodiment of an apparatus according to the invention.
The roller expander 40, unmodified, is commercially
available. The model shown as an example is available
from Elliott Industrial Equipment Co. of Brampton,
Ontario, Canada, and of Dayton, Ohio as series no.
480. A blow up of the spacer section is shown in
Figure 4B.
The roller expander 40 includes a tapered rod
42 having a thick end 44 and a thin end 46. Adjacent
the thick end 44 is a stop 48, that here consists of
a chuck. The stop 48 fits into an air gun (not shown,
but also readily commercially available). The tapered
rod 42 slides into the bore of the hollow mandrel 54.
Mandrel 54 is threaded on its outside, and threads
into the collared nut 56, and into the stop 58. The
stop 58 is here a back collar that the end of the
threaded mandrel threads into. The stop 58 and the
collared nut 56 are held on the mandrel by set screws
not shown. As used in the claims, the stop 58 is the
2 ~ 3 4 ~
first stop and the stop 48 is the second stop,
although in some roller expanders the first stop will
be the threaded end of the mandrel. That is, the
second stop will butt up against the mandrel itself.
The back collar protects the threaded mandrel from
contact with the stop 48 (or the spacers as will be
described). An enlarged expander section 62 of the
mandrel 54 receives the thin end 46 of the tapered rod
42. Pins 64 protrude through slots 66 in the mandrel
and are secured there by tabs (not shown). A locking
nut 70 screws onto the threaded extremity of the
tapered rod 42. A plurality of spacers 72 fit over the
tapered rod 42 between the first stop 58 and the
second stop 48. The slotted end 62 of the mandrel 54
and pins 64 together form an expansion device as
referred to in the claims.
Figure 5 shows the roller expander 40 in place
within the damaged inlet end 12 of a parent tube 10.
The tapered rod 42 protrudes through the mandrel 54
and expander device 62 and as shown fully expands the
pins 64 into contact with the inside diameter of the
insert 20. The collared nut 56 holds the roller
expander 40 in the inlet end 12. The depth of the
expander section 62 in the parent tube 10 is
adjustable by rotation of the threaded mandrel 54
within the collared nut 56. Care must be taken to
ensure that the mandrel does not become dislodged into
the parent tube.
Figures 6 and 7 show the design of the spacers
72. For each .062" thickness of spacer, for the roller
expander shown, there will be .001" less expansion.
Various thicknesses 74 of spacers are recommended to
give a variety of expansions. These are listed in a
table at the end of the disclosure, for use with the
2034~
Elliott roller expander series 480, together with the
recommended dimensions of the counterbore 75, width
76, outside diameter 77 and inside diameter 78.
The process and apparatus of the invention is
believed to work with any roller expander that has the
equivalent of the first and second stops, including
all of the models available from Elliott.
Operation of Preferred Embodiments
The manner of operation of the invention is as
follows. It is assumed that a damaged parent tube is
being repaired with the equipment described above, or
with the substantial equivalent of that equipment.
First, determine the inside diameter of the parent
tube at an undamaged part of the parent tube adjacent
the inlet end. Measurements are preferably taken with
micrometers along the parent tube at 1" intervals to
a depth of 12" and recorded. Next, determine the
outside diameter of the insert. From this measurement
and the measurement of the inside diameter of the
parent tube, the amount of expansion needed for the
insert may be determined. Knowing the amount of
expansion required, select a roller expander capable
of expanding the insert larger than the inside
diameter of the parent tube, preferably by no more
than about .005", and preferably about .001" to .002".
Next, adjust the relative stopping positions of the
first stop and the second stop such that the tapered
rod is slidable into the expansion device no further
than is required to expand the insert to a diameter
substantially equal to the inside diameter of the
parent tube less the thickness of the insert.
Substantially equal means within about .002" for the
embodiment and the spacers described here.
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This is done in the preferred embodiment by
selecting appropriate spacers, as determined by the
tables appearing at the end of this disclosure for the
roller expander shown, and placing them on the tapered
rod 42 between the first stop 58 and the second stop
48. This adjusts the relative stopping positions of
the two stops, and prevents the tapered rod from being
forced into the mandrel 54 and the end section 62 of
the mandrel greater than a pre-set amount. In this
manner, the amount of expansion of the expander
section of the mandrel 54 can be precisely controlled.
A test piece should be expanded first to
ensure approximate concentricity of the insert and the
parent tube, and to add or subtract spacers before the
final insert is added. The test insert should be
expanded outside the parent tube to avoid any damage
to the parent tube. Preferably, the expansion of the
test insert will be about .005" under the dimension of
the inside diameter of the parent tube, so that final
adjustments may be made to the selection of the
spacers, and thus to avoid subsequent damage to the
parent tube. Once final adjustments are made, a final
insert is selected with the appropriate adjustment
spacers. The final insert is then placed in the
parent tube in known manner, and the roller expander
inserted to the appropriate depth, again in known
manner. Once the insert and the roller expander are
in place, the tapered rod is forced into the bore of
the mandrel until the first stop is stopped by the
second stop. Once these steps are completed, the
insert should be
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expanded into the parent tube as shown in Figure 5,
with a complete metal to metal seal without over
expanding the parent tube.
Alternative Embodiments
A person skilled in the art could make
immaterial modifications to the invention described
and claimed in this patent without departing from the
essence of the invention.
SPACER THICKNESS SIZING IN THOUSANDS OF AN INCH
Thickness .016 .094 .125 .156 .188 .219 .250 .281 .312 .34~ .625
Counterbore .031 .031 .062 .062 .062 .062 .062 .062 .062 .062 .062
Widlh .250 .250 .25C~ .250 .250 .250 .250 .250 .25() .25() .25U
MEASUREMENTS IN THOUSANDS OF AN INCH
Outside Diameter .125 .250 .375 .500 .625 .750
* *
Inside Diameter .500 .750 1.125 1.250 1.500 1.500
~ Width o~ ring will be .125
.062 SPACER = .001 LESS EXPAI~ISION
