Note: Descriptions are shown in the official language in which they were submitted.
The present invention relates to the cleaning of the inside or
inside surface of coiled metal tubing utilizing a liquid cleaning medium,
preferably an organic cleaning fluid, which is introduced into the tubing,
followed by evaporation of the medium which adheres to the tube's surface.
There has been a longstanding problem due to the fact that copper
tubes corrode as a result of the depositing of carbon or carbon compounds on
the inside surface of the tubing. This is particularly true in those cases
in which tubing is utilized in the sanitation field. The carbon film or
coating results, for exampleg from the thermal decomposition of a medium which
has been used during drawing of the tube to a smaller diameter. In the case
of tubing formed from soft material which has been soft annealed following
the last drawing step, such decomposition products are produced during the
annealing step. But even in the case of hard tubes which have not been
annealed, such a potentially damaging carbon film may be produced, for
example, upon brazing two lengths of tubes together and/or for example,
when heating the tubing to facilitate bending thereof. It has been found
that the carbon film produced as a result of such a heating process is
virtually innocuous if less than .1 milligrams per dm square of grease is
found on the inner surface of the tubing.
In order to remove a solid film of any kind from the inside surface
of a tube, it has been suggested to employ a degreasing medium such as
perchloroethylene or trichloroethylene and to cause a certain quantity of
such a medium to be moved through a coil of tubing by, for example, rotating
the entire coil. Subsequently, hot air is circulated through the tubing
in order to evaporate any remaining degreasing medium and to thereby dry
the surface of the tubing. While this method provides efficient degreasing,
it is very expensive because it is a rather slow procedure which greatly
~,s
harms the speed of production.
In accordance with another prior proposal, steam is introduced into
the tubing, i.e. water vapor, to which a certain amount of degreasing medium
has been added. This addition may be made several times during the procedure.
It has been found, however, that by means oE this method the thickness of any
remaining degreasedlayer can be reduced to below the dangerous level only if
this particular method is repeatedly applied. ~eedless to say, this proposal
is quite uneconomical.
It is an object of the present invention to provide a new and im-
proved method for cleaning the inside surface of coiled metal tubing in a
manner which is more economical than the practices which have been used in
the past.
It is another object of the invention to provide a new and improved
method of reducing grease deposits on the inside of coiled metal tubing to
an amount of less than .1 milligrams grease per dm square (or 10 milligrams
per square meter).
The method of the invention may be generally defined as introducing
into coiled tubing from one end thereof a cleaning fluid, introducing at one
end of the tubing a plug having an outer diameter approximately equal to the
inner diameter of the tubing, and moving the plug by means of externally
applied pressure through the entire tube length so that this plug element
drives the cleaning medium through the tubing. After the foregoing procedure,
the pressure in the tubing is reduced, whereupon any cleaning fluid still
resident in the tube can evaporate.
When practising the invention, one needs only three to five liters
of cleaning fluid to clean a length of tubing of about 1000 meters. It is
important that the speed with which the plug is propelled through the tubing
be sufficiently high that the cleaning fluid will cover the entire surfaceof the tubing. As the plug emerges from the other end of the tubing, the
pressure source is removed and the internal pressure is gradually reduced.
In case the tubing is subsequently to be used for household purposes, one
has to consider the fact that the grease solvent, such as perchloroethylene
or trichloroethylene are poisonous. In such cases, the plug may be propelled
through the tubing by, for example, pressurized ni-trogen, and the vapor
emerging from the other end of the tubing should be sucked out of the tubing
instead of merely relying on the reduction of pressure which occurs at the
end where the plug was initially inserted.
It was found that the tubing is very satisfactorily degreased. The
high degree of effectiveness is believed to be attributable to the speed
with which the cleaning fluid is forced along the inner wall surface, causing
turbulence within the fluid which flushes grease out of even the minutest
pores in a surface of the tubing. Moreover, the plug is propelled through
the tubing with little or no play so that the remaining cleaning fluid film
is very thin. This, in turn, means that the amount of liquid remaining is
very thin. After evaporation, the residual solid deposit layer amounts to
less than 0.1 milligram per dm square, thus meeting the desideratum of the
invention.
It can readily be seen that it is important that the residual liquid
film should be very thin. For this reason it was found to be advantageous
to employ a plug which is porous, in the sense that it is provided with many
small capillary ducts. A felt plug has, for example been found to be very
suitable. Such a plug may have a larger diameter than the interior diameter
of the tubing before being introduced into the tubing. When the plug is
forced into the tubing it is slightly compressed. As the felt plug engages
the cleaning fluid, the plug will be penetrated by the fluid. In view of
the originally larger diameter, the plug will intensively clean the inner
surface of the tubing and the resulting remaining cleaning fluid film should
be very thin. Moreover, it has been found advantageous to have the length
to diameter ratio of such a felt plug between :L.l and 2Ø
It is a feature of the invention that the desired degree of cleaning
can be achieved in single stage, i.e. without repeating the filling and
evacuating steps. While single stage treatment normally suffices, the stages
can be repeated where the cleaning requirements are particularly stringent.
If they are required, the repeated stages can be carried out in immediate
sequence. The first cleaning step may be provided as described above, and
without using additional cleaning fluid~ one may simply force a second (but
dry) plug through the tubing. This dry plug will wipe substantially all the
cleaning fluid film off the inside surface of the tubing so that the then
remaining cleaning fluid film will be so thin that the amount of grease re-
maining in the tubing is negligible.
Surprisingly, it has been found that the method of the invention
is advantageous from an additional point of view. Certain copper specks and
particles of dirt may have remained in the tubing after the last drawing
step. These specks and particles will be removed by the procedures described
above.
While the specification concludes with claims, particularly pointing
out and distinctly claiming the subject matter which is regarded as the
invention, it is believed that the invention and its objects, features and
advantages will be better understood from the following description taken in
connection with the accompanying drawing, which is a somewhat schematic
illustration of the invention.
The drawing shows a coil 1 of copper tubing 2 having an outer
diameter of 15 millimeters and a wall thickness of about 1 millimeter, the
-- 4 --
inner diameter of the tubing being about 13 millimeters. The entire tubing
within the coil 1 has a length of about 1,000 meters. In order to practise
the invention, liquid cleaning fluid, for example, 5 liters of pure tri-
chloroethylene, is filled from a tank 3 into one end, for example the end 4,
of the tubing 2, whereupon that end is closed by means of a felt plug 5.
The felt plug 5 has an outer diameter of about 14 millimeters so that, when
the plug has been introduced into the tubing, the plug is slightly compressed.
A source 6 of nitrogen, controlled by means of a valve 7, is then connected
to end 4 of the tubing 2, and the valve 7 is opened. The source 6 may be
a nitrogen bottle or the like containing nitrogen under a pressure of, for
example, 20 bars.
As soon as the valve 7 is opened, the nitrogen emerges from the
bottle 6 and propels the plug 5 through the coil 1. With the above-described
dimensions, it was found that the speed of the plug through the tubing is
about 6 to 7 meters per second. The plug 5 drives the 5 liters of cleaning
fluid in front of it, whereby of course a minor pressure reduction occurs
and a small amount of liquid remains deposited on the tube wall through which
the plug has just passed. The speed of the liquid through the tubing is
such that turbulence is set up and a thorough flushing and cleaning action
occurs throughout the entire coiled tubing 2.
Cleaning fluid will emerge from the end 8 of the tubing, followed
by the plug 5. At this point, the entire tubing will be filled with fairly
highly pressurized nitrogen. Upon removal of the bottle 6 from the end 4,
the nitrogen can discharge from the tubing at both ends 4 and 8. It was
found that the liquid cleaning fluid that remained as a film will evaporate
quickly, and, after about 2 minutes, the nitrogen together with evaporated
cleaning fluid, will have left the tubing, leaving the tubing completely dry.
The cleaning process can be carried further by flushing the entire tubing
through with nitrogen so that all vestiges of the cleaning fluid are removed.
The coil is subsequently uncoiled, straightened, and cut into desired lengths
for further usage.
Tests have yielded the following results. Typically, a tube of the
type described above had, before the treatment, a grease content on the inner
surface of about 5 milligrams per dm square. After practising the cleaning
method described above, the grease content was reduced to 0.06 milligrams per
dm square, which is well below the tolerable limit. Moreover, it was sig-
nificant that this extremely low grease content and grease deposit on the
inner surface varies very little over the entire length of the tube length.
The preferred pressurized medium is nitrogen. Onc can9 however,also use pressurized air, but if air is used care must be taken that the air
does not contain any grease.
The invention is not limited to the embodiments described above.
All changes and modifications thereof, not constituting departures from the
spirit and scope of the invention, are intended to be covered by the appended
claims.
