FI72755C - FOERFARANDE FOER INVAENDIG RENGOERING AV METALLROER I RINGFORM. - Google Patents

Description

1 72755

Method for cleaning the inner surface of annular metal tubes

The invention relates to a method for cleaning the inner surface of annular metal-5 pipes with a liquid cleaning agent, in which method the cleaning agent together with the plug is conveyed by pressure through the tube and then the cleaning agent adhering to the wall of the tube is evaporated.

It is known that the corrosion of ku-10 twin pipes used for sanitary purposes is in most cases due to the carbon on the inner surface of the pipe. This carbon film is formed, for example, when the pipes are pulled, when the added drawing aid is thermally decomposed. In soft tubes, which are softened after the last drawing step, the decomposition products are already generated during soft annealing. But even in hard pipes that are not annealed, such a harmful carbon film can be formed, e.g. when joining the pipes together by brazing or heating the pipes to the most flexible ones.

It has been found that the carbon film formed on heating is almost harmless when the inner surface of the tube contains less than 0.1 mg / dm of grease.

Today, the grease film is removed from inside the tube by circulating a degreasing agent, e.g. perchlorethylene or trichlorethylene, in a tube ring or series of tubes, after which the tube is dried by circulating warm air to evaporate the degreaser residues. This method removes fat very well, but it still becomes very expensive because it is slow and interrupts the normal manufacturing process.

On the other hand, it has been proposed to introduce water vapor into the pipe, in which case a certain amount of degreasing agent is added to the steam once or several times. However, it has been shown that this treatment allows the desired reduction of the fatty film only by repeating the procedure several times. It goes without saying that this method is economically unprofitable.

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Accordingly, it is an object of the invention to provide a method which economically makes it possible to reduce the fat film to an amount of less than 0.1 mg / dm of fat.

According to the invention, this object is solved by introducing a small amount of degreasing agent, preferably an organic solvent such as perchloroethylene, into the tube, then inserting a cap of capillary material with a diameter slightly larger than the inner diameter of the tube, and running the plug and degreasing agent through at such a rate that eddy currents are generated in the degreaser.

In the method according to the invention, only a small amount of solvent, e.g. 3-5 liters, is needed to clean the pipe. In this case, it is essential that the speed at which the plug 15 is conveyed through the pipe is so high that the pipe is in constant contact with the detergent dose. After the plug has left the pipe, the pressurizing means is disconnected from the pipe and the resulting overpressure is allowed to slowly equilibrate. When using, for example, solvents such as perchloro- or trichloro-20-ethylene, it is advantageous to remove the solvent-containing pressure medium leaving the end of the pipe, preferably nitrogen, in order to prevent health problems.

The good degreasing efficiency can be explained by the fact that when the cleaning agent is conveyed at a high speed along the wall of the pipe 25, vortices are formed which flush even the smallest pores of the surface of the grease pipe. In addition, it is ensured that the detergent film left behind by the plug as it passes through the tube is very thin and thus the grease well remaining after evaporation of the detergent is so thin that its amount is less than 0.1 mg / dm of grease.

In order to achieve this very thin film, it is advantageous to carry out the invention by using a plug of hair-porous material, preferably a felt plug, the diameter of which is slightly larger than the inner diameter of the tube.

35 If the plug comes into contact with the cleaning agent, the cleaning agent dampens the plug and, if oversized, the plug 3 72755 enhances the cleaning of the inner surface of the pipe and allows the desired, very thin film of cleaning agent to be formed. The length to diameter ratio of the felt plug must be 1.1 to 2.0.

The requirements initially set can be achieved with a single use of the method according to the invention. If significantly lower fat values are required, the method may optionally be repeated. If a dry felt plug is passed through the tube 10 immediately after the detergent and the plug have left the tube, values of 2 well below 0.1 mg / dm of fat are obtained. A dry felt plug removes the detergent film adhering to the pipe wall.

A considerable additional advantage of the method according to the invention is also the fact that the copper karst formed in the process of drawing the pipe is also removed from inside the pipe.

The invention will be described in more detail by means of an embodiment.

To a copper tube having an outer diameter of 15 mm, a wall thickness of 1 mm and a total length of about 1000 m and bent into a series of rings was initially added 5 liters of pure trichlorethylene. A felt plug with an outer diameter of 14 mm was inserted into the tube through the filling head and the end of the tube was connected to a pressurizing means, preferably a pressurized nitrogen tank. The pressure in the nitrogen tank is approx. 20 bar.

When the nitrogen tank valve was opened, the felt plug moved through the pipe coil at a speed of approx. 6-7 m / s. The plug pushed forward with a dose of detergent that rinsed the entire surface of the tube throughout. After the solvent and plug were removed from the ring set, the nitrogen-30 tank was disconnected from the tube. The solvent-nitrogen was then removed from both ends of the tube. After the pressure had stabilized, which took about two minutes, the tube was completely dry. The tube was then straightened and cut.

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Prior to treatment, the inner surface of the tube contained 5 mg / dm 35 grease. After the described treatment, the fat content was determined to be 0.06 mg / dm. With the exception of small deviations, this very low fat content was the same along the entire length of the tube.

In the described example, 5 nitrogen was used as the pressure medium. But other pressurized media can also be used, including compressed air, in which case it is necessary to ensure that the compressed air is oil-free.