DE2617406A1 - METHOD FOR TREATMENT OF COPPER PIPES - Google Patents

Description

UR. IN O. F. WUESTHOFF

DK.E.v.PKOIIMANN DK. IN". J). BIiIIITKNS DIPL.ING. K. GOETZ PATENTANWÄLTE

8 MUNICH »O SCHWEIGEHSTRASSE ■! Ι.ΕΙΌΝ (OSB) OO 20 ^] L? 1 "7 /, Π C.

τκϊ, κχ 5 24 070

TKLKOItAMMi; :

Munich

-47 72b

Description of the patent application

TREFIMETAUX

28, rue de Madrid, 75383 Paris Cedex 08

France

concerning

Process for treating copper pipes

The invention relates to a new method for treating drawn tubes made of red copper or a copper alloy, with which the formation of deposits of elemental carbon or carbon compounds the inner surface of the tubes is avoided; these deposits originate from the decomposition of the drawing oils during tube annealing.

ORIGINAL INSPECTED

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The problem of the hole - or scar-

-Corrosion that occurs in installations made of red copper or copper alloys through punctual perforations appears without this disadvantageous appearance so far effectively and definitely has been able to fix. Research in this area has shown that this scar-like corrosion on the deposits of carbon residues on the inner wall of the pipe, which one represent more or less continuous film.

It is known that the origin of these carbon deposits is to be looked for in the manufacturing process of the pipes themselves, because the inner and outer surfaces of the pipes with drawing oils treated to facilitate cold drawing; the remaining film of drawing oil becomes during the subsequent annealing decomposes and carbonizes and thus causes the carbon deposits that adhere firmly to the inner wall of the pipe. This carbonaceous film consists either of elemental carbon or of heavy residues of the Distillation or cracking of the drawing oil, which reacts with copper due to electro-chemical processes and leads to hole - «- or scar-like corrosion.

In the case of red copper pipes, commonly used for plumbing are used, it is known that only certain household wastewater promote such corrosion. Because the considerable total length of the red copper sewer pipes laid, however, does not match the actually observed Number of perforations and water leaks significant for the user.

The copper alloy tubes used for the heat exchangers Used by power plants, refineries, ships and desalination plants, this form of occurs

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scar-like corrosion with punctiform perforations has so far been less common.

Attempts have long been made to determine the extent of the carbonaceous content caused by the decomposition of the drawing oils To reduce deposits and thereby improve the resistance of the annealed pipes to any household water, even particularly aggressive water. The specialist literature recommends a maximum content of

0.2 mg / dm carbon at each point on the inner surface of the Pipe. But even with a salary of less or less

equal to 0.5 mg / dm, which is currently difficult to achieve systematically in the course of the manufacturing process; " would already be a considerable reduction in the scar-like or pitting corrosion and, as a result, the corrosion that occurs Cause perforations.

In order to achieve such results, the specialist literature recommends treatment methods that involve removal of residual traces of drawing oil before the tubes are annealed, or, alternatively, the removal of the carbon-containing ones Deposits after the usual annealing.

These are, for example, degreasing agents the pipes with known organic solvents, developed and tested by various pipe manufacturers became. But the residues of the drawing oil, which are generally found in the imperfections on the surface of the drawn tubes are viscous and encrusted, require not only a dissolving effect, but also a mechanical effect Take away. Practice has shown that such means are used effectively only with straight pipes of limited length can be.

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Other methods involve treating the tubes immediately after the usual annealing, even after one or more further drawing operations, through the pipes with superior mechanical strength and inferior Sensitivity to unwanted deformations during transport and installation can be achieved should.

These means consist in treating the inner wall of the pipe with grains of sand, alumina or aluminum oxide or metal granules conveyed with a rapid stream of a gas or liquid such as air or Water. , These agents have the risk of pitting in straight pipes of short length, for example 12 m or less. However, the effectiveness of these procedures decreases rapidly and indeed / not only with the increasing length of the pipes to be treated, but also because the abrasive grain or the Granules are increasingly rubbed off and take on a spherical shape.

Finally, these known means have proven to be ineffective in the case of very long pipes especially with pipes of 50 m and rolled up in bundles about that. In addition, the inevitable lengthening of the manufacturing cycles leads to a reduction in performance.

All of the known disadvantages have induced the applicant to continue investigations in this area and to develop a new process for the treatment of pipes made of red copper or copper alloys, which offers a real solution to the difficulties faced by those skilled in the art.

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The inventive method for treating red copper tubes drawn in the presence of a drawing oil or copper alloy, which causes the formation of carbonaceous deposits on the inner wall of the pipe is reduced as a result of the decomposition of the drawing oil during annealing, is characterized in that the tubes are opened an adequate temperature for the development of a sufficient vapor pressure of the drawing oil is heated and at the same time a carrier gas for the drawing oil vapors to flow through.

It has been shown that the drawing oils used for drawing mandrels (pipes) are more natural or synthetic Origin develop a considerable vapor pressure at temperatures that are below the temperatures

which cause the decomposition of the drawing oil as a result of polymerization, any other reaction that leads to the formation of elemental carbon ₍ or as a result of a reaction with the copper itself.

The drawing oil vapors formed then have to be displaced from the tube with a gas flow before they can settle on the Inner wall in the form of partially degraded heavy products such as tar, resins, organic compounds combined with copper or as strongly adhering deposits of elemental carbon.

The interval of adequate temperatures for the treatment of the pipe is determined by a thermal gradient, whose minimum value is the room temperature and whose maximum value is the annealing temperature of the tube. The carrier gas can thus, during the entire annealing cycle, which increases the temperature, maintaining it at the corresponding annealing temperature and cooling to room temperature. The blowing in of the gas stream can of course also be used for a time corresponding to a fraction of the temperature

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rature increase can be made. Finally, the gas flows can also be achieved with the help of a fast jet of the flowable medium in question at one or more temperatures, selected according to expediency, introduced will.

The volume of the gas flow ₍ determined under normal conditions of temperature and pressure ₍ is at least twice the internal volume of the pipe to be treated.

The carrier gas introduced into the tube, which takes the vapors of the drawing oil with it when it is heated, can come from various Sources: the slightly reducing combustion gases can be used to create a bright glow without Ensure oxidation, for example of propane burned with a certain oxygen deficit. One can also use a gas that is inert to the copper or the copper alloys as the gas flow, for example nitrogen, COp, water vapor or their mixtures.

The purge gas can also be enclosed in a cartridge beforehand as a gas, compressed gas, liquid, Solid or in the form of a substance that splits off a gas when heated.

In this case, the cartridge is connected to one end of the tube before it enters the furnace and releases the gas continuously as the temperature rises or for a shorter period of time as above said; this period of time is limited either by the physico-chemical properties of the gas-generating Substance or by tearing open the cartridge cap y which has been calculated to give way at a certain temperature.

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Depending on the furnace selected for the treatment, the required heating cycle for the desired tube annealing is determined The vapors of the drawing oil can either be continuously mixed with the purge gas during the entire heating and cooling cycle can be removed or by briefly blowing in the flushing or carrier gas at certain points.

The inventive method can also be applied to the using a known process annealed tubes. In this case, the pipes are rinsed hot after glowing, provided that the drawing oil used does not decompose and the. maximum annealing temperature definitely has been fixed.

The method according to the invention can be applied just as well straight tubes with a length of, for example, 5 to 12 ι as well as tubes in the form of collars, whose unrolled length can even be more than 1000 m ■.

The inventive method can be very useful perform various devices.

In the case of glowing in the passing by means of the Joule effect or in any other way of tube coils with considerable unrolled length can be close to one another in the Rinse the axis of the reel or the decoiler of the rotating part continuously.

In the case of a static annealing furnace, the straight tubes or bundles that make up the charge can be connected to one another either in parallel or one behind the other and either a slightly reducing carrier or purge gas supplied from a single source outside the furnace, or from one or more Gas cartridges

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connected to the free ends of the tubes or bundles, a neutral flushing or carrier gas can be supplied. In the event of In a pull-through tunnel furnace, the collars or straight tubes connected in series become continuous flushed in the opposite direction to the direction of passage and the gas is fed in in any suitable manner. According to a variant, each pipe coil or group of coils is connected to a cartridge for neutral gas.

In special circumstances the rinsing of the drawing oil fumes be advantageously replaced with a slightly reducing or neutral gas by the extraction the vapors of the drawing oil and the gas contained in the tube are reduced to a vacuum with the help of a pump group or equal to 1 Torr, thereby causing purging inside the pipe. Of course, in this embodiment of the process the overall system that is pumped out (one or more pipes or bundles in an expedient manner connected to each other) must be hermetically sealed at its end.

Finally, in the case of pipes applied in the hardened (cold) state 1/4 or 1/2 hard, optionally manufactured by a final drawing without a mandrel after annealing and consequently without drawing oil on the inner surface of the pipe, the method according to the invention is absolutely effective, to remove the harmful deposits of the decomposed drawing oil.

With the aid of the method according to the invention, tube coils made of red copper with unit lengths of 50 to 400 m could be treated and their average carbon content reduced to about 0.1 mg / dm and even less without the value 0.3 mg / dm at any point on the inner wall of the tubes. to exceed dm.

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If, on the other hand, the annealing was carried out without flushing the inside of the tube, the carbon content fluctuated considerably along this line the pipe bundle with an unrolled length of, for example, 50 m / generally it was very small at the ends, however, reached 0.5 mg / dm2 and more at half the length with extreme values up to 1.2 mg / dm.

In such tube coils, annealed without rinsing, the average carbon content could be determined in the case of certain drawing oils reduce to 0.15 mg / dm and less followed by a 3 min rinse (after the glow) with reducing agent Gas from 350 to 400 ° C.

The following examples relate to pipe coils and straight pipes made of red copper; of course you can The method according to the invention also applies to pipes made of any Apply copper alloys that are used to manufacture heat exchangers.

example 1

40 tube bundles made of red copper, diameter 12 × 14 mm, unit length were placed in a furnace for static annealing 50 m, treated; each pipe bundle was connected to a feed for inert gas (technical nitrogen R).

The whole was covered with a hood; then a pre-purge with nitrogen was carried out in order to displace all remaining air residues from the furnace or the interior of the pipe bundles. Throughout the annealing process - heating up to 550 ⁰ C, dwell time at 55O ° C for 1 h and cooling - maintaining a continuous flow of nitrogen into the tube bundles.

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In order to determine the carbon content inside the pipe after the treatment, pieces of pipe were used with an inner surface / 20 cm, the outer surface of which had been stripped of all carbon residues by pickling with 25 to 30% nitric acid. After thorough rinsing and drying, the carbon was "determined using the device according to Wosthoff This device consists of a tubular furnace which is preheated to about 700 ⁰ C;. The pipe section is introduced into the furnace and subjected to the action of pure oxygen, which ensures the rapid and complete combustion of existing carbonaceous deposits without losing the released CO _2. The amount of released CO ₂ is determined with the help of precise measurements of the fluctuation of the electrical conductivity of a sodium hydroxide solution of known concentration before and after absorption of the C0 ₂ -Gas.

The mean carbon content corresponding to the released CO ₂ was 0.1 mg / dm for each of the 5 pipe bundles analyzed and showed a very low scatter (fluctuation) for the 50 pipe sections that were analyzed per pipe bundle.

A comparative test with 40 similar tube coils without nitrogen purging during the annealing cycle resulted in an average carbon content of 0.36 mg / dm ² with extreme values of up to 0.8 to 0.9 mg / dm ² .

Example 2

In a pulling furnace a group unrolled length of 50 mm was made of red copper pipe bundles _f diameter 10 χ 12, m, treated. Each of the 10 tube bundles was connected at one end to a single cartridge made of steel, loaded with 24 g of CQ2 under pressure and closed with a lid

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made of 99.5% aluminum, exposed surface 17.3mm, Thickness 1.5 mm.

This cover was designed so that it gave way spontaneously under the action of the CC ^ gas pressure when the temperature of the tube reached about 50O ⁰ C. A sudden jet of gas that then ran through the pipe took all the stagnant lubricating oil vapors with it and drove them out of the pipe in the form of smoke

Under these conditions, the test pieces determined on each of the 10 evenly distributed along the 10 pipe bundles were Carbon content below. 0.1 mg / dm.

In contrast, the carbon content of 10 tube coils of the same type, which had been annealed in the same way, was the same

were, however, without gas purging, about 0.6 to 0.9 mg / dm on half the length of the pipes, while on the two Ends of each pipe bundle the carbon content is only maxi-

times 0.25 mg / dm.

Example 5

The oven according to Example 2 was used to

20 straight tubes to be statically annealed; Pipe diameter 12 χ 14 mm, length 8 m unit, this length corresponding to a relatively constant temperature zone of 500 to 55O ⁰ C in an oven. Each tube was hermetically compressed at one end; the other end was connected to a suitable pipe made of mild steel and connected to a primary pump group, output 100 m ^ / h, arranged outside the furnace. After setting the vacuum, the 20 tubes were in the form of a bundle in

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introduced the annealing furnace and held at 500 to 550 ⁰ C for 1 h; the pumping action was maintained throughout the cycle.

All 10 sample parts, which were taken at regular intervals along 5 pipe coils for analysis purposes,

resulted in a carbon content of less than 0.1 mg / dm - A further precision or accuracy was not possible with the applied analytical method described above possible.

For comparison, tubes of the same type were annealed in the same way in the same furnace, but without applying one Vacuum during the annealing cycle; the analyzes showed a

Scatter of the carbon content from 0.15 to 0.76 mg / dm and this despite a very superficial oxidation inside the pipe due to the originally present air.

Example 4

In the pull-through furnace according to Example 2, tube coils made of red copper were treated; for every pipe coil the unrolled length was 50 m, the diameter 12 x14 mm.

The pipe coils were connected in series on the table at the entrance of the furnace, in the course of the Advance at a speed of about 1.3 m / min to the furnace door.

Each tubing collar remained for about 10 minutes in the heating zone, then passed into the range of the ambient temperature of 650 ° C and then for 20 min in the cooling zone and exited to 50 ⁰ C with a temperature of about 40 microns.

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During the 30 min residence time of a pipe bundle in the treatment room a slightly reducing gas stream was passed in the opposite direction. A Set of special connection pieces made of high-temperature steel used, with the help of which the pipe coils between each other and the pipe bundles coming out of the furnace with the movable supply line for the purge gas (with a slight Air deficit (burned propane) could be quickly connected and disconnected again.

Under these conditions, that of 10 specimens treated at regular intervals, 4.5 m, along the 8 was Tube bundles had been removed, in no case more than 0.1 mg / dm.

In the case of pipe coils treated without gas purging for comparison, the carbon content was with maximum values in the range from 0.51 to 0.68 mg / dm ² .

Claims; 728188

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Claims (6)

Claims (Iy method of treating pipes made of red copper or Copper alloys after drawing in the presence of a drawing oil to avoid or reduce adhering carbon deposits from the decomposition of the drawing oil during annealing, characterized in that the tube is opened a temperature is heated in order to evaporate the drawing oil, and at the same time a purge gas is passed through or the drawing oil vapors sucks. 2. The method according to claim 1, characterized in that one during the entire annealing cycle purges with gas. 3. The method according to claim 1, characterized in that only during part of the Rinses heat-up time until glowing. 4. The method according to claim 1 to 5, characterized in that with at least the purging twice the volume of gas, based on the pipe volume and normal conditions. 5. The method according to claim 1 to 4, characterized in that the gas is a weak reducing combustion gas or inert gas is used. 6. The method according to claim 5, characterized in that the inert gas is nitrogen, COp and / or water vapor used. 609847/0655 8155