SK278911B6 - Pipe made of copper or copper alloy and manufacturing process thereof - Google Patents

Abstract

The copper or alloy pipe pit corrosion resistant is equipped with a layer of oxides on the internal surface. The oxide layer thickness, consisting of crystals based on copper oxides fixed on basic metal is in the range of 0,01 up to 0,09 microns and the crystals closed to copper oxides, with oriented structure (1, 1, 1) especially, have a size of corns 0,05 microns. The procedure closed to the production of this pipe is based on step closed to removal of fats with the use of solvent and on the step closed to continual lighting in a range of 600 up to 730 Celsius degrees and with the continual velocity of 220 m/min, while the lighting atmosphere inside the pipe is set according to the pipe diameter and velocity of the continual processing inside the pipe, while this atmosphere consists of 1 up to 25 volume percent, 5 up to 15 volume percent of oxygen and 75 up to 99 volume percent, at about 85 up to 95 volume percent of nitrogen, especially.

Description

According to other methods, annealing is carried out in a reducing atmosphere and the formed hydrocarbon film is then removed from the inner surface of the tubes by an abrasive agent. This means is introduced into the pipe either by means of compressed air or pressurized water.

Finally, it is known from DE-OS 30 04 455 to adjust the content of residual hydrocarbon in that the heat treatment after degreasing of the pipe is carried out in an oxygen-containing atmosphere, such as a mixture of oxygen, helium and argon gases.

However, in heat treatment under oxidizing conditions, especially when these conditions are stable, there is a danger that the oxide layers formed are poorly trapped, have a greater thickness and, if porous, are avoided, thus avoiding negative effects and also preventing corrosion. In addition, oxide layers with a thickness greater than or equal to 0.2 .mu.m can be cracked or dropped in a subsequent mechanical treatment, such as bending.

Similar problems arise when the tubes have to undergo a cross-sectional treatment after the heat treatment under oxidizing conditions to form a semi-hard state. The deformation forces then also cause the oxide layer formed on the inner surface to crack and fall off. The peeled oxides can then cause malfunctions within the individual plant units.

SUMMARY OF THE INVENTION It is an object of the present invention to provide internally oxidized tubes of copper or copper alloys with a particularly high local corrosion resistance in which the oxides formed on their inner surfaces do not lead to adverse corrosion resistance or pipe safety effects.

SUMMARY OF THE INVENTION

This task is accomplished by a copper or copper alloy tube resistant to pitting corrosion, with a layer of oxides on the inner surface, in particular for medical use, according to the invention, which is based on the layer thickness of oxides consisting essentially of crystals of copper oxides attached to the base the metal is in the range of 0.01 to 0.09 µm and the copper oxide crystals, especially with the oriented structure (1.1, 1), have a maximum grain size of 0.05 µm.

The process according to the invention is essentially based on solvent degreasing, continuous annealing in a temperature range of about 600 to 730 ° C and a continuous speed of 50 to 220 m / min, depending on the pipe diameter and the continuous processing speed. within the tube it sets a annealing atmosphere consisting of 1 to 25% by volume, in particular 5 to 15% by volume of oxygen and 75 to 99% by volume, especially about 85 to 95% of nitrogen.

According to a preferred embodiment, the tube is soft annealed in the last step.

According to a further preferred embodiment, it is further drawn to its semi-hard state.

According to yet another preferred embodiment, the drawing thereof is further hardened.

With the method of the invention, almost every value within a given range can be adjusted very precisely by changing the method parameters. The person skilled in the art is able to determine the operating conditions for annealing, in particular the annealing time under oxidising conditions, as well as the composition and pressure of the gas mixture necessary for this.

In order to economically manufacture the tubes as well as to uniformly coat the oxides on the inner surface of the tubes, a feature of the process according to the invention is that of continuous annealing, that is, a continuous process.

Unexpectedly, the research found that, contrary to the perception of the professional world, the very low layer thicknesses of the oxides on the inner surface of the tubes guarantee sufficient corrosion protection even in aggressive waters. Likewise, no corrosion deterioration occurs when the cross-section is deformed by up to 20% or after extreme bending of up to 180 °.

If the oxide layer on the inner surface of the tubes shows damage by cracking or peeling, this can be easily detected by the eye. For these investigations, the tubes were cut in the longitudinal direction when they were previously deformed, for example when they were bent up to 180 °. The oxide layer was labeled attached to the base metal when the inner surface of the tubes after deformation showed no signs of cracking or peeling.

By observing the oxide layer on the base metal using a scanning electron microscope, it was found that the grain size of the copper oxide crystals did not exceed 0.05 µm. The visual image of the oxide layer is characterized by a high surface uniformity over the inner tube surfaces examined so far. The oxide layer has a light red color and has a high reflective ability when light falls.

Furthermore, it has been found that the oxide layer crystals consist of Cu ₂ O (cuprous oxide - cuprite) and have a particularly oriented (1,1,1) structure.

BRIEF DESCRIPTION OF THE DRAWINGS

The enclosed figure shows in a 10,000-fold magnification a Cu ₂ O layer adhered to the inner surface of the tube, whereby it is possible to recognize in particular the most uniform surface of the layer or its slight roughness.

SK 278911Β6

DETAILED DESCRIPTION OF THE INVENTION

So far, it has been assumed that there is a simple relationship between the thickness of the oxide layer and the remaining hydrocarbon content on the inner surface of the tubes:

The thinner the oxide layer is formed, the less is the remaining hydrocarbon content. However, the reduction of the remaining hydrocarbon content to below 0.03 mg / dm ² has so far been achieved only by extremely costly degreasing of the inner surfaces of the tubes prior to annealing under oxidizing conditions. The oxidation annealing itself had to take place in an atmosphere containing about 85% of a mixture of noble gases - helium and argon.

Finally, the internally oxidized pipes of the invention now show that a residual hydrocarbon content of less than or equal to 0.05 mg / dm ² is not necessarily required to prevent corrosion damage. Rather, the uniformity and the low thickness of the oxidation are substantial, the layer thickness being less than 0.2 µm, preferably less than 0.1 µm.

In order to produce the internally oxidized tubes according to the invention, the inner surfaces of the round copper tubes, for example with phosphorus-deoxidized copper, have to be degreased in an appropriate manner, for example as described in DE-OS 32 07 135. the tubes were below 0.4 mg / dm ² prior to oxidation annealing.

The individual copper pipe lengths at the ends connected to each other by gas permeable couplings were annealed in a continuous process by resistive or induction heating at a temperature ranging from 600 to 730 ° C, with a controlled gas mixture being blown into the tubes. Depending on the continuous velocity determined between 50 and 220 m / min, as well as the tube cross-section, the atmosphere inside the tubes was set.

The gas mixture consisted in particular of 5 to about 15% by volume of oxygen and 85 to 95% by volume of an inert gas such as cost-effective nitrogen. By constantly monitoring the temperature and continuous annealing parameters as well as the oxygen content of the gas atmosphere, a very uniform copper oxide layer having a thickness within the desired range could be set.

As a result of many experiments carried out, it has been found that the preferred layer thickness of the copper oxides attached to the base metal was substantially within the range between 0.03 and 0.09 µm. This thin layer of copper oxides remains completely attached even after the copper tube has been reformed by up to 20% by reducing the cross-section or up to 180 ° bend. The peeling or cracking of the oxide layer after transformation could not be detected even under a microscope at 40x magnification.

The good adhesion of copper oxides is of particular importance when semi-hard copper tubes are to be produced. In order to adjust the semi-hard state, the soft-annealed copper tubes must be deformed with a reduction in cross-section, for example drawn from a dimension of 19 mm to a diameter of 15 mm.

The hard-drawn copper tubes are usually converted to the desired final dimension without the need for crystallization annealing to be inserted between successive drawing steps.

To produce a thin addition of copper oxides on the inner surface of the tubes, the tubes are then heat treated at temperatures of about 250 ° C for a short time so that the mechanical properties cannot be adversely changed.

Claims (6)

PATENT CLAIMS 1. Copper or copper alloy tube resistant to pitting corrosion, with a layer of oxides on the inner surface, particularly for medical use, characterized in that the thickness of the layer of oxides consisting essentially of crystals of copper oxides adhered to the base metal ranges from 0.01 to 0.09 μιη and the copper oxide crystals, in particular with the oriented structure (1, 1, 1), have a maximum grain size of 0.05 μπι. The method of manufacturing a pipe according to claim 1, characterized in that it comprises the steps of solvent degreasing and continuous annealing in a temperature range of about 600 to 730 ° C and a continuous velocity of from 50 to 220 m / min. A annealing atmosphere consisting of 1 to 25% by volume, in particular 5 to 15% by volume of oxygen and 75 to 99% by volume, in particular about 85 to 95% by volume of nitrogen, is set inside the pipe of the pipe diameter and the throughput rate. Method according to claim 2, characterized in that in the last step it is soft annealed. The method according to claim 2, characterized in that it is further drawn to a semi-hard state. A method according to claim 2, characterized in that it is further drawn to a hard state. Use of a pipe as claimed in claim 1 as a corrosion-resistant installation pipe with a residual hydrocarbon content in the range of 0.05 to 0.15 mg / dm ² and an oxide layer thickness in the range of 0.03 to 0.09 µm.