DK169750B1 - Internally oxidized pipe, method of making such pipe and use of such pipe - Google Patents

Description

The invention relates to a pipe of the kind specified in the preamble of claim 1. The invention further relates to a method for producing an internally oxidized tube and using an internally oxidized tube.

5 Pipes of copper or copper alloys are used as pipelines in the sanitary field, e.g. for cold and hot water, but also in capacitors and heat exchangers. To avoid corrosion damage, especially with the appearance of local cavity etching sites, it has already been proposed to remove the 10 charcoal residues that are on the inner surface of the pipe and tend to form carbon deposits as much as possible before degassing by degreasing agents, f. eg. by organic solvents such as tri- or perchlorethylene.

Further methods disclose conducting the annealing in a reducing atmosphere and then liberating the inner surface of the tubes from the resulting carbon membrane by means of an irradiation agent. In this connection, the irradiator is introduced into the tube either by compressed air or pressurized water.

Finally, DE-A-3,004,455 and FR-A-2,500,613 disclose internally 20 oxidized copper or copper alloy tubes whose oxide layer adhering to the base metal is in the thickness range of 0.1 to 3 μτα. and at the same time has a low residual carbon content of less than or equal to 0.05 mg / dm 2. These properties are set by the fact that the heat treatment is carried out after degreasing the pipes in an oxygen-containing atmosphere, such as e.g. a specific gas mixture of oxygen, helium and argon. However, in a heat treatment under oxidizing conditions, especially when it is carried out stationary, there is a risk that the oxide layers that are formed have a poor adhesion, a greater thickness and, if necessary, are porous. also on the corrosion conditions, can not be avoided. In addition, in the exemplary embodiments of DE-A-3 004 455, a medium thickness oxide layer can see 1 μτη in a subsequent machining of the pipes, e.g. when bending, easily crack or jump off.

GB 169750 B1 2 • Similar problems exist when the tubes after a heat treatment under oxidizing conditions to produce the semi-hard state must also be subjected to a cross-sectional reducing operation. The deformation forces then also lead to cracks or scratches and to bursts of the oxide layer formed on the inner surface. The released oxides can then lead to disruptions within the individual units of an installation.

It is an object of the present invention to provide internally oxidized copper or copper alloy tubes with particularly high durability to corrosion corrosion where the oxides present on the inner surface of the tubes do not, by unfavorable design or by detaching, lead to adverse effects on the tubes. corrosion resistance or on the functional safety of the installation.

This object is achieved according to the invention by the characterizing part of claim 1. Advantageous further embodiments of the subject matter of the invention are apparent from the dependent claims.

A preferred method of producing an internally oxidized tube is characterized by the method of claim 5. In this connection, the internally oxidized tube produced by this method has a thickness of the copper oxide layer, preferably in the range of 0.03 to less than 0.09 μιη. By this method, it is possible to set almost any value within the specified range by changing the process parameters. The skilled artisan is thereby enabled in the production to determine the relevant operating conditions for the annealing, especially the duration of the annealing under oxidizing conditions, as well as the composition and pressure of the required gas mixture.

In order to economically manufacture the tubes in addition to a uniform design of the oxide coating on the inner surface of the tubes, it is a necessary process characteristic to carry out the annealing treatment on passage, ie. by a continuous process of DK 169750 B1.

The invention further relates to the initial use of the internal oxidized copper pipe having the properties set forth in claim 6.

5 Surprisingly, studies have found, contrary to the previous view in the art, that already very small oxide layer thicknesses on the inner surface of the tubes also in aggressive water provide adequate protection against corrosion corrosion. Even after a cross-sectional deformation of up to 20% 10 or after, extreme bends up to 180 °, no deterioration of the corrosion conditions occurs.

Whether the oxide layer on the inner surface of the tubes has scratches or burst damage can easily be determined with the naked eye. For the purpose of these studies, the tubes were cut longitudinally to those which had already been deformed, e.g. bent until 180 °. The oxide layer is calculated as adherent to the base metal when, after deformation, the inner surface of the tube shows no signs of damage by scratches or bursts.

Observations of the oxide layer present on the base metal by a scanning electron microscope have shown that the grain size of the copper oxide crystals does not exceed a value of 0.05 μτη. The visual appearance of the oxide layer stands out in contrast to the hitherto examined interior surfaces of the tubes 25 at a very uniform surface. The oxide layer has a pink color and exhibits a high reflectivity in light. Furthermore, it could be stated that the crystals of the oxide layer consist of Cu 2 O (Cuprit) and preferably have an oriented (1,1,1) structure. The figure of the drawing shows, at a magnification of 10,000 times 30, the Cu2 layer adhering to the inner surface of the pipe, where one can especially notice the very uniform surface of the layer, or the poor roughness of the surface, respectively.

DK 169750 B1 4 • So far it has been assumed that there is a simple relationship between the thickness of the oxide layer and the residual carbon content on the inner surface of the pipes:

The thinner the oxide layer is formed, the smaller the residual carbon content. Admittedly, a reduction of the residual carbon content to a value below 0.03 mg / dm 2 could already be achieved by an extremely expensive degreasing of the inner surface of the tube before annealing under oxidizing conditions. The oxidizing annealing itself was hereby to be carried out in an atmosphere exhibiting approx. 85% of a mixture of inactive gases of helium and argon.

The internally oxidized pipes of the invention now show that a residual carbon content of less than or equal to 0.05 mg / dm 2 is not necessarily required to avoid corrosion damage. Essentially, on the contrary, the uniformity and small thickness of the layer thickness ranges from 0.01 to 0.09 μτα, and the copper oxide crystals preferably have an oriented (1,1,1) structure and a maximum grain size of 0.05 μια.

To prepare the internally oxidized tubes of the invention, the inner surface of the annular copper tubes, e.g. of phosphorus deoxidized copper degreased by a method as described in DE Publication 32 07 135. The residual fat content of the inner surface of the tube was prior to the oxidizing annealing treatment below 0.4 mg / dm 2. Each time, single pipe lengths of the continuous pipes connected to gas-permeable connectors at continuous ends were poured by means of a resistive or inductive heating at a temperature in the range of 600 to 730 ° C, and where the Internally, a controlled gas mixture was introduced. Depending on the flow rate that could be determined between 50 and 220 m / min, as well as the cross section of the pipes, the atmosphere was adjusted in the pipes. Preferably exists

Claims (6)

1. Pipes resistant to pitting and consisting of copper or a copper alloy with an oxide layer at the inner tube surface, especially for use in sanitary DK 169750 B1 6. region, characterized in that the thickness of the oxide layer adhering to the base metal, which consists mainly of copper oxide crystals, ranges from 0.01 to 0.09 μτη and oriented with a preferable (1,1,1) structure copper crystals 5 have a maximum grain size of 0.05 μτη. Pipe resistant to pitting corrosion according to claim 1, characterized in that it is in a softened state after the last deformation step. Pipe resistant to pit corrosion according to Claim 1, 10, characterized in that it is in semi-hard condition. Pipe resistant to pitting, according to claim 1, characterized in that it is in a hard-drawn state. Process for preparing an internally oxidized tube according to any one of claims 1 to 4, characterized by the following process steps: degreasing with a solvent continuous annealing in the temperature range from approx. 20 600 to 730 ° C and a throughput speed of 50 to 220 m / min, whereby, depending on the pipe diameter and the throughput annealing rate, an annealing atmosphere consisting of 1 to 25% by volume, preferably 5 to less than 15, is set in the tube. volume% oxygen and 75 to 99 volume%, preferably 85 to 95 volume% nitrogen. Use of an internally oxidized tube according to any one of claims 1 to 5 as hollow corrosion resistant installation tube having a residual carbon content of 0.05 to 0.15 mg / dm 2 and an oxide layer thickness of 0.03 to 0.09 μιη.