IL91145A

IL91145A - Tubing with inside oxide layer

Info

Publication number: IL91145A
Application number: IL9114589A
Authority: IL
Original assignee: Kabelmetal Ag
Priority date: 1988-08-12
Filing date: 1989-07-28
Publication date: 1995-07-31
Also published as: ES2036763T3; YU118689A; ZA896043B; DE58901399D1; JP2895095B2; RO109463B1; FI893785A0; FI90136B; FI90136C; PT91428B; SK278911B6; KR940010772B1; DE3827353A1; FI893785A7; IE61097B1; CS8904206A2; EP0356732A1; IL91145A0; NO177688B; SU1716974A3

Abstract

Corrosion damage to tubes made of copper or copper alloys by local pitting is usually triggered by the residues of drawing oil located on the inner surface and/or by oxide layers of poor adhesion. To achieve an especially high resistance of internally oxidised tubes to pitting or to prevent an uneven formation or detachment of the oxides located on the inner surface, according to the invention the thickness of the copper-oxide layer adhering to the basic metal is limited to values of between 0.01 and 0.2 mu m. Preferably, the copper-oxide crystals have a maximum grain size of 0.5 mu m and possess an oriented structure. The good adhesion of the copper-oxide layer formed on the inner surface of the tube preferably by continuous annealing is preserved even when the tubes have been subjected to a machining reducing their cross-section, for example by bending or drawing. [EP0356732A1]

Description

TUBING/ WITH INSIDE OXIDE IAYER BACKGROUND OF THE INVENTION The present invention relates to tubing made of copper or a copper alloy having an oxidation layer on the inside particularly for use in the field of sanitation and health related industries pipe lines for drinking water etc. The invention relates particularly to such tubing as well as to making tubes with an oxide layer on the inside.

! Copper or copper alloy tubing may be used generally for a fresh water, drinking water supply, hot or cold, but also in conjunction with condensators, heat exchangers and So forth. In order to avoid corrosion and particularly the setting up of local local corrosion pitting it has been suggested to proceeding in the processing of tubing as follows.

A certain residue of material that was used as lubricant during drawing the tubing may still be found as a filter on the inside of the tubing, and they are prone to invite carbon deposits. This residue should be removed prior to annealling, primarily through a decreasing medium such as an organic solvent i.e. perchioroethylene. Other methods propose to provide the annealling in a reduced atmosphere and to thereby free the inner surface of the tubing from the carbon film through a spray medium. The medium is inserted or injected in the tube either by pressurized air or high pressure water. 2 I ! More interesting is the proposal from German printed patent application 30 04 455 which discloses ensuring of low residue in carbon by heat treating the tube, following its degreasing in an oxygen containing atmosphere e.g. by means of a gas blend which is comprise of oxygen, helium, and argon. As heat treatment obtains under oxidizing conditions, particularly when arried out in a stationary stack, there is the danger that the oxide layer that forms adheres rather poorly and is relatively thick.

Even worse, the layer may be porous which renders it more or less i permeable and useless as far as corrosion protection is concerned. i I Oxide layers which have a thickness larger than 0.2 micrometers can easily crack and even spall and flake off pursuant to subsequent working of the tubing through bending or the like. Similar problems arise if tubes, following a heat treatment under oxidizing conditions, are subjected to a reduction in cross section in order to make sure that they are at least semihard. The deforming in this case will also produce spelling, cracks, fissures or the like as far as the oxide layer on the inside is concerned. Flaked off oxide particles and layer portions may well lead in an aggregated state to interference particularly as far as the installation is concerned.

I i DESCRIPTION OF THE INVENTION , as protection against corrosion is concerned.

Whether or not the oxide layer on the inside surface of the tube is prone to crack develop fissures, spaliing undergoes flaking or ablation etc. can easily be determined with the naked eye. A tube that was cut open in longitudinal direction following a i deformation such as 180 degrees bending shows the oxide layer to be adhering to the base or substrate, the inner surface of the tube, and did not indicate any kind of damage by means of ablation, cracks or the like. i I DESCRIPTION OF THE DRAWINGS ! ; 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, the objects and features of the invention and further objects, features and advantages thereof will be better understood from the following description taken in connection with the accompanying drawings in which: I I The Figure shows a photomicrograph of art oxide layer as per the preferred embodiment.

The inventive inner tubing shows that the residue carbon content to be smaller or at the most 0.05 mg/dm2 is not necessary to avoid corrosion damage. Decisive is the uniformity and low thickness of the oxidation layer itself not of the carbon content underneath. The Jayer thickness should remain definitely below 0.2 micrometers preferably even below 0.1 micrometers.

In order to manufacture tubing with an inner oxidation layer as per the invention the air surface of the copper tubing is e.g. degreased as described in the German patent application 32 07 135. The particular degreasing is not of any importance. Any other degreasing method may well do. The copper is preferably of the phosphorus deoxidized variety. The residue grease on the inner surface of the tube was, prior to oxidizing annealling, below 0.4 mg/dm2. Depending on the length of the tubing, the full lengths were end to end connected through gas permeable fittings and connector pieces and they are thus permeable during continuous passage through a furnace wherein annealling obtains under, utilization of resistance or inductive heating using a temperature range of 600 to 730 degrees C. The gas blend referred to above was introduced into the tube through the permeable connectors. The speed of passage should not fall below 50 m and should not higher than 220 m/minute. The speed chosen depends on the cross section of the tubing. Appropriate feeding of the gas the atmosphere in the inside of the tubing was adjusted to be between 5 and 15 % by volume oxygen, and 85 - 95% by volume nitrogen or any other suitable inert gas with nitrogen being the most economical one to use. Temperature and speed Were monitored continuously, and, if necessary were varied so that the continuous annealling on utilization of the particular oxygen content was carried out such that a very uniform copper oxide layer obtained. The thickness indeed is in the stated range.

As a consequence of practicing the invention in a variety of ways it was found that the preferred thickness of the copper oxide that adheres to the copper or copper containing substrate is basically between 0.03 and 0.09 micrometers. It was found moreover that this very thin copper oxide layer completely adheres and remains adhering even if the copper tubing was cross sectionally deformed by 20% or if the tubing was bent by 180 degrees. Spelling, cracks, fissures and so forth were not noticeable either with a naked eye or with a microscope of up to 40% enlargement.

The very good adhesion of the copper oxide is of particular importance if semi hard copper tubing is to be made, the adjustment of the "semi-hard" state requires soft annealled copper tubing which subsequently is reduced in cross section wherein particularly the dimension was reduced from 8 mm to 15 mm. Hard drawn copper tubes are then formed to the desired final dimension without interposing recrystalllzation annealling in between the individual drawing steps. 1 In or er to provi e a very t n copper ox e ayer on e inner surface of the tubing the tubing will be briefly heated up to 250 degrees C and not maintained in that range for a long time in order to make sure that the mechanical properties of the tubing are not interfered with.

The invention is not limited to the embodiments described above but ail changes and modifications thereof, not constituting departures from the spirit and scope of the invention, are intended to be included.,

Claims

1. Hole corrosion resistant copper or copper alloy tubing including an interior oxide layer, especially for use in sanitary installation, characterised thereby the said oxide layer attached to the metal and consisting substantially of copper oxide crystals is of a thickness of between 0,01 and 0,09 mm, the said copper oxide crystals being advantageously of (1 ,1 ,1 ) structure and being of maximal size of 0,05 mm.

2. Tubing according to Claim 1 characterized thereby that following an ultimate step of the processing method, the tubing material is at a soft condition of incandescent treatment.

3. Tubing according to Claim 1 characterized thereby that following an ultimate step of the processing method, the tubing material is at a semi hard condition.

4. Tubing according to Claim 1 , characterized thereby that following an ultimate step of the processing method, the tubing material is at hard-drawn condition.

5. Method of preparing tubing of Claims 1-4 characterized by the steps of degreasing by a solvent continuous annealing treatment at temperature ranges of substantially between 600 and 730 °C at a passage speed of 50-200 m/minutes, dependant on the tube diameter and the passage speed, there is adjusted, in the interior of the tube, an incandescent athmosphere consisting of 1-25 Vol.% - preferably up to 5 - and below 15 Vol.% of oxygen and 75-95 Vol.% of nitrogen. P. O. Box 3 3 1 1 6, Te l-A viv Attorneys (or Applicant