The invention refers to a method for the construction of an installation pipe made of copper with a cohesive layer of tin-coating of the internal surface.

The invention further refers to the use of this copper tube as an installation pipe, with a reduced yield of copper ions in potable water with a pH lower than 6.5.

Seamless copper tubes are used as installation pipes, and in particular for the transfer of potable water, meeting the existing requirements of 3 mg/It maximum allowable yield of copper ions in water, following a 12 hour stillness.

In the event of using the copper tube for the transfer of potable water with a pH lower than 6.5 and/or with a high content of free"carbonic acid" (Ks>1. 0 mol/m3), it is desirable to reduce the yield in copper ions.

Various efforts have been made all over the world so far towards this goal.

One of these is coating the internal surface of the copper tube with pure tin powder followed by its incandescence. This way the copper and tin form an alloy of 25 to 35 mm thick. The drawbacks of this method is that this layer has a short lifespan while the yield of ions increases over time.

There is also a chemical method for tin-coating the internal surface of the copper tube, known for many years now. This method is inferior as regards the cohesivity of the tin and its adherence to the copper.

The goal of this invention is to construct an installation pipe made of copper, with an internal surface coated with a tin layer which is cohesive, has an excellent adherence and controllable thickness, so that the long-term yield of copper ions in

potable water remains much lower than the aforementioned required marginal values.

According to the invention, the internal surface of the copper tube is tin-coated by electrolysis following its hot extrusion or cold degradation, using the following steps: a. Cleaning the copper tube using an electro-chemical method. b. Tin-coating by electrolysis by inserting the tube into a tank containing an electrolyte solution with electrode motion inside it. The velocity of continuous motion of the electrode and the intensity of the current are set according to the desired end thickness of the tin-coating of the internal surface. c. Washing and drying the coated tube.

This is followed by deformation of the copper tube cross-section, by one or more degradations, until the final dimension is achieved.

This invention offers a tin layer in the internal surface of the copper tube, which is cohesive (pore-less), with good adherence and controllable thickness.

The aforementioned advantages are the result of the electrolytic method used.

In this way, the reduced yield of copper ions in potable water is ensured, which remains below the 1mg/lt level, following a 12 hour stillness. It is pointed out that the international trend is to reduce the current maximum allowable limit (3 mg/It).

The invention is described in detail below, with references to the attached figures, of which: Figure 1 (on a 1: 20 scale) depicts a side view (top of the figure) and a cross- section (bottom of the figure) of the general layout of the facility for tin-coating the copper tube's internal surface by electrolysis.

This figure shows the tin-coating tank (1), with a tube (2) 12 metres long inserted inside it, in constant level electrolyte (3). The electrolyte recirculates continuously by means of a pump (4), is cleaned by means of a filter (5) and heated by means of electrical resistors (6) in a heating tank (7).

The tin anode (8) is supported at the edge of an electrically isolated bar (9) which may move horizontal by means of a bar conveyor (10). At the edge of the bar (11), the connection of the positive connector of a direct current power source can be seen, while the negative connector of the source can be seen at point (12) on the copper tube.

The bottom of the figure depicts a cross-section of the facility, where the facility for collecting the copper tube from an initial buffer (13) by means of a conveyor (14), the cleaning system (15) and the intermediate buffer (16) before the tin-coating tank (1) can be seen. Following it, the washing baths (17 and 18) and the final storage and drying location (19) can be seen.

Figure 2 (on a 1: 20 scale) depicts the layout of the electrolysis tank with the tin anode (8) at the position where electric power supply begins, and Figure 3 (on a 1: 5 scale) depicts the detail of the tin-coating tank (1) from the side where the tin anode (8) enters on figure 1.

The tin anode (8) which is supported by the bar (9) can be seen in it. This bar is electrically isolated by means of the insulation (20), is supported by the support roller (21) and its front is fitted with supports (22) which guide the electrode concentrically inside the tube (2).

According to this invention, tin-coating by electrolysis takes place on the inside surface of a tube made of copper de-oxidised by means of phosphor, following the stage of hot extrusion or following cold degradation.

This tube may have a length of 2 to 25 metres long, an internal diameter of 40 to 150 mm and a thickness of 3 to 15 mm. Its internal surface should also be free of

oxides and particles of any nature. This can be achieved by means of known electro-chemical cleaning methods.

The tubes are inserted by using mechanical means into an electrolysis tank. This tank is at least 200 mm longer than the copper tube, and its width and depth should be adequate for the number of tubes that will be tin-coated.

A cylinder shaped tin wire of smaller diameter than the internal diameter of the copper tube is used as an anode. The copper tube itself serves as the cathode and the usual salts for tin-coating in an acid environment are used as the electrolyte.

The tin-coating conditions, i. e. the composition of the bath, the temperature and the current density are the standard ones, known and recommended by the electrolyte suppliers.

A mechanical grip collects the copper tube from a storage location and places it on V-shaped supports inside the tin-coating bath. The insertion of the tube into the bath takes place at an angle, so that its quick repletion is facilitated (see figure 1).

After the tube is seated, the tin anode wire is inserted, supported by a conveyor bar, until it reaches its other end (see figure 2). The tin anode wire consists of a pure tin cylinder, with a diameter 10 to 20 mm smaller than the internal diameter of the copper tube and a length greater than 100 mm.

The concentric movement of the tin anode wire inside the tube is ensured by supports fitted between the tin anode wire and the supporting bar (see figure 3).

When the anode reaches the edge of the tube (see figure 2), a direct current power source is connected, with the negative connector on the tube and the positive connector on the tin anode wire, while at the same time the bar begins to be withdrawn. The withdrawal velocity and the current intensity depend on the desired thickness of tin-coating, which can be up to 30 mm. The current is supplie during the withdrawal of the bar (so that the bar supports will not injure the tin- coated surface) and is interrupted when the tin anode wire reaches the edge.

After the tin anode wire exits, the already tin-coated tube is transported by means of a grip to two consecutive washing baths and is finally placed on the drying and storage space. A known washing technology is applied for washing, so as to remove the electrolyte residues by means of de-ionised water.

The already tin-coated tube is subjected to consecutive degradations, until the final dimensions are achieved.

The tin-coating thickness in the resulting tube is about 2 mm.