The invention concerns method for controlling the effect of corrosion prevention in a connected pipe system by means of a reference electrode, where the corrosion prevention can be an electrolysis plant as an example.

The known way of adjusting an electrolysis plant for corrosion protection is to let the treatment take place in dependence of a water consumption, typically a maximal treatment, when there is a water consumption and a minimal without, where the signal typically comes from a water meter with a mounted reed relay.

To some extent the choice of the maximal and the minimal current has been empirically chosen and subsequent adjustments can be necessary, where the choice of treatment intensity has partly been determined on basis of assumption and experience. However, control of the chosen treatment intensity is often done by cutting out pipes from the plant and have them closer examined, possibly by an EDAX analysis, but this implies a substantial economic load and is a partly, subjective choice of intervals, where control is desired. Furthermore, this validation is not possible until weeks or months after start-up.

Electrolysis plants are typically mounted in a boiler in either full-or part stream, supplied with anode and/or cathode of aluminium, zinc or other sacrifice, which is added a current through an impressed voltage, thus resulting in the metal dissolving as ions, and led into the pipe system by the water flow, where on the metal surfaces a desired protective layer is formed.

Typically, an impulse water meter gives a signal to the rectifier, and adjusts the current intensity according to the default values. This adjustment is often necessary, because an upper limit value for the permitted amount of aluminium in drinking water is fixed.

The invention states a method where on current and dynamic basis control can be made of the effect of an electrolysis plant in service. This will be explained in the following.

If in the pipe system without direct electrical loading of the electrolysis plant, a mounting is made of a thread of platinum-, mix-oxide or the similar with similar stabile potential electrically isolated from the pipe system, by a short-circuit

between thread and pipe, it will be possible to measure the galvanic current, which is going between the thread and the pipe material, which as an example could be a galvanized pipe. The measure period needs only to be milliseconds, whereupon it is disconnected.

Surprisingly, it has turned out that by start up of an electrolysis plant, you will get an immediate reaction of the current in descending direction, and that equivalently quickly, one will get an increasing current, if the treatment stops.

It is the nature of electrolysis to form a protective layer on all surfaces made of metal below hydrogen in the electrochemical series. Once such a protective layer is formed, the galvanic current between measure thread and pipe will approach zero, and it will no longer be possible to measure a difference between connected and disconnected electrolysis plant in current passage in the reference cell.

This implies two phases: 1. By start-up of electrolysis plant, you can after a short while with measurement, demonstrate an effect of the corrosion protection plant, where the reason must be the negative aluminate ions blocking for the positive metal ions-which are an expression of corrosion-in an opposite polarization, increasing the resistance, thus reducing the galvanic current.

By turning off the electrolysis plant, the current in the reference cell will increase, confirming that a protective layer cannot yet be formed.

2. After a period in service, the current intensity in the reference cell will be constantly low, with or without connected electrolysis plant, because a protective layer has been formed. these pieces of information can inform about the condition of the plant by control, but they can also be used as control signals for the treatment intensity, where it can be chosen to let the plant work with maximal treatment in periods without water consumption in order to use the electrolytic inhibitor in the best way.

On a hot water plant several reference cells can be mounted, as an example one on inlet, and one on return pipe, where it can be rational to make the

measurement on the two cells in series, for in this way to get an indication about the condition of the entire plant. This is easily done, because both pipes are in the same room. On cold-water plants this possibility does not exist directly, because there is no circulation.

The invention is also very suitable for industrial water plants, where at start-up a considerable dosing amount of electrolytically dissolved ions can be made, since there are not the same demands for the water quality as for drinking water, and at the same time it is possible to use several metals, which are amphoteric, which have a special ability to work as inhibitors.

In principle, the system works by measuring a current in the reference cell at fixed time intervals. For as long as the current is decreasing, a given dosing by electrolysis is maintained. When the current has reached a minimum, the treatment will be reduced, alternatively it will stop, but still measurements will be made at fixed time intervals, and the corrosion preventing plant will be resumed, should the current rise again.

By means of simple electronics, it is possible to build the reference cell in the steering board for the electrolysis, where the intervals between measurements can vary on wish, and by each measurement a comparison is made between previous and the latest reference cell measurement, which will then determine adjustment of the added voltage, and with that the current to the electrodes of the electrolysis plant.

Choice of electrode material will typically be aluminium, but also other amphoteric metals can be suitable, zinc and tin as examples.

In the same way, with a reference electrode it will be possible to control a chemical dosing plant, and also adjust the dosing amount after visual measure control of the cell, or by relevant electronics letting this control the amount of added chemicals.

In the figure an example is shown of a mounting, where 1 is a 3 mm platinum thread, embedded in a plastic plug 2, mounted in a galvanized tee pipe 3.

Between the tee-piece 3 and the platinum thread 1, on an ammeter 4, the galvanic current is measured. It can be suitable to place a PTC-resistance 5 with physical contact to the pipe to compensate for differences in temperature, which would otherwise influence the measurement.