WO1985003311A1

WO1985003311A1 - Cathodic protection monitoring method and device

Info

Publication number: WO1985003311A1
Application number: PCT/EP1985/000049
Authority: WO
Inventors: Roger Alexander
Original assignee: Alexander Corrosion Technology Ltd.
Priority date: 1984-01-24
Filing date: 1985-01-24
Publication date: 1985-08-01
Also published as: EP0169901A1; AU4068285A

Abstract

Method and device simulating corrosion taking place on a structure which is subjected to a corrosion control system. The electrical behaviour of that corrosion can be observed while the device, which is submerged in the same electrolyte, is connected to and disconnected from the structure. The corrosion control current may pass into the structure through metal (2) and conductor (4) or through metal (1) to conductor (3), through a meter, connected to conductor (3), to conductor (5) and metal (8) against the corrosion current in the electrolyte contained by metal (8) to metal (2) and then via conductor (4) to the structure. If the corrosion prevention current overcomes the corrosive activity the meter reading is reduced to zero or reversed in direction.

Description

CATHODIC PROTECTION 10 ITOK^ G METHOD AND DEVICE

Technical field;

This invention relates to a corrosion control moriitoring method and device. It enables the user to ascertain the adequacy of a corrosion control system installed to protect a buried or submerged structure.

Corrosion can be caused by impurities introduced into the metal during manufacture. The impurities and the metal have different electrical properties. When both are immersed in an electrolyte, a corrosion cell is formed between the pure and the impure metals (Figure 1) . The electrical circuit that is formed, causes a current to flow from the metallic anode into the electrolyte. Where this occurs, metal is lost into solution ^• and the structure is damaged. At another location, the current passes from the electrolyte to the metal and no corrosion damage occurs at this (cathode) point. A corrosion control system is designed to stop the metal loss at the anode. In a system, called cathodic protection, a D.C. current is caused to flow into the environmental electrolyte and from there, onto the surface of the structure.

Background art:

At present the effectiveness of the corrosion control system is assessed using a voltmeter to measure electrical potential differences and a theoretical level of protection exists at which sufficient current is thought to pass onto each part of the structure to prevent corrosive activity. The system of using electrical potential differences is not satisfactory in many ways and consequently no criteria for protection has proved infallible. Disclosure of invention:

The corrosion control monitoring system is innovative in that it simulates the corrosion process taking place on the struc¬ ture, while this corrosion can be electrically measured. The design of the device allows the observation of the electrical behaviour of the corrosion cell while it is being connected and disconnected from the structure, and thus with and without the influence of the corrosion control system. It can there¬ fore be seen if the system is capable of stopping corrosion. This is achieved by the innovation of encapsulating a sample of electrolyte to form a corrosion cell within the device.

The wiring circuit allows the corrosion prevention system to act upon the simulated corrosion cell in the same way as it would act upon a natural corrosion cell on the surface of structure.

The circuit of the device is completed when the corrosion current passes through the environment in which the device is placed.

Brief description of drawings:

A specific eirfaodiment of the invention will now be described by way of example with reference to the accompanying drawings in which

Figure 1 shows the principle of the corrosion cell.

Figure 2 shows a typical cathodic protection system.

Figure 3 shows^'in perspective a view of the base and end of the device. Figure 4 shows in perspective a view of the top and end of the device.

Figure 5 shows a secrion through the device.

Referring to the drawings the device comprises three pieces of metal 1, 2, and 8. They are set in an electrically insulating material 7, and connected to separate electrical conductors 3, 4 and 5 passing out of the device through lead 6.

Current passes from steel plate 2 into a sample electrolyte which has been placed into the cavity formed by the copper 8, and the inulating material 7. The current then passes through the conductor 5, and through an electrical current measuring and/or direction indicating device to conductor 3. The current then passes to the steel plate 1 and from the device into the environment on which the device has been placed.

From the environment the current passes onto the other steel plate 2 to complete the circuit. The magnitude and direction _ of the current is noted by the operator observing the elec¬ trical current measuring and/or direction indication device.

Electrical conductor 4 is then connected to the metal of the structure.

The magnitude and direction of the indication given by the electrical current measuring and/or direction indicating device are again noted.

Best mode for carrying out the invention:

Ideally, the metals of which the device is partly made, should be the same as the metals to be found on the structure to be monitored. For general use concerning steel structures, it is sufficient that a mild steel anode, and a copper cathode be used to produce and electrαrotive-force of about 0.600 V.

Industrial applicability:

The invention is applicable in all fields of technology where corrosion of structures, which are at least partly submerged or buried and thus in presence of an electrolytic environment, can occur and cathcdic protection can be utilized.

Claims

1. A method to determine the effect of a corrosion control system upon a structure which is at least partly immersed in an electrolyte and in which it is liable to corrode, characterized in that a corrosion cell is used, which cell is constructed in such a way that the electrical current resulting from the electrolytic action at the anodic metal to electrolyte, interface, passes through that electro¬ lyte which is contained out of contact with the environ¬ mental electrolyte, into a metallic cathode contact which is connected to^* n electrical current measurement and/or direction indicating device, and which allows the current to pass through an electrical conductor to metal which is placed in contact with the environment in which the aforementioned structure is at least partly immersed being the same environmental electrolyte in which the outer surface of the said anodic metal is immersed or the outer surface of a metal which is in electrical connec¬ tion with the said anodic metal, is immersed, and that an electrical contact is made between the anodic metal of the said internal corrosion cell, to the structure which is under the influence of the corrosion control system, thus providing a conductive path from the environmental electrolyte from the outer surface of the metal of which the inner surface forms the anode of the internal cor- rosion cell within the device or providing a conductive path from the environmental electrolyte from the outer surface of the metal which is in electrical contact with the anodic metal of the internal corrosion cell, which electrical contact may or may not include an electrical current measuring and/or direction indicating device, to the said structure which is under the influence of the corrosion control system.

2. A method according to claim 1 wherein a sample of the environmental electrolyte is contained in electrical separation from the external environment, except that the electrical current developed at the corroding anodic interface is electrically conducted through an electrical measuring and/or direction indicating device, and through a metallic contact to the external environment form where it re-enters the device via a second metalic contact with the external environmental electrolyte in the same manner as a natural corrosion cell would if it was in the same location.

3. A method according to claims 1 or 2 wherein the external surfaces of two pieces of metal of identical chemical composition, are put into contact the environmental electrolyte thus completing the electrical circuit allowing corrosion to take place on the inner surface of the first piece of metal and the resulting electrical current to pass through an encapsulated electrolyte to a dissimilar third piece of metal being cathodic to the first piece of metal, and from the cathodic metal to pass through an electrical current measuring and/or direction indicating device, returning to the second piece of metal which is in contact with the environmental electrolyte.

4. A method according to claims 1, 2, or 3, wherein the corrosion current passes from the anodic surface of the encapsulated corrosion cell through the cathodic metal of. the said cell and through an electrical conductor available for the operator of the device to connect into circuit, a means of measuring and/or indicating the direction of an electrical current which is generated by the electrolytic reaction within the device, or that such a means of measuring and/or indicating the direction of the said current, be made temporarily or permanently part of the device.

5. A device for carrying out the method according to claims 1, 2, 3 or 4 characterized in that it is divided into two units connected by electrical conductors to achieve the same circuit as described in claim 1, and by which means, one unit contains metallic environmental contact and the other unit contains encapsulated electrolyte by means of which an electrical current is caused to pass through an electrical current measuring and/or direction indicating device and from there to the other unit which on contact with the environmental electrolyte allows the current to pass through that environmental electrolyte to the external surface of the metal of the other unit, which metal forms the anodic surface of the corrosion cell contained within that unit.

6. A corrosion monitoring device substantially as described herein with reference to Figures 3 to 5 of the accompanying drawings.