RU2339740C1 - Bicameral copper-sulfate nonpolarisable reference electrode - Google Patents

Abstract

FIELD: metallurgy, coating.

SUBSTANCE: invention concerns protection from corrosion underground metal constructions and can be used for instrumentation of summary and polarisation potentials, for instance for piping. Electrode contains current non-conducting body with electrolytic chamber with built in it copper deep stream with signal track and potential sensor installed on body, at that electrolytic chamber body is filled by electrolyte consisting of distilled water, copper sulfate and ethylene glycol, ceramic porous diaphragm and ion-exchange membrane, at that current non-conducting body is additionallt outfitted by bentonitic chamber filled by bentonitic clay, soaked in water, and installed in it bottom part with ability of chambers' jointing, at that in point of chambers' jointing there are installed plastic stabilisation disk, ion-exchanger membrane and plastic disk with forced in it ceramic porous diaphragm, and in bottom part on the body of bentonitic chamber it is installed plastic disk with forced in it ceramic porous diaphragm, which is implemented with ability of electrolytic contact providing of electrode with ground.

EFFECT: service life increasing of reference electrodes and stability of itself potential, expansion of usage area with different chemical composition and moisture.

1 dwg, 1 ex

Description

FIELD OF THE INVENTION

The invention relates to the protection against corrosion of underground metal structures, in particular to two-chamber non-polarizing copper-sulfate reference electrodes, and can be used to measure the total and polarization potentials, for example, of a pipeline.

State of the art

A non-polarizable reference electrode is known, containing a non-conductive housing with a coupling, filled with an electrolyte from a saturated solution of copper sulfate in a mixture of water and ethylene glycol, a copper rod located in the housing, an ion-exchange membrane, a potential sensor mounted on the housing, and the potential sensor equipped with a removable nozzle on the electrode housing at least two ion-exchange membranes are mounted, and the bottom of the coupling mounted on the housing has perforation (see US Pat. RU No. 2122047, class C23F 13/00, publ. 20.11.1998).

The disadvantage of this electrode is the shortened service life caused by the use of ion-exchange membranes, which do not exclude the penetration of groundwater into the housing of the reference electrode, and in soils with a high content of metal ions, such as calcium, the reaction of copper ions replaces copper ions with calcium ions and, as a result , an irreversible change in the self-potential of the electrode. The use of two ion-exchange membranes limits the use of the electrode in dry soils due to the lack of contact of the electrode electrolyte with the outer membrane, which leads to drying of the outer membrane and an increase in the internal resistance of the electrode until the conductivity is completely lost.

Known equipment for determining the bias of the potential difference between the underground metal structure and the reference electrode, containing a voltmeter with an internal resistance of at least 20 kOhm per 1 V scale, recording or showing a copper-sulfate reference electrode, a steel reference electrode, with which measurements are carried out in the control measuring points, wells, pits, etc. contact method using recording or indicating devices, while the positive terminal of the measuring device is connected to the structure, the negative to the reference electrode, followed by processing the measurement results, and the difference between the measured potential of the structure and the value of its stationary potential is calculated by the formula

ΔU = U _ISM -U _s ,

where U _ISM is the least negative or most positive over the measurement period, the instantaneous potential difference between the structure and the copper-sulfate reference electrode;

U _with - stationary potential of the structure

(see. Unified system of protection against corrosion and aging. Underground structures. General requirements for protection against corrosion. GOST 9.602-89, Moscow).

The disadvantage of this equipment is its relatively low service life.

The closest in technical essence and the achieved positive effect and accepted by the authors for the prototype is a long-acting comparison electrode containing a non-conductive housing with a porous bottom filled with an electrolyte, a copper rod located in the housing and a potential sensor mounted on the housing, while it is equipped with an ion-exchange membrane mounted on the porous bottom of the body, and the electrolyte contains a saturated solution of copper sulfate in a mixture of water and ethylene glycol in a ratio of 3: 2-2: 1.

The electrode uses an ion-exchange membrane obtained by rational graft copolymerization of acrylic or methacrylic acid in an amount of 100-170% on a biaxially oriented polypropylene film (see ed. St. SU No. 1601199, class C23P 13/00, published on October 23, 1990). .

Signs of the prototype, coinciding with the essential features of the claimed invention, the following. The long-acting comparison electrode contains a copper rod, a dielectric housing filled with an electrolyte from a saturated solution of copper sulfate in a mixture of water and ethylene glycol. The electrode also has a ceramic porous diaphragm and an ion-exchange membrane. A potential sensor is mounted on the housing.

The reason that impedes obtaining the required technical result for the prototype is the use of only an ion-exchange membrane, which insufficiently prevents the penetration of groundwater into the electrode and the electrolyte into the soil, which leads to depletion of the electrolyte and its modification due to the replacement of copper ions in the electrolyte by ions of other metals contained in the ground, and, as a result, to a change in the electrode potential.

Disclosure of invention

The objective of the invention is to develop a two-chamber copper-sulfate reference electrode non-polarizable, having an increase in the life of the reference electrode and the stability of its own potential, expanding the area of use in soils with different chemical composition and humidity.

The technical result that can be obtained using the present invention is to increase the service life of the reference electrodes and the stability of its own potential, expand the area of use with different chemical composition and humidity.

The technical result is achieved using a two-chamber non-polarizable copper-sulfate reference electrode containing a non-conductive case with an electrolytic chamber with a copper rod mounted in it with a signal conductor and a potential sensor mounted on the case, while the body of the electrolytic chamber is filled with an electrolyte consisting of distilled sulfate water copper and ethylene glycol, and the ratio of water to ethylene glycol is 2: 1, a ceramic porous diaphragm and an ion-exchange membrane, with this non-conductive housing is additionally equipped with a bentonite chamber filled with bentonite clay, soaked in water in a ratio of 1: 1, and installed in its lower part with the possibility of articulating the chambers using a plastic nut, while at the junction of the chambers are installed: a plastic stabilizing washer, an ion-exchange membrane and a plastic washer with a ceramic porous diaphragm pressed into it, and a plastic washer with ceramic pressed into it is installed on the bottom of the bentonite chamber body porous diaphragm, which is configured to provide electrolytic contact of the electrode with soil.

The technical result that can be obtained by carrying out the present invention is achieved as follows. The electrode housing consists of two chambers made of a non-conductive material, an electrolytic chamber filled with an electrolyte, and a bentonite chamber. An ion exchange membrane and a ceramic porous diaphragm are installed at the junction of the chambers. A second ceramic porous diaphragm is installed at the base of the electrode to close the volume of the bentonite chamber.

The essential features of the claimed invention are as follows.

The non-polarizing copper-sulfate reference electrode contains a non-conductive housing consisting of two chambers. The electrolytic chamber is filled with an electrolyte from a saturated solution of copper sulfate in a mixture of water and ethylene glycol; a copper rod is located in the chamber. The bentonite chamber is filled with bentonite clay powder soaked in water in a volume ratio of 1: 1, while the bentonite clay has a gel-like state. An ion exchange membrane and a ceramic porous diaphragm are installed at the junction of the chambers. A second ceramic porous diaphragm is installed at the base of the electrode to close the volume of the bentonite chamber. A potential sensor is mounted on the electrode housing.

Unlike the prototype, the housing of the claimed electrode consists of two chambers. The electrolytic chamber is filled with electrolyte. The bentonite chamber is filled with bentonite clay soaked in water. The use of bentonite is due to its properties - the ability to swell during hydration. With limited space for free swelling in the presence of water, a dense gel forms, which prevents further penetration of moisture while maintaining ionic conductivity. The use of a bentonite chamber significantly limits the penetration of groundwater into the electrolytic chamber and the electrolyte into the soil, which allows to increase the life of the electrode, while maintaining the stability of its potential.

Brief Description of the Drawings

The drawing shows the proposed two-chamber copper-sulfate reference electrode non-polarizable, General view.

The implementation of the invention

The non-polarizable two-chamber copper-sulfate reference electrode contains a non-conductive case with an electrolytic chamber 1 with a copper rod 2 mounted to it, to which a signal conductor 3 is connected. The body of the electrolytic chamber 1 is filled with electrolyte 4, which includes distilled water, copper sulfate and ethylene glycol. The volume ratio of water and ethylene glycol is 2: 1. The content of copper sulfate ensures the saturation of the solution with the release of free crystals. A potential sensor 5 is attached to the housing of the electrolytic chamber 1 with a signal conductor 6 attached to it, while the non-conductive housing is equipped with a bentonite chamber 7 filled with bentonite clay 8 soaked in water in a volume ratio of 1: 1. At the junction of chambers 1 and 7, there are installed: a plastic stabilizing washer 9, an ion-exchange membrane 10 and a plastic washer with a porous ceramic diaphragm pressed into it 11. The sealing of the electrolytic chamber 1 is ensured by a rubber gasket 12. The chambers 1 and 7 are joined by means of a plastic nut 13. Plastic a washer with a ceramic porous diaphragm 14 pressed into it, which provides electrolytic contact of the electrode with soil, is fixed in the lower part on the bentonite chamber body 7 with a plastic nut 15.

A two-chamber non-polarizable copper-sulfate reference electrode is operated as follows.

Example. Three samples of standard copper-sulfate reference electrodes ESN-MS1 with one ion-exchange membrane, ESN-MS2 with two ion-exchange membranes and the proposed two-chamber comparison electrodes were taken as samples. All electrodes were placed in containers filled with saturated calcium chloride solution.

The potentials of all electrodes with respect to the silver chloride reference electrode had a value of 120 mV, with a tolerance of less than ± 30 mV. The choice of a solution of calcium chloride is justified from the point of view of the practice of using copper-sulfate electrodes, since it is in soils with a high calcium content that the reduced service life of standard electrodes is noted. The tests consisted of two-week cycles. During the first week, the electrodes were kept in a saturated solution of calcium chloride. Then the electrodes were removed from the solution, placed on a perforated surface and blown with a stream of air heated to 40-50 ° C from the air heater for 8 hours a day for five days, to simulate the use of electrodes in dry soils. Further, the electrodes were again immersed in a solution of calcium chloride. All subsequent two-week cycles began with the measurement of potentials relative to the silver chloride reference electrode. The tests lasted 6 months. The first to fail (the main criterion for failure was the deviation of the electrode potential by more than ± 30 mV from the potential of 120 mV with respect to the silver chloride reference electrode) two ESN-MS2 electrodes - after the first test cycle. The third ESN-MS2 failed after the second two-week test cycle. During the tests, the ESN-MS1 electrodes showed a stable tendency to lower potential and after the first three months all 3 electrodes failed. At the time of completion of the tests, two-chamber electrodes had a potential of 120 ± 15 mV.

At the end of the test, all electrodes were dismantled. In the electrodes of the ESN-MS, the electrolyte was transparent, with a yellowish tinge, on the inner side of the membrane, on the side of the electrolyte, there was a precipitate in the form of white flakes. The electrolyte of two-chamber electrodes had a blue tint characteristic of copper sulfate with the presence of undissolved crystals.

A non-polarizing silver chloride comparison electrode is installed in the soil in the immediate vicinity of the underground structure, in particular, a pipeline (not shown) connected to a conductor that goes to the surface of the earth. To measure the potential difference between the conductor (not shown) connected to the underground structure and the signal conductor 3 connected to the copper rod 2 of the electrode, a DC voltmeter having an input resistance of at least 20 kOhm / V at a measurement limit of 0-3 V or close to the specified measurement limit, and the positive terminal is connected to the conductor from the underground structure, the negative terminal of the voltmeter is connected to the signal conductor 3.

The polarization potential measurements are performed using instruments containing a current chopper, for example 43313.1, ORION - IP01, while the terminal “C” of the device is connected to the conductor from the underground structure, the terminal “IE” is connected to the conductor 3 connected to the copper rod 2 of the electrode, and terminal "VE" - to the signal conductor 6 connected to the potential sensor 5.

Thus, the proposed design can significantly increase the life of the copper-sulfate electrode, compared with existing industrial designs, while maintaining its own potential regardless of the chemical composition of the soil and its moisture content.

The non-polarized two-chamber copper-sulfate reference electrode can be used as a long-acting stationary electrode in the electrochemical protection systems of underground metal structures, in particular pipelines, to create electrolytic contact with the ground in determining the effectiveness of the corrosion protection of these structures. Regarding the electrode, measurements are made of the potentials of the structure, both total (with ohmic component) and polarization. Also, the electrode can be used as a potential source in the control system of automatic cathodic protection stations.

The invention in comparison with the prototype and other known technical solutions has the following advantages:

- increase the service life of the reference electrodes;

- the stability of its own potential;

- expansion of the area of use with different chemical composition and humidity;

- high reliability of the reference electrode.

Claims (1)

The two-chamber copper-sulfate reference electrode is non-polarizable, containing a non-conductive case with an electrolytic chamber with a copper rod mounted in it with a signal conductor and a potential sensor mounted on the case, while the case of the electrolytic chamber is filled with electrolyte consisting of distilled water, copper sulfate and ethylene glycol, moreover the ratio of water to ethylene glycol is 2: 1, a ceramic porous diaphragm and an ion-exchange membrane, characterized in that the non-conductive housing is additional It is equipped with a bentonite chamber filled with bentonite clay soaked in water in a ratio of 1: 1 and installed in its lower part with the possibility of articulating the chambers using a plastic nut, while a plastic stabilizing washer, an ion-exchange membrane, and a plastic washer pressed into a ceramic porous diaphragm, and in the lower part on the body of the bentonite chamber there is a plastic washer with a ceramic porous diaphragm pressed into it, which flax with the possibility of providing electrolytic contact.