CN105527550B - A kind of method for supervising detection dissimilar metal state of insulation in conducting solution - Google Patents
A kind of method for supervising detection dissimilar metal state of insulation in conducting solution Download PDFInfo
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- CN105527550B CN105527550B CN201510921271.5A CN201510921271A CN105527550B CN 105527550 B CN105527550 B CN 105527550B CN 201510921271 A CN201510921271 A CN 201510921271A CN 105527550 B CN105527550 B CN 105527550B
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- 239000002184 metal Substances 0.000 title claims abstract description 75
- 229910052751 metal Inorganic materials 0.000 title claims abstract description 75
- 238000009413 insulation Methods 0.000 title claims abstract description 56
- 238000000034 method Methods 0.000 title claims abstract description 11
- 238000001514 detection method Methods 0.000 title abstract 2
- 238000005260 corrosion Methods 0.000 claims abstract description 54
- 230000007797 corrosion Effects 0.000 claims abstract description 45
- 238000012544 monitoring process Methods 0.000 claims abstract description 14
- 150000002739 metals Chemical class 0.000 claims description 39
- 239000010405 anode material Substances 0.000 claims description 10
- 238000010586 diagram Methods 0.000 claims description 6
- 230000000694 effects Effects 0.000 claims description 5
- 239000000463 material Substances 0.000 claims description 5
- 238000003487 electrochemical reaction Methods 0.000 claims description 2
- 239000007769 metal material Substances 0.000 claims description 2
- 230000035945 sensitivity Effects 0.000 claims description 2
- 238000012360 testing method Methods 0.000 abstract description 14
- 230000008878 coupling Effects 0.000 abstract description 3
- 238000010168 coupling process Methods 0.000 abstract description 3
- 238000005859 coupling reaction Methods 0.000 abstract description 3
- 230000003628 erosive effect Effects 0.000 abstract 1
- 238000010292 electrical insulation Methods 0.000 description 5
- 238000004364 calculation method Methods 0.000 description 3
- 239000011248 coating agent Substances 0.000 description 3
- 238000000576 coating method Methods 0.000 description 3
- 238000002955 isolation Methods 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 238000004088 simulation Methods 0.000 description 2
- 229910001369 Brass Inorganic materials 0.000 description 1
- 239000010951 brass Substances 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 230000002035 prolonged effect Effects 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/12—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing
- G01R31/1227—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials
- G01R31/1263—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials of solid or fluid materials, e.g. insulation films, bulk material; of semiconductors or LV electronic components or parts; of cable, line or wire insulation
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- General Physics & Mathematics (AREA)
- Testing Resistance To Weather, Investigating Materials By Mechanical Methods (AREA)
Abstract
A kind of prison detection dissimilar metal method of state of insulation in conducting solution belongs to corrosion monitoring instrument technical field.The present invention proposes the division according to metal erosion grade, it is determined that different insulative grade classification principle between coupling dissimilar metal, so that shunt circuit Plays resistance value is provided during galvanic corrosion current monitoring in conducting solution for dissimilar metal.Thus, according to the size of current monitored in test loop, galvanic corrosion state of the dissimilar metal in conducting solution is judged.The present invention is proposed using bypass in parallel, measures by-pass current.According to size of current, the dissimilar metal electric insulating state in conducting solution is judged.It is demonstrated experimentally that the present invention can judge galvanic corrosion state of the dissimilar metal in conducting solution very well.
Description
Technical Field
The invention relates to a method for monitoring the galvanic corrosion state of dissimilar metals in a solution, belonging to the technical field of corrosion monitoring instruments.
Background
When two different metals are contacted in a corrosive medium, the metal with the negative self-corrosion potential is accelerated to corrode. This is galvanic corrosion. Generally speaking, the greater the potential difference between dissimilar metals, the more severe the galvanic corrosion. To prevent galvanic corrosion, insulating gaskets are typically used, or an insulating coating is applied to isolate the different pieces of metal to be joined. However, as the service life of the gasket and the coating which play the insulation function is prolonged, the insulation performance of the gasket and the coating can be reduced, and even the insulation performance can be failed. This inevitably leads again to accelerated corrosion of one of the coupled dissimilar metals from the metal having the negative corrosion potential.
At present, the test method for the galvanic current is only used for experimental research tests. Under actual working conditions, the experimental method for testing the galvanic couple current between dissimilar metals cannot be implemented or is difficult to implement. Although it is also proposed to evaluate the galvanic corrosion state of the coupled dissimilar metals in the solution by measuring the voltage difference between the dissimilar metals and by determining the insulation condition between the dissimilar metals. However, as shown in fig. 1, when the input impedance of the voltmeter is also large, the resistance in the circuit decreases and the current flowing through the circuit becomes larger than it is actually when the parallel test is performed. Unless the test resistance of the voltmeter is much greater than the insulation resistance. This is not possible because the insulation resistance tends to be large. For this reason, this method cannot accurately determine the galvanic corrosion state of the coupling dissimilar metal in the solution.
Based on the principle, the invention provides a principle of determining different insulation grades between coupling dissimilar metals according to the grade division of metal corrosion, thereby providing a standard resistance value in a parallel circuit for monitoring the galvanic corrosion current of the dissimilar metals in a conductive solution. Therefore, the galvanic corrosion state of the dissimilar metal in the conductive solution is judged according to the monitored current in the test loop.
Disclosure of Invention
1. Combining the metal corrosion resistance grade and the galvanic corrosion sensitivity classification of dissimilar metals, the judgment standard of the insulation state between dissimilar metals is provided, and the judgment standard is shown in table 1.
2. A calculation method corresponding to the insulation resistance values of dissimilar metals under different insulation state conditions is provided:
1) calculating the corresponding corrosion current density (i) according to the corrosion depth of the anode metal material in the pair of dissimilar metal couples under different insulation statesa) I.e. by
2) The self-corrosion potential difference (. DELTA.V) between dissimilar metals was calculated according to the formula (2), i.e.
3) Calculating the minimum insulation resistance value (R) required by the anode material in the dissimilar metal paired material under different insulation states according to the formula (3)0) I.e. by
Wherein,
the self-corrosion potentials of the cathode and the anode of the coupled material are respectively.
VL: annual depth of corrosion in mm/y
ρ: density of anode material, g/cm3.
n is the number of charges lost by the electrochemical reaction of anode material atoms;
m is the atomic weight of the anode material, g.
3. A schematic circuit diagram of galvanic corrosion monitoring of dissimilar metals in a conductive solution is provided, as shown in FIG. 2.
As shown in FIG. 2, the potential difference (△ V) between dissimilar metals is considered as a DC power source, the solution resistance (R) is the internal resistance of the power source, and the insulation resistance (R) is the resistance on the external circuit
I＝I2＝△V/(R+r) (4)
In order to measure the couple current I, the invention proposes to use an external circuit, connected in parallel with a standard resistor R'. The standard resistance is the minimum insulation resistance value (R) of the anode material in the dissimilar metal pairing material in different insulation states calculated according to the formula (3)0). In this case, the galvanic corrosion current is
I＝I1+I2＝△V/(R//R′+r) (5)
Wherein R// R 'represents that the insulation resistance R is connected with the standard resistance R' in parallel.
To further discuss the effect of the parallel reference resistance R 'on the galvanic corrosion current under operating conditions, the derivative of R' can be obtained by equation (5), and the result is shown in equation (6):
as can be seen from the formula (6), since the derivative of the galvanic corrosion current I to the parallel standard resistance R 'is negative, it is shown that the standard resistance R' is increased, so that the influence on the galvanic corrosion current under the working condition can be reduced.
When the parallel standard resistance R' is equal to the insulation resistance R, i.e. R ═ R, then
From the equation (7), since the insulation resistance R itself is large and △ V is small, the influence on the measurement of the galvanic corrosion current I of dissimilar metals in solution is still small when the parallel standard resistance is equal to the insulation resistance, and therefore, it is possible to measure the galvanic corrosion current between dissimilar metals under the operating conditions by using the schematic diagram shown in fig. 2.
4) A method for monitoring the galvanic corrosion current of different metals in conducting solution and judging its insulating state is disclosed.
In the conductive solution, when the insulating effect between the dissimilar metals is completely good, the potential difference of the dissimilar metals is substantially constant. In this case, the insulation resistance is greater than the minimum insulation resistance (R) calculated by equation (3)0). When a standard resistor R' is connected in parallel according to FIG. 2, and R ═ R0When, as can be seen from FIG. 2 and equation (5), I1>I2. If it is adoptedBy 2I1The galvanic corrosion current I in the conductive solution instead of dissimilar metal is larger than the actual state. Therefore, in this case, only when the current I is monitored1Less than the ratio of the self-corrosion potential difference of dissimilar metal to the parallel standard resistance, i.e. IaWhen is at timeIt can be judged that the state of insulation between the dissimilar metals starts to be shifted from the completely insulated state to the insulation holding state.
When the insulation effect of the dissimilar metal does not fail obviously, the potential difference of the dissimilar metal begins to be reduced gradually as the insulation resistance is reduced. When the insulation resistance is equal to the parallel standard resistance R', also from FIG. 2 and equation (5), I1＝I2. If 2I is adopted1The galvanic corrosion current I of the conductive solution instead of dissimilar metals is consistent with the result of the actual state. In this case, when monitoring the current I12 times the value of, i.e. 2I1Less than the ratio of the self-corrosion potential difference of dissimilar metal to the parallel standard resistance, i.e. IaWhen is at timeIt is judged that the insulation state between the dissimilar metals starts to be lost.
5) A control program of a galvanic corrosion monitor for dissimilar metals in a conductive solution is provided.
The invention provides a method for measuring bypass current by adopting a parallel bypass. And judging the electrical insulation state of the dissimilar metal in the conductive solution according to the current magnitude. As shown in particular in fig. 5.
Drawings
FIG. 1 is a schematic diagram of voltage measurement between dissimilar metals by voltage method
FIG. 2 is a schematic diagram of monitoring the galvanic corrosion state of dissimilar metals in a conductive solution
FIG. 3 shows the simulated change of electrochemical parameters of couple pair when the standard resistance of the shunt test bypass is 20K ohm
FIG. 4 shows the simulated change of electrochemical parameters of the couple pair when the standard resistance of the shunt test bypass is 200K ohm
FIG. 5 is a flow chart of the present invention
Detailed Description
Taking a couple pair composed of B10 and brass H62 as an example, the change rule of the voltage difference and the measured current between the two dissimilar metals under the working condition is simulated and calculated. As shown in fig. 3 and 4.
According to table 1, it can be calculated that the potential difference under the completely electrically insulated state of B10/H62 is 0.175V, the minimum insulation resistance is 200K ohms, and the corresponding maximum galvanic current is 0.85 microampere; the maximum insulation resistance of the initial loss of the electrical insulation state is 20K ohms, and the corresponding minimum galvanic current is 8.5 microamperes.
When the standard resistance of the test bypass parallel connection is 20K ohm, according to the circuit diagram shown in FIG. 2 and the variation trend of the potential difference E shown in FIG. 3, the actual galvanic corrosion current I and the test bypass current I can be simulated and calculated1. Similarly, if the standard resistance of the test bypass parallel connection is 200K ohms, the actual galvanic corrosion current I and the test bypass current I under the working condition are simulated and calculated1See fig. 4.
As can be seen from FIG. 3, the actual couple current I and the test bypass current I1There is a junction where the galvanic current is around 2.4 microamperes. According to the previous calculation, the maximum insulation resistance of 20K ohms, for the initial loss of the electrical insulation state, corresponds to a minimum galvanic current of 8.5 microamperes. That is, in the state where the electrical insulation state is initially lost, the galvanic corrosion current I shown in fig. 2 is 8.5 microamperes. According to the parallel principle, the current I of the bypass is tested when the electrical insulation resistance is reduced to 20K ohms1And 4.25 microamperes. That is, when the current in the test bypass was 4.25 microamperes, the electrical isolation condition beganIs initially lost. Compared with the current value calculated by actual simulation, which is 2.4 microamperes, the value is slightly larger, which indicates that the monitoring method is more conservative.
Similarly, to monitor the complete electrical isolation state, the simulation calculation results are shown in fig. 4 when the shunt standard resistance is tested to 200K ohms. Similarly, the monitored current value is 0.85 microampere.
Claims (1)
1. A method of monitoring the insulation state of a dissimilar metal in a conductive solution, comprising:
1) combining the metal corrosion resistance grade and the dissimilar metal galvanic couple corrosion sensitivity classification, providing a judgment standard of the insulation state between dissimilar metals:
2) the method for calculating the insulation resistance value of the dissimilar metal under different insulation states is provided:
(1) according to the corrosion depth of the anode metal material in the pair of dissimilar metal couples under different insulation states, calculating the corresponding corrosion current density iaI.e. by
(2) The self-corrosion potential difference (. DELTA.V) between dissimilar metals was calculated according to the formula (2), i.e.
(3) Calculating the minimum insulation resistance value R required by the anode material in the dissimilar metal paired material under different insulation states according to the formula (3)0I.e. by
Wherein,
respectively is the self-corrosion potential of the cathode and the anode of the paired materials;
VL: annual depth of corrosion in mm/y
ρ: density of anode material, g/cm3
n is the number of charges lost by the electrochemical reaction of anode material atoms;
m is atomic weight of anode material, g
3) Provides a circuit diagram of the principle of monitoring the galvanic corrosion of dissimilar metals in a conductive solution
The potential difference △ V between dissimilar metals is regarded as a direct current power supply, the solution resistance R is the internal resistance of the power supply, and the insulation resistance R is regarded as the resistance on an external circuit, so that the galvanic corrosion current between the dissimilar metals is
I＝I2＝△V/(R+r) (4)
The insulation resistor R is connected with a standard resistor R' in parallel; the standard resistance is calculated according to the formula (3) to obtain different insulations of anode material in dissimilar metal paired materialMinimum insulation resistance value R in state0(ii) a In this case, the galvanic corrosion current is
I＝I1+I2＝△V/(R//R′+r) (5)
Wherein R// R 'represents that the insulation resistance R is connected with the standard resistance R' in parallel;
the derivative of R' is obtained by using formula (5), and the result is shown in formula (6):
when the parallel standard resistance R' is equal to the insulation resistance R, i.e. R ═ R, then
4) Monitoring the galvanic corrosion current of dissimilar metals in a conductive solution and judging the insulation state of the dissimilar metals;
in the conductive solution, when the insulating effect between dissimilar metals is completely good, the potential difference of the dissimilar metals is basically constant; in this case, the insulation resistance is larger than R0(ii) a When a standard resistor R' is connected in parallel, R ═ R0Whenever the current I is monitored1Less than the ratio of the self-corrosion potential difference of dissimilar metal to the parallel standard resistance, i.e. IaWhen is at time Judging that the insulation state between dissimilar metals begins to be changed from a complete insulation state to an insulation holding state;
when the insulation effect of the dissimilar metal is not obviously invalid, the potential difference of the dissimilar metal begins to be gradually reduced along with the reduction of the insulation resistance; when the insulation resistance is equal to the parallel standard resistance R', in this case, when the current I is monitored12 times the value of, i.e. 2I1Less than self-corrosion potential difference of dissimilar metal and parallel standard electricitySpecific value of resistance IaWhen is at timeIt is judged that the insulation state between the dissimilar metals starts to be lost.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN110687378A (en) * | 2019-10-17 | 2020-01-14 | 中国人民解放军海军工程大学 | Dissimilar metal electrical isolation monitoring device |
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| CN113791025A (en) * | 2021-09-13 | 2021-12-14 | 国网山东省电力公司电力科学研究院 | Galvanic couple type corrosion sensor, preparation method and application |
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