CN108680493B - Method for measuring corrosion current density in galvanic corrosion of metal welding joint part - Google Patents
Method for measuring corrosion current density in galvanic corrosion of metal welding joint part Download PDFInfo
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Abstract
The invention discloses a method for measuring corrosion current density in galvanic corrosion of a metal welding joint part, which comprises the steps of measuring by using a measuring device of the galvanic corrosion of the metal welding joint part, analyzing and processing an acquired current signal by a computer, outputting galvanic corrosion current, determining a cathode and anode area on the surface of a welding joint sample according to a galvanic corrosion current time diagram, judging the galvanic corrosion sensitivity of each part of the welding joint, firstly calculating the corrosion current density, knowing the corrosion speed difference between a cathode area and an anode area after calculating the galvanic corrosion current density, judging the anode and the cathode and the corrosion speed difference between the anode and the cathode according to the obtained value and the positive and negative values, and finally calculating to obtain the corrosion current density.
Description
The invention relates to a divisional application of a parent application of a measuring device and a measuring method for galvanic corrosion of a metal welded joint part, wherein the application date of the parent application is 2016, 4 and 29 days, and the application number is 2016102867138.
Technical Field
The invention belongs to the field of a measuring device for galvanic corrosion, and particularly relates to a measuring device and a measuring method for galvanic corrosion of a metal welding joint part.
Background
Galvanic corrosion, also known as bimetallic corrosion. When two or more different metals or different structures (such as welding seams) of the same metal are contacted in a conductive medium, the corrosion galvanic cell is formed due to different electrode potentials. Under the electrolyte water film, corrosion macro cells are formed, which accelerate corrosion of negative potential metals therein. Factors influencing galvanic corrosion include environment, medium conductivity, area ratio of cathode and anode, and the like. Galvanic corrosion generally depends on the potential difference between dissimilar metals. The electric potential here refers to the actual electric potential of two metals or different structures of the same metal (e.g. weld) in the electrolyte solution (corrosion medium), respectively, i.e. the corrosion potential of the metal in the solution. Among them, in general, a cathode having a high potential and an anode having a low potential are used, and particularly, when the area of the anode is small, a couple of a small anode and a large cathode is formed, which causes the corrosion to be accelerated. The greater the potential difference, the greater the rate of corrosion may be, with other conditions unchanged. The reason why the potential is thermodynamic data is probably that the speed of the corrosion process cannot be exactly expressed by the thermodynamic data, and even the contrary conclusion sometimes appears because of the difference of the external environment. Therefore, measurement of the kinetic process data, i.e. galvanic corrosion current, becomes of particular importance. The corrosion speed difference between different materials or different structures can be calculated through the measured corrosion current. Thereby judging the corrosion behavior of the equipment in a specific environment.
Welding is an important process link in engineering manufacturing, and many parts are connected together by welding. Since the structure of the welded joint is inevitably affected during welding, even if the two connecting members and the welding material are made of the same material, the welded joint can be subjected to galvanic corrosion in a corrosive environment due to the nonuniform structure. The method for researching the corrosion of the metal welding joint part mainly comprises the following steps: salt spray tests, immersion tests (full immersion, intermittent immersion, etc.) and electrochemical tests (potentiometric, galvanic, polarimetric, electrochemical impedance, etc.). The former can only obtain weightlessness data and surface corrosion morphology, can not obtain corrosion current data, and consumes long time. Although the electrochemical method can obtain electrochemical information, most of the electrochemical methods are limited to respectively research a single area, and the working electrode prepared in a laboratory has the defects of complex processing, time consumption and the like, and can not realize online nondestructive detection.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a device and a method for measuring the galvanic corrosion of the metal welding joint part, which detect the corrosion galvanic current between each area on the surface of the metal welding joint on line so as to judge the anode area and the cathode area, obtain the galvanic corrosion degree of each area on the surface of the metal welding joint and judge the galvanic corrosion sensitivity of the metal welding joint.
In order to solve the technical problems, the invention is realized by the following technical scheme:
the measuring device for the galvanic corrosion of the metal welding joint part comprises a testing probe, an ion channel, an electrochemical measuring device and a computer, wherein:
the electrochemical measuring device is connected with the computer, transmits the collected electrochemical signals to the computer, and the computer analyzes and processes the collected current signals and outputs the numerical value of the galvanic corrosion current within the testing time;
the working end and the grounding end of the electrochemical measuring device are respectively connected with two welding samples to be measured for collecting signals; the test probe comprises a first test probe and a second test probe, the first test probe and the second test probe are identical in structure and are respectively fixed on two welding samples to be tested, the test probe consists of an upper probe cover, a probe main body, a lower probe pipe and a magnetic fixing bolt, the lower end of the upper probe cover is connected with the probe main body, a sealing ring is arranged at the joint of the upper probe cover and the probe main body, the lower probe pipe is arranged in the center of the lower end face of the probe main body, the magnetic fixing bolts are symmetrically arranged at four corners of the lower end face of the probe main body, and magnets are arranged at the tail; a sample contact ring is arranged on the lower end surface of the lower probe tube; an ion channel connecting hole penetrating through the upper probe cover is formed in the upper probe cover and in the axial direction of the upper probe cover, a cavity is formed in the probe main body and the interior of the lower probe end, and the ion channel connecting hole and the cavity are coaxially connected into an integrated solution storage cavity after the upper probe cover, the probe main body and the lower probe end are connected into a whole;
one end of the ion channel is arranged in the ion channel connecting hole of the probe upper cover of the first test probe, and the other end of the ion channel is arranged in the ion channel connecting hole of the probe upper cover of the second test probe so as to communicate the solution storage cavities of the two test probes.
In the technical scheme, the solution under the actual working environment of the metal welding joint is arranged in the solution storage cavity so as to simulate the working environment of the part to be tested.
In the above technical solution, the ion channel can conduct ions and cannot conduct electrons, and a plastic pipe is selected and filled with a material which can conduct ions and cannot conduct electrons, such as sponge, solution, gel, and preferably a silicone tube filled with saturated potassium chloride gel is used as the ion channel.
In the above technical solution, the test probe is integrally made of an insulating material, such as teflon.
In the technical scheme, the first test probe is arranged in a base material area, a heat affected area or a welding area (namely a welding seam area) of a sample to be tested; the second test probe is arranged in a base material area, a heat affected zone or a welding area (namely a welding seam area) of the sample to be tested, so that the two probes are matched to respectively measure the welding seam area and the heat affected zone; a heat affected zone, a base material; galvanic corrosion currents between the weld zone, the parent metal, and between different heat affected zones.
When in use, the method comprises the following steps:
In the step 1, if the surface of the sample to be tested is uneven and rough or belongs to a nonmagnetic material, the test probe is directly fixed by using white silica gel or epoxy resin.
And 3, respectively connecting the sample to be tested with the working end and the grounding end of the electrochemical measuring device, starting the electrochemical measuring device for testing, and simultaneously recording signals by using a computer.
In the technical scheme, the first test probe is arranged in a base material area, a heat affected area or a welding area (namely a welding seam area) of a sample to be tested, and the sample to be tested provided with the first test probe is connected with a working end of the electrochemical measuring device; the second test probe is arranged in a base material area, a heat affected area or a welding area (namely a welding seam area) of the sample to be tested, and the sample to be tested provided with the second test probe is connected with the grounding end of the electrochemical measuring device; thus, the two probes are matched to respectively measure a weld joint area and a heat affected zone; a heat affected zone, a base material; galvanic corrosion currents between the weld zone, the parent metal, and between different heat affected zones. The galvanic corrosion current measured by the method is the difference value of the corrosion current of the tissue of the area covered by the first test probe relative to the tissue of the area covered by the second test probe in a conducting state, i.e. I is I1-I2。
In the technical scheme, before the measurement is started, the sample to be tested provided with the first test probe is connected with the working end of the electrochemical measuring device to form a conducting state, the sample to be tested provided with the second test probe is disconnected with the grounding end of the electrochemical measuring device, and transient pulse current at the moment of connection is obtained when the test is started.
In the above technical solution, the computer records the signal acquired by the electrochemical measurement device, and at the instant when the sample to be tested provided with the second test probe is conducted with the ground terminal of the electrochemical measurement device, due to the transient pulse current caused by the potential difference, the galvanic corrosion current signal is continuously read, and after the galvanic corrosion current is stabilized, the acquisition is stopped after the galvanic corrosion current is continuously acquired for a period of time (for example, 200 to 1000 seconds). And copies the resulting data to a TXT document or other format of record file. And analyzing and processing the acquired current signal by the computer, outputting the galvanic corrosion current, determining the cathode and anode areas on the surface of the welding joint sample according to the galvanic corrosion current time chart, and judging the galvanic corrosion sensitivity of each part of the welding joint.
Compared with the prior art, the invention has the beneficial effects that: the device can detect corrosion galvanic couple current between each area on the surface of the metal welding joint so as to judge the anode area and the cathode area, obtain the galvanic couple corrosion degree of each area on the surface of the metal welding joint and judge the galvanic couple corrosion sensitivity of the metal welding joint.
Drawings
FIG. 1 is a schematic structural view of a test probe according to the present invention;
FIG. 2 is a schematic diagram of the wiring of the galvanic corrosion current experiment of the heat affected zone to the parent metal zone according to the present invention;
FIG. 3 is a schematic illustration of the wiring scheme of the present invention;
FIG. 4 is a diagram of galvanic corrosion current of a heat affected zone to a parent metal zone for performance testing according to the embodiment of the present invention;
FIG. 5 is a diagram of galvanic corrosion current of the heat affected zone versus the weld zone for performance testing in accordance with the present technique;
FIG. 6 is a diagram of galvanic corrosion current of the base material region to the welding region for performance testing according to the embodiment of the present invention.
The device comprises a probe, a solution storage cavity, a probe lower pipe, a magnetic fixing bolt, a sample contact ring, a magnet, a working end, a grounding end, a welding area, a heat affected area, a base material area, a first test probe, a second test probe, a working ring of the first test probe, a working ring of the second test probe, an ion channel, an electrochemical measuring device and a computer, wherein the ion channel is 1, the probe upper cover is 2, the sealing ring is 3, the probe main body is 4, the solution storage cavity is 5, the probe lower pipe is 6, the magnetic fixing bolt is 7, the sample contact ring is 8, the magnet is 9, the working end is 10, the grounding end is 11, the welding area is 12, the heat affected area.
Detailed Description
The invention is described in further detail below with reference to specific embodiments and with reference to the following figures:
as shown in the attached figures 1-3, the device for determining the galvanic corrosion of the metal welding joint part comprises a test probe, an ion channel, an electrochemical measuring device and a computer, wherein:
the electrochemical measuring device is connected with the computer, transmits the collected electrochemical signals to the computer, and the computer analyzes and processes the collected current signals and outputs the numerical value of the galvanic corrosion current within the testing time;
the working end and the grounding end of the electrochemical measuring device are respectively connected with two welding samples to be measured for collecting signals; the test probe comprises a first test probe and a second test probe, the first test probe and the second test probe are identical in structure and are respectively fixed on two welding samples to be tested, the test probe consists of an upper probe cover, a probe main body, a lower probe pipe and a magnetic fixing bolt, the lower end of the upper probe cover is connected with the probe main body, a sealing ring is arranged at the joint of the upper probe cover and the probe main body, the lower probe pipe is arranged in the center of the lower end face of the probe main body, the magnetic fixing bolts are symmetrically arranged at four corners of the lower end face of the probe main body, and magnets are arranged at the tail; a sample contact ring is arranged on the lower end surface of the lower probe tube; an ion channel connecting hole penetrating through the upper probe cover is formed in the upper probe cover and in the axial direction of the upper probe cover, a cavity is formed in the probe main body and the interior of the lower probe end, and the ion channel connecting hole and the cavity are coaxially connected into an integrated solution storage cavity after the upper probe cover, the probe main body and the lower probe end are connected into a whole;
one end of the ion channel is arranged in the ion channel connecting hole of the probe upper cover of the first test probe, and the other end of the ion channel is arranged in the ion channel connecting hole of the probe upper cover of the second test probe so as to communicate the solution storage cavities (and solutions) of the two test probes.
In the technical scheme, the solution under the actual working environment of the metal welding joint is arranged in the solution storage cavity so as to simulate the working environment of the part to be tested.
In the above technical solution, the ion channel can conduct ions and cannot conduct electrons, and a plastic pipe is selected and filled with a material which can conduct ions and cannot conduct electrons, such as sponge, solution, gel, and preferably a silicone tube filled with saturated potassium chloride gel is used as the ion channel.
In the above technical solution, the test probe is integrally made of an insulating material, such as teflon.
In the technical scheme, the first test probe is arranged in a base material area, a heat affected area or a welding area (namely a welding seam area) of a sample to be tested; the second test probe is arranged in a base material area, a heat affected zone or a welding area (namely a welding seam area) of the sample to be tested, so that the two probes are matched to respectively measure the welding seam area and the heat affected zone; a heat affected zone, a base material; galvanic corrosion currents between the weld zone, the parent metal, and between different heat affected zones.
When in use, the method comprises the following steps:
In the step 1, if the surface of the sample to be tested is uneven and rough or belongs to a nonmagnetic material, the test probe is directly fixed by using white silica gel or epoxy resin.
And 3, respectively connecting the sample to be tested with the working end and the grounding end of the electrochemical measuring device, starting the electrochemical measuring device for testing, and simultaneously recording signals by using a computer.
In the technical scheme, the first test probe is arranged in a base material area, a heat affected area or a welding area (namely a welding seam area) of a sample to be tested, and the sample to be tested provided with the first test probe is connected with a working end of the electrochemical measuring device; the second test probe is arranged in a base material area, a heat affected area or a welding area (namely a welding seam area) of the sample to be tested, and the sample to be tested provided with the second test probe is connected with the grounding end of the electrochemical measuring device; thus, twoThe probes are matched to respectively measure a weld zone and a heat affected zone; a heat affected zone, a base material; galvanic corrosion currents between the weld zone, the parent metal, and between different heat affected zones. The galvanic corrosion current measured by the method is the difference value of the corrosion current of the tissue of the area covered by the first test probe relative to the tissue of the area covered by the second test probe in a conducting state, i.e. I is I1-I2。
In the technical scheme, before the measurement is started, the sample to be tested provided with the first test probe is connected with the working end of the electrochemical measuring device to form a conducting state, the sample to be tested provided with the second test probe is disconnected with the grounding end of the electrochemical measuring device, and transient pulse current at the moment of connection is obtained when the test is started.
In the above technical solution, the computer records the signal acquired by the electrochemical measurement device, and at the instant when the sample to be tested provided with the second test probe is conducted with the ground terminal of the electrochemical measurement device, due to the transient pulse current caused by the potential difference, the galvanic corrosion current signal is continuously read, and after the galvanic corrosion current is stabilized, the acquisition is stopped after the galvanic corrosion current is continuously acquired for a period of time (for example, 200 to 1000 seconds). And copies the resulting data to a TXT document or other format of record file. And analyzing and processing the acquired current signal by the computer, outputting the galvanic corrosion current, determining the cathode and anode areas on the surface of the welding joint sample according to the galvanic corrosion current time chart, and judging the galvanic corrosion sensitivity of each part of the welding joint.
And (4) processing galvanic corrosion current data. Before analyzing the corrosion current, the magnitude of the corrosion current density should first be calculated. The corrosion current density is the product of the corrosion current and the corrosion area, wherein the area is the area of the sample to be tested in contact with the (simulation) solution in the sample contact ring of the test probe on the sample to be tested connected with the working end of the electrochemical measuring device (i.e. the area of the sample contact ring), but not the working area of the counter electrode end (the area of the sample to be tested in contact with the simulation solution in the sample contact ring of the test probe on the sample to be tested connected with the grounding end of the electrochemical measuring device). The corrosion current density is calculated by the following formula:
ID＝I/s
s＝πR2
wherein, IDAnd (3) the density of the galvanic corrosion current, I the galvanic corrosion current, s the working area and R the radius of the working ring of the test probe (the radius of the sample contact ring).
When a multi-probe is used for testing, the working area is the total working area of the test probes connected to the working end of the electrochemical working device (i.e., the sum of the areas of the contact rings of each sample).
Determination of galvanic corrosion behavior and corrosion imbalance. After calculating the galvanic corrosion current density, we only know the difference of the corrosion speed of the cathode region and the anode region, i.e. ID＝IYang D-IYin D. Although it can be determined which one is the anode, which one is the cathode, and the difference between the corrosion rates by the value of the positive and negative values. But the absolute values of the corrosion rates of the two are unknown. However, in general, when galvanic corrosion occurs between two materials having different self-corrosion potentials, the material is cathodically polarized at a high potential to decrease the corrosion rate, and the material is anodically polarized at a low potential to increase the corrosion rate. When the difference between the self-etching potentials is large, I is considered to beYang DIs far greater than IYin DI.e. ID≈IYang D. When the self-corrosion potential difference between the two is small, further calculation should be performed by combining with tests such as polarization curves.
And (4) determining the corrosion speed of the metal welding joint. When the self-corrosion potential difference between the two is large, the local corrosion speed of the metal can be calculated through the corrosion current density.
The reaction electric quantity per unit time is Q ═ tID
The total reaction mass per unit time is m-QM/Fn
Wherein t is time, n is the difference between the valences of the reactant and the product, F-96500 is the Faraday constant, and M is the molar mass of the reactive atoms.
Therefore, the etching rate A is m/ts
Wherein A is in g-m2h, s is the electrode reaction area (i.e., the working area used in calculating the corrosion current density).
The depth of etching can also be expressed as B ═ 24X 365A)/1000d
Wherein B is mm/year, d is the density of the material, and g/cm is the unit3
For the above formula, carry in I respectivelyD、IYang DAnd IYin DThe local corrosion speed of different areas can be calculated.
The contact part of the first welding joint sample and the solution in the working ring of the first test probe is a working electrode, and the contact part of the second welding joint sample and the solution in the working ring of the second test probe is a counter electrode; the diameter of the working ring in the lower tube of the probe is selected to be not more than the width of the measured tissue, and the diameter is selected to be 5 mm; the working ring and the metal sample are ensured to be in close contact through adjusting the magnetic fixing bolt, and liquid leakage prevention work is well done; adding a solution required by a welding joint experiment into the solution storage cavity of the probe main body; the thickness of the ion conduction pipeline is consistent with that of the connection hole so as to prevent the solution from leaking; the ion conduction pipeline is made of flexible material (silicone tube) and keeps good contact with the solution in the probe body.
The steps of using the test probe of the invention to test the galvanic corrosion current between different tissues of the welded joint are as follows:
(1) the lower tube of the test probe and the magnetic fixing bolt are connected to the probe body, and the first test probe and the second test probe respectively use the magnetic fixing bolt to enable the working ring to be adsorbed on different structures of the first welding joint and the second welding joint. Therefore, the working rings of the first test probe and the second test probe are adsorbed at the corresponding tissues under each group of tests. Then, a 3.5 wt% aqueous solution of sodium chloride (seawater simulant) was added into the solution storage chamber of the probe body. The sample in this example is T4003 stainless steel, and the surface has been polished, and no solution leaks during the experiment, so no further solution leakage prevention measures are required. After the solution is injected, the sealing ring is placed, the probe upper cover is screwed on the upper part of the probe main body, and then the silicone tube containing saturated potassium chloride gel inside is inserted into the flexible ion conduction pipeline connecting hole and is ensured to be closely contacted with the solution, so that an ion conduction channel is formed between the two probes.
(2) Connecting the test probe with the electrochemical work station: fig. 2 is a wiring diagram of the experiment, and fig. 2 is a wiring diagram of a galvanic corrosion current test of a heat affected zone to a parent metal zone, and the tissues covered by the working ring should be different in the galvanic corrosion current test between other tissues. It is worth noting that: in order to obtain transient corrosion current conduction between different tissues, the working end of the electrochemical workstation is ensured to be in contact with the first welding joint sample before testing, and the grounding end of the electrochemical workstation is disconnected from the second welding joint sample. When the test begins, the electrochemical workstation ground is then connected to the second weld joint coupon.
(3) Setting test parameters: in the experiment, a ZF-100 electrochemical workstation produced by Shanghai Square electric company Limited is adopted to carry out transient galvanic couple current test, the scanning frequency is 20Hz, and the scanning time is 15 minutes. The galvanic corrosion current graphs of the T4003 stainless steel welded joint samples of different structures in the experiment are shown in the figures 4-6. The difference of the average corrosion rate of different tissues of the material under the environment can be obtained through the magnitude of the steady-state galvanic corrosion current in the figures 4-6.
The calculation results of the average value of the steady-state galvanic corrosion current between different areas by measurement calculation are shown in the following table:
in the galvanic corrosion current test, if the obtained current is a positive value, it represents that the corrosion speed of the working electrode is greater than that of the counter electrode, that is, the corrosion speed of the region covered by the working ring of the first test probe is faster. While a larger value of galvanic corrosion current represents a larger difference in corrosion rates. From this we can derive the relationship between the corrosion rates of the three tissues: the heat affected zone > the base material zone > the weld zone.
In the initial stage of the test, the direction and the magnitude of the transient galvanic corrosion current obtained at the moment of communicating the grounding end of the electrochemical workstation with the second welding joint can be used for judging the potential relationship and the difference value of the two. In this experiment, the transient galvanic corrosion current obtained by three tests is a positive value, and it can be determined that the relationship between the corrosion potentials of the three tissues is: the heat affected zone is smaller than the base material zone and smaller than the welding zone. According to the relationship, the corrosion resistance of different structures of the T4003 stainless steel welded joint is as follows: the heat affected zone is smaller than the base material zone and smaller than the welding zone.
The present invention has been described in detail, but the above description is only a preferred embodiment of the present invention, and is not to be construed as limiting the scope of the present invention. All equivalent changes and modifications made within the scope of the present invention shall fall within the scope of the present invention.
Claims (10)
1. A method for measuring corrosion current density in galvanic corrosion of a metal welded joint part is characterized in that a measuring device for the galvanic corrosion of the metal welded joint part is used for measuring, the measuring device for the galvanic corrosion of the metal welded joint part comprises a test probe, an ion channel, an electrochemical measuring device and a computer, wherein: the electrochemical measuring device is connected with the computer, transmits the collected electrochemical signals to the computer, and the computer analyzes and processes the collected current signals and outputs the numerical value of the galvanic corrosion current within the testing time;
the working end and the grounding end of the electrochemical measuring device are respectively connected with two welding samples to be measured for collecting signals; the test probe comprises a first test probe and a second test probe, the first test probe and the second test probe are identical in structure and are respectively fixed on two welding samples to be tested, the test probe consists of an upper probe cover, a probe main body, a lower probe pipe and a magnetic fixing bolt, the lower end of the upper probe cover is connected with the probe main body, a sealing ring is arranged at the joint of the upper probe cover and the probe main body, the lower probe pipe is arranged in the center of the lower end face of the probe main body, the magnetic fixing bolts are symmetrically arranged at four corners of the lower end face of the probe main body, and magnets are arranged at the tail; a sample contact ring is arranged on the lower end surface of the lower probe tube; an ion channel connecting hole penetrating through the upper probe cover is formed in the upper probe cover and in the axial direction of the upper probe cover, a cavity is formed in the probe main body and the interior of the lower probe end, and the ion channel connecting hole and the cavity are coaxially connected into an integrated solution storage cavity after the upper probe cover, the probe main body and the lower probe end are connected into a whole; one end of the ion channel is arranged in the ion channel connecting hole of the probe upper cover of the first test probe, the other end of the ion channel is arranged in the ion channel connecting hole of the probe upper cover of the second test probe so as to communicate the solution storage cavities of the two test probes, and the solution under the actual working environment of the metal welding joint is arranged in the solution storage cavity so as to simulate the working environment of the part to be tested; the measuring method comprises the following steps:
step 1, fixing a test probe on the surface of a welding sample to be tested by utilizing a magnet and a magnetic fixing bolt and tightly attaching the test probe, performing liquid leakage prevention treatment at a joint by utilizing an insulating material, and tightly attaching the sample contact ring to the surface of the welding sample to be tested;
step 2, adding a pre-configured solution into the solution storage cavity to simulate different working states of the welding sample to be tested, wherein the part of the welding sample to be tested in the sample contact ring is the testing area of the welding sample to be tested, and soaking the pre-configured simulated solution in the area; communicating the solutions in the solution storage cavities of the two test probes by using an ion channel;
step 3, connecting the welding sample to be tested with the working end and the grounding end of the electrochemical measuring device respectively, starting the electrochemical measuring device for testing, and recording signals by a computer; the computer analyzes and processes the collected current signal, outputs galvanic corrosion current, can determine the cathode and anode area of the surface of the welding sample to be detected according to the galvanic corrosion current time chart and judges the galvanic corrosion sensitivity of each part of the welding joint, wherein:
firstly, calculating the corrosion current density, wherein the corrosion current density is the ratio of the corrosion current to the corrosion area, the area is the area of a to-be-detected welding sample which is in contact with a solution in a sample contact ring of a to-be-detected welding sample connected with the working end of the electrochemical measuring device, namely the area of the sample contact ring, and the corrosion current density is calculated by the following formula:
ID＝I/s
s＝πR2
wherein, IDThe density of the galvanic corrosion current, I is the galvanic corrosion current, s is the working area, and R is the radius of the working ring of the test probe, namely the radius of the sample contact ring; when multiple probes are used for testing, the working area is the total working area of the test probes connected to the working end of the electrochemical measuring device, i.e. the sum of the areas of the contact rings of each test sample.
2. The method for measuring corrosion current density in galvanic corrosion at a welded metal joint according to claim 1, wherein the first test probe is disposed in a base material region, a heat affected zone or a weld zone, i.e., a weld zone, of the welded sample to be measured, and the welded sample to be measured, in which the first test probe is disposed, is connected to a working end of the electrochemical measuring device; the second test probe is arranged in a base metal area, a heat affected area or a welding area, namely a welding seam area, of the welding sample to be tested, and the welding sample to be tested provided with the second test probe is connected with the grounding end of the electrochemical measuring device; the two probes are matched to respectively measure a weld joint area and a heat affected zone; a heat affected zone, a base material; and the galvanic corrosion current between the welding seam area and the parent metal, namely between different heat affected areas is used as the difference value of the corrosion current of the area structure covered by the first test probe relative to the corrosion current of the area structure covered by the second test probe in a conducting state.
3. The method according to claim 1, wherein before the start of the measurement, the welding sample to be measured of the first test probe is connected to the working end of the electrochemical measuring device to form a conducting state, and the welding sample to be measured of the second test probe is disconnected from the ground end of the electrochemical measuring device to obtain a transient pulse current at the moment of connection when the measurement is started, and then the signal of the galvanic corrosion current is read continuously, and after the galvanic corrosion current is stabilized, the collection is stopped after the collection is continued for a while.
4. The method for determining corrosion current density in galvanic corrosion of a metal welded joint according to claim 1, wherein the insulating material used in step 1 of the test is epoxy glue, white silica gel or 502.
5. The method according to claim 1, wherein the ion channel is capable of conducting ions and not conducting electrons, and the plastic pipe is filled with a material capable of conducting ions and not conducting electrons.
6. The method for measuring corrosion current density in galvanic corrosion of a metal welded joint according to claim 5, wherein a silicone tube filled with saturated potassium chloride gel is used as an ion channel.
7. The method for determining the corrosion current density in galvanic corrosion at a metal welded joint according to claim 1, wherein the test probe as a whole is made of an insulating material.
8. The method for determining the corrosion current density in galvanic corrosion at the metal welded joint according to claim 7, wherein the insulating material selected for the test probe is polytetrafluoroethylene.
9. The method for determining the corrosion current density in the galvanic corrosion of the metal welded joint part according to claim 1, wherein in the step 1 of the test, if the surface of the welded sample to be tested is uneven and rough, or belongs to a nonmagnetic material, the test probe is directly fixed by using white silica gel or epoxy resin.
10. The method for determining the corrosion current density in the galvanic corrosion of the metal welded joint part according to claim 3, wherein the collection is stopped after the galvanic corrosion current is stabilized and the collection is continued for 200 to 1000 seconds.
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| CN107884334A (en) * | 2017-11-21 | 2018-04-06 | 北京市燃气集团有限责任公司 | A kind of galvanic corrosion test system and its method of testing |
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| CN108918407A (en) | 2018-11-30 |
| CN108680493A (en) | 2018-10-19 |
| CN108918407B (en) | 2020-07-17 |
| CN105954186B (en) | 2018-09-11 |
| CN108680492B (en) | 2020-09-01 |
| CN105954186A (en) | 2016-09-21 |
| CN108680492A (en) | 2018-10-19 |
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