CN109030337B - A test system for corrosion and anti-corrosion layer peeling of buried metal pipelines based on SECM - Google Patents
A test system for corrosion and anti-corrosion layer peeling of buried metal pipelines based on SECM Download PDFInfo
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- G01Q—SCANNING-PROBE TECHNIQUES OR APPARATUS; APPLICATIONS OF SCANNING-PROBE TECHNIQUES, e.g. SCANNING PROBE MICROSCOPY [SPM]
- G01Q60/00—Particular types of SPM [Scanning Probe Microscopy] or microscopes; Essential components thereof
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Abstract
The invention discloses a buried metal pipeline corrosion and anticorrosive coating peeling test system based on SECM, which comprises an alternating current stray current loading system, an electrolytic bath system and a scanning electrochemical microscope test system; the alternating-current stray current loading system is used for providing an interference source of alternating-current stray current suffered by a buried metal pipeline, the electrolytic cell system is used for simulating actual engineering conditions of corrosion of the buried metal pipeline under different soil environments, and the scanning electrochemical microscope testing system is used for obtaining a localized micro-area image and charge transfer characteristics of the metal corrosion process at a damaged point of an anticorrosive coating under the action of the stray current and analyzing data. The testing system can simulate the local corrosion of the pipeline and the peeling of the anticorrosive coating caused by the flowing in/out of the damaged point of the anticorrosive coating of the buried metal pipeline by stray current under different soil environments, stray current intensity, anticorrosive coating types and anticorrosive coating damaged area ratios.
Description
Technical Field
The invention relates to the technical field of buried metal pipeline corrosion and anticorrosive coating peeling test, in particular to a buried metal pipeline corrosion and anticorrosive coating peeling test system based on SECM.
Background
The external anti-corrosion coating technology is a very effective method for reducing the corrosion of the buried metal pipeline and prolonging the service life of the buried metal pipeline. The ideal corrosion protection layer is defect-free and has a barrier and shielding effect against corrosive media. However, due to the complexity of the coating process and mechanical impact during the construction process, the anticorrosive coating on the pipeline inevitably has some defects such as pinholes and damages, or due to the long-term action of various corrosion factors in the soil during the long-term service, the corrosion inhibitor is adhesive failure and further has defects such as damages and peeling of the surface of the anticorrosive coating. Stray current is the current that flows outside of the designed or specified loop to become one of the important contributors to corrosion leakage of buried metal pipelines. Because the stray current generated by the electrified railway, the high-voltage transmission line and the like has serious influence on the safe operation of the pipeline, particularly the oil pipeline with the defect of damaged and peeled anticorrosive coating in a long distance forms serious local corrosion and anticorrosive coating peeling phenomena at the defect part of the anticorrosive coating, thereby seriously threatening the safe operation of the pipeline.
The traditional metal corrosion mechanism research generally adopts macroscopic electrochemical testing methods, such as a polarization curve method, an alternating current impedance spectrum technology, a corrosion potential and noise technology and the like, and the macroscopic change result of the whole sample is obtained by the traditional electrochemical testing methods, so that the local corrosion information of the sample cannot be reflected. Particularly, for a buried metal pipeline containing an anticorrosive coating, when corrosion occurs at a damaged point of the anticorrosive coating, the traditional macroscopic electrochemical testing method cannot detect electrochemical information of a metal matrix/solution interface, and further cannot reflect the process and local characteristics of local corrosion and anticorrosive coating stripping of metal. In recent years, people are always exploring the research on the electrochemical process of local corrosion, and the micro-area scanning probe technology can distinguish the electrochemical characteristics of different areas of materials, so that a new way is provided for the research on the local surface technology, and the micro-area scanning probe technology is widely applied to the field of metal corrosion. The scanning electrochemical microscope System (SECM) technology is widely applied to the field of corrosion research, the SECM is a powerful tool for researching the electrochemical process of a micro-area, and the SECM has the greatest characteristic of being capable of carrying out real-time, on-site and three-dimensional space observation on a research system in a solution system and has unique chemical sensitivity. When the SECM microprobe is scanned very close to the surface of the substrate electrode, the oxidation-reduction current of the scanning microprobe has the characteristic of feedback, Faraday current images formed at different positions of the substrate electrode can directly represent the surface appearance and the electrochemical activity distribution of the substrate electrode, the surface appearance of the substrate can be described through feedback electric signals, the complex process of local corrosion is researched, and the method makes up the defect of measuring the local corrosion property of metal by a macroscopic electrochemical method.
Disclosure of Invention
Aiming at the defects in the problems, the invention provides a buried metal pipeline corrosion and anticorrosive coating peeling test system based on SECM.
In order to achieve the above object, the present invention provides a buried metal pipeline corrosion and anticorrosive coating peeling test system based on SECM, comprising:
the alternating stray current loading system is used for providing an interference source of the buried metal pipeline subjected to the alternating stray current;
the electrolytic cell system is used for simulating the actual engineering condition of corrosion of the buried metal pipeline in different soil environments;
and the scanning electrochemical microscope test system is used for acquiring a localized micro-area image and charge transfer characteristics in the metal corrosion process at the damaged point of the anticorrosive coating under the action of stray current and analyzing data.
As a further improvement of the present invention, the ac stray current loading system includes: the system comprises an auxiliary platinum sheet electrode, an anticorrosive coating damage sample, a soil simulation solution and an alternating current signal source, wherein the auxiliary platinum sheet electrode and the anticorrosive coating damage sample are both in the soil simulation solution;
one end of the alternating current signal source is connected with the auxiliary platinum sheet electrode, and the other end of the alternating current signal source is connected with the anticorrosive coating damage sample to form a stray current loop.
As a further improvement of the invention, a current meter and a switch are connected in series on a lead between the alternating current signal source and the anti-corrosion layer damaged sample.
As a further improvement of the present invention, the ac stray current loading system further includes: a timer interrupt;
the timing interrupter is connected in parallel to the alternating current signal source and used for controlling the time of alternating current loading.
As a further development of the invention, the electrolytic cell system comprises: the clamping device is used for containing the container of the soil simulation solution and clamping the damaged sample of the anticorrosive coating, and the clamping device is installed on the container.
As a further development of the invention, the container comprises: the device comprises a shell, a bottom plate, a bolt and a base;
the shell is fixedly connected with the base plate through sealant, four symmetrical threaded holes are machined in the outer ring of the base plate, four groups of bolts are placed in the threaded holes, the bottom of each group of bolts is connected with the base through threads, and the bolts are adjusted to enable the damaged sample of the anticorrosive coating to be in a horizontal state.
As a further improvement of the present invention, the clamping device comprises: the sealing structure comprises an epoxy packaging resin sleeve, a sealing O ring, an upper threaded end cover, an external thread reducing joint, a rubber gasket and a lower hexagonal nut;
the anticorrosive coating damage sample is packaged in the epoxy packaging resin sleeve, and the epoxy packaging resin sleeve is sleeved in the sealing O ring; the upper surface of the sealing O ring is in contact with the inner surface of the upper threaded end cover, and the lower surface of the sealing O ring is in contact with the large-diameter groove of the external thread reducing joint; when the threaded end cover and the external thread reducing joint are screwed, the epoxy encapsulation resin sleeve is tightly combined with the sealing O ring; the lower end of the external thread reducing joint is convexly provided with an outer hexagonal end face, the small-diameter end of the external thread reducing joint is inserted into the bottom plate, the lower end face of the bottom plate is in contact with the rubber gasket, and the external thread reducing joint is in close contact with the bottom plate by screwing the lower hexagonal nut.
As a further improvement of the present invention, the scanning electrochemical microscope test system comprises: the device comprises a scanning probe, a reference electrode, an auxiliary platinum sheet electrode, an anticorrosive coating damage sample, an SECM electrochemical workstation, a PC (personal computer), a probe fixing frame, a motor controller and a three-dimensional mobile platform;
the SECM electrochemical workstation is connected with the PC, a four-electrode system is adopted, a WE1 electrode of the SECM electrochemical workstation is connected with the scanning probe, a WE electrode is connected with the anticorrosive coating damage sample, a RE electrode is connected with the reference electrode, and a CE electrode is connected with the auxiliary platinum sheet electrode;
the scanning probe is connected with the three-dimensional moving platform through the probe fixing frame, and the three-dimensional moving platform is used for realizing three-dimensional movement of the scanning probe; and three stepping motors of the three-dimensional mobile platform are all connected with the motor controller, and the motor controller is connected with a PC (personal computer).
As a further improvement of the invention, three guide rail sliding tables of the three-dimensional mobile platform are distributed along an X, Y, Z space coordinate system, a Y-direction guide rail sliding table is fixed on an upper bottom plate of the X-direction guide rail sliding table through bolts, a Z-direction guide rail sliding table is fixed on the upper bottom plate of the Y-direction guide rail sliding table through a triangular support frame, and the scanning probe is fixed on the upper bottom plate of the Z-direction guide rail sliding table through a probe fixing frame;
the three guide rail sliding tables have the same structure, and the Y-direction guide rail sliding table comprises a motor, a motor support, a coupler, a screw support seat, a screw, an upper base plate, a ball screw nut seat, a baffle, a base plate, a guide rail sliding block and a lower base plate; the motor is fixed on the motor support through screws, the motor support is fixed at the right end of the lower bottom plate, the baffle is fixed at the left end of the lower bottom plate, and the guide rail sliding blocks are symmetrically fixed on the lower bottom plate in a front-back mode; the motor is connected with the lead screw through a coupler; the screw rod supporting seat is positioned on the left side of the coupler and is fixed on the lower bottom plate through a screw; the ball screw nut seat is sleeved on the ball screw nut, and the ball screw nut seat and the upper bottom plate are fixed through screws; the upper surface of the backing plate is connected with the lower surface of the upper base plate, and the lower surfaces of the backing plate are connected with the upper surfaces of the four sliding blocks of the guide rail sliding block.
Compared with the prior art, the invention has the beneficial effects that:
the testing system can simulate the local metal corrosion and anticorrosive layer peeling experiments caused by the inflow/outflow of stray current into/out of damaged points of the anticorrosive layer under different soil environments, stray current intensities, anticorrosive layer types and different anticorrosive layer damaged area ratios of the buried pipeline; the test system has the advantages of simple structure, simple and convenient test method and good test result repeatability, can effectively provide local micro-area images and charge transfer characteristics in the pipeline metal corrosion and anticorrosive coating stripping processes, can carry out real-time, on-site and space observation on the metal corrosion process, and is suitable for developing laboratory researches on buried metal pipeline corrosion and anticorrosive coating stripping tests.
Drawings
FIG. 1 is a block diagram of a buried metal pipeline corrosion and erosion protection layer peeling test system based on SECM according to an embodiment of the present invention;
FIG. 2 is an isometric view of a three-dimensional mobile platform according to one embodiment of the present disclosure;
FIG. 3 is a cross-sectional view of a sample with a damaged epoxy encapsulating resin cover encapsulating an anticorrosive coating according to an embodiment of the present invention;
FIG. 4 is a cross-sectional view of a clamping device according to an embodiment of the present invention;
FIG. 5 shows an epoxy-coated X80 steel coupon at 50A/m using the present invention2A SECM line scanning test result chart under alternating current interference;
FIG. 6a shows an epoxy-coated X80 steel coupon at 50A/m using the present invention2Scanning a test result graph of the SECM surface soaked for 0h under the alternating current interference;
FIG. 6b shows an epoxy-coated X80 steel coupon at 50A/m using the present invention2Scanning a test result graph of the SECM surface soaked for 5 hours under the alternating current interference;
FIG. 6c shows an epoxy coated X80 steel coupon at 50A/m using the present invention2Scanning a test result graph of the SECM surface soaked for 10 hours under the alternating current interference;
FIG. 6d shows an epoxy coated X80 steel coupon at 50A/m using the present invention2And (5) scanning test result graphs of the SECM surface soaked for 24 hours under alternating current interference.
In the figure:
I. an alternating stray current loading system; II. An electrolytic cell system; III, scanning an electrochemical microscope test system;
1. scanning the probe; 2. a reference electrode; 3. an auxiliary platinum sheet electrode; 4. a sample with a damaged anticorrosive layer; 5. a soil simulating solution; 6. an alternating current signal source; 7. a timer interrupt; 8. an SECM electrochemical workstation; 9. a PC machine; 10. a wire; 11. a housing; 12. a base plate; 13. a bolt; 14. a base; 15. epoxy encapsulation resin cover; 16. sealing the O ring; 17. an upper threaded end cap; 18. the external thread reducing joint; 19. a rubber gasket; 20. a lower hexagonal nut; 21. a motor; 22. a motor support; 23. a coupling; 24. a lead screw supporting seat; 25. a lead screw; 26. an upper base plate; 27. a ball screw nut; 28. a ball screw nut seat; 29. a probe holder; 30. a baffle plate; 31. a triangular support frame; 32. a base plate; 33. a guide rail slider; 34. a lower base plate; 35. a motor controller; 36. provided is a three-dimensional moving platform.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
The invention is described in further detail below with reference to the attached drawing figures:
as shown in fig. 1 to 4, the present invention provides a SECM-based buried metal pipeline corrosion and corrosion protection layer peeling test system, comprising: the system comprises an alternating-current stray current loading system I, an electrolytic cell system II and a scanning electrochemical microscope testing system III; the alternating-current stray current loading system I is used for providing an interference source of alternating-current stray current suffered by a buried metal pipeline, the electrolytic cell system II is used for simulating actual engineering conditions of corrosion of the buried metal pipeline under different soil environments, and the scanning electrochemical microscope testing system III is used for obtaining a localized micro-area image and charge transfer characteristics in a metal corrosion process at a corrosion protection layer damage point under the action of the stray current and analyzing data. Specifically, the method comprises the following steps:
the alternating stray current loading system I of the present invention includes: the device comprises an auxiliary platinum sheet electrode 3, an anticorrosive coating damage sample 4, a soil simulation solution 5, an alternating current signal source 6, a timing interrupter 7, an ammeter A1 and a switch K1, wherein the auxiliary platinum sheet electrode 3 and the anticorrosive coating damage sample 4 are all in the soil simulation solution 5. One end of an alternating current signal source 6 is connected with the auxiliary platinum sheet electrode 3, and the other end of the alternating current signal source is connected with an ammeter A1 and a switch K1 in series and then connected with the anticorrosive coating damage sample 4 to form a stray current loop. The timing interrupter 7 is connected in parallel to the alternating current signal source 6 and used for controlling the time of alternating current loading and improving the experimental precision; the various parts of the experiment were connected using wires 10.
The electrolytic cell system II of the present invention includes: the device comprises a container for containing soil simulation solution 5 and a clamping device for clamping a damaged sample 4 of the anticorrosive coating, wherein the clamping device is arranged on the container. The container comprises a shell 11, a bottom plate 12, a bolt 13 and a base 14, and the clamping device comprises an epoxy packaging resin sleeve 15, a sealing O-ring 16, an upper threaded end cover 17, an external thread reducing joint 18, a rubber gasket 19 and a lower hexagonal nut 20. Wherein: casing 11 is through sealed gluey and bottom plate 12 fixed connection, and the outer lane processing of bottom plate 12 has four symmetrical screw holes, puts into four groups of bolts 13 in the screw hole, and the bottom of every group bolt 13 is passed through the screw and is linked to each other with base 14, realizes through adjusting bolt 13 that anticorrosive coating damage sample 4 is in the horizontality. The anticorrosive coating damage sample 4 is packaged in an epoxy packaging resin sleeve 15, and the epoxy packaging resin sleeve 15 is sleeved in a sealing O ring 16; the upper surface of the sealing O ring 16 is contacted with the inner surface of an upper thread end cover 17, and the lower surface is contacted with a large-diameter groove of an external thread reducing joint 18; when the threaded end cover 17 and the external thread reducing joint 18 are screwed, the epoxy encapsulation resin sleeve 15 is tightly combined with the sealing O ring 16 to prevent liquid leakage; the lower end of the external thread reducing joint 18 is convexly provided with an external hexagonal end surface, the small-diameter end of the external thread reducing joint 18 is inserted into the bottom plate 12, and the external thread reducing joint and the bottom plate are in clearance fit; the lower end face of the bottom plate 12 is in contact with a rubber gasket 19, and the external thread reducing joint 18 is tightly contacted with the bottom plate 12 by screwing down the hexagon nut 20 so as to prevent liquid leakage.
The scanning electrochemical microscope test system III of the invention comprises: the device comprises a scanning probe 1, a reference electrode 2, an auxiliary platinum sheet electrode 3, an anticorrosive coating damage sample 4, an SECM electrochemical workstation 8, a PC (personal computer) 9, a probe fixing frame 29, a motor controller 35 and a three-dimensional moving platform 36, wherein the three-dimensional moving platform 36 is a high-precision three-dimensional moving platform; wherein: the SECM electrochemical workstation 8 is connected with the PC 9, the SECM electrochemical workstation 8 adopts a four-electrode system, a WE1 electrode of the SECM electrochemical workstation 8 is connected with the scanning probe 1, the WE electrode is connected with the anticorrosive coating damage sample 4, the RE electrode is connected with the reference electrode 2, and the CE electrode is connected with the auxiliary platinum sheet electrode 3; the scanning probe 1 is connected with the three-dimensional moving platform 36 through the probe fixing frame 29, and the three-dimensional moving platform 36 is used for realizing the three-dimensional motion of the scanning probe 1; the three stepping motors 21 of the three-dimensional moving platform 36 are all connected with a motor controller 35, and the motor controller 35 is connected with the PC 9.
The three guide rail sliding tables of the three-dimensional moving platform 36 are distributed along an X, Y, Z space coordinate system, the three guide rail sliding tables are identical in structure, and each guide rail sliding table comprises a motor 21, a motor support 22, a coupler 23, a screw support seat 24, a screw 25, an upper base plate 26, a ball screw nut 27, a ball screw nut seat 28, a baffle 30, a base plate 32, a guide rail sliding block 33 and a lower base plate 34; the Y-direction guide rail sliding table is fixed on an upper base plate 26 of the X-direction guide rail sliding table through bolts, the Z-direction guide rail sliding table is fixed on the upper base plate 26 of the Y-direction guide rail sliding table through a triangular support frame 31, and the scanning probe 1 is fixed on the upper base plate 26 of the Z-direction guide rail sliding table through a probe fixing frame 29. The structure of the guide rail sliding table will be described by taking a Y-direction guide rail sliding table as an example:
the motor 21 is fixed on the motor support 22 through screws, the motor support 22 is fixed at the right end of the lower bottom plate 34, the baffle 32 is fixed at the left end of the lower bottom plate 34, and the guide rail sliding blocks 33 are symmetrically fixed on the lower bottom plate 34 in front and back; the motor 21 is connected with a screw rod 25 through a coupler 23; the screw rod supporting seat 24 is positioned at the left side of the coupler 23 and is fixed on the lower bottom plate 34 through a screw; the ball screw nut seat 28 is sleeved on the ball screw nut 27, and the ball screw nut seat and the ball screw nut 27 are in interference fit; the ball screw nut seat 28 and the upper bottom plate 26 are fixed through screws; the upper surface of the backing plate 32 is connected to the lower surface of the upper base plate 26, and the lower surfaces are connected to the upper surfaces of the four blocks of the rail block 33.
The invention provides a testing method of a buried metal pipeline corrosion and anticorrosive coating peeling testing system based on SECM, which comprises the following steps of carrying out metal local corrosion and anticorrosive coating peeling experiments caused by stray current flowing into/out of anticorrosive coating damage points under different soil environments, stray current intensities, anticorrosive coating types and different anticorrosive coating damage area ratios; the method specifically comprises the following steps:
step one, X80 pipeline steel is adopted as an experimental material, and the size of a sample is 10mm multiplied by 2 mm. One side of the sample is spot-welded with a lead-out wire, and the sample is encapsulated by an epoxy encapsulating resin sleeve 15. And sequentially polishing the working surface of the sample to a mirror surface by No. 400, No. 600 and No. 800 waterproof abrasive paper, cleaning by deionized water and acetone, drying by cold air blow drying, and drying for later use. The anticorrosive layer is made of organic epoxy resin, and the epoxy resin E51 and the polyether amine D230 are mixed according to the mass ratio of 3: 1, standing for half an hour, uniformly coating the surface of a treated X80 steel sample by using a coating rod, after the coating is completely cured, making a coating damage defect of 5mm multiplied by 0.5mm on the center of the X80 steel sample by using a knife to form a sample 4 with an anticorrosive coating damage, and finally clamping the packaged sample in an electrolytic cell system.
And step two, before SECM scanning, leveling the bottom of the electrolytic cell, because the distance between the probe and the bottom has important influence on the current detected by the probe, leveling by using a level meter in the experiment, leveling by placing the level meter right above the sample, adjusting four screws at the lower part of the electrolytic cell according to the position of the bubble in the level meter, and indicating that the X80 steel sample is leveled until the position of the bubble is right in the center of the level.
Step three, opening an alternating current signal source 6, a timing interrupter 7 and a closing switch K1, applying alternating current stray current interference to the X80 steel sample coated with the epoxy coating, wherein the alternating current density is 50A/m2The frequency is 50Hz, and scanning experiments are carried out by using an SECM feedback mode at 0h, 5h, 10h and 24h respectively.
And step four, opening the SECM electrochemical workstation 8, the motor controller 35 and the PC 9, arranging the motor controller on a control interface of the PC to enable the three-dimensional moving platform to return to an initial point, then adjusting the position of the scanning probe 1, placing the scanning probe at the central position of a coating damage point of the X80 steel sample, setting two scanning modes of the SECM, wherein the position of the SECM is about 1mm away from the surface of the sample along the positive direction of the Z axis of the space coordinate system, and the scanning mode is surface scanning, wherein the scanning range is 1000 Mum multiplied by 1000 Mum. The other is line scanning along the X direction of a space coordinate system, the scanning range is 1000um, the scanning speed is 10 mu m/s, and the potential of the probe is set to be 0V. After the parameters are set, the experiment of the SECM scanning electrochemical microscope is carried out.
And step five, after the experiment is finished, lifting the scanning probe length along the Z-axis direction, then taking down the scanning probe, slightly wiping the moisture on the surface of the probe, and putting the probe into a probe box for storage. And finally, disconnecting all power supplies, leading out the soil simulation solution in the electrolytic cell, taking down the sample, and observing the corrosion and stripping morphology of the X80 steel sample by using a body type microscope.
FIG. 5 shows an epoxy-coated X80 steel coupon at 50A/m using the present invention2Scanning test results of the SECM lines under alternating current interference; the current value detected by the SECM probe can be expressed by equation (1).
i＝4nFDCa (1)
In the formula:
f is the Faraday constant;
c-the concentration of KI;
d-diffusion coefficient of KI;
a-diameter of the probe;
n is the number of electrons in electrode reaction;
when the applied stray density is increased, the corrosion reaction of X80 steel at the defect of coating damage is accelerated, the number n of electrons released by the corrosion of X80 steel is increased, the current i detected by the SECM probe is increased, the width of the defect at the current peak scanned by the probe after the sample is soaked for 24h is widened along with the prolonging of the action time of the alternating stray current, the boundary between the substrate and the coating becomes unobvious, the coating at the defect at the surface is stripped, and the coating at the defect at the time is stripped.
FIG. 6a, FIG. 6b, FIG. 6c and FIG. 6d show the samples of epoxy-coated X80 steel at 50A/m according to the present invention2Soaking SECM surfaces for 0h, 5h, 10h and 24h under alternating current interference to obtain a test result graph; as can be seen from FIG. 6a, the width of the coating defect is 500 μm, and the peak current at the defect is-5.92X 10-11A. As can be seen from FIG. 6b, an application of 50A/m is applied2After soaking for 5h under AC interference, the width of the defect is increased to 700 μm, and the peak current is increased to-1.51 × 10-10A. After soaking for 10h, the defect width is obviously widened to 1000 μm, and the current peak isThe values did not change significantly. After 24h of soaking, the width of the defect position is rapidly increased to 1800 mu m, the peak current is obviously increased to-3.85 multiplied by 10-10A. Indicating that corrosion and coating stripping of the X80 steel are exacerbated at the coating failure defect.
The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes will occur to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
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