JP5146360B2 - Method and apparatus for detecting rust in steel structures - Google Patents

Description

  The present invention relates to a method and an apparatus for detecting rust on a steel surface in a steel structure in a soil and concrete buried state.

  Steel structures that are buried in soil or concrete are often subjected to anticorrosion work such as surface treatments such as organic linings such as polyethylene and painting, and anticorrosion, in order to prevent corrosion of steel materials in the exposed environment for a long period of time. ing.

  However, in the case of organic lining and coating, in the case of soil buried pipes such as gas pipes and water pipes, the anticorrosion surface is damaged or partly peeled off due to damage caused by construction for other purposes in the surrounding area, and the steel is brought into the environment. If exposed, the original anticorrosion performance may be lost.

  Corrosion and rust occur in this way where the steel surface is exposed to the environment for some reason.

  Conventionally, the corrosion of steel structures in the embedded state like these cannot be easily inspected because the access restriction becomes an obstacle, and as a result, the location of the abnormal part is under such a restriction. The drilling survey was carried out by humans.

  As an inspection technique utilized for grasping the position of an abnormal part, for example, a method using local distortion of an electric field by an abnormal part (Patent Document 1 and Patent Document 2) or a method using distortion of a magnetic field (Patent Document 3).

  If these techniques are utilized, it is possible to identify to some extent an abnormal part of a steel structure in a soil or concrete buried state without excavation.

  However, even if the location of the abnormal location can be identified to some extent by non-excavation, although it is a limited location survey, the excavation cost is high and it is difficult to conduct it frequently. is there. Therefore, it is necessary to evaluate the risk that corrosion has occurred at the abnormal location before drilling, judge the necessity of drilling investigation, and determine the priority, but identify the abnormal location described above. The inspection method cannot grasp the state of corrosion at these abnormal locations.

As a technology to detect corrosion,
(A) Method using potential difference caused by contact with different metal (Patent Document 4)
(B) Electrical resistance method (Patent Document 5)
(C) Method for estimating corrosion from resistance of buried soil (Patent Document 6)
There is.

  However, with regard to (a) and (b), it is necessary to simultaneously bury a metal different from the structure, a wire for measuring resistance, etc. at the stage of burying the structure, and there are difficulties in application to existing structures. It cannot be determined whether or not the defect location itself has corrosion.

  Regarding (c), the risk in the environment is only evaluated, and the corrosion itself is not judged.

  In addition, pig inspection has recently been put into practical use in buried conduits. According to this inspection method, it is possible to measure the inner diameter and the remaining thickness from the inner surface of the pipe by flowing an ultrasonic wave or a leakage flux pig with the fluid inside the conduit.

  However, in order to construct them, it is necessary to equip a piglancher, and it cannot be applied to an existing object that does not have a launcher. It is not possible to judge whether or not is due to corrosion.

  On the other hand, in most cases, the anticorrosion applied to the buried steel structure is managed by measuring the ground potential of the steel structure.

  However, this management method is the average value management of the whole structure, and it is not management that reflects the state in the abnormal part sensitively, and depending on the case, corrosion has occurred in the abnormal part. Even so, there is a risk of mismanagement that it is normal on average. Therefore, there is a need for a detection technique that can estimate the presence or absence of corrosion at a limited location called a defect.

JP-A-6-288958 Japanese Patent Laid-Open No. 2001-19156 JP 2001-255304 A JP 56-18744 A Japanese Patent Laid-Open No. 50-10695 JP 58-37398 A

  The present invention has been made in view of the circumstances as described above, and the presence or absence of corrosion (rust) at an abnormal location of a steel structure in an embedded environment is determined in a non-excavated state at a remote location (in the case of soil burial, ) To detect.

  In order to detect rust of a steel structure in an embedded state, the present inventors first focused on the surface potential that changes depending on the surface state of the steel. It is known that the surface potential of steel can be measured even when a distance from the target surface is used if an electrode is used and the environment is a conductive substance, and changes depending on the presence or absence of surface rust. Corrosion can be detected by detecting rust formed as a result of corrosion.

  As the surface potential, the natural potential is most easily measured. However, if the steel and the rust formed on the surface thereof are in a stable material state, the natural potential is uniquely determined. Therefore, when using the presence or absence of rust for detection, it is necessary to determine the presence or absence of rust by comparing the absolute value (magnitude) of the potential.

  However, even if the natural potential is measured at an actual site, since the noise is large, the absolute value of the potential fluctuates greatly, and it is difficult to simply determine the presence or absence of rust based on the size.

  In order to solve the above problem, the present inventors conducted a sincere study on the behavior of the surface potential (natural potential) of rust. By applying a cathodic current), the rust material formed on the surface can be forcibly changed (reduced), and as a result, the surface potential (natural potential) with the steel surface has multiple current patterns. It has been found that the conditions change with common characteristics in all conditions.

  The present invention takes advantage of this fact, and applies an applied current (for example, a standardized square wave cathode current) so that this forced change (reduction) occurs on the surface of the steel, and the steel generated at that time. Rust is detected by quantitatively evaluating the behavior and amount of change in the surface potential (natural potential) over time. When there is rust, the surface potential (natural potential) shows a uniform behavior even when the pattern to be applied is changed, and the amount of change is large, but when there is no rust, the behavior is common. In addition, it was found that it is possible to detect using the feature that the amount of change is small.

  That is, the present invention is based on the above idea, and specifically includes the following configuration.

(1) A surface potential generated by the applied current is applied to a steel surface by applying a plurality of applied currents having a frequency of 0.01 Hz to 10 Hz and different frequencies, and using an electrode installed at a remote location in a non-excavated state. measured, a rust detection method of the steel structure to determine the presence or absence of rust on the basis of the change direction and variation of 24 hours of the surface potential, the previous SL changes direction with respect to the plurality of applied current baser It shifted, and rust detection method of a steel structure change amount before SL to the plurality of applied current to and determines that there rust if it exceeds 200mV to.

  (2) The method for detecting rust in a steel structure according to (1), wherein the applied current is a cathode current normalized to a square wave type.

(3) By means of the applied current using applied current conducting means for conducting a plurality of applied currents having a frequency of 0.01 Hz to 10 Hz and different frequencies on the steel surface, and an electrode installed at a remote location in a non-excavated state. Steel having surface potential measuring means for measuring the generated surface potential, and rust presence / absence judging means for judging the presence or absence of rust based on the direction and amount of change of the surface potential measured by the surface potential measuring means in 24 hours a rust detection device manufacturing structure, the rust presence determination means shifts prior SL changes direction less noble relative to the plurality of applied current, and varying previous SL to the plurality of applied current A rust detection device for a steel structure, characterized in that it is a means for determining that rust is present when the amount of conversion exceeds 200 mV.

  (4) The rust detecting device for a steel structure according to (3), wherein the applied current is a cathode current normalized to a square wave type.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to detect the rust of the steel surface in the remote location in the non-digging state in the steel structure in the soil and concrete buried state.

It is a figure which shows the application image on the spot. It is a schematic diagram which shows the application pattern of a square wave type cathode current. It is a figure which shows the behavior of the surface potential at the time of applying a square wave type cathode current. It is a figure which shows a detection step flow. It is a figure which shows the test apparatus in an Example. It is a figure which shows the test electrode in an Example. It is a figure which shows the time-dependent change of each feature point of the surface potential in a rust electrode. It is a figure which shows the time-dependent change of each feature point of the surface potential in a rust-free electrode. It is a figure which shows the 24-hour variation | change_quantity of each feature point of the surface potential in a rusted electrode. It is a figure which shows the 24-hour variation | change_quantity of each feature point of the surface potential in a rust-free electrode.

  Hereinafter, the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows an application image in the field in the present invention.

  A standardized current is supplied to the defect 2 existing on the surface of the steel structure 1 through the application electrode 5 from the current application device including the function generator 3 and the galvanostat 4, and the reference electrode 6 and the electrometer 7 are supplied from the ground. Is used to measure the surface potential (natural potential) of the steel structure 1 over time. The function generator 3 is a device for generating output signal waveforms of various shapes, and the galvanostat 4 is a device for quantitatively controlling the current flowing through the working electrode.

  As the application electrode 5, in addition to a metal electrode such as platinum or copper, a carbon electrode can be used. Although a metal electrode can be used as the reference electrode 6, if the measurement time is long, an error may occur in the measurement result due to corrosion of the reference electrode itself, so a copper / copper sulfate electrode, a silver / silver chloride electrode, etc. It is preferable to use a stable electrode.

  Although not shown in FIG. 1, an arithmetic processing unit is installed for determining the presence or absence of rust on the surface potential measured using the reference electrode 6 and the electrometer 7 based on the direction and amount of change. ing.

  FIG. 2 schematically shows a square wave type cathode current application pattern. By using two or more kinds of currents having different application patterns (application time and application cycle time), detection with higher accuracy can be performed.

  In the case of soil buried conduits, there is a possibility of being affected by stray currents when detected. The stray current is mainly 50 Hz or 60 Hz, which is a commercial frequency, so use a low-frequency or higher-frequency current to remove noise with a low-pass filter or high-pass filter, respectively, rather than a current close to that frequency. The accuracy can be improved by performing the measurement.

  The behavior of the surface potential (natural potential) is measured in a form in which the square wave is broken as shown in FIG. 3 corresponding to each waveform pattern. As shown in FIG. 3, this collapsed shape is characterized by immediately after applying the cathode current (point A), immediately before stopping the cathode current application (point B), immediately after stopping the cathode current application (point C), and immediately before applying the cathode current (point C). There are four feature points (D point). The change with time of the potential at each feature point is measured, and the presence or absence of rust is determined based on the direction and amount of change. For all waveform patterns, when the surface potential at all feature points changes uniformly in the base direction and a large amount of change exceeding 200 mV is confirmed during the measurement time, the target steel Judge that there is a high possibility of rust on the surface. Regarding the amount of change used for determination, since the cathode current application time is long and tends to increase as the frequency decreases, it is possible to increase the accuracy of the determination by using an applied current pattern that takes them into consideration. Further, the measurement time is preferably as long as possible. However, in the field measurement, the accuracy is improved by intermittently measuring from midnight to 6:00 when noise is low.

  FIG. 4 shows a rust detection step flow.

  First, a plurality of square wave cathode currents having different frequencies are selected. Here, as an example, three types of frequencies of 0.01 Hz, 1 Hz, and 10 Hz are selected.

  Next, the behavior of the surface potential of steel when a frequency having each pattern is applied is measured over time from the ground using a reference electrode. In the measurement, it is preferable to measure from the high frequency side rather than the low frequency side. This is because the application time is long at the low frequency, and as a result, the amount of change in the surface potential becomes large and minute rust is detected. This is because it becomes difficult.

  The direction and amount of change of the surface potential measured in this way for 24 hours are evaluated, and when the change direction shifts to the base for all frequencies and the amount of change exceeds 200 mV, it is determined that there is rust. Otherwise, it is judged that there is no rust.

  FIG. 5 shows a test apparatus used in this example.

  A carbon steel pipe buried in soil for 20 years or more in an actual environment was dug out, and steel having rust and rust on the surface were cut out and processed into a test electrode 8 having a configuration as shown in FIG. Place each electrode in a separate acrylic container, embed it in soil (resistivity: 1000 Ω · cm), energize a square-wave cathode current from the function generator 3 and the galvanostat 4, and the surface of each electrode The behavior of the potential was continuously measured for 24 hours using the reference electrode 6 and the potentiometer 7, and changes due to the presence or absence of rust were investigated.

  Table 1 shows the application pattern conditions of the square wave cathode current. In addition, platinum was used as the application electrode 5, and a silver / silver chloride electrode was used as the reference electrode 6.

  FIG. 7 shows the change over time in the surface potential at each characteristic point (see FIG. 3) when a rusted electrode is used as the test electrode 8 in conditions 1 to 3 which are current application patterns having a frequency of 0.01 Hz. . In FIG. 7, the horizontal axis represents the measurement time [Hr], and the vertical axis represents the surface potential [V vs. Ag / AgCl], condition 1 is indicated by a circle, condition 2 is indicated by a triangle, and condition 3 is indicated by a square.

  From FIG. 7, in conditions 1 to 3 of all feature points, the surface potential tended to shift uniformly in the base direction after 24 hours as compared with the initial application start. This tendency was the same in conditions 4 to 9 which are current application patterns with frequencies of 1 Hz and 10 Hz.

  FIG. 8 shows changes with time of the surface potential at each characteristic point when a rust-free electrode is used as the test electrode 8 in conditions 1 to 3 which are current application patterns having a frequency of 0.01 Hz. In FIG. 8, the horizontal axis represents measurement time [Hr], and the vertical axis represents surface potential [V vs. Ag / AgCl], condition 1 is indicated by a circle, condition 2 is indicated by a triangle, and condition 3 is indicated by a square.

  From FIG. 8, the common uniform behavior as seen with the rusted electrode was not observed in the condition 1 to condition 3 of each feature point. This tendency was the same in conditions 4 to 9 which are current application patterns with frequencies of 1 Hz and 10 Hz.

  Regarding the amount of change in the surface potential in 24 hours (= potential after 24 hours−potential at the start of application), FIG. 9 shows the case of the electrode with rust and FIG. 10 shows the case of the electrode without rust. In the figure, the horizontal axis represents the time rate θ (= application time / (application time + no application time)), and the vertical axis represents the surface potential change [V] for 24 hours.

  9 and 10, it can be seen that in the case of the electrode with rust, a large amount of change exceeding 200 mV was shown in all the characteristic points, whereas in the case of the electrode without rust, most of the amount of change was less than 100 mV. It was.

  From the above results, the behavior of the surface potential change observed when a square-wave cathode current is applied is clearly different between when the steel surface has rust and when there is rust. In the current application condition, the surface potential shifts uniformly toward the base over time, and the amount of change is large. On the other hand, when there is no rust, there is no uniform directionality in the change in surface potential, and the amount of change Was found to be small. Using this feature, it was possible to determine the presence or absence of rust on steel in the embedded environment by measuring the change in response of the surface potential using a reference electrode placed at a location far from the target. .

DESCRIPTION OF SYMBOLS 1 ... Steel structure 2 ... Defect 3 ... Function generator 4 ... Galvanostat 5 ... Applied electrode 6 ... Reference electrode 7 ... Potentiometer 8 ... Test electrode 10 ... Conductor 11 ... Glass tube 12 ... Epoxy resin 13 ... Steel 14 ... Rust

Claims (4)

Applying a plurality of applied currents having different frequencies at a frequency of 0.01 Hz to 10 Hz on the steel surface, and measuring the surface potential generated by the applied current using an electrode installed at a remote location in a non-excavated state, a rust detection method of the steel structure to determine the presence or absence of rust on the basis of the change direction and variation of 24 hours of the surface potential shifts previous SL changes direction less noble relative to the plurality of applied current and rust detection method of a steel structure change amount before SL to the plurality of applied current to and it determines that there rust if it exceeds 200 mV.   The method of detecting rust in a steel structure according to claim 1, wherein the applied current is a cathode current normalized to a square wave type. Surface generated by the applied current using an applied current energizing means for energizing a steel surface with a plurality of applied currents having a frequency of 0.01 Hz to 10 Hz and different frequencies , and an electrode installed at a remote location in a non-excavated state Steel structure comprising surface potential measuring means for measuring potential, and rust presence / absence judging means for judging the presence / absence of rust based on the direction and amount of change of the surface potential measured by the surface potential measuring means in 24 hours a rust detection device, the rust presence determination means, prior SL changes direction with respect to the plurality of applied current is shifted to less noble, and change amount before SL to the plurality of applied current is A rust detection device for steel structures, characterized in that it is means for determining the presence of rust when exceeding 200 mV.   The rust detecting device for a steel structure according to claim 3, wherein the applied current is a cathode current normalized to a square wave type.

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