JPS6153560A - Corrosion rate detection element for metal material - Google Patents

Abstract

PURPOSE:To perform the diagnosis of safety margin and estimation of residual life on an object to be inspected, by providing a container made of an electric insulator having an opening adapted to get tight on the object being measured at one end thereof and a reference electrode and an opposed electrode at the specified position in the center of the container. CONSTITUTION:A reference electrode 7 is provided at the position 4-30mm. inward from the tip of an opening in the center of a container while an opposed electrode 8 is at the position as far as more than 1.0 fold the inner diameter of the container behind the reference electrode 7. Then, a corrosion rate detection element 18 is fixed on the surface of a steel pipe pile 15 to be inspected with a fixing jig 17 incorporating a magnet 16 to determine a polarization resistance with a polarization device 13. An AC impedance method is used in this measurement. A potential is provided in a range of + or -15mV from the natural dip potential at a measuring point by a sine function and the response of current thereto is measured to calculate the polarization resistance from the impedance obtained with respect to various frequencies from 1mHz-10kHz.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a detector for detecting the corrosion rate of a metal material used in an electrolyte-containing solution such as seawater or river water.

(Prior art) Conventionally, the degree of corrosion of four gold materials has been detected using a coupon test, which calculates the corrosion rate from the weight loss due to corrosion of a sample placed in the same environment as the target. 2) Target metal Same as - Electrical resistance method that calculates the corrosion rate from the change in electrical resistance of a gold conductor placed in the environment. 3) Measure the remaining wall thickness of the object using an ultrasonic thickness gauge, and calculate the corrosion rate from the amount of corrosion thinning. 4) For example, the Corrosion Prevention Association Spring Academic Conference Proceedings V
o1.19B2, pp. 262-264, there is a method of detecting pitting corrosion using a corrosion monitoring probe.

Methods 1) and 2) require a long period of time to obtain results;
Moreover, it is used to investigate the corrosive environment, and cannot directly detect the corrosion rate of the metal being measured.

Method 3) only determines the average corrosion rate of the metal to be measured from the time it is used until the time of measurement, and the measurement does not require complete removal of rust or deposits on the surface of the object to be measured. This requires a lot of effort.

Regarding 4), it is a type in which current is passed through a small hole at the tip of the probe, and it does not aim to quantify the corrosion rate by limiting the measurement range and performing uniform 5+ poles on the target surface.

(Problems to be Solved by the Invention) The present invention is intended to easily measure the corrosion rate of metal materials in a short period of time. 'This provides a complete detector.

(Means for solving the gap i (m point)) The present invention is characterized by uniformly polarizing a range specified by an apparatus between a metal material placed in a solution containing an electrolyte and a polarization electrode. This is a detector for measuring 1 polarization resistance.The 9+ extremely low resistance Rp thus obtained is:
The constant K, which was found separately (varies depending on the environment and the material of gold X, is about several mV to 20 mV) and 1°. r r ” K /
From the relationship Rp, the corrosion current I C0rr is converted to 40 μA/cM = 0.47, . 7 years
From the relationship, it can be converted into corrosion rate.

Hereinafter, the present invention will be explained in detail based on specific examples.

In recent years, methods for detecting the corrosion rate of Kinbare surfaces at a practical level include the AC impedance method, constant current method, coulostatic pulse method, constant current double waveform method (double wave number method), etc. , several methods have been reported. This detector can be applied to any of these methods, and can be used to measure actual figurines in the field. As a result of studies by the present inventors, the necessary conditions for detecting the corrosion rate of an actual structure are as follows.

■The polarization range of the probe used to measure corrosion rate can be artificially limited. ■ Uniform polarization within a limited range (the density of the current line is uniform, or the ponential line is parallel to the metal surface to be measured). (2) The counter electrode chamber of the detector must be large enough that changes in liquid properties due to polarization can be practically ignored. ■In order to reduce the effect of liquid resistance and to clearly separate it from the resistance value obtained by bifurcation, the reference electrode should be placed close to the surface to be measured with a trench of approximately 4M, and the potential should be measured at the center of the surface to be measured.

A detector shown in FIG. 1 will be described as an embodiment of the present invention that satisfies these conditions.

This detector is roughly divided into a detector tip 6, a detector outer wall 10, a counter electrode 8, and a reference electrode 7. First, the detector tip 6 is replaceable depending on the shape and corrosion status of the metal to be measured, and is made of a relatively thick (10 ms or more) insulator. This is due to the ease of mounting of the insulator 5, which ensures close contact between the detector and the object to be measured, and the thickness of the tip of the detector, which is sufficient even if a gap occurs between the object to be measured and the detector light leakage. This is to provide a large resistance and minimize leakage from the current line.

In order to confirm the close contact between the object to be measured and the detector and to check for leakage of the current line, it is effective to install the current leakage detection electrode 19 outside the opening of the detection side. Furthermore, if necessary, an insulating cover 20 may be provided outside the tip of the detector. The detector outer wall 10 is made of an electrical insulator such as acrylic resin or vinyl chloride resin, and the distance between the counter electrode and the metal to be measured is 10. 8 or more is required.

This is the insulator surface that makes up the outer wall of the container,
Since the potenyal lines □ are orthogonal, the gold to be measured: 4th place 1st
4, a point line parallel to the object to be measured is obtained, and it is possible to uniformly shade the countermeasure metal. Further, when the inner diameter of the container is about 301117 J, this together with the size of the counter electrode 8 constitutes a sufficient counter electrode chamber so that changes in liquid properties due to one polarization can be ignored.

The countershade 8 may be made of platinum or other material that does not corrode easily in seawater.
In the case of this device, it is sufficient to have a surface area of about 20 crA, considering the intended use. As the reference electrode 7, a silver/silver chloride electrode, a sweet tooth electrode, a copper/copper sulfate electrode, etc. can be used. Since the position of the reference pole changes depending on the shape of the object to be measured at the tip of the detector, the position can be changed in accordance with its replacement.

This sets the potential 711+1 constant reference shade to the optimum position:
(m, 11 constant target is 54η ~ 30 mxn).If it gets any closer to the measurement target, it will cause measurement errors, and if it is too far away, the accuracy of separating the 9+ rich resistance and the resistance of the solution or deposits will deteriorate. Deteriorate. Furthermore, from a practical point of view, in order to withstand use in the field, it is possible to provide a reference electrode guard using a nylon wire or the like to the extent that it does not impede the uniformity of the melt flow IJ.

The polarization device 12 applies a slight 91 return current or polarization voltage to the corroding metal material 9, and detects the voltage change between the reference electrode and the eclipsed metal, or the difference between the corroded metal and the counter electrode. This is a device that measures polarization resistance by approximating the ohm law measurement from the current flowing between (C).Note that polarization resistance is inversely proportional to corrosion rate, so the smaller the polarization resistance, the faster the corrosion rate.

(Example) A detector as shown in FIG. 1 was manufactured, and the corrosion rate was measured for a steel pipe pile.

The detector has an inner diameter of 30 ia and a total length of 150 as.
The outer diameter of the tip of the detector is 5ONJR. The material was made of acrylic resin, and an insulator made of highly elastic non-contact rubber was attached to the opening in contact with the object to be measured, in order to limit the current line within the measurement range. Platinum was used as the counter electrode, and a silver/silver chloride electrode was used as the reference electrode.

Figure 2 shows the measurement situation. Corroded steel pipe piles that had been installed for 20 years were measured. (Outer diameter 700 closed, initial wall thickness 1
2) The IIK award speed detector 18 of the present invention was fixed to the surface of a steel pipe pile using a fixing jig 17 incorporating a magnet, and the polarization resistance was determined using a polarization device 13. The AC impedance method was used for measurement, and ±15% was measured from the natural immersion potential of the measurement point.
A potential was applied as a sine function in the mV range, and the current response thereto was measured. Measurement range is 1mHz to 10K
Hz, and the polarization resistance was calculated from the impedance obtained for each frequency.

The measurement results are shown in Figure 3. The polarization resistance values are clearly different in three regions: directly below the mean tidal surface, where the tide is acting, directly below the mean tidal surface, and underwater, indicating that the corrosion rate is higher in the region where the tide is acting. Recognize.

When we also investigated the remaining wall thickness using an ultrasonic thickness gauge, we found that the amount of corrosion thinning was greater in the tidal zone than in the underwater area, and even from past average values, the corrosion rate in the area affected by the tidal effect was lower. It was confirmed that it was early. j (Effects of the Invention) As described above, the present invention can detect the corrosion rate of a metal material in a solution containing an electrolyte such as seawater or river water. This makes it possible to understand the corrosion status of steel structures currently in use. Furthermore, when combined with a method of measuring remaining wall thickness using ultrasonic waves or the like, it is possible to diagnose the safety level of equipment and estimate the remaining lifespan with higher accuracy.

[Brief explanation of the drawings] Figure 1 d is an explanatory diagram of the corrosion rate detector of the present invention, Figure 2 is an explanatory diagram of the actual structure measurement method, and Figures 3 (a) and (b) show the measurement results. This is a diagram. 1: Waterproof connector 2: 0 ring 3; Reference electrode fixing guide 4: Waterproof system 5: Elastic insulator 6: Detector tip 7: Reference electrode 8: Counter electrode 9: Metal material to be measured 10: Detector External wall material 11: Reference pole guard 12: Polarization device 13, polarization device 14: Floor plate 15: Steel pipe pile 16: Magnet 17: Detector fixing jig 18: Corrosion rate detector 19:
8 poles 20 for detecting current leakage: Insulating cover Figure 1 (α) (b) Corruption arrest ratio (Kagidare) procedure correction Display of the JF (Jizugo) Incident 1982 Patent Application No. 174169 2 Name of the invention Person who corrects metal material 1-ch corrosion rate detector 3 Relationship to the case Patent applicant Location 2-6-3 Otemachi, Chiyoda-ku, Tokyo Name (665) Shin Nippon Representative Takeshi 1) Yutaka 4th generation Osamu Address 3-3-3, Nihonbashi, Chuo-ku, Tokyo Date of amendment order Month, day, 1939 (shipment date)
6. Number of inventions increased by amendment 7. Subject of amendment IF/J of detailed explanation of invention in specification (
1) Details: h'46L'112 rows 1 measure is 54 mm
Correct J from 1 object to 4 mm l. Ki ■

Claims (1)

[Claims] A container made of electrically insulating material has an opening in close contact with the measurement target at one end, a reference electrode is placed in the center of the container at a position 4 to 30 mm inside the tip of the opening, and a reference electrode is placed behind the reference electrode. A corrosion rate detector for metal materials, characterized in that a counter electrode is provided at a position at least 1.0 times the inner diameter of the container.