JPS60260839A - Electrochemical method for measuring degree of deterioration - Google Patents

Abstract

PURPOSE:To estimate the degree of deterioration of creep ductility by making constant potential polarization measurement with a metallic material to be measured as an anode and measuring the anode current density in an anode current stagnating region. CONSTITUTION:An electrolytic cell 2 is mounted to the measuring point of the metallic material 1 to be measured in a manner that an electrolyte 3 contacts directly with the material 1. The cell is sealed 4 by rubber or clay to prevent the leakage of the electrolyte 3. The polarization measurement is carried out after connecting the material 1 as the anode to the positive voltage side of a potentiometer 6 and connecting an inert electrode inserted into the electrolyte 3, for example, a platinum electrode 5 as a cathode to the negative voltage side of the potentiometer 6. The measurement is executed by measuring the anode current at a specified potential sweep speed after the cathode reduction at the natural electrode potential or below. The stagnating region of the anode current density appears near the critical potential for passivation on the anode polarization curve on gradual deteriorating of the material. The stagnating region has a close relation with the creep rupture ductility of the material. The degree of deterioration of the material is known by comparing and evaluating such stagnating region value, by which the prediction of the remaining life is made possible.

Description

[Detailed Description of the Invention] [Industrial Application Field J] The present invention aims to reduce the degree of aging that occurs in materials such as turbine rotors and casing pulp that have been used for long periods of time under high temperature and pressure, which manifests as changes in structure and changes in high temperature ductility. Concerning non-destructive evaluation methods.

[Prior art 1] For example, forged steel products for power generation turbine buhunds that are used under high temperatures and high pressures deteriorate due to changes in structure, crack initiation and propagation, and decreased notch toughness during long-term operation. The material properties change over time.

Therefore, if the degree of change in the material is not accurately grasped, failures and other inconveniences may occur during operation, resulting in inconveniences in power supply.

However, conventionally, in order to inspect and evaluate the degree of deterioration of a material, it is necessary to cut the material out of the product and perform destructive tests such as microstructural observation and mechanical testing, and the plant has to be stopped for a long time. There was a problem.

[Structure of the Invention] The present invention is intended to solve these problems, namely, the plant shutdown period and destructive inspection.It is an object of the present invention to electrochemically measure seven-node polarization behavior without cutting out materials that have been used for a long time. The present invention provides an electrochemical method for measuring the degree of deterioration of materials, which is similar to firewood, by which the degree of deterioration of the material can be evaluated and the remaining life can be predicted.

That is, the present invention provides a constant potential measuring device in which a metal material used under predetermined conditions is surrounded with an electrolyte in a liquid-tight manner, the metal material is brought into contact with the electrolyte, the metal material is used as an anode, and an inert electrode is used as a cathode. The degree of degradation of creep ductility is estimated from the 7-node current density in the 7-node current stagnation region near the passivation critical potential. The present invention consists in a method for measuring the degree of electrochemical deterioration of metallic materials.

To perform polarization measurements, place the electrolytic bath [enclosure (2) 1] at the measuring point of the product body (1) to be measured, and place the electrolyte (3) in the body (1).
1) to make 7 nodes, and seal it with rubber, clay, etc. to prevent electrolyte solution (3) from leaking.
4), and the main body (1) (7)
), an inert electrode inserted into the electrolyte, for example a platinum electrode (cathode) (5), is connected to the negative voltage side of the potentiometer (6). In addition, (7) is a bridge capillary, (8) is a saturated Amagi electrode (SCE), and (9) is C1.
It is a saturated solution (Figure 1).

Since the material to be measured is usually a low-alloy network, the electrolyte used is preferably a weakly acidic solution, such as a 0.5-IN aqueous solution of sodium sulfate or a saturated aqueous picric acid solution. Further, the measurement is performed using a constant potential method that allows continuous measurement of the 7-node dissolution region, the immobile fi region, and the hyperpassive region.

[Embodiments of the Invention] During measurement, after cathodic reduction is performed below the natural electrode potential, the anode current is measured at a constant potential sweep rate.

In this way, a 7-node polarization curve is obtained, but as the material deteriorates, a 7-node current stagnation region (SACM) appears near the passivation critical potential, and increases as the degree of deterioration increases. This SACM has a close correlation with the creep rupture ductility of the material, so by comparing and evaluating this SACM value, the degree of deterioration of the material can be determined and the remaining life can be predicted.

Figure 2 shows 1% Cr- used for 105 hours under each operating condition.
1% Mo-1/4% ■ Seven-node polarization curve measured using samples (^-1, B-4, B-5, B-6, and B-7) collected from casings FIG.

In the same figure, at 0 volts [vs. the saturated Amagi electrode (the peak near the SCE month is the melting region, and the part of the curve that falls between 0.2 and 0.4 volts is the passive region), and at 1.4 volts or more, The part where the curve rises suddenly is the over-fault region. Furthermore, the locations indicated by arrows represent the secondary 7-node current density (SACM). If the relationship between 5ACN and creep ductility is plotted from the same figure, Figure 3 is obtained. The usage conditions of the samples used in Fig. 2 are as follows: ^-1; 566°C x 10g time B-4; 538°C x io' time B-5; 494°C x 10' time B- 6; 368°C x 105 hours B-7 - Unused Therefore, by measuring the anode polarization curve of the test piece based on FIG. 3, the degree of creep deterioration of the material can be predicted non-destructively.

[Effects of the Invention] The effects of the present invention are that the degree of deterioration of materials can be quickly evaluated and the remaining life can be predicted without requiring plant shutdown or non-destructive testing.

[Brief explanation of drawings]

The tJSi diagram is a schematic diagram of the electrochemical anode polarization measuring device, Figure 2 is a diagram showing changes in the constant potential anode polarization curve depending on operating conditions, and Figure 3 is a diagram showing the relationship between creep ductility and secondary anode current density. be. In the diagram: 1... Main body of the product to be measured (7), 2... Enclosure,
3... Electrolyte, 4... Seal, 5... Cathode, 6... Potentiometer, 7... Capillary for bridge, 8... Saturated Amagi electrode, 9... KCI saturated solution patent Frequently appearing Japan Steel Works, Ltd.

Claims (1)

[Claims] The metal material used under predetermined conditions is surrounded with an electrolyte solution in a liquid-tight manner, the metal material and the electrolyte are brought into contact, and the metal material is used as an anode and an inert electrode is used as a cathode to connect to a constant potential measuring device to perform electrolysis. The process consists of performing potentiostatic polarization measurements between a cathode inserted in a liquid and estimating the degree of creep ductility deterioration from the 7-node current density in the 7-node current stagnation region near the passivation critical potential. Electrochemical degradation measurement method for materials.