JPH0650927A - Detecting method for crack or fracture caused by stress corrosion cracking - Google Patents

Abstract

PURPOSE:To make it possible to detect the generating time of stress corrosion cracking readily and accurately by connecting a material to be measured and a counter electrode, a calomel electrode, which is connected to the material to be measured with a liquid path, a potentiometer and the like, and monitoring and detecting the change in potential. CONSTITUTION:A material to be measured 3 such as carbon steel and a counter electrode 1 such as platinum are inserted into a container 9 containing corrosion solution 2 at a specified interval. A calomel electrode 7 indicating a reference potential is electrically connected to the material to be measured 3 with an agar bridge 8 obtained by mixing and freezing agar and potassium chloride in a glass tube. These three electrodes, a potentiometer 6, ammeter 4, a resistor 10 and an external power supply 5 are electrically connected by using conductor wires and the agar bridge 8, and a circuit is formed. As the solution 2, sea water or the like under the same conditions as the actually using conditions or hydrochloric acid or sulfuric acid of about 5-10% is used. The resistance of the resistor 10 is changed so that the potential becomes constant between the material to be measured 3 and the counter electrode 1, and the value is measured with the potentiometer 6. When cracks and the like occur in the material to be measured because of stress corrosion cracking, the resistance is changed, and the corrosion potential is changed considerably largely. Thus the occurrence of cracks and the like can be detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for electrically detecting the occurrence of cracks or cracks due to stress corrosion cracking of metal products.

[0002]

2. Description of the Related Art Stress corrosion cracking is a crack that occurs when a material is stressed and placed in an environment with a corrosive action. The stress is a residual stress caused by heat treatment or welding, and an external force. But it works the same way. There are two types of stress corrosion cracking: anodic behavior (dissolution) and cathodic behavior (hydrogen generation). Such stress corrosion cracking is characterized in that cracks and cracks are generated much earlier than expected from the state where the stress and the corrosion factor are independent of each other. Therefore, when using a material that is expected to cause stress corrosion cracking as a material for offshore structures, it is necessary to take measures such as stress relief in advance.
In order to prevent damage accidents, it is necessary to determine the replacement time of parts and then consider the supply of those parts. Therefore, it is necessary to recognize in advance the time from the start of use of the metal material to the occurrence of stress corrosion cracking and further fracture (damage).

In order to meet this demand, conventionally, the occurrence of cracks and cracks due to stress corrosion cracking has been confirmed by reproducing actual use conditions in a laboratory and visually observing for a long time. However, even if only confirming the occurrence of minute cracks or cracks in the accelerated test,
Since it takes at least several hours to 10 days to occur, it takes time and labor, and in addition, there is a limit to accurate confirmation by visual inspection.

[0004]

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method for easily and accurately detecting the time of occurrence of stress corrosion cracking by electrochemical means.

A further object of the present invention is to pre-recognize the replacement timing of the material to be used by predicting the period until the stress corrosion cracking of the material occurs in advance.

[0006]

Therefore, in the present application, therefore, the object to be measured 3 of metal, the counter electrode 1, the container 9 containing the corrosive solution 2, the calomel electrode 7, the potentiometer 6, the ammeter 4, the variable resistance are used. 10 and an external power source 5, the device under test 3 and the counter electrode 1
Is largely immersed in the corrosive solution in the container 9, and the DUT 3 is also connected to the calomel electrode by a liquid junction, and the DUT 3 and the counter electrode 1
And the calomel electrode 7 is connected to one end with a conductive wire, and a test device electrically connected to the potentiometer 6, the ammeter 4, the resistor 10 and the external power source 5 is prepared; The potential difference between the counter electrode 1 and the counter electrode 1 is constant; the change in the potential of the DUT 3 is monitored by the potentiometer 6. When a sudden change in the potential occurs, cracking or rupture due to stress corrosion cracking occurs. A method of detecting the above is provided as a means for solving the above problems. Note that carbon steel, alloy steel, spring steel, or the like is used as the object to be measured.

FIG. 1 shows, by way of example, the apparatus used to carry out the method of the invention. The corrosive solution 2 is placed in the container 9, and the DUT 3 and the counter electrode 1 are inserted into the container 9 with a constant space. The calomel electrode 7 is a reference potential showing a constant potential at a constant temperature. This is electrically connected to the DUT 3 by an agar bridge in which agar and potassium chloride are mixed in a glass tube and solidified to prevent flow. On the other hand, the counter electrode 1 uses a platinum or graphite electrode. DUT 3, counter electrode 1, potentiometer 6, ammeter 4, resistor 10,
The external power source 5 and the ROMEL electrode 7 are electrically connected to each other by using a conductive wire and an agar bridge as shown in FIG. 1 to form a circuit. As the shape of the object to be measured, an actual product may be used, or a sample having a maximum diameter of 30 mm and a maximum length of about 100 mm may be prepared and used. The corrosive solution may be seawater or the like under the actual use conditions, but 5 to 10% hydrochloric acid or sulfuric acid is also used.

The variable resistor 10 is changed so that the potential between the DUT 3 and the counter electrode 1 becomes constant. This is because the potentiometer 6 measures cracks due to stress corrosion cracking and changes in resistance due to occurrence of cracks.

When cracks or cracks due to stress corrosion cracking occur in the object to be measured 3, the resistance changes, and as a result, the corrosion potential changes. This potential changes considerably when cracks or cracks occur. Therefore, by measuring the change in the potential, it is possible to accurately know the occurrence of cracks or cracks due to stress corrosion cracking.

[0010]

EXAMPLES In order to demonstrate that the detection method of the present invention can accurately and electrically detect the occurrence of cracks and cracks due to stress corrosion cracking, the following tests were conducted.

First, a bolt (SCM42) is measured as an object to be measured.
The actual product of 2) was used. It has been carburized and tempered as well as tempered. The surface hardness is 494 to 525.
It was Hv. A hydrochloric acid solution having a concentration of 5 to 10% was used as the corrosive solution, and the test was performed at room temperature.

A large change was observed in the corrosion potential about 50 hours after the start of the test. This change is as shown in FIG. That is, the potential measured at about 50 hours was more inclined than the previous potential to the base side. After a further 60 hours, the bolt broke.

The broken bolts were observed after 60 hours.
This is shown in FIGS. 3 and 4 by changing the breaking location. When a crack is generated by stress corrosion cracking, the crease pattern on the fracture surface is not concentrated at one point at the starting point and is characterized by a wide area. This bolt has
It was confirmed that this characteristic fracture surface due to stress corrosion cracking appeared.

[0014]

According to the detection method of the present invention, the crack generation time due to stress corrosion cracking and further the rupture time can be accurately measured, and the test accuracy can be improved. At the same time, unmanned operation during the test can be achieved, and the economic efficiency can be further improved.

[Brief description of drawings]

1 is a schematic view of an apparatus capable of implementing the detection method of the present application.

FIG. 2 is a diagram showing changes in corrosion potential with respect to time.

FIG. 3 is a photograph showing a cross section of a metal bolt broken by stress corrosion cracking.

FIG. 4 is a photograph showing a cross section of a metal bolt broken by stress corrosion cracking.

[Explanation of symbols]

 1 Counter electrode 2 Corrosion solution 3 Object to be measured 4 Ammeter 5 External power supply (battery) 6 Potentiometer 7 Calomel electrode (reference battery) 8 Agar bridge 9 Container 10 Resistance

[Procedure amendment]

[Submission date] July 23, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

1 is a schematic view of an apparatus capable of implementing the detection method of the present application.

FIG. 2 is a diagram showing changes in corrosion potential with respect to time.

FIG. 3 is a photograph showing a cross section of a metal structure of a metal bolt that is broken by stress corrosion cracking.

FIG. 4 is a photograph showing a cross section of the metal structure of a metal bolt that is broken by stress corrosion cracking.

Claims (2)

[Claims] 1. A metal sample 3, a counter electrode 1, and a corrosive solution 2.
A container 9 in which is placed, a calomel electrode 7, a potentiometer 6, an ammeter 4, a variable resistor 10 and an external power source 5,
And the counter electrode 1 is mostly immersed in the corrosive solution in the container 9, and the DUT 3 is also connected to the calomel electrode by a liquid junction, and the DUT 3, the counter electrode 1 and the calomel electrode 7 are connected at one end to each other with a lead wire, Prepare a test device electrically connected to the potentiometer 6, the ammeter 4, the resistor 10 and the external power source 5; the variable resistor 10
To make the potential difference between the DUT 3 and the counter electrode 1 constant; the potential difference of the DUT 3 is monitored by the potentiometer 6; A method for detecting the occurrence of cracks or fractures due to corrosion cracking. 2. The method according to claim 1, wherein carbon steel, alloy steel or spring steel is used as the object to be measured.