258
C. Ye et al.
the initial two-channel AE activity is similar and the value is small, wherein the
channel 1 activity is slightly larger than the channel 2. At approximately 5632 s, the
channel 2 AE signal activity increases rapidly, and remains substantially at this high
activity value except for a slight decrease in the vicinity of 12,000 s. For channel
1, the AE activity remained essentially the same throughout the test. According to
the signal activity distribution, the test process can be divided into two stages: 0 to
5632 s is one stage, and 5632 to 13,721 s is the second stage.
Figure 22.3 is a time history diagram of the characteristic parameters commonly
used in AE technology. Through the time history distribution of the characteristic
parameters, it can be found that, besides Fig. 22.3a, b, there are significant differences
in signal characteristic parameters of each channel in different test phases during the
test. In addition to the higher amplitude value, the first stage signal activity and hit
number as well as the count, rise time, duration, and energy characteristic parameters
are significantly smaller than the second stage. In addition, there are significant
differences in the values of the characteristic parameters of the signals collected by
the two different channels. In the first phase, the two channel characteristic parameters
are basically the same. In the second stage, the 2-channel AE activity, the number
of AEhit, the count, the energy, the rise time, and the duration time are significantly
higher than 1 channel; and the amplitude is lower than 1 channel. The list of feature
parameter distribution ranges is shown in Table 22.2.
Pitting corrosion of metals is generally considered to begin with the surface with
an oxide film. Under the action of certain living anions (such as Cl
− ) in the medium,
the oxide film is first destroyed, and a passivation-activated battery is formed on the
surface of the metal to be etched into small holes. As the Cl
− in the solution migrates
into the pores, a concentrated solution of metal chloride (such as FeCl 2 ) is formed in
the pores. Decomposition of the chloride solution leads to an increase in the acidity
of the solution in the pores, which is further enhanced by corrosion [8]. Regarding the
acoustic emission mechanism during pitting corrosion, Rongsheng and Gangqiang
[9] believe that pitting corrosion is caused by film rupture, and a step pulse force
is applied to the metal accompanying the film rupture process, thereby generating a
stress wave, that is, AE phenomenon. The rupture of tiny hydrogen bubbles caused by
corrosion will also produce AE signal with the same principle as membrane rupture.
Corresponding to the mechanism of pitting formation and the mechanism of
pitting AE source, the time history distribution of the characteristic parameters of
AE signals monitored by the experiment reflects the different stages of metal pitting
damage. In this test, the AE signal was monitored by immersing the sample in the
solution for about 25 s, indicating that the corrosion potential in the test corrosion
system is higher than the pitting potential of zirconium. After the sample is immersed
in the solution, the zirconium metal first acts on the surface passivation film and Cl
−
in the solution. In the first stage (before 5632 s), the test solution system should
mainly occur due to the destruction of the surface oxide layer of the zirconium metal
leading to the continuous formation of the metal surface nucleation. At this stage, the
AE signal source should be mainly destroyed by the passivation film on the surface
of the zirconium metal, the AE activity is small, and the number of hit is small. The
amplitude of the AE signal is relatively high, while the duration, rise time, count, and
C. Ye et al.
the initial two-channel AE activity is similar and the value is small, wherein the
channel 1 activity is slightly larger than the channel 2. At approximately 5632 s, the
channel 2 AE signal activity increases rapidly, and remains substantially at this high
activity value except for a slight decrease in the vicinity of 12,000 s. For channel
1, the AE activity remained essentially the same throughout the test. According to
the signal activity distribution, the test process can be divided into two stages: 0 to
5632 s is one stage, and 5632 to 13,721 s is the second stage.
Figure 22.3 is a time history diagram of the characteristic parameters commonly
used in AE technology. Through the time history distribution of the characteristic
parameters, it can be found that, besides Fig. 22.3a, b, there are significant differences
in signal characteristic parameters of each channel in different test phases during the
test. In addition to the higher amplitude value, the first stage signal activity and hit
number as well as the count, rise time, duration, and energy characteristic parameters
are significantly smaller than the second stage. In addition, there are significant
differences in the values of the characteristic parameters of the signals collected by
the two different channels. In the first phase, the two channel characteristic parameters
are basically the same. In the second stage, the 2-channel AE activity, the number
of AEhit, the count, the energy, the rise time, and the duration time are significantly
higher than 1 channel; and the amplitude is lower than 1 channel. The list of feature
parameter distribution ranges is shown in Table 22.2.
Pitting corrosion of metals is generally considered to begin with the surface with
an oxide film. Under the action of certain living anions (such as Cl
− ) in the medium,
the oxide film is first destroyed, and a passivation-activated battery is formed on the
surface of the metal to be etched into small holes. As the Cl
− in the solution migrates
into the pores, a concentrated solution of metal chloride (such as FeCl 2 ) is formed in
the pores. Decomposition of the chloride solution leads to an increase in the acidity
of the solution in the pores, which is further enhanced by corrosion [8]. Regarding the
acoustic emission mechanism during pitting corrosion, Rongsheng and Gangqiang
[9] believe that pitting corrosion is caused by film rupture, and a step pulse force
is applied to the metal accompanying the film rupture process, thereby generating a
stress wave, that is, AE phenomenon. The rupture of tiny hydrogen bubbles caused by
corrosion will also produce AE signal with the same principle as membrane rupture.
Corresponding to the mechanism of pitting formation and the mechanism of
pitting AE source, the time history distribution of the characteristic parameters of
AE signals monitored by the experiment reflects the different stages of metal pitting
damage. In this test, the AE signal was monitored by immersing the sample in the
solution for about 25 s, indicating that the corrosion potential in the test corrosion
system is higher than the pitting potential of zirconium. After the sample is immersed
in the solution, the zirconium metal first acts on the surface passivation film and Cl
−
in the solution. In the first stage (before 5632 s), the test solution system should
mainly occur due to the destruction of the surface oxide layer of the zirconium metal
leading to the continuous formation of the metal surface nucleation. At this stage, the
AE signal source should be mainly destroyed by the passivation film on the surface
of the zirconium metal, the AE activity is small, and the number of hit is small. The
amplitude of the AE signal is relatively high, while the duration, rise time, count, and