29 Difference Analysis of Acoustic Emission Testing …
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29.2.1.4 The Rest Time Before Inspection
The oil stored in the tank is fluctuating when the oil is pumped into or out the tank,
and a large amount of noise signals will be received by the AE sensors on the surface
of the tank wall, so it will affect the evaluation results of the corrosion state of the
tank bottom.
The rest time of the oil before inspection is more than 12 h in most companies. In
ASTM, the suggested rest time for oil is 24 h [4]. In PetroChina, the time is 12–24 h,
and crude oil needs a longer period of time for rest, light oil is allowed a shorter
period of time.
29.2.1.5 Data Acquisition Time
The data acquisition duration varies greatly in different companies. Such as in
Austria, the acquisition duration is 24 h, and in European standard [6] is at least
1 h. Some companies suggest the data acquisition duration is 2 h [8]. In PetroChina,
acoustic emission testing experiments show that most of the data collected during
the daytime are affected by noise signal by comparing the AE data collected during
day time with the one collected during night time.
So we collected 12 h of the data at night in order to avoid noise interference in
the daytime, such as the irradiation of the sun, vehicles, and so on.
29.2.2 Difference Analysis of Data Evaluation
Data evaluation has much difference in different countries or companies, so we
have summarized four aspects that affected the accuracy of the evaluation results
respectively.
29.2.2.1 Data Processing Method is Different
Data processing methods are different according to the published papers. Paper [9]
said that overall corrosion grading is based on the total number of AE hits accumulated during the test, and potential leak sources are identified by clusters of
events.
Paper [10] said that AE parameters like signal duration or peak amplitude were
used for data processing. And one weak point of this approach was that the dependence of these parameters on the distance between AE source and sensors had to be
estimated.
Paper [8] said that the most important parameter is the number of registered hits,
which depends on tank size, viscosity of the product, applied threshold, etc.
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29.2.1.4 The Rest Time Before Inspection
The oil stored in the tank is fluctuating when the oil is pumped into or out the tank,
and a large amount of noise signals will be received by the AE sensors on the surface
of the tank wall, so it will affect the evaluation results of the corrosion state of the
tank bottom.
The rest time of the oil before inspection is more than 12 h in most companies. In
ASTM, the suggested rest time for oil is 24 h [4]. In PetroChina, the time is 12–24 h,
and crude oil needs a longer period of time for rest, light oil is allowed a shorter
period of time.
29.2.1.5 Data Acquisition Time
The data acquisition duration varies greatly in different companies. Such as in
Austria, the acquisition duration is 24 h, and in European standard [6] is at least
1 h. Some companies suggest the data acquisition duration is 2 h [8]. In PetroChina,
acoustic emission testing experiments show that most of the data collected during
the daytime are affected by noise signal by comparing the AE data collected during
day time with the one collected during night time.
So we collected 12 h of the data at night in order to avoid noise interference in
the daytime, such as the irradiation of the sun, vehicles, and so on.
29.2.2 Difference Analysis of Data Evaluation
Data evaluation has much difference in different countries or companies, so we
have summarized four aspects that affected the accuracy of the evaluation results
respectively.
29.2.2.1 Data Processing Method is Different
Data processing methods are different according to the published papers. Paper [9]
said that overall corrosion grading is based on the total number of AE hits accumulated during the test, and potential leak sources are identified by clusters of
events.
Paper [10] said that AE parameters like signal duration or peak amplitude were
used for data processing. And one weak point of this approach was that the dependence of these parameters on the distance between AE source and sensors had to be
estimated.
Paper [8] said that the most important parameter is the number of registered hits,
which depends on tank size, viscosity of the product, applied threshold, etc.