450
W. Wu et al.
location (two-dimensional location such as plane and cylinder location) are the most
common AE sources localization methods at present.
Location of AE sources is usually based on simple geometric models: line, plane,
cylinder, sphere, and cone. However, as a matter of fact, this approach does not
always obtain good results for the following reasons [1]:
1. In many cases, irregular and complicated geometry of an object cannot be reduced
to simple shapes.
2. The complex characteristics of acoustic wave propagation (such as sound
velocity, attenuation, waveform, propagation path and so on).
3. The properties of the materials and the internal medium.
Therefore, the simple location schema on irregular-shaped objects often leads to
chaotically placed AE sources.
Due to the complicated geometry, irregular shape and thick-wall steel plate of
the steel bifurcated pipe in hydropower station, the acoustic velocity and structure
directly affect the location accuracy of AE source. In this paper. the location accuracy
of AE sources in hydraulic test of steel bifurcated pipe is analyzed from the point of
view of sound velocity and irregularity of structure.
40.2 The Structure of Steel Bifurcated Pipe and AE
Sensors Layout
The arrangement of AE sensors of a steel bifurcated pipe of asymmetric Y-shape in
hydraulic test is taken as a case study. The inner diameters of the main pipe, branch
pipe, and inscribed sphere are 3200 mm, 2200 mm and 3840 mm respectively, and the
bifurcation angle is 77°; The thickness of the bifurcated pipe varies from 42 to 50 mm
and the thickness of the crescent rib is 120 mm; the material is steel 07MnCrVR of
600 MPa grade strength. The main areas of AE detection are the key load-carrying
parts, the parts of stress concentration due to large geometric constraints, and the
parts with high difficulty coefficient of welding: the crescent rib, and the main cone
as well as the transitional cone, which are shown in Fig. 40.1b named area A1 and
A2.
AMSY-6 (38 channels) detection system of Vallen Systeme GmbH is used to
carry out the AE monitoring of the steel bifurcated pipe in hydraulic test. The type of
sensor is VS150-RIC, high sensitivity resonance sensor (100–400 kHz) with a center
frequency of 150 kHz, and with a built-in preamplifier gained 34 dB. The working
parameters of the AE system during the test are set as shown in Table 40.1. The
AE signals generated during the hydraulic test are transient, so location of TDOA is
calculated.
Sensors are arranged on the external surfaces of the bifurcated pipe, channel group
I of 11 sensors are placed in the area of A1. Among them, 9 sensors are arranged
on both sides of the combined welds between the crescent rib and the shell plate
of the branch pipes, 260 mm away from the center of the rib. The space between
W. Wu et al.
location (two-dimensional location such as plane and cylinder location) are the most
common AE sources localization methods at present.
Location of AE sources is usually based on simple geometric models: line, plane,
cylinder, sphere, and cone. However, as a matter of fact, this approach does not
always obtain good results for the following reasons [1]:
1. In many cases, irregular and complicated geometry of an object cannot be reduced
to simple shapes.
2. The complex characteristics of acoustic wave propagation (such as sound
velocity, attenuation, waveform, propagation path and so on).
3. The properties of the materials and the internal medium.
Therefore, the simple location schema on irregular-shaped objects often leads to
chaotically placed AE sources.
Due to the complicated geometry, irregular shape and thick-wall steel plate of
the steel bifurcated pipe in hydropower station, the acoustic velocity and structure
directly affect the location accuracy of AE source. In this paper. the location accuracy
of AE sources in hydraulic test of steel bifurcated pipe is analyzed from the point of
view of sound velocity and irregularity of structure.
40.2 The Structure of Steel Bifurcated Pipe and AE
Sensors Layout
The arrangement of AE sensors of a steel bifurcated pipe of asymmetric Y-shape in
hydraulic test is taken as a case study. The inner diameters of the main pipe, branch
pipe, and inscribed sphere are 3200 mm, 2200 mm and 3840 mm respectively, and the
bifurcation angle is 77°; The thickness of the bifurcated pipe varies from 42 to 50 mm
and the thickness of the crescent rib is 120 mm; the material is steel 07MnCrVR of
600 MPa grade strength. The main areas of AE detection are the key load-carrying
parts, the parts of stress concentration due to large geometric constraints, and the
parts with high difficulty coefficient of welding: the crescent rib, and the main cone
as well as the transitional cone, which are shown in Fig. 40.1b named area A1 and
A2.
AMSY-6 (38 channels) detection system of Vallen Systeme GmbH is used to
carry out the AE monitoring of the steel bifurcated pipe in hydraulic test. The type of
sensor is VS150-RIC, high sensitivity resonance sensor (100–400 kHz) with a center
frequency of 150 kHz, and with a built-in preamplifier gained 34 dB. The working
parameters of the AE system during the test are set as shown in Table 40.1. The
AE signals generated during the hydraulic test are transient, so location of TDOA is
calculated.
Sensors are arranged on the external surfaces of the bifurcated pipe, channel group
I of 11 sensors are placed in the area of A1. Among them, 9 sensors are arranged
on both sides of the combined welds between the crescent rib and the shell plate
of the branch pipes, 260 mm away from the center of the rib. The space between