·Table of Contents
·Methods and Instrumentation
High Speed UT Data Acquisition with 500 MHz Sampling RateC. Broere, R. Krutzen
Results of the following measurements will be shown:
Fast data acquisition and high sampling frequencies are needed to meet accurate flaw size detection and inspection speed requirements.
|Fig 1.1: Lay out of the NERASON 1090 measurement system|
The Nerason flexible probes are based on the immersion ultrasonic pulse/echo and/or pitch-catch techniques. Ultrasonic waves are generated by electronically pulsing an ultrasonic transducer. The ultrasonic transducer serves the dual role of transmitter and receiver of ultrasound. The ultrasound waves emitted by the transducer propagate through a liquid and are directed at a rotating mirror. The rotating mirror reflects and redirects the ultrasound to the tube wall so that it enters the tube wall at the correct angle. There are many different probes for tubes in the range of 8-82 mm ID and specially designed to examine tubes for the following information and/or defects:
2.2 Auxiliary equipment
The auxiliary equipment is needed for driving the probe through the tube and supplying the coupling liquid, normally water, to the probe.
2.3 Local Control Unit
The Local Control Unit, which can be placed at a distance of 150 m from the aquisition station consist of several control and power units to enable the remote control of the measurements.
2.4 Data Acquisition
The Nerason 1090 data acquisition system consists of a standard high level PC equipped with an Analog-Digital Converter card (ADC card) connected to the internal PCI-bus. All software modules are designed to give the user total freedom in configuration, data acquisition, data processing, screen lay out design and hardware components usage.
Main features are:
|Fig 1.2: Nuson's High Speed Analog Digital Converter Card|
2.5 Analysis Station and Data Storage Unit.
The Analysis Station and Data Storage Unit, which can be physically the same unit as the Acquisition station, consist primarely of dedicated software to analyse the data and a clever storage medium.
3.1 General wastage measurements in tubes with an ID of 15-80 mm
|Fig 1.3: 12 mm Wall thickness probe||Fig 1.4: Wall thickness measurement technique.|
|Fig 1.5: 3D plot of test tube||Fig 1.6: Damage under support plates|
3.2 Detection of small circumferential cracks in 7/8"(22 mm OD) tubing in an area with tube wear.
Tube wear can occur for example at the support plate location in a steam generator.
The remaining wall thickness can be measured and cracks can be detected and sized in such an area.
Figure 1.6 shows a drawing of such a location with a data presentation of the wall thickness measurement. The so called "C scan" plot shows green as the nominal wall thickness and red as a thinner wall thickness.
Figure 1.7 shows a data presentation of a crack found at such a location. The depth and length of the crack is automatically determined by the analysis software.
|Fig 1.7: Crack size plot|
3.3 Detection of small axial cracks in the small radius U bend region of 7/8" (22 mm OD) tubing.
Special probes ( see figure 1.8) are designed for detection of cracks in tight radius U-bends. Figure 1.9 shows the most likely location of cracks to occur and a so called "Bscan" presentation of the defect area. This type of defects request a high level UT analysist to evaluate the data. This way of analysis enables 10-20% trhuwall cracks to be detected and sized.
|Fig 1.8: Ubend row 1 probe||Fig 1.9: U bend ID axial and circumferential cracking|
3.4. Crack measurements in 10mm tubing.
Figure 1.10 shows a probe specially designed for very small tubing of 10 mm ID.
|Fig 1.10: 9 mm window probe for tube sheet inspection|
|Fig 1.11: Max inspection speed for crack detection (one channel system)|
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