Fig 1: Diagram of instrument sets of rail ultrasonic inspection
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| NDT.net - June 2001, Vol. 6 No. 6 |
3-Channel ultrasonic flaw detectors were used in normal rail inspection to assure the quality of production. Without the using of computers, the operators have to stare at the screen of the flaw detectors and concentrate on the alarms and echograms in a high intensity. So the result of inspection on a large degree depends on the influence of subjectivity of the operators.
But for the heavy rails which were used for high speed trains(200KM/H), the requirement of the nondestructive testing was enhanced significantly. At least ten or more transducers and channels of ultrasonic flaw detector must be employed to test the heavy rail. So it is very essential to use computers to process and record the ultrasonic testing data.
In this work, we introduce an automatic ultrasonic inspection system which is used on the producing line of heavy rail.
The system composed of a 16-channel digital ultrasonic flaw detector, a 32 points(16-in & 16-out) programmable controller, a manage & record personal computer and the probe system for picking rail transport and defect signals.
When a rail get in the probe area of this system with producing speed, the controller detect it and hold the ultrasonic transducers onto the testing parts of the rail automatically. So the flaw detector can detect the existing of defects in the rail and capture the echogram of it. Then the record computer get an inspection record of this rail. No manual operation is needed but for defect rail processing in total of the procedure.
There are four monitors to demonstrate the procedure of rail inspection in the system. The first one demonstrates the controller states which dedicate the rail passing the probe area. The second one demonstrates the defect map record of the rail. The two others display the same content of the echogram of flaw detector. There are three display models to display the echograms, 16-channel,4-channel or mono channel. One of the echogram monitor is put in the operating room and another is put outside of the room to ease the adjusting of the ultrasonic transducers.
Keywords: heavy rail, ultrasonic, automatic, online, inspection
Originally, 3-channel ultrasonic test systems were used in normal rail online ultrasonic inspection. It use three transducers, the first one for testing the rail head, the second one for rail web, and the last one for rail foot. The percentage of the tested area over the rail section is very small, less than 10%.
Sound alarm ultrasonic flaw detector makes operator must concentrate on the screen to notice the alarm channel and analysis the alarm reason immediately. Because of noise and disturbance often makes error alarms, the operators were tired for long time work. The test results relies on the influence of subjectivity of the operators.
Each probe mounted on a mechanical arm which are drove by pneumatic elements. The control signals to drive arms putting transducers onto or taking it off the rail were picked directly by the electric-magnetic probes under each ultrasonic transducer. The delays of mechanical arms response to the control signal make the length of the rail end which lacks of testing be significantly long. Or otherwise the arms be damaged by the rail end in transport.
For heavy rail which is used for running high speed trains(200km/h), the quality requirements are enhanced. For example, the percentage of the ultrasonic test area over the head section of the rail must be more than 60% . For this purpose, ten or more transducers and channels must be employed in automatic ultrasonic inspection system. We have developed such a system which has 16 channels of total digitized ultrasonic flaw detector.
Besides the flaw detector, The system also composed of a computer linked programmable controller and a digital inspection recording PC(Fig.1).
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Fig 1: Diagram of instrument sets of rail ultrasonic inspection
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A digital 16-channel ultrasonic flaw detector is used in the automatic inspection system. As show in Fig.2, the flaw detector has four sub-controllers, each one controls four ultrasonic transmitters and four receivers. The ultrasonic echo waveform was converted to digital series and processed by sub-controller to find out the flaw echo amplitude, the time delay of flaw echo and the bottom echo amplitude. The UT data and digitized waveform of each unit were conveyed to a master PC through a high speed bus type interface. This master PC display the waveforms on the screen in three models, sixteen channels totally, any four channels or any one channel. The master PC catches out the waveform which has a flaw to record. The test data is processed to eliminate the mistake alarms caused by noise and disturbance. The processing result can be read by record PC on a interface circuit.
Fig 2: Diagram of multi-channel digital ultrasonic flaw detector.
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Two monitors are used to display the same content of the waveform. One in the operate room and another outside the room in order to ease the adjusting of the ultrasonic transducer.
As show in Fig.3, four photoelectric switches and two photoelectric rotary encoders are placed on the roller line. Each encoder and the two switches besides it consist a probe group. The two groups of probe are placed on the two sides of the array of ultrasonic transducers.
Fig 3: Distribution of transducer sets and optical probe sets.
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The programmable controller circuit has sixteen digital output pointers, sixteen digital input pointers and two encoder counters. With four digital input pointers and two pulse counters, The PC of the controller can get the location information of the rail which is in the inspection area, and calculate the location of the rail. The speed of rail transfer is also carried out on time.
Ten digital output pointers are used to control the mechanical arms which hold the ultrasonic transducers. Linked with a PC, the drive delay time of each mechanical arm, transfer speed and location of the rail, and location of the arm are used together to calculated the pre control time. This makes it put the ultrasonic transducer onto the rail position accurately, and deduce the rail terminal dead area of ultrasonic testing. Two output pointers are used to alarm the flaw exist and mark on rail.
Another PC is used in system to record the inspection procedure independently. When a rail is transfer into the inspection area, the controller increase the rail order and locate the rail. The location data are read by recorder. Simultaneously, the recorder get the UT data from the flaw detector. The flaw amplitude, location on the rail, length of distribution, and depth are recorded. Until the rail go out the test area, The inspection record of this rail is save on hard disk, and then waiting for next rail come in. The inspection result can be output to a printer in a report form.
Three individual PC systems are used in the system(show in Fig.1).Each one do some relatively independently tasks. They are linked together with a bus-type interface, and work collaboratively. After system calibration, The continues inspection of the rails online is all in automatically. No manual interposing is needed but just process the inspection result.
The chance of error alarm made from noise and disturbance is deduced because of the data processing of the digital flaw detector.
The ultrasonic test dead area of terminal of rail is deduced by use of an PC based automatic rail location system.
But a higher speed processor is suggested to be used in multi-channel flaw detector to enhance the data process ability. And then the inspection speed can be increased(in our system , the highest speed is no more than 0.6 meter per second).
We thanks here to the workers and engineers of rail factory of steel group corporation of Panzhihua. And also to the workers and engineers of ail factory of steel group corporation of Baotou, and others work together with us in the application of the system.
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