Table of Contents ECNDT '98
Session: Nuclear Industry
Digital Image Processing in X-Ray Control of Welds.H.-D. Dau - Philips Industrial X-Ray, Germany.
A. Kouznetsov - JSC Maschinbuilding Plant, Russia.
Corresponding Author Contact:
YXLON International X-Ray GmbH, Essener Straße 99, Gebäude 227,
D-22419 Hamburg, Germany
Email: firstname.lastname@example.org, URL: NDTnet Exhibition - YXLON
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OJSC ´MSZ' is the major factory of Russia engaged in the production of nuclear fuel for NPPs and fleet reactor units. Quality and reliability - these are the main requirements during manufacturing fuel assemblies - guarantee a safe reactor operation. Manufacturer of fuel assemblies should provide for all sided tests at each production step using newest technology available on the market.
Welds are important elements of fuel assembly design and they have to be 100 % inspected. One of the methods of non-destructive welds inspection at our enterprise used to be radiographic method with the registration on X-ray film. Increasing requirements to higher test productivity and operability led to the necessity of using automated X-ray imaging systems.
An important factor for such systems is that radioscopy is carried out in real time. This allows, compared to standard radiography, a more convenient detection of small and difficult to locate defects. Modern X-ray imaging systems are free from all drawbacks of handling X-ray film and allow to perform a fast archiving and search for information.
It was 'Philips Industrial X-Ray' that offered a possibility of creating such a system. This company has a great experience in developing and manufacturing automatic industrial X-ray inspection systems. In 1992 this company developed for OJSC 'MSZ' an autonomous X-ray inspection system MU 115 F for the detection of slits in fuel rods. In 1995 they started creating the system MU 80 F which was mounted and commissioned in June 1996.
The X-ray tube and image intensifier are mounted at the manipulator in such a way that the central X-ray beam penetrates horizontally the part to be inspected before being converted into a visible image by the image intensifier. The possibility of shifting along the axis of the X-ray beam both the tube and the image intensifier - in relation to the specimen is foreseen; this gives the possibility to change the inspection scheme. It is also possible to vary the beam angle for the inspection of circular welds.
To increase the image quality the X-ray tube as well as the image intensifier are equipped with motor-driven lead diaphragms reducing the scatter radiation. The MU 80 F system incorporates a metal-ceramic X-ray tube with a focal spot size of 0.2 mm and max. power loading of 320 W.
During the inspection process the X-ray tube and the image intensifier jointly move along part to be tested which is located between on a roller support providing for the rotation.
Due to the fact that the weight of the inspected parts may reach 100 kg the possibility to position and remove parts by means of a telpher is foreseen; in this case the manipulator is put to the limit position.
The complete system control for the operation of the MU 80 F is located in the operators control room. A special designed control rack (Fig.3) incooperates the manipulator control devices, the X-ray control unit, the monitors (X-ray image and operator menue) and the PC with the computer system for the image processing system PXV 2000.
This PC based system meets with its technology the increasing market requirements with regard to communication with other equipment, measurement of image structures, determination of statistical data, and the archiving of fluoroscopic images. It incorporates a professional high-speed framegrabber board for digitalization and processing the analog videosignal supplied by the camera of the X-ray image intensifier. The digital 8 Bit- image ( 256 Greylevels) will be stored in a frame buffer 1K x 1K after being noise reduced by an integration depending on the noise level of the video signal.
The further steps will be carried by the operator from the control room activating the X-ray system first. After entering the sample regarding program number the manipulator moves into its first stored inspection automatically. A laser beam is used for the indication of the X-ray beam position rsp. the defect location that provides for the possibility to perform accurate and fast repair of the weld. The "live" X-ray image will be displayed on the monitor. In case of a defect the operator starts the image processing. To increase the throughput of the inspection and to ensure an easy use of the system special automatic functions (macro) were programmed.
The great experience of the engeneers from 'Philips Industrial X-Ray' and the carefully specified task from the customer allowed to create a unique system for the semi-automatic X-ray inspection to measure the size and quantity of defects in weldings by substituting the X-ray film.
The system MU 80 F was installed within 2 weeks and started right after mounting without any interruption of continuous production of fuel assemblies.
During commissioning a joint comparative analysis of X-ray graphic and X-ray imaging methods was carried out together with specialists of OJSC 'MSZ' directly on the products; during the analysis penetrometers were used as well, and in both cases the detection sensitivity was monitored. The image processing program of the MU 80 F allows to get high quality image with required sensitivity about 1 - 2 % in case of stainless steel.
The results of the comparative analysis of the welds control using both methods, proved the identity of the welds quality control.
For the two years of operation there were no drawbacks discovered in this system and it functioned successfully during the mass products control providing for all the requirements to the product quality.
Moreover careful study of the system allowed the factory specialists to develop the method of estimating depth of defects along the X-ray beam that was not foreseen by the general description of PXV 2000 possibilities.
At the same time the operational experience of MU 80 F shows that the development of the X-ray imaging soft- and hardware digital methods of image processing and archiving reached such a level at which using such systems in industrial control becomes economically profitable when meeting high quality control requirements.