Development of Tools and Methods for Radiation Nondestructive Testing of Materials and Products
Abstract Generated abstract
This article surveys the development of radiation methods and equipment for nondestructive testing of materials and industrial products, emphasizing the growing need for continuous, automatic, and comprehensive quality control in large-scale and high-reliability engineering. It reviews international and Soviet work on X-ray, gamma, isotope, betatron, accelerator, scintillation, electron-optical, and television-based flaw detection and introscopy systems, with examples of equipment introduced into industrial production. The paper argues that further progress requires coordinated development and serial production of radiation sources, detectors, and automatic inspection systems. It outlines three main research directions: active prevention of hidden defects during production, post-manufacture nondestructive inspection, and testing of products during operation or long-term storage.
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DEVELOPMENT OF TOOLS AND METHODS FOR RADIATION NONDESTRUCTIVE TESTING OF MATERIALS AND PRODUCTS
V. I. Gorbunov
The development of nondestructive methods and means for testing materials and products is a natural result of the demands of technical progress and of those qualitative changes that are observed in the course of the development of science and technology.
The postwar period may be characterized by the grandiose development of technical progress, by advances in physics, technical electronics, engineering cybernetics, etc. Modern industrial development is characterized by the concentration of material and technical resources, scientific and engineering developments in a single facility under construction.
A significant number of costly facilities—such as thermal power units of hundreds of thousands of kilowatts, hydraulic turbines, nuclear reactors, main pipelines, airliners, and spacecraft—become unique from the very beginning of their construction. This is why society’s expenditures on their construction can be justified only if the facilities operate without interruption. From the foregoing it becomes entirely obvious that no selective quality control of products and materials from which parts and assemblies are made can provide a guarantee of accident-free and reliable operation of facilities. The cause of an accident of a spacecraft, thermal power or main unit, or main pipeline—on whose development and creation tens and hundreds of millions of rubles are spent—may be the failure of one of the numerous and most inconspicuous parts; of a poorly executed section of weld, etc. Thus, “the problem of a one-hundred-percent guarantee of the reliability of all vitally important assemblies and parts, as well as of the quality of all basic materials used in the construction of such facilities, has become an urgent task of national importance”1.
For many branches of industry, such as metallurgy, machine building, chemical industry, and others, the introduction of high-speed technological processes is characteristic. Control of such processes is inconceivable without the broad use of modern means of automation and cybernetics. However, the application of the powerful modern arsenal of technical means for the purposes of comprehensive automation
high-speed technological processes is in most cases not effective because of the lack of input data characterizing product quality and the technological process.
The absence of developed methods for obtaining input data directly from the objects being inspected has sharply raised the question of developing automatic means of inspection in flow production. It should be noted that the unsatisfactory state of methods and means of automatic inspection is characteristic of worldwide practice as a whole.
In the Program of the CPSU and in the directives of the XXIV Congress of the CPSU on the five-year plan for the development of the national economy of the USSR for 1971–1975, special attention is given to further improvement in the quality of manufactured products. “The main tasks of industry in the new five-year period consist ... in raising the technical level and efficiency of production, and in radically improving the quality of products”2.
It is quite obvious that the task of comprehensively improving product quality in all branches of industry, ultimately connected with the problem of reliability and techno-economic efficiency, can be solved only under the condition that new methods and devices are created which make it possible to ensure high-productivity, automatic quality control of materials and products. At the same time, the continuous growth of requirements for the reliability of assemblies, machines, and structures creates the need for a further increase in information about the internal properties and quality of inspected products without destroying them and at a high speed of processing this information. It is not possible to satisfy the enumerated requirements by means of the known methods of flaw detection, which in most cases make it possible to carry out selective quality control of products with single-element information.
In recent years, as a natural result of the demands of modern technical progress both in our country and abroad, a new direction in science and technology has arisen and begun to develop—introscopy. The main task of introscopy is precisely the creation of methods and means for the high-speed acquisition, processing, and recording of the most complete, i.e., multielement, information directly from the internal regions of the bodies and processes being studied or inspected. From what has been said it becomes clear that only introscopy will ultimately make it possible to obtain the most complete information about the properties and quality of the inspected products.
The development of methods and means of introscopy has a determining influence on the development of modern flaw detection. Moreover, the practice of developing modern methods and means of nondestructive testing of materials and products shows that introscopy is, in essence, a new stage in the development of flaw detection, based on the latest achievements of science and technology.
Introscopy and modern flaw detection are based on the broad use of the most diverse types and spectra of penetrating radiations, such as ultrasonic vibrations, magnetic and electromagnetic fields, X-rays and gamma rays, neutron fluxes, optical spectra, radio waves of the centimeter and millimeter ranges, and others.
The development of methods and means of modern radiation flaw detection and introscopy, along with the use of other sources of electromagnetic radiation, is of considerable scientific as well as practical interest. This is evidenced by the large number
work being carried out both in our country and abroad in the field of radiation flaw detection and introscopy.
The present world level of development of radiation nondestructive methods and means for inspecting materials and products can be characterized by the development and introduction into industrial production of automatic and semiautomatic flaw detectors and introscopes that make it possible to conduct continuous inspection of materials and products.
The development of such flaw detectors and introscopes required, above all, the creation of new sources of radiation and the improvement of already known ones. At present, a number of foreign firms are producing X-ray, radioisotope, and accelerator installations whose designs have been developed specially for the purposes of flaw detection and introscopy. Along with the improvement of stationary X-ray and radioisotope installations, much attention is being given to the creation of portable X-ray apparatus and gamma installations. Thus, the firms General Motors, General Electric (USA), Toshiba, Shimadzu, Hitachi (Japan), and others have created portable X-ray apparatus with voltages of 30–200 kV, which can be carried by one or two persons; portable equipment and new types of containers have been created, making it possible to use radioactive isotopes with different energies. The firms Brown Boveri (Switzerland), Toshiba (Japan), and others have created and are producing in series betatrons for inspecting products of large thickness; the firms General Electric (USA), Metropolitan Vickers, and others have created, for the same purposes, linear electron accelerators, Van de Graaff accelerators, and other types of accelerators with energies of 2–3 MeV.
In the field of developing and creating radiation receivers for product inspection, alongside the improvement of radiography, principal attention is being given to visual and ionization methods of inspection. A number of firms in the USA, Holland, and Japan have created new electro-optical converters for visual inspection; television systems have been created and are being used that employ the sensitivity of transmitting vidicons directly to X-radiation; closed-circuit television systems based on vidicons and orthicons in combination with screens and image intensifiers have been created. Research is being conducted on the creation of solid-state semiconductor image converters; work continues on increasing the resolving power of closed-circuit television systems and scintillation methods of recording radiation during the radiography of products; multidynode systems are being developed for receiving and amplifying weak radiation.
The successes obtained as a result of research and the development of methods and means of radiation inspection have enabled a number of foreign firms to create and introduce into production several types of semiautomatic and automatic flaw detectors and introscopes.
The development abroad of radiation nondestructive inspection methods using X-ray and accelerator installations is proceeding along the path of creating semiautomatic introscopes based on the use of electro-optical converters for visualization, closed-circuit television systems, etc.
At some plants, X-ray and betatron introscopes have been introduced. Thus, at the United States Steel plant (USA), welds of small thickness are inspected by means of an X-ray introscope; at the Napa plant of Kaiser Steel (USA), since 1963 an improved system for inspecting welded pipes has been used, in which X-ray fluoroscopy and television are employed simultaneously; the installation
developed by the firm “Picker–X-ray KORN.” At the tube plant of the firm “Thyssen” (FRG), an X-ray installation with an electro-optical converter is used for inspecting welds 20 mm thick. The productivity of the installation is 14 km of welds per 1 month of operation. At the metallurgical plant of the firm “Felix Reinrohr” in Duisburg-Ruhrort (FRG), an installation for radiographing blooms by means of a betatron with radiation energy of 31 MeV was tested. With the aid of an electro-optical converter from the firm “Philips” (Holland) and a television system, the visible image of a shrinkage cavity was observed in order to determine the optimal crop length. A 31 MeV betatron installation, equipped with an electro-optical converter and a television system, has also been installed at the “Fischer” plant (Switzerland) for inspecting hot ingots.
Along with bremsstrahlung radiation, gamma radiation from radioactive isotopes is successfully used abroad for inspection.
The shortcomings of the photographic method of gamma flaw detection have led to the development and creation of the most advanced automatic scintillation gamma flaw detectors. At the “Muazevr” plants of the firm “de Wendel Co.” (France), a gamma flaw detector with a scintillation radiation receiver is used for inspecting hot blooms. Inspection productivity is 3–13 m/min.
Another gamma flaw detector, also developed in France, makes it possible to inspect ingots up to 200 mm thick at a speed of 120 m/min. The radiation source is Co^60 with an activity of up to 1000 curies. Gamma flaw detectors for continuous inspection of seamless tubes are used at the plant of the firm “Sumitomo Kindzoku Koge” (Japan); for sorting tinplate sheets by thickness at the plant of the firm “Lai Treyding” (USA); and at the plant of the firm “Dortmund-Herder” (FRG), gamma flaw detectors are used for inspecting hot blooms.
In the USSR, enterprises and institutions of various ministries and departments are engaged in the development of radiation methods and means of nondestructive testing.
The development of sources of penetrating radiation for radiation flaw detection is carried out at the “Aktyubrentgen” plant; the development of gamma flaw detectors—at VNIIRT; linear electron accelerators—at MEPhI; microtrons—at the Institute of Physical Problems of the Academy of Sciences of the USSR; betatrons, microtrons, and synchrotrons—at Tomsk Polytechnic Institute and the Special Design Bureau of the Moscow Electric-Lamp Plant. In the work of VNIIRT, new designs of gamma flaw detectors of the “Gazprom,” RID-21, RID-22, and RID-33 types are described. Linear electron accelerators developed at MEPhI, taking account of design developments, can be applied in radiation flaw detection and introscopy.
Induction electron accelerators—betatrons—developed and manufactured by the Scientific-Research Institute of Electrophysical Equipment and at TPI are used for inspecting materials and products at industrial enterprises of the country.
At the Scientific-Research Institute of Introscopy, means are being developed for seeing inside opaque bodies and media on the basis of the conversion of various types of penetrating radiation into optically visible images or other multi-element and coded information reflecting the qualities and properties of the media being inspected. Work in the same direction is being carried out at the Scientific-Research Institute of Electronic Introscopy of TPI.
In the field of research and development of radiation receivers for radiation flaw detection and introscopy, significant work has been carried out at the Scientific-Research Institute of Introscopy on the development and creation of universal electron-optical converters of the “Unicon” type and multiline systems.
On the basis of theoretical and experimental studies and the results obtained, as well as using the developed methods of ra—
…of nondestructive testing of materials and products; in certain institutions, semiautomatic and automatic radiation flaw detectors and introscopes have been manufactured, introduced, or are being prepared for introduction into production. X-ray and isotope introscopes developed at the Research Institute of Introscopy have been introduced at enterprises of the Ministry of the Aviation Industry. A number of semiautomatic isotope flaw detectors have been developed at TsNIITMash.
At the Research Institute of Electronic Introscopy, several types of radiation flaw detectors and introscopes have been developed and introduced into production. Thus, for the first time, a comprehensive six-sided flaw detector for inspecting thick-walled welded joints was developed and introduced at the Barnaul Boiler Plant. The flaw detector makes it possible to conduct continuous automatic inspection of welds up to 300–350 mm thick and up to 100 mm wide, with a productivity of up to 300 km of welds per month.
Other types of comprehensive betatron flaw detectors and introscopes have been created and are being introduced into production. The comprehensive betatron flaw detector BD-3, developed for the A. A. Zhdanov Izhora Plant, makes it possible to inspect welded joints up to 400 mm thick at a speed of 1.5 m/min and with high sensitivity to defect detection.
In addition to high-productivity betatron flaw detectors, other types of X-ray and isotope flaw detectors have been developed at the Research Institute of Electronic Introscopy and introduced at enterprises of various ministries; these make it possible to carry out high-productivity automatic inspection of products made of various materials.
Vertical isotope flaw detectors VID-1, VID-2, VID-4 and X-ray flaw detectors RDS-1-200, “Redkhord,” and others have been introduced.
The VID-1, VID-2, and VID-3 installations make it possible to perform automatic inspection of products with a density of about 2 g/cm³ and a thickness of up to 700 mm, aluminum products up to 350 mm thick, and steel products up to 150 mm thick, using Co⁶⁰ with an activity of 50 g·equiv Ra as the radiation source. With the same inspection productivity, which is 1 m²/h, the detectability of defects for VID-1, VID-2, and VID-3 is, respectively, 1.5, 1, and 0.5%.
The VID-4 flaw detector provides, all other conditions being equal and with defect detectability of 0.5%, an inspection productivity of 5 m²/h.
The RDS-1-200 X-ray scintillation flaw detector makes it possible to inspect products 400 mm in diameter with defect detectability of 0.25% and inspection productivity of up to 2 m²/h.
At present, an automatic radiation inspection installation for the length of the acceptable portion of hot-rolled blooming stock is being developed at the Research Institute of Electronic Introscopy. The radiation source is a 35 MeV betatron with a radiation-pulse frequency of 100–150 Hz and a dose rate of 600 R/min at one meter. Inspection of hot-rolled stock up to 250–300 mm thick can proceed at a speed of 1–2 m/s, with automatic delivery of information to the shears control system and to the system for rational cutting of the metal.
This, in brief, is the state of methods and means of radiation nondestructive testing in our country and abroad.
As already noted, at the present stage of industrial development, in order to carry out one-hundred-percent inspection, it is necessary to create automatic methods and means for testing materials and products.
This is one of the principal requirements of practically all branches of industry. To satisfy this requirement, in particular with respect to methods and means of radiation flaw detection and introscopy, in our opinion it is necessary:
- Organize the development and serial production of various radiation sources in accordance with the requirements of modern defectoscopy and introscopy. Radiation sources for nondestructive testing methods should include:
a) X-ray apparatus in the energy range 20–300 keV;
b) direct-action accelerators in the energy range 0.5–3 MeV for the generation of bremsstrahlung;
c) electron accelerators (linear accelerators, small-size betatrons, microtrons) in the energy range 3–6 MeV for the generation of bremsstrahlung;
d) electron accelerators (betatrons, microtrons, high-current betatrons) in the energy range 6–35 MeV for the generation of bremsstrahlung and electron radiation;
e) isotopic sources of gamma radiation;
f) neutron generators of fast neutrons;
g) isotopic sources ($\alpha$-particles) for obtaining fast neutrons.
- Organize the development and serial production of radiation detectors in accordance with the requirements of modern defectoscopy and introscopy. Radiation detectors for nondestructive testing methods should include:
a) electron-optical converters of X-ray, gamma, and hard bremsstrahlung radiation with high resolving power;
b) multipin radiation receivers;
c) solid-state semiconductor image converters;
d) sensitive transmitting vidicons for X-ray and gamma radiation;
e) highly sensitive closed-circuit television systems based on vidicons and orthicons in combination with screens and image intensifiers;
f) scintillation single crystals and mosaics for recording radiation.
On the basis of the listed sources and receivers of various types of radiation, it is possible to organize the development and manufacture of pilot-industrial and industrial semi-automatic and automatic defectoscopes and introscopes meeting the requirements of the various sectors. In particular, even now it appears possible, provided that design bureaus and pilot production are strengthened, to begin the development and creation of automatic and semi-automatic defectoscopes for various branches of domestic industry.
If, however, we consider as a whole the proposals concerning the principal directions for the development of scientific-research and experimental-design work in the field of creating and introducing means and methods of nondestructive radiation testing, then, in our view, the development of scientific-research and experimental-design work should proceed in at least three directions:
Development and advancement of active methods and means of nondestructive testing
This direction is (both in the USSR and abroad) mainly at the stage of promising scientific-research developments. The ultimate goal of research in this direction is the creation of means and methods of active nondestructive testing.
not permitting, in the technological process itself, the creation in materials and products of hidden defects.
Development and creation of methods and means of nondestructive testing of materials and products after their manufacture
The most highly developed area at present, both in the USSR and abroad, is the development of nondestructive testing methods.
The principal tasks in research and experimental-design work in this area in the country are the above-listed measures for the development and production of radiation sources and receivers and, ultimately, the creation of high-productivity automatic systems of introscopes and defectoscopes.
Development and creation of methods and means of nondestructive testing of products during their operation or long-term storage
At present, work in this area is basically at the stage of exploratory research and development.
The ultimate goal of research and experimental-design work in this area is automatic quality control of products in operation or in long-term storage (including the fatigue characteristics of materials).
Such, in general, are the directions in the development of research and experimental-design work in the field of creating and introducing means and methods of nondestructive testing.
It is especially necessary to note that, in all the indicated directions, research and development should be carried out comprehensively, i.e., with the simultaneous use of different types and spectra of penetrating radiation, ranging from high-energy gamma quanta to radio waves of the millimeter and submillimeter ranges and from high-frequency elastic oscillations to corpuscular radiation.