X-RAY INTROSCOPEs FOR QUALITY CONTROL OF WELDED JOINTS IN PIPE STRINGS AT WELDING BASES

D. I. Sviryagin, A. A. Solodovnikov,
A. D. Maksimenko, V. P. Kargin, S. V. Avraamov,
V. F. Ulanovskii

(Presented by the scientific seminar of the Research Institute of Electronic Introscopy)

One of the weak points in the technological process of pipeline construction remains the quality control of welded joints made by semiautomatic and flow-line welding. Because of the complexity and high cost of inspection operations, at present the quality of only 10–20% of the total number of welded seams is checked. The Aleksandrovskoe—Tomsk—Anzhero-Sudzhensk oil pipeline and the Tomsk water conduit are no exception in this respect. In this connection, at the Research Institute of Electronic Introscopy at TPI, several variants of X-ray introscopes were investigated, and one of them, in the form of a mock-up specimen, underwent field tests under winter conditions at a welding base during construction of the Ust-Balyk—Ufa—Almetyevsk—Omsk oil pipeline on pipes 1220 mm in diameter. In all the variants investigated, the radiographic examination of the pipes was performed through one wall, with the X-ray apparatuses (RUP-200-5, Picker-Andrex) placed inside the pipe and the radiation receiver outside.

In one of the introscopes, an X-ray electron-optical converter RU-135, a Yu-3 lens, a mirror with an external reflecting surface set at an angle of 45° to the optical axis of the lens, a field lens, and a prismatic binocular image splitter with a tube were used as the radiation receiver and information-transmission channel. Figure 1 presents a photograph of this radiation receiver. It is mounted on a stand and positioned above a section of pipe with a circumferential seam that was subjected to radiographic examination. This photograph also illustrates the geometry of the radiographic examination. The RUP-200-5 apparatus, together with the transporting carriage, is placed along the center inside the pipe and is fixed opposite the seam by means of special hinged expanding devices. Counterweight balancers installed on the RUP-200-5 apparatus, when the pipe rotates, keep the latter constantly in one position, i.e., in this case with the exit window upward. The end-face rotator, visible in the background, provides uniform rotation of the pipe, adjustable in speed, during quality control of the circumferential seam. Radiation protection is provided by a special cabin with lead lining, through which the image-transfer optics passes and in which the operator’s workstation with the control panel—the introscope—is located. The cabin is absent from the photograph.

Such an introscope is extremely simple in its design and in operation and has high reliability; however, it can provide transmission only—

Fig. 1. Mock-up of an X-ray electron-optical pipe introscope

up to 3–4 brightness gradations of the image and a contrast sensitivity, according to GOST 7512–69, of the order of 5–6% with a steel-pipe wall thickness of 14–18 mm. It can be used at welding bases to inspect welded joints when welding pipes into strings, and at pipe plants to inspect longitudinal seams in the production of large-diameter pipes, i.e., under stationary conditions where there is no need to change the spatial position of the radiation receiver.

In another introscope configuration, the converter of the spatially modulated X-ray flux into a visible image is likewise the RU-135 device; however, the television channel of the PTU-27 unit, with an LI-421 vidicon in the transmitting camera, serves to transmit information to the video-control unit (VCU) located in front of the operator. The shadow X-ray image from the output screen of the RU-135 is transmitted to the vidicon phototarget by two inversely coupled Yu-3 lenses, which made it possible to reduce the “screen–target” distance to 130–140 mm; this accounts for the comparatively small overall dimensions of the entire radiation receiver. The photograph presented in Fig. 2 gives a general view of the mock-up of such an introscope. As before, the radiation source is the RUP-200-5 apparatus, located inside the pipe. The irradiation geometry remained the same. Above the pipe, with the aid of a stand with a bracket, the radiation receiver is fixed; it is connected by a multicore cable to the video-control unit VCU mounted on a support. In this introscope there is no need to place the operator next to the pipe being inspected; consequently, the need for a special protective cabin is also eliminated. Since the operator can be removed from the irradiation zone to the distance required to reduce the X-ray-radiation dose rate to an admissible value, the length of the cable between the radiation receiver and the VCU is determined by require-

Fig. 2. Mock-up of an electron-optical television pipe introscope

by “distance protection,” i.e., it lies within the range of 25–40 m. The more complex circuit and design of this introscope also resulted in lower operating reliability compared with the introscope described earlier; at the same time, however, this introscope also provides better contrast sensitivity, equal to 3–4% with 5–6 transmitted brightness gradations in the image. In addition, it has a certain versatility, since it can be used both for inspecting seams made by rotary semiautomatic welding and for inspecting seams made by overhead welding when joining pipe sections into a “string” on pipeline routes, when the radiation source and receiver must be rotated around the pipe and radiography must be carried out through two walls.

To ensure mobility and to carry out rapid in-process inspection, introscopes can be mounted on specially equipped motor vehicles or trailers. However, equipping such introscopes with X-ray apparatus involves serious difficulties associated with the design configuration and characteristics of the latter. The most suitable would be an apparatus of monoblock design, without high-voltage cables supplying high voltage to the X-ray tube, with radiation energy of 350–400 keV, a dose rate of 150–200 R/min at a distance of 500 mm from the anode, comparatively small dimensions, and a monoblock weight not exceeding 200–250 kg. An introscope with such an apparatus, made according to the scheme described above, would make it possible to radiograph welded seams through two walls both on pipe sections fabricated at welding bases and on pipes welded into a “string” directly along the routes of pipelines under construction. Unfortunately, such X-ray apparatus is not currently produced by industry. Therefore, primary attention was devoted to developing bench-type variants of the X-ray electron-optical television introscope (TRIT-1, TRIT-2), intended for quality control of welded butt joints at welding bases.

The functional diagram of such an introscope is shown in Fig. 3. Here the numeral 1 designates the RUT-200-5 apparatus, installed on a self-

Fig. 3. Functional diagram of an electron-optical television pipe introscope.

traveling carriage and equipped with a counterweight that keeps it in one and the same position during radial rotation of the pipe string; 2 — radiation receiver, suspended on the track and positioned by the operator opposite the weld being inspected; 3 — pipe string, the welded joints of which are subjected to radiographic examination; 4 — pipe rotator, equipped with an electric drive for rotating the string during examination of the welds; 5 — television cable connecting the radiation receiver with the VCU and the control console; 6 — drum with a collector device for winding and paying out the cable feeding the RUP-200-5 unit and the carriage with a remotely controlled electric drive for moving the unit inside the pipe string; 7 — radiation shielding (on both sides), absorbing scattered radiation emerging from the open ends of the string; 8 — laboratory car, where the operator’s workplace is located and the control console is installed; 9 — video-monitoring device with a hardware video-information analysis unit; 10 — device for automatic recording on chart paper the results of hardware analysis 11.

The introduction into the introscope system of a hardware unit for video-information analysis and a device for automatically recording the analysis results made it possible to increase the local flaw-detection sensitivity of the introscope to 0.5–0.7% of the thickness of the joint being inspected and provided the inspection and testing service with an objective document in the form of a defectogram of the weld, representing the result of an analysis of the density of the weld material along a line (or narrow strip) selected by the operator.

The introscope considered here does not provide complete automation of the inspection operations, and the operator has to manually position the radiation receiver opposite the joint being inspected and then, after switching on the X-ray unit from the console and using a remotely controlled self-propelled carriage, aim the radiation source at the joint to be examined and at the input window of the radiation receiver, checking the accuracy of the aiming from the image on the VCU screen. This noticeably reduces the productivity of the flaw-detection operator and diminishes the economic effect from introducing the installation. Therefore, the efforts of the development team are directed not only toward further improving the characteristics of the radiation source and receiver, the transmission channel, and the blo-

methods of information processing, but also at improving the design of the entire complex and the complete mechanization and automation of inspection operations.

REFERENCES

1. F. Ekkart. Electron-optical image converters and X-ray image intensifiers. Gosenergoizdat, 1961.
2. S. V. Rumyantsev. Radiation flaw detection. Atomizdat, 1968.
3. F. N. Kharadzha. General course in X-ray engineering. “Energiya,” 1966.
4. Nondestructive Testing. Handbook. Edited by R. McMaster. “Energiya,” 1965.
5. Ch. G. Postarnak. The use of television in flaw detection. 1964.
6. Television (General Course), edited by P. V. Shmakov. “Svyaz,” 1970.
7. V. A. Dobromyslov, S. V. Rumyantsev. Radiation introscopy. Atomizdat, 1972.