The article considers reasons for the use of acoustic emission together with kinetic identification for estimating the degree of production pipeline metal damage, operating under low-cycle loading conditions. A proposed criterion makes it possible to detect achievement of a level of metal damage above 60-70%.The contemporary concept of technical diagnostics and nondestructive monitoring is based on methods for detecting macrodefects in the form of disruption of continuity, reducing the strength of a structural area [1]. If during a short pipeline operating time formation of malfunctions depends on loading conditions and the bahavior of defects, present during manufacture and performance of repair work, then metal damage during prolonged operation under conditions of cyclic (low-cycle) loading, occurs intensely throughout the whole volume of metal, especially in areas of stress and strain concentration. In order to consider the dynamics of a change in mechanical properties of the metal, it is necessary to develop a nondestructive rapid evaluation method for metal damage. The main method for this may be acoustic emission (AE), making it possible to detect sources with energy corresponding to movement of individual groups of dislocations. Recording and analysis of acoustic emission signals, caused by dislocation processes, makes it possible to assess the degree of dislocation mobility, which specifies the degree of metal embrittlement. It is possible to initiate the work of dislocation sources by metal plastic deformation during indentation.Evaluation of the compatibility of results of analyzing AE parameters with tension and indentation are provided in Fig. 1.Comparison of the main spectral characteristics of an AE signal with indentation and uniaxial tension of steel 20 specimens has shown [2] that with both material loading schemes the AE spectral composition is qualitatively identical, i.e., signals of the same type are recorded. This confirms an assumption about single material deformation mechanisms with tension and indentation. The feature detected made it possible to move to a nondestructive method for evaluating processes that occur during metal plastic deformation.During indentation in undamaged metal, the AE signal spectral portrait consisted of one clear peak. With an increase in damage within the spectral portrait additional second peak (maximum) appears, distant from the main peak by not less than 10 kHz. With a further increase in damage, the second peak becomes clearer, and shifts in the direction of higher frequency [3]. With a ratio of height of the second peak to that of the first (Fig. 2) more than 0.1, the degree of metal damage is 60-70% [4].This relationship was followed both for the basic metal and welded joint metal. Thus, the criterion obtained makes it possible to evaluate the degree of metal cyclic damage and to determine the stage of damage.
In the present work mathematical modeling of a CHP system based on Micro Gas Turbine (MGT) with Inverted Brayton Cycle (IBC) (also known as subatmospheric) is provided. Nominal electric power of the facility is 10 kW. Engineering calculation based modeling is conducted to determine optimal parameters of each component, electrical and total efficiency at full load. Further dynamic modeling is provided for the components with determined optimal parameters. With chosen optimal parameters of the scheme components and coolant temperature the dynamic (time-dependent) modeling of disturbance from the nominal state with no control, ramp down and ramp up of power load (a) and heat load (b) with the activated control system was provided. An iteration based approach of MGT modeling is suggested. The difficulties in the system control under reduction of heat consumption are revealed and challenged. The final objectives of the research are comparison of the IBC with the conventional Brayton cycle for MGT application from the electric efficiency, dynamic behavior and controllability points of view, creation of the control system for such a facility.
Structures for tube -tube sheet welded joints (TTSWJ) and schemes for x-radiographic monitoring are considered. Monitoring problems connected with further development of heat exchanger structures, and their solution, are defined. Description of a developed and manufactured test example of an automated device for TTSWJ x-radiographic monitoring with programmed control is provided. The device makes it possible to monitor for one exposure joints with a diameter from 8 to 20 mm. The manual operating part includes placing an unexposed film holder into the device and its removal after exposure. Fulfillment of exposure conditions (voltage, current, etc.) and subsequent passage around a TTSWJ is accomplished automatically by a prescribed regime. The test example is tested on TTSWJ specimens and models made of titanium and stainless steel; results are provided.An integral part of contemporary heat exchangers, operating with hazardous or corrosive media (atomic power, chemical industry, etc.), are tube -tube sheet welded joints (TTSWJ) whose construction has been defined in [1] (Fig. 1).Stainless steel and titanium alloys are normally used as the weldable material. A requirement for carrying out 100% nondestructive monitoring of these welded joints is explained by the metallurgical and structural features of welded joints, for which the main monitoring method is radiographic (RM). TTSWJ RM reveals pores, tungsten inclusions and other volumetric discontinuities.The generally accepted schemes for x-raying TTSWJ have been determined in [2]. Monitoring by a scheme (Fig. 2) provides relatively good productivity (obtaining a photograph of a whole welded joint by one exposure), although it requires use of small sharply focused radiation sources, with radionuclide iridium-192 with a typical size of the active part of 1.0 × 0.5 mm used as such sources for some decades.Research and development aimed at replacing iridium-192 (the effective radiation energy of iridium-192 is ~400 keV, and it has a relatively short half life of ~74 days) by other radionuclides has not ceased, for example by ytterbium-169, but they have not been used extensively in industry.The sensitivity of RM for steel TTSWJ using iridium-192 and films of class C3 (EN 548-1) is normally W11 (0.32 mm) for a wire standard (IQI).Direct confirmation of the complexity of performing RM by the scheme (see Fig. 2) is a limitation [3, para. 9.11.15]: "welding of tubes in a tube plate with a normal internal diameter, tubes up to 15 mm, is not amenable to radiographic monitoring if there are no special indications in the construction documentation."
A brief analytical review of the events of the VII International Industrial Forum “NDT Territory. Non-Destructive testing. Tests. Diagnostics” and the “XXII Аll-Russian Scientific and Technical Conference on Non-Destructive Control and Technical Diagnostics” held simultaneously with it. All events were held at the Expocenter Central Exhibition Complex in Moscow. The exhibition of instruments and tools of NK and TD was accompanied by a business program. Within the framework of the forum, round tables were held on topical issues of non-destructive testing and technical diagnostics. The exhibition was attended by more than 57 companies, and information support was provided by a number of news agencies, including the “Spectrum Publishing House” and “RIA Standards and Quality” (“World of Measurement” magazine). In addition to equipment for non-destructive testing and technical diagnostics, modern test equipment, testing and analytical equipment begins to appear on the stands of exhibitors. This year there was a focus on hightech solutions for engineering, metallurgy, oil and gas and other industries. The final of the competition for NK specialists and the award ceremony took place. For the first time, the “Salon of Innovations and Startups 2020” was organized at this Forum, in which representatives of 20 organizations took part. The forum demonstrated a high technical level of non-destructive testing, their metrological support, as well as certification and standardization.
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