Volume 48, Nº 8 (2018)

Stress-corrosion defects in the output pipeline of a compressor station are subjected to metallographic analysis and mechanical tests. The pipeline consists of pipe imported in the 1980s. Diagnostic data obtained in nondestructive monitoring of such pipelines are analyzed, and the effectiveness of various diagnostic methods in detecting stress-corrosion defects in large-diameter pipe is assessed. The grade of steel in the pipeline is identified. The cracks are identified by type and morphology, and their development is determined. Nonmetallic sulfide inclusions have no influence on pipeline failure in the stress-corrosion conditions considered. The sulfur content in the corrosion products is no more than the sulfur content in the metallic sample. In some samples, the sulfur content may be decreased except for local sections with nonmetallic sulfide inclusions. Electron-microscope images show that such nonmetallic inclusions do not promote failure. The results of cyclic tests of cracked samples cut from the pipeline are presented. The test conditions are selected in accordance with recent operating conditions of the compressor station. According to the results, pipe with defects at the initial stage of development exhibits considerable durability in the tests. In fact, the cracked samples withstand (1.6–7.5) × 10⁶ cycles under transverse cyclic flexure in a single plane, in the absence of corrosive fluid. In practice, the number of such cycles is no more than 120–200 per year, in normal pipeline operation. Hence, a pipeline with stress-corrosion defects in their initial stage of development will last a long time if its metal wall is protected from the action of corrosive fluid.

A system for regulating the parameters of electrostimulated drawing (the temperature in the deformation zone and the drawing force) is considered. This system produces a control signal for the unit generating powerful current pulses. The basic operating principle is periodic discharge of a precharged capacitor to a low-resistance load. For regulation of the pulse amplitude and increase in system power, the uncontrollable dc source in the charger is replaced by two irreversible thyristor converters, which are in series and operate in the same direction. That produces a controllable voltage at the power capacitors. To optimize capacitor charging, a two-loop subordinate control system is employed: the external loop regulates the voltage, while the internal loop regulates the current that charges the capacitors. The high speed of the transient processes in electrostimulated drawing—in particular, the rapid temperature rise in the deformation zone on account of the large current pulse (up to 10 kA) and the high pulse frequency (up to 400 Hz)—means that manual control is practically impossible. To boost the reliability and quality of electrostimulated drawing using a powerful current-pulse generator, an automatic control system for electrostimulated drawing is developed. It includes a single-loop system for regulating the drawing force and also delayed temperature feedback in the deformation zone. The dependence of the drawing force and temperature on the frequency of the current pulses is established by means of laboratory research and calculations using both new and familiar methods. A model of the proposed control system in MATLAB-Simulink software permits analysis of the operating conditions in electrostimulated drawing under automated control. The model is consistent with the actual parameters obtained in research on the electroplastic effect. The proposed model permits improvement in the characteristics and operating conditions of electrostimulated drawing. The formalized structure of the system, the proposed model of the system in MATLAB-Simulink software, and the oscillograms of the transient processes are considered. The single-loop automatic control system for the drawing force, with flexible temperature feedback in the deformation zone, permits optimization of the operating conditions and improvement in the reliability of electrostimulated drawing. The proposed system is recommended for use in studying electrostimulated deformation and also for the control of wire drawing in production conditions

When using local automatic control systems, the temperature and excess pressure of the hot gas in a chamber furnace are generally chosen independently, without regard for their interrelationships. At the same time, regulation of the fuel and air consumption involves changes in not only the temperature but also the pressure in the furnace chamber. That, in turn, changes the gas transfer with the surroundings and has a considerable influence on the temperature in the working chamber. As a result, the combustion of the gaseous fuel is excessive, and consequently furnace operating costs are increased unnecessarily. With constant volume of combustion products in such furnaces, control of the thermal power entails combining different components of the gaseous fuel with specified temperature in the working volume. On the basis of Bellman dynamic programming, the control of the heat-treatment cycle in the furnace may be optimized by selecting the optimal fuel composition (in terms of fuel cost) for each quantization period. The fuel cost is regarded as a linear function of the mean consumption of the individual fuel components in the quantization periods. Its minimum value for each instant is found by linear programming. An algorithm is developed for determining the optimal consumption of individual components of the gaseous fuel and also the consumption of the excess air, which is used in automatic control of the temperature and excess pressure of the hot gas within the working volume of the furnace. The proposed automatic control system not only permits optimization of the heating process in terms of the cost of the individual fuel components but also ensures autonomous control of the temperature and excess pressure of the hot gas in the working volume of the chamber furnace. With real-time control and cost optimization of the fuel components, the system is self-adjusting.

The influence of increased pulverized-coal consumption on lining failure and the associated heat losses in the cooling system (as well as the increase in the coke consumption required to cover those losses) is assessed on the basis of data from automated lining monitoring in the blast-furnace shop at PJSC Zaporizhstal.

A single dependence of the power factor on the arc current is established for all steelmaking arc furnaces. On that basis, universal furnace characteristics may be calculated, determining the functional relationship of the active, reactive, and apparent power with the arc current. By that means, precise and simple calculation of the electrical characteristics is possible for arc furnaces of any power, with any primary and secondary transformer voltages, including superpowerful furnaces with reactors on the step-up side of the transformer. Detailed analysis of all the arc characteristics is consistent with current notions regarding the physical processes in arc furnaces.

The microstructure, fine structure, and mechanical properties of high-strength low-alloy steel with boron are studied after two different rolling technologies: (1) high-temperature hot rolling; (2) two-stage controlled rolling with accelerated cooling and subsequent quenching with tempering. The tempering temperature corresponding to irreversible tempering brittleness of the first kind is established. The reasons for embrittlement at that temperature are analyzed.