卷 52, 编号 15 (2016)

Features of crack development kinetics in steels under creep are investigated from positions of fracture mechanics. It is shown that the creep crack growth rate can be approximated by a power dependence on parameter C* or on the stress intensity factor. At the same time, exponents of these dependences are a function of characteristics of long-term strength or material creep. For description of the creep crack rate, it is proposed to use the reduced stress intensity factor, which takes into account the character of the stress distribution in the design section and the crack development time. The experiment verifies the advantages of using the reduced stress intensity factor as a correlation parameter describing the creep crack growth rate.

Oil and gas facilities—reservoirs, gas pipelines, oil pipelines—belong to industrial facilities of high risk. Uncontrolled development of accident scenarios at oil and gas facilities associated with explosions and fire may lead to significant damages and human casualties. This article presents possible scenarios of occurrence, development, and probability of realization of accidents at oil and gas facilities operated in extreme natural and climatic conditions of the North. Measures aimed at reducing the hazards are suggested.

For a comprehensive assessment of safety of hazardous facilities, an accident risk ratio is used. Existing methodologies of risk assessment do not account for technical conditions of the facility and the degree of its defectiveness. This work demonstrates the possibility and necessity of a broader use of nondestructive testing (NDT) and technical diagnostics (TD) to estimate the probability of an accident, formulates the requirements for analyzing the risk, and establishes the line of development for these approaches. We consider the issues related to introducing new requirements for NDT and TD, which deal with representing the quantitative values of NDT, i.e., reliable data on the size of defects and measurement errors. We prove the necessity of using the methods of probabilistic fracture mechanics for assessing the real values of accident probability.

The microstructure and the mechanical properties of stud metal (steel 40Kh) M90×4 for fixing covers of large hydraulic units were studied. The mechanical properties were determined by static, dynamic, and cyclic tests of samples cut out of a stud in the longitudinal and transverse directions and at different distances from the surface. The character of the change in the microstructure and the mechanical properties over the cross section of a stud was determined. Static and cyclic tests of model and actual studs together with nuts were performed. The load and stress values under which the chain cutting of turns of a threaded joint occurs were determined. A strong influence of the scale factor on the durability of studs was established by cyclic tests.

This article presents a review of safety validation, calculations of initial and residual life, reliability, and survivability of equipment critical structures based on analyzing stress-strain states following the results of diagnostics and monitoring of parameters of their current and limit states with consideration of accumulation of operational damageability. On the basis of the assessment of the stress-strain states and changes in properties of structural materials and their defectiveness, we studied the possibility of determining the consumed part of the lifespan, residual life, survivability, and reliability of critical elements in machines and structures. We proved that integrated implementation of control, nondestructive testing, defectometry, technical diagnostics, fracture diagnostics, and monitoring of critical equipment elements offers new opportunities of controlling the lifespan and safety of highly hazardous facilities.

The effect of Sc and Sc + Zr on the structure and properties of Al–Mg–Si alloys is studied using the methods of hardness measurement, resistivity, mechanical properties, and light and electron microscopy. A considerable strengthening of Al–Mg₂Si alloys doped with transition metals (Sc or Sc + Zr) during natural aging and its almost complete absence during artificial aging are established. The observed effects are explained using electron microscopy and local X-ray analysis.

Results of laser-flash measurements of the specific heat capacity of samples of metallic materials (12Kh18N9T stainless steel, VZhM-4 nickel superalloy) coated with heat-resistant silicate enamel in a temperature range of 20–1300°C are described. In this temperature range, the coating is characterized by a high emissivity factor with a constant magnitude of 0.9. Analysis of the measurement results for the specific heat capacity of the steel samples and comparison of these results with the reference data and the most reliable literature data reveal that a decrease in the apparent specific heat capacity in a temperature range of 850–1100°C is attributed to an exothermic heat effect. The deviation of the measurement results from the reference data is no more than 3%. New data on the heat capacity of the VZhM-4 nickel alloy are derived. The temperature dependences of the apparent (with allowance for the heat effect of dissolution of the γ' phase) and true specific heat capacities are described. The discrepancy between the calculated and measured values does not exceed 2%.