PSI - Issue 22

S.V. Belodedenko et al. / Procedia Structural Integrity 22 (2019) 51–58 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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amalgamation rule, are most appropriate (PVI, βΣ exp10, Fig. 1). As a result of valid studies, it was found that the rules for amalgamating PW, PVI correspond to the principle P Σ → P ikmin . However, they are sensitive enough to increase the number of system elements. With their increase it is difficult to achieve the desired principle. To solve this problem, one must understand what the cause of such a phenomenon is. The rule of multiplication of the PS is fair for independent events. If there are deviations from this rule, then it is assumed that these are the consequences of the mutual influence of the elements of the system. This effect is manifested during operation. When forecasting the system's reliability, there is the amalgamation effect that involves a significant reduction of the magnitude P Σ relative to the P ik values. The amalgamation effect is formalized, as P Σ << P ikmin . It is the outcome of uncertainty . Failure of the system occurs under the influence of the dominant damaging process for the most vulnerable element. Combating the effect of the amalgamation is the procedure for identifying (updating) the model of the operation process. Its result is the simplification of a complex technical system to the simple, whose robustness is valued on the principle of weak link. Thus the principle P Σ → P ikmin is realized. The structure of amalgamating formulas, which exclude excessive conservatism when calculating the reliability of the system, is found. New rules for amalgamating based on the risk indicator and on the basis of Lindley's distribution are obtained. It is recommended to use it for a large number of (more than 10) critical elements of the system and for multi-site damage. With less number of them it is suggested to use a more usual form of the resource safety index. It well meets the situation of several (4-7) degradation processes on the element of the technical system. 4. Research of casing blast furnace The application of risk analysis methods is demonstrated by the example of assessing the technical condition of the blast furnace casing. The wall (shell) of a blast furnace (BF) is a complex multilayer composition consisting of lining, coolers, compensating space (gap) and directly a steel casing. A downtimes blast furnace on the cause of shell failures is on average 20% and reaches more than 40% of all downtimes (Chechenev, 2011). The most characteristic scenario of the failure of the BF shell is as follows: burnout (wear) lining → failure of the cooler → cracking (or bulging) of the casing area → break of the casing (depressurization of the furnace) (Belodedenko & Chechenev, 2015). The time of the each subsequent stage is shorter than of the previous one. New realities of the operation of the metallurgical complex in accordance with the standards of "Industry 4.0" require an increase in the BF campaign for more than 25 years with 95% available (van Laar & Engel, 2016). In view of this, the goal was to test the capabilities of the casing metal for such a long-term operation under real conditions. The objective is achieved by studying the degradation of the properties of the metal casing after the operational work and by determining the residual life of the casing. The BF casing 1033 m 3 volume, made of 30 mm thick sheets of steel 09G2S (analogs - 13Mn6, A 516-55) was investigated. The BF was operated for 14 years, after which it was decided to terminate the campaign. At the same time, the examination of the BF shell showed that it is in unsatisfactory condition as a result of rigid operating and maintenance conditions. Up to 75-50% of the shaft casing surface deformed (bulging), 30% of coolers failed, the residual lining thickness was 30-40% (Ibragimov et al., 2018). Samples for research were cut from three sections of the dismantled shell. From the uncooled section of the shaft (1 zone, height 24.9 m), from the cooling area of the shaft (zone 2, height 20 m), from the tuyere area of the casing (zone 3). Samples for mechanical tests had a full thickness (that is, the surface was not treated), a width of 12 mm. They deformed according to the scheme of 3-point bending in the plane of greatest rigidity at a distance between the extreme supports 110 mm. Estimated block of loading consists the three stress levels σ i , which have a relative parameter of action c i (Chechenev, 2011). The form of the block depends on the parameters of the overloading level c ol = 0,1-0,4. Then the parameter of the base levels will be c 1 = c 2 = 0.5 (1-c ol ). The stress levels of the block are defined as σ 1 = 100 МРа, σ 2 = 140МРа, σ ol1,2 = 300МРа ( shaft, zone 1 and zone 2), σ ol3 = 340МРа ( tuyere zone, zone 3). For these stresses, the amplitudes of strains ε ai were determined on the model of strengthening. To calculate the stationary fatigue durability of the BF casing, a fairly simple equation is used: lgNi = (0,0176 / ε ai ) 0,5 .