On the contemporary SINTAP approach and its application to the evaluation of the serviceability of welded joints of stea
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ON THE CONTEMPORARY SINTAP APPROACH AND ITS APPLICATION TO THE EVALUATION OF THE SERVICEABILITY OF WELDED JOINTS OF STEAM PIPELINES OF THERMAL POWER PLANTS I. R. Dzioba,1 O. Z. Student,2 and A. D. Markov2
UDC 621.181:669.018
The SINTAP approach is used for the evaluation of the serviceability of a welded joint after ∼ 19 ⋅ 104 h of its operation in the steam pipeline of a thermal power plant. The characteristics of strength and crack resistance required for calculations are determined on specimens cut out from the corresponding zones of the investigated welded joint. It is assumed that the welded joint is loaded by a uniform tensile stress, that residual stresses are also present in the metal of the weld, and that a semielliptic crack propagates in the base metal and the metal of the weld from the external surface of the pipeline. The theoretically established parameters of the critical state of a pipe element with welded joint are in good agreement with the expert conclusions concerning the causes of failure of the pipeline.
At present, the problem of estimation of the serviceability of power-generating equipment is extremely urgent for the Ukraine, where the period of operation about 80% of the equipment would become greater than 30 yr at the end of 2005 [1]. Thus, in order to justify the periodicity of inspections and guarantee the reliability of operation of the equipment, it is necessary to perform the profound analysis of the current state of the metal. The required method aimed at the estimation of the serviceability of the metal must include a complex of procedures taking into account the maximum possible number of factors affecting the investigated characteristics. In the process of operation, the units of thermal power plants suffer periodic startups and shutdowns. As a result of periodic heating and cooling, additional stresses are induced in structural elements. These stresses are added to the stresses caused by internal pressure and, hence, the resulting stresses can reach the critical level [2, 3]. Moreover, welded joints often contain microdefects. Under the combined action of stresses and corrosive media (steam), these microdefects are transformed into macrocracks [4–7]. The analysis of the properties of the metal of operating steam pipelines shows that, despite the preservation of its strength and fracture toughness on the admissible level even after long-term operation (for more than 2 ⋅ 105 h), the failures of these pipelines now become more and more frequent [8–10]. This is caused by the degradation of the metal [7, 11] observed in the form of a significant decrease in its crack resistance [7, 11–15]. All these factors should be taken into account in the evaluation of the serviceability of steam pipelines. The best way to do this is to use the two-parameter approach. The theoretical foundations of the two-parameter approach have been developed for the last 35 years [16– 24]. Simple criterional equations capable of determination of the ultimate state of elements made of high-plasticity materia
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