Modern approaches to determining the standardised parameters of vibration state of NPP steam pipelines

During the operation of NPP steam pipelines the main damaging factors are not only corrosion and erosion leading to thinning of the pipe wall but also fatigue damage resulting not only from temperature self-compensation efforts, but also high vibration load. As practice shows, the most promising direction of ensuring the vibration resistance of steam pipelines at present is the computational and experimental study of the stress-strain state of pipelines under vibration loading. This work shows that the strength of the most commonly used standard sizes of steel pipelines under the influence of vibration loads is determined in accordance with Russian State Standard R 59115.9-2021. Taking into account the stress concentration, the amplitudes of the conditional elastic reduced stresses were determined for the 4 variants of the calculation schemes accepted for consideration. The permissible amplitude of stresses from an operating condition of 60 years is determined. It is shown that the permissible voltage amplitude for the design temperature t = 350°C will be no more than 46.4 Mpa for a pipe made of 12X18H10T. As for NPP pipelines, the normalized vibration parameters in the regulatory documentation were not established until 2022, when the following vibration velocity limits were adopted for pipelines of nuclear power plants in Russian State Standard R 59115.11-2021, vibration resistance testing is not required: nmax up to 15 mm/s, nmsv up to 7 mm/s. Thus, currently in the Russian regulatory documentation there are no normalized values of vibration parameters (as a rule, vibration velocity) for pipelines selected depending on the frequency of vibration exposure. It is proposed to develop and introduce into the regulatory documentation frequency-dependent criteria for limiting vibration parameters of NPP pipelines, specified in accordance with the actual operating conditions of these pipelines.

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