Determination of actual wall thicknesses of equipment and pipelines exposed to flow-accelerated corrosion on the example of conical reducers

Abstract

Flow-accelerated corrosion is a common type of damage to heat engineering equipment and pipelines. This process is subject to almost all elements of the condensate-feed and steam pipelines of turbine sets of nuclear and thermal power plants. Other types of metal thinning, in most cases, occur in conjunction with this process. In accordance with the requirements of the Federal Norms and Rules in Nuclear Energy, it is necessary to conduct regular non-destructive testing of thermal mechanical equipment using the method of ultrasonic thickness measurement to measure the thickness of walls, followed by assessment of compliance of the product quality and determination of the predictive value for the next in-service inspection. To estimate the rate of thinning and predict the value of thinning, it is necessary to know the values of actual wall thicknesses of pipeline systems at the initial time, which is usually not known. The actual wall thickness at the initial time is usually assumed to be equal to the nominal value without taking into account possible deviations, which is not always a reasonable solution in terms of assessing the rate of flow-accelerated corrosion. Functions are obtained that describe the profile of thinning with high accuracy. The coefficients included in the equation have a physical meaning: the actual wall thickness, the value of thinning and the area of local corrosion on the inner surface of the reducer. The developed approach is based on approximation of results of non-destructive testing, which allows to distinguish between areas exposed and not exposed to the mechanism of flow-accelerated corrosion in conical reducers. This makes possible to determine the thickness of the wall of a conical reducer of pipeline at the time of its being put in operation and to assess the rate of thinning based on a single control procedure, which reduces the possible rejection of metal and increases the accuracy of predictive calculations. This approach increases the safety and reliability of operation of conical reducers.