Damage State Assessment of Metal Pipes of a Power Plant, Subjected to Thermal Stresses

Abstract

During the operating of industrial equipment and installations, elastoplastic deformations may occur over time in their most demanding areas due to thermal stresses, mechanical stresses (due to internal pressure, weight, inertial forces) or thermomechanical stresses resulting from their combination. Thermal stresses are cause by the non-uniformity of the expansions produced by the temperature differences, by the non-uniformity of the coefficients of linear thermal expansion of the materials used in isothermal or non-isothermal operating conditions. Increasing the temperature reduces the material strength by creating elastoplastic deformations and thus, to the loss of available plasticity of the material. The sudden change in operating regimes and the increase in the number of these regime changes at high temperatures, is one of the main causes of the faster accumulation of degradation, and the reduction of components remaining life. On the other hand, environmental factors have an important influence on the operating behaviour of equipment, since they favour the induction of corrosion or erosion-corrosion phenomena due to the flow of fluid circulated through installations at high temperatures. The complexity of the thermomechanical stresses, to which materials are subjected during operation, leads to the need for periodic assess of their characteristics through specific tests and analyses. Paper presents the results of analyses and tests performed to assess the damage state of pipes from a thermal power plant system, results that allow to estimate the service remaining life of the pipeline system for a proper operating in safe conditions.