Monitoring of transient thermal stresses in pressure components of steam boilers using an innovative technique for measuring the fluid temperature

High thermal loads of the thick-walled components arise during the start-up and shutdown in the thermal power units, both classical and nuclear. The thermal stresses should be determined on-line during start-up of the power unit, to avoid reducing the lifetime of the so-called critical pressure components. It is necessary to know the time variations in fluid temperature, and heat transfer coefficient on the internal surface of the pressure components to determine the transient distribution of temperature and thermal stresses in the critical components of boilers. The thermal stress can only be calculated correctly if the temperature of the flowing fluid is accurately measured. Unfortunately, massive industrial thermometers used in power units are not able to measure the transient temperature of the fluid with sufficient accuracy due to their high thermal inertia. The goal of the paper is to present the use of the new measurement technique to determine the unsteady temperature of the superheated steam. The temperature of superheated steam was measured after the second stage of superheater using the proposed measuring technique and conventional industrial thermometers that are used today. The tests carried out showed very clearly the advantage of the proposed method over conventional thermometers. (C) 2019 Elsevier Ltd. All rights reserved.