Oxide scale based thermo-structural analysis of boiler tube using finite element and thermal resistance network modeling

In this paper, the thermo-structural analysis of a boiler tube using thermal resistance network and finite element simulation was studied. The boiler tube samples that have been exposed to high temperature service conditions in a sugar factory for last eight years were considered in the modeling. The oxide scale thickness measurement on the steam side of the tube sample was done by using metallographic surface polishing on the base metal. In order to model and analyze the heat transfer and stress distribution in the boiler tube, four different thicknesses of the oxide layers, 0.25 mm, 0.5 mm, 0.75 mm, and 1 mm, were selected based on the surface-polished results. The temperature gradient results obtained using a thermal resistant network across thickness were given as 438 °C, 468 °C, 494 °C, and 518 °C for selected oxide scale thicknesses of 0.25 mm, 0.5 mm, 0.75 mm, and 1 mm, respectively. In the case of the steady-state thermal modeling using Ansys software, the corresponding temperature distribution of 440 °C, 470 °C, 496 °C, and 519 °C was achieved. The 3D finite element analysis also showed that the effect of oxide scale on tube wall overheating resulted in high operationally induced stress under combined internal pressure and thermal load.