Finite Element Analysis

In a high temperature skirt supported vessel, sudden drop in temperature through bottom dish end to skirt support may leads to the very high thermal stresses. Many times failure has been observed at the skirt to shell circumferential weld due to high temperature gradient. To reduce the rate of drop in temperature at the dish end to skirt junction, an air pocket needs to be provided. Air pocket helps to reduce the rate of heat transfer, thermal gradient across the thickness as well as thermal expansion. This air pocket is called as Hot Box.

Design analysis is performed to evaluate the temperature profile, stress distribution at the skirt to shell junction using Finite Element Analysis. Steady state thermal analysis is performed at design temperature. ANSYS 19.2 used to analyze the heat transfer through radiation in the hot box and heat transfer through convection for skirt to air or insulation to air. Furthermore, along with the temperature loading, we also have considered the internal pressure, maximum operating weight of vesseland wind/seismic loading. The acceptance criterion is as per ASME sec VIII, Div 2, Part 5 “Design by Analysis requirement”: The evaluation is done as per Part 5.2.2.2 and Clause 5.2.2: Elastic Stress analysis method of ASME Sec. VIII Div.2.