Stress Analysis of Vessel Live Steam Tubular Heater

FEA Model of Lower Portion of Vessel
FEA Model of Cross Section of Vessel
FEA Model of Lower Portion of Vessel

Stress analysis to determine the structural integrity of the pressure boundary and tubesheets in a vessel live steam tubular heater. The purpose of the evaluation was to obtain pressure stress and to establish a minimum shell wall and tubesheet thickneses based on the results of the stress analysis. The finite element method was used to simulate the structural responses of the vessel when subjected to operating pressures.

Finite Element Analysis

ANSYS finite element analysis software was used to perform all analyses. A detailed three-dimensional model of the entire vessel, including tubesheets, liquor box and tubes was constructed. Tubesheets, shell and connecting flanges were modeled with 3-D solid elements. Heads and dividing plates were modeled with shell elements. Equivalent material properties were used for the perforated areas of the tubesheets. Tubes were simulated with beam elements having the tube’s geometrical and material properties. Contact elements were used at gasket locations where the divider plates in the top head were connected to the top tubesheet. Pressure loading applied to the vessel is tabulated below.

For stresses in the perforated areas of the tubesheet stresses are multiplied by the tubesheet ligament efficiency. In the ligament efficiency calculation, credit is taken for half of the tube wall thickness.

To fully evaluate the vessel, the following three analyses were performed:

    1. Vessel subjected to tube side pressure of 150 and shell side pressure of 125 psi
    2. Vessel subjected to tube side pressure of 150 psi only
    3. Vessel subjected to shell side pressure of 125 psi only
Design Data
Shell Side
Tube Side
Design Pressure
125 psi
150 psi
Design Temperature
450 F
450 F

The Allowable Stresses were based on ASME Boiler and Pressure Vessel Code Safety Margins. Stresses were were found to be below the allowable values at all locations.


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