FEA Analysis of Waterbox Design Upgrades

Four waterboxes were for use in an alumina fluid cooler. The purpose of the analysis was to determine the structural integrity of the waterboxes for a MAWP of 80 psi, and if necessary, to redesign and/or stiffen them accordingly. ANSYS Finite element analysis software was used to simulate the structural responses of the waterbox when subjected to internal pressure.

Since all four waterboxes have the same geometry, only one waterbox was modeled for analysis. A detailed three-dimensional model of the entire waterbox design was modeled, including inlet/outlet openings, cover plate, tubesheet, and tubes. The waterbox structure was modeled with 3-D solid elements, while the tubes were simulated with beam elements. Equivalent material properties were used for the perforated areas of the tubesheets. These properties were calculated based on the tube and tubesheet geometries and ligament efficiency of the perforation.

The allowable stresses are based on the ASME Boiler and Pressure Vessel Code Section VIII Div. 2 criteria. The Primary Membrane plus Bending stresses are limited to 1.5 times the allowable membrane stress. Primary plus secondary stresses are limited to 2Sy to assure shakedown. For stresses in the perforated areas of the tubesheet stresses are divided by the tube sheet ligament efficiency. In the ligament efficiency calculation, no credit was taken for the tube wall thickness. 

Various deformation and stress results were determined on the waterbox when subjected to an increase in internal pressure to 80 psi. The analysis determined that a pressure increase would not cause failure of the waterbox. 

O’Donnell Consulting Engineers Performs (Thermal, Structural, Vibration & Fatigue) FEA Analysis to ASME & other Codes for Clients in Various Industries.