ASME B&PV Code Section VIII Division 2 (Part 5) analysis was performed using ANSYS finite element analysis on a feedwater heater. The vessel is essentially symmetric about the vertical centerline plane; therefore, only one half of the unit was modeled. Since the vessel is modeled with three degree-of-freedom solid elements only, X-direction translations are required to be constrained to achieve symmetry on the vertical plane.

The following assumptions were used:
• Linear elastic material behavior with small displacements
• The geometry, loading and boundary conditions consistently have one plane of symmetry down the axis of the vessel. Then analyses were completed on a half model of the heater with symmetry boundary conditions applied on the cut boundary. Nozzle N5 was treated as having half symmetry.
• The tubesheet was modeled as solid material, with appropriate adjustments in the values of Elastic Modulus and Poisson ratio to account for the effects of the holes at a representative 400°F.
• No credit was taken to increase the ligament efficiency for the effect of tubes
• The evaluation allowable values were conservatively taken at 450°F

Shown above is a closeup section of the finite element model of the feedwater heater.

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