ASME Section VIII Division 1 (FEA) Analysis on Feedwater Heater

ASME Section VIII Division 1 Finite Element Analysis (FEA) performed on a low pressure feedwater heater using ANSYS software. The vessel is essentially symmetric about the vertical centerline plane; therefore, only one half of the unit was modeled.

Since the vessel was 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 feedwater and its components are comprised of carbon, stainless and Cr-Mo steels.

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. Analysis was then performed 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
• The evaluation allowable values were conservatively taken at 450°F

Pressure vessels have specifically defined regions where simple criteria are far too conservative. Such regions include highly localized geometric discontinuities, stress concentrators, and thermal stresses that “shakedown” over a few cycles to an acceptable and safe level. 

The cover, channel, channel flange, gasket, tube sheet, and tube joints of the Low Pressure Feedwater Heater were evaluated for stresses and displacements. Each of these items was found to satisfy the design requirements.

Shown above is a closeup section of the finite element model of the feedwater heater (tube not shown).

O’Donnell Consulting Performs Engineering Analysis to ASME Section VIII on Equipment for Clients in Industries including Manufacturing, Petrochemical and Energy