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Thermal Analysis

In order to evaluate stresses induced in a valve body by differential thermal expansions and thermal gradients, a multi-step analysis is performed at Remosa.

As a general rule, Codes indicate that a mechanical model cannot take into account the presence of refractory or anti-abrasion linings. Nevertheless, these materials are fundamental to evaluate the distribution of temperature across a section of the valve. Remosa's approach is based on the use of several different models, each one generated for a specific analysis, or to focus the attention on a detail for the valve (e.g.: welds, nozzles, flanges).

The mechanical model, as previously described, is usually based on 3-D plate/shell elements in order to obtain stresses evaluated as bending and membrane stresses using Tresca formulation.

The thermal model introduces an axisymmetric formulation, even though it's also possible to create a full 3D thermal model of the valve. Using these models, it is possible to take into account the presence of several materials as those used to build the anti-abrasion lining, the refractory lining, and all the different materials used to build the valve structure itself. Applying a correct set of thermal boundary conditions and using the proper set of thermal properties, it is possible to obtain a temperature distribution across the model.

The obtained thermal results are then used as load for the mechanical analyses: stress/strain assessment, but also buckling, strain growth, fatigue, displacement. In this stage of the analysis all the non-structural elements (refractory, anti-abrasion lining, cardboard) are taken out from the FEA model. Only structural parts are considered.

The stress analysis can be linear/elastic or nonlinear/plastic, depending on the addressed failure mode, and on the applied Code Rule. The calculation of displacement and stresses is performed using the FEA numerical solver. The results are then handled with proprietary postprocessors, developed by Remosa Technical Department.

In a thermal analysis the evaluations of boundary thermal conditions and heat exchange coefficients by radiation, natural and forced convection are critical factors for the reliability of the results. In order to refine the numerical formulation used to evaluate these critical factors, the temperature recording done by REMOSA during refractory drying or hot-stroking test is used to compare theoretical results obtained by thermal analysis with the results obtained on the field.

back to part 1 - Design back to part 2 - Finite Elements Analysis

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