A transient model calculation for the welding distortion of tube plates for high pressure heat exchangers was created with Ansys Workbench and the welding simulation tool VWS from CADFEM on behalf of SBN.
A layer of corrosion-resistant material is welded onto the forged blanks of a tube plate made of pressure vessel steel. The aim was to determine the welding distortion in advance, depending on plate dimensions and material combination.
To be able to predict the welding distortion, a parametric model was created in Ansys Workbench. With the welding simulation tool VWS from CADFEM the mechanical dilatation behaviour including plasticity was determined.
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Schoeller-Bleckmann Nitec, a leading manufacturer of high-pressure equipment for the petrochemical industry, supplies heat exchangers amongst other similar products. Their inner surfaces are exposed to corrosive substances like ammonia and urea. Therefore, a layer of a corrosion-resistant material is welded onto the forging blank of the tube plate, which is made of pressure vessel steel. This welding buildup over large areas inevitably results in welding distortion. For this reason, the surface must be turned flat after welding. If the welding distortion is greater than the welding thickness, this would remove the cladding completely. In order to obtain a flat workpiece despite welding distortion, a cone is prefabricated onto the forging blank (Fig. 1 above), which has to be designed according to the plate dimensions and material combination. This could not be determined in advance until now.
By calculating the welding distortion for the respective dimensions and materials, the component can be manufactured correctly. The slope resulting from the FE calculation (Fig. 2) is directly used as a new design rule to determine the appropriate cone height according to the respective tube plate proportions. This has eliminated the risk of excessive welding distortion or incorrect cone height, so that high costs for reworking and delays in delivery are now a thing of the past. In addition, the engineers at Schoeller-Bleckmann Nitec have further expanded their knowledge with regard to large-area build-up welding. This enables them to define or adjust the decisive parameters for process behavior in a more targeted manner.
To be able to predict the welding distortion, a parametric model was created in Ansys Workbench. On this basis the temperature distribution at any time (transient) can be calculated and with the welding simulation tool VWS from CADFEM the mechanical dilatation behavior (thermal expansion) including plasticity can be determined. Consequently, the distortion can be predicted for a wide range of plate dimensions, material combinations and process parameters.