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SPX is a multi-national company that is a manufacturing leader, providing its customers with highly specialised and innovative, engineered solutions to solve critical business problems.
The company entered the filtration market in the 1950s and now specialises in process design and engineered filtration solutions. SPX manufacture equipment for water and wastewater applications including chemical storage, flocculation, reservoir supply, drinking water, cooling water, irrigation, metal processing and many more.
SPX Flow technology was required to produce a design for a sea water filter for Hyundai, which would serve to remove foreign matter from the feed pump inlet. The filter was to be used on a vessel in an offshore application. The filter was designed in accordance with ASME guidelines. SPX required CADFEM UK CAE Ltd. to carry out a Finite Element Analysis (FEA) to establish if the designed filter flange would be able to withstand an increased design pressure.
This case study describes the analysis of the filter flange using the ANSYS suite of simulation software.
A 3-D model of the flange filter was created within ANSYS using drawings supplied by SPX. Due to the symmetry of the simplified geometry and the nature of the loading (internal pressure only), a 3D, 4.5 degree sector of the model of the flange filter was created within ANSYS.
The model created consisted of the top cover (without penetrations), the girth flange (to which the head was welded) and associated welds, the studs and nuts and a portion of the main cylindrical shell of the vessel body (down to the junction with the main nozzle perforations).
The model incorporated half a stud and half the pitch to the adjacent stud. The model was restrained vertically at the base of the cylindrical “skirt”. The 3-D sector of the model with the area of interest highlighted is shown in the graphic to the top right.
The FE mesh was made up of higher-order 3-D solid elements and 3-D contact elements (see graphic, bottom left).
A large-deflection, nonlinear, static structural analysis was carried out in ANSYS. The aim of the analysis was to check the size, strength and number of bolts to see if they were adequate to withstand the new pressure.
The analysis was carried out for two values of internal pressure 90psi and 145ps.
The maximum stresses in the main structure of the model were all found to be below the specified yield of the material.
A stress intensity linearization was also carried out on a path in the main structure.
Within ANSYS, an option is available to allow a separation of stresses through a section, into membrane and bending stresses. The stress linearization option requires a path to be defined by two nodes and the results are then mapped onto that path. The stress linearization tool takes the nodal data for the complex stress pattern found along the path and breaks it down into components: Membrane, Bending and Membrane + Bending. The membrane and membrane + bending stresses have been compared with the code allowed limits.
The maximum membrane bending stress value from the analysis was found to satisfy the criteria of 1.5 x design strength. The graphics below show the defined path and a graphical representation of the linearization results.
SPX Flow Technology performed ASME code calculations for the bolts considering the internal pressure of 145psi. The required cross sectional area of the bolts was found to be less than the actual cross sectional area of the bolts, therefore the current bolt size was considered to be satisfactory under the increased internal pressure.
The thickness of the head was also found to be sufficient for the uprated pressure of 145psi.
Through the use of ANSYS and CADFEM UK CAE Ltd.’s consulting services, SPX were able to quickly and confidently predict if the flange filter could withstand an increase in pressure. The finite element analysis of the flange filter provided an invaluable way of assessing design performance prior to installation.
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