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FEM Analysis of a flange with connections

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Case study description

CASE STUDY DESCRIPTION

• The client requires a FEM analysis of a blind flange with nozzle connections. It must follow the ASME Section VIII Div.1 (ASME II-D) .

• Since the loads are going to be applied in one of the nozzles, the rest of the equipment is not modeled (the fail will be produced previously in the connection between the nozzle and the blind flange than in other zones).

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FEM Model

Complete mesh Nozzles mesh

• The blind flange material is SA-105 and the connections are made of SA-333 Gr.6. Both materials have the same Young modulus and Poisson coefficient, but the admissible limit of the ASME code is different.

• The elements of the model are quadratic hexahedron. A mesh sensibility study was performed to validate the mesh.

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Loads & Boundary Conditions

The following boundary conditions and loads were applied to the model:

• BC1:Embedment at the body faces that will be in contact with the flange that connects with the equipment.

• Internal pressure in the internal surfaces of the blind flange and the nozzles.

• Admissible loads defined by the client in the loaded nozzle (a rigid element is used for the transmission).

Embedment constraint

Internal pressure zones

Rigid element for the load transmission

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Results

• The total displacement results show a maximum displacement of 5.9e-5m in the top part of the loaded nozzle. The blind flange and the other nozzles are mainly displaced by the internal pressure effect.

• The Von Mises stresses results show a maximum stress of 97.6MPa in the base of the loaded nozzle. The blind flange had a maximum stress of 60.3MPa in the connection with the loaded nozzle.

Total displacements Von Mises Stresses

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Conclusions

The maximum Von Mises stresses calculated in the different parts are shown in the summary table below. The admissible stresses following ASME Section VIII Div.1 (ASME II-D) are also included, calculating the security factor.

• All the components have a safety factor higher than 1 remaining in elastic behavior under the applied acceleration loads.

• The critical component with the lowest safety factor is the ”Nozzle V3” with a safety factor η=1.2

• The blind flange and its connections accomplish the ASME Section VIII Div.1 (ASME II-D) under the defined loads.

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Benchmark. CivilFEM vs. ANSYS

• A comparison of CivilFEM vs. ANSYS Von Mises stresses results is shown below.

Von Mises stress. Load Case: vertical acceleration. CivilFEM = 1.54E+7m ANSYS = 1.60E+7m Difference = 3.75%

Von Mises stresses obtained with CivilFEM powered by Marc Von Mises stresses obtained with ANSYS WB 17.1

The difference is under a 0.1%, a very good validation for the model performed.