A finite element analysis (FEA) was requested for a fiberglass coupler used in centrifugal cast fiberglass pipes. The aim was to evaluate the structural integrity of the coupler under various conditions.
Analysis
The analysis covered couplers for DN600, DN1200, DN2400, and DN3600 pipes. These filament wound couplers (FWCs) feature a long cylindrical sleeve with an EPDM gasket containing four individual rings to provide the pressure seal. The couplers were designed to withstand maximum long-term pressures of 32, 16, or 10 Barg, respectively.
The FEA aimed to calculate the stresses and strains in the coupler and evaluate them against an allowable stress envelope based on the Tsai-Wu failure criterion. Two primary cases were considered:
- Nominal Case: The glass-reinforced plastic (GRP) pipes are inserted into the coupler with coinciding centerlines, and the system is then pressurized.
- Mitered Case: One side of the coupling has a pipe mitered at an angle no larger than 3°, inserted into the coupler with a deflected centerline.
The FE model was constructed using axisymmetric elements, excluding ovalization effects. Additional calculations ensured all potential ovalization impacts were considered.
Results
The FEA results indicated that stresses in the coupler were mainly due to axial bending. This bending stress resulted from internal pressure acting on part of the internal surface of the coupler. The influence of centerline angle was minor for the range of miter angles examined.
For the DN2400 coupler, the initial design was too thin depending on the width of the pressure seal. An increase in thickness was implemented, and a sensitivity study was conducted to investigate the impact of the pressure seal width on the coupler. This study guided the selection of additional laminate thickness required to meet the Tsai-Wu failure criterion.
The analysis showed that stresses from ovalization were negligibly small and most significant during installation. The results also demonstrated that pressure-induced stresses were nearly independent of the range of miter angles and centerline deflection angles considered.
By addressing these factors, the study ensured that the coupler design met the necessary safety and performance standards.
