Thermal Stress Simulations
Physixfactor has managed to avoid expensive maintenance cycles by investigating the thermal stress development in tubing systems for the petrochemical industry. During operation, sometimes the system must be cleaned and high temperature fluid are used to flush the system. Inducing peak stress which cause over time weak parts with a danger of leakage. Beacuse this should be avoided at all time the construction on the right was simulated for time dependent stresses during the heat cycle. We could propose a new way of mounting the pipes in order to avoid excessive stresses,
Thermal Stress Calculation
During a cleaning cycle in the petrochemical industry the heat exchangers might suffer from extreme stress calculations due to the high thermal gradients. Finite Element Method (FEM) software can reveal the time dependent stress cycle in this system. This example is about a thermal stress calculation in Exxon Mobile pipes. During the production of polymers, raw materials from petroleum are processed at high, constant temperatures. A heat exchanger provides cooling during the production of a polymer. The heat exchanger is flushed with a cleaning fluid approximately once or twice a week to keep it functioning optimally. During flushing, high stresses occur in the complex geometric structure in a short time due to the large temperature fluctuations. A thermal stress calculation was deemed necessary by Exxon Mobile. In the case the critical spot for excessive stress and wear could be indentified.
Thermal expansion, time dependent stress
The situation was recorded at the location of the petrochemical plant and the complex fluid flow was mapped using working drawings. Due to the complex geometric structure of the heat exchanger, the structure in the FEM model had to remain simple. Essential points and boundary conditions that cause the tensions were implemented into the model. With this approach the variable temperature profile of a hot flushing fluid and the voltage calculation could be set up. The video to right shows the mechanical effect of the temperature pulse in the system. Due to the asymmetric thermal load during the flushing cycle the tubing systems suffers from bending stress.
Thermal Stresses in a Heat Exchanger
Thermal stress cycles can lead to early fialure in heavy duty product as shown in this figure to the right. It is a heat exchanger for the chemical industry and apart from the fact that it should be resist to corrosion and should also withstand a high number of temperature cycles during its operational lifetime. With COMSOL we were able to trace the weak parts in the construction once the loads where investigated of the HEX in the field. The multiphysics approach of COMSOL is highly suitable for these type of thermal FEM simulations. Special attention was paid to the meshing of the product for a fast and robust convergence of the solver.