With a stress simulation in Finite Element Method software, a thermal stress can be calculated. In this example, thermal stress simulations were done on Exxon’s pipes. Raw materials derived from oil are processed at high constant temperatures during the production of polymers. A heat exchanger takes care of cooling during the production of polymers. About one or two times a week this heat exchanger is flushed with cleaning fluid, to keep it in optimal condition. During the flushing large temperature fluctuations occur in a short time, which causes thermal stress in the complex geometric construction.
Localise thermal stress
The project goal was to localise the places with highest thermal stress in a heat exchanger that undergoes this temperature variation during the flushing a few times a week.
At the site of the petrochemical plant the status was assessed and the blueprints were used to map the complex fluid flow. Due to the complex geometric construction of the heat exchanger the setup in the FEM model had to be kept straightforward. Essential points and boundary conditions that cause the stress were added to the model. With this approach the varying temperature of the hot flushing liquid and its influence on the stress could be assessed over time.
The result of this FEM simulation was an 80% decrease of peak stress in the material, which improved its life span. The thermal cycle was simulated over time and this way improvements of design were based on the acquired in-depth understanding.
- Stress reduction during the flushing cycle is 80%.
- Efficiency of Heat Exchanger increased by 30%.
- Stress corrosion is now avoided.