Overview
Stress Engineering Services Canada (SESC) recently completed a comprehensive thermal fatigue assessment of a vessel used in natural gas dehydration. This study leveraged advanced simulation techniques, Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA), to predict fatigue life under cyclic thermal loading. The results offer valuable insights for operators seeking to extend equipment life, reduce unplanned downtime, and even possibly increase productivity of the process.

Challenge
These vessels operate under extreme thermal and pressure conditions. During the regeneration phase, the vessel undergoes repeated heating and cooling cycles, which induce thermal stresses at critical locations such as welds, joints, and material interfaces. Over time, these stresses can lead to microcrack formation and eventual failure - posing risks to safety, reliability, and operational efficiency.

Approach

• CFD Modeling: A transient thermal model was built in ANSYS Fluent to simulate heat transfer during the regeneration phase. The model included porous zones to represent the vessel bed and used shell conduction to simplify complex geometries like refractory linings and weather shields.
• FEA Modeling: Using ABAQUS, a linear-elastic structural model was created to evaluate stress responses. Temperature data from the CFD model was mapped to the FEA mesh, and boundary conditions—including nozzle loads, internal pressure, and catalyst bed weight—were applied dynamically over time.
• Fatigue Assessment: Stress cycles were analyzed at 25 locations using ASME Section VIII Div. 2 guidelines. The three most critical areas identified were the inlet nozzle, catalyst bed support beam, and outlet refractory connection.

Results
The analysis revealed that the vessels had acceptable remaining life for the proposed operating conditions, to the point where more aggressive optional operating conditions could be explored to increase the process yield.  Additionally, the study highlighted the Bourdon effect - stress amplification due to pipe bends - as a key contributor to localized stress concentrations.

Impact
This predictive modeling approach enables operators to:

• Extend equipment life by identifying fatigue hotspots before failure occurs.
• Optimize maintenance schedules based on data-driven insights.
• Improve safety and reliability in high-temperature, high-pressure environments.
• Facilitate process improvements to boost yield enables evaluation of operational changes that enhance regeneration efficiency and product recovery. 

SESC’s integrated CFD-FEA methodology provides a powerful tool for assessing thermal fatigue in pressure vessels. By simulating real-world operating conditions, this approach supports proactive asset management and enhances operational resilience in the energy sector.  Please reach out to [email protected] or [email protected] for more information or to book a Lunch & Learn with your team.

Corporate summary

Stress Engineering Services Canada delivers expert engineering problem solving services focused on providing clients the right answers on time and on budget. Located in Calgary, Alberta, our services are primarily centered around the testing, inspection, assessment and life extension of operating equipment in plants, pipelines, power stations, upstream facilities, and more. For more information, call 403.256.2527 or visit our LinkedIn page.