Dynaflow Research Group conducted a comprehensive stress analysis on three critical components of a high-pressure heat exchanger: the stationary tubesheet, cone-shaped channel, and shell with a cone at 1 meter from the tubesheet. This analysis was crucial for ensuring the integrity and safety of the heat exchanger under extreme operating conditions.
Design Specifications and Challenges
The heat exchanger was designed to withstand a remarkably high tube-side pressure of 690 barg, with a shell-side pressure of 10 barg. Two design cases were considered:
- A standard case with a 20°C temperature difference between tube and shell sides.
- An upset case with a 100°C temperature difference across the tubesheet.
The substantial pressure differential of 680 barg across the tubesheet necessitated a thickness exceeding 300 mm, as determined during the pre-analysis phase. The channel side was similarly designed with a high thickness to match the tubesheet.
Analysis Methodology
The stress analysis adhered to ASME B&PV Code Section VIII Division 2 standards. A finite element model was developed, incorporating:
- Temperature and pressure effects
- Individual tube holes in the tubesheet model
- Spring elements to represent tube stiffness
A parallel analysis using ASME Section VIII, Division 1, paragraph UHX was conducted to gain additional insights into the tubesheet’s behavior.
Results and Interpretations
The analysis revealed complex stress patterns in the high-thickness tubesheet, making standard interpretation of the ASME B&PV code challenging. Key findings included:
- Detailed distribution of bending and shear stresses through the thick tubesheet
- Non-trivial stress classification due to the extreme thickness
- Insights into the effective stiffness and Poisson’s ratio of the perforated tubesheet
Weld Analysis
A separate finite element model was employed to analyze the tube-to-tubesheet welds. Boundary conditions for this model were derived from the main finite element analysis results, focusing on tensile loads.
Conclusion
This comprehensive stress analysis provided crucial insights into the behavior of a high-pressure heat exchanger under extreme conditions. The study highlighted the importance of advanced modeling techniques and careful interpretation of results when dealing with non-standard designs.
