Recirculating pipe systems are the lifelines of many industrial operations, facilitating the transfer of fluids essential for various processes. These recirculating pipes find applications in Chemical processing industry, Power generation, Manufacturing, Food and Beverage industry, Water treatment plants, etc. However, ensuring the optimal performance and longevity of these systems can be challenging due to factors like corrosion, stress concentrations and inefficient flow distribution.
In this blog, we will explore how Finite Element Analysis was utilized to optimize Recirculating pipe systems within industrial settings, focusing on a case study involving the study of stress buildup on the lug supports of piping systems.
Background:
In a piping system comprising of Recirculating pipes and a heat exchanger with an evaporator, the transfer of loads to the lugs of the pipe supports is facilitated by various operational processes. The evaluation of stress accumulation on these lug supports concerning temperature fluctuations and internal/external pressure variations is conducted by implementing the Finite Element Method (FEM).
This allowed for the meticulous examination of how temperature changes and internal/external pressures affect the structural integrity of the overall piping system. With FEM, valuable insights into potential vulnerabilities were gained and targeted design modifications were implemented to enhance the resilience and longevity of the Recirculating piping assembly in diverse operating conditions.
Methodology:
The assembly consists of a recirculating pipe situated between a heat exchanger and an evaporator as shown in Fig.1. While the heat exchanger and evaporator each have their own support, the lugs of the recirculating pipe also bear the load from both pieces of equipment. To thoroughly analyze the entire assembly, Finite Element Analysis (FEA) is employed since loads are being transferred to the support lugs.
The load cases for the entire assembly are determined following the guidelines of ASME Sec. VIII Div. 2:
Load Case 1 considers operating temperature, design internal pressure, and thrust caused by internal pressure which is shown in Fig.2.
Load Case 2 involves operating temperature, external pressure, and thrust due to internal pressure which is shown in Fig.3. Additionally, thrust forces from inter condenser balancing are included in the analysis.
To ensure structural stability under design pressure loads, it is imperative that the structure be stabilized. Stress Categorization Lines are plotted at areas of maximum stress obtained after FE analysis, following the guidelines outlined in ASME Sec. VIII Div. 2. These lines help categorize stress levels across the structure.
The results are analyzed using Ansys, a software tool widely utilized for engineering simulations. Stress Categorization Lines are carefully drawn to include all aspects of the structure’s shape and features.
Analysis Procedure:
The Finite Element study on the recirculating pipes assembly was done using Ansys, a popular software for advanced simulation. Ansys can simulate how structures respond to forces and heat, helping engineers understand their behavior. It’s useful for analyzing stress, deformation, and other factors affecting a system’s performance. With Ansys, engineers can model complex shapes and materials accurately, and visualize results to make better decisions.
A methodical procedure was undertaken that began with the establishment of contacts amongst various components. In alignment with relevant working conditions and their corresponding geometric types, conformal bodies were sorted into respective categories such as nozzle bodies, shell bodies, flanges, and connecting bolts.
A structured mesh formation was achieved by considering both the functions of parts and the adherence to standard quality criteria. This crucially generated mesh serves to capture geometry accurately via a process commonly known as discretization or meshing.
The concluding phase entailed executing simulations in Ansys Workbench which offered valuable insights into system performance and reliability metrics. Utmost precision maintained throughout these procedures effectively guaranteed optimal accuracy of results.
Boundary Conditions:
The vessel under scrutiny is subject to self-weight stemming from gravitational forces; here we factored in Earth’s standard gravity applied directionally downward. Load cases have been comprehensively defined according to ASME Sec VIII Div 2 provisions; these are categorised based on diverse design pressure types whilst internal pressure is enacted accordingly. Nozzles’ thrust forces adhere strictly to balance per ASME guidelines incorporating vessels’ pressure consideration while lug supports assume displacement loading roles.
Collective geometry possesses radial expansion allowances altogether representing all boundary conditions along with intimately connected local coordinate systems depicted in load case imagery representations.
Results and Conclusion:
The results obtained from the Finite Element Analysis (FEA) of the recirculating pipes assembly include stress distribution, deformation, and pressure-related analyses. The stress distribution was compared with ASME Section VIII, Division 2 standards, considering factors such as bending stress, membrane stress, and peak stress. The FEA validation showed good agreement with calculated values for hoop stress in the shell.
The analysis also considered the effects of design pressure loadings on the structure, ensuring stability and preventing failure.
The post-processing analysis conducted with Ansys demonstrated that the peak deformation in the piping assembly when subjected to internal pressure conditions reached 11.92 mm, accompanied by an utmost equivalent stress of 307.38 MPa. In terms of exterior pressure conditions, a noticeable distortion of 6mm was reported with a prime equivalent stress amounting to 277.9 MPa.
It is important to note that the stress values measured at lug regions for both interior and exterior pressure states were comfortably within permissible thresholds set forth by industry standards. For precision and reliability, all relevant comparisons regarding induced stress variables were performed adhering strictly to protocols laid out in ASME guidelines.
Result Validation:
The validation process involves comparing the FEA results with calculated values for stress due to pressure, specifically hoop stress in the shell away from discontinuity. This comparison is carried out using the equation specified in ASME Section VIII, Division 2, Part 4, Clause 4.3.10.2. Input parameters such as the outer diameter of the shell, inner diameter of the shell, internal pressure, and weld joint factor are included in this process.
After the validation equation is solved, the calculated stress value is compared with the stress obtained from the FEA analysis. If the FEA results closely match the calculated values, it is indicated that the FEA model accurately represents the behavior of the system under the specified conditions. This validation process helps ensure the reliability and accuracy of the FEA results, providing confidence in the structural analysis and design decisions made based on the simulation outcomes.
Future improvements and Design upgrades:
Based on the FEA results, Ideametrics’ engineers have brainstormed and suggested some design improvements for the recirculating pipes assembly. These improvements include:
- Stress Reduction: Make design changes like rounding sharp corners, adding extra support ribs, or adjusting shapes to lower stress points found during the FEA analysis. This can strengthen the assembly’s structure.
- Material Upgrade: Explore using stronger or more resistant materials against corrosion and wear. Choosing better materials can make the recirculating pipes assembly more durable and reliable in different conditions.
- Improved Temperature Control: Enhance insulation or cooling systems around the pipes to manage thermal stress and ensure stable operation in desired temperature ranges. Also, think about adding joints or flexible connections to handle temperature changes more effectively.