Finite Element Analysis of Stress in Unequal Extrusion Tee Pipes

Literature Overview

This paper, published in the Journal of Petrochemical Universities (2010, Vol. 23, Issue 3, pp. 86–89) by Su Hede et al. from Gansu Lanke Petrochemical High-Tech Equipment Co., Ltd. and Lanzhou University of Technology, presents a finite element analysis of stress distribution in large unequal extrusion tee pipes under internal pressure. The research was supported by the Gansu Provincial Natural Science Foundation (Grant 0803RJZA011). The study uses ANSYS software to analyze the stress state of extrusion tees and investigates the influence of shoulder transition radius on tee strength.

Core Technical Content

The research employed ANSYS finite element software to perform stress analysis on large unequal extrusion tee pipes subjected to internal pressure. The key findings include:

1. High stress concentration at the main-branch pipe intersection: The intersection zone exhibits significantly elevated stress levels compared to other regions of the tee.
2. Quadratic relationship between maximum stress and inner transition radius: When the outer transition radius is fixed, the maximum stress varies approximately as a quadratic function of the inner transition radius.
3. Empirical correlation formula: Based on the finite element results and relevant literature, an empirical correlation formula for calculating the maximum stress in extrusion tees was proposed.

The stress analysis revealed that the geometric transition at the main-branch intersection is the critical region for strength assessment. The shoulder transition radius (both inner and outer) plays a crucial role in determining the stress concentration factor, and optimizing these radii can significantly improve the structural integrity of the tee.

Key Technical Parameters

Engineering Practice Implications

Extrusion tees are widely used in petrochemical and pressure vessel applications where seamless, high-integrity fittings are required. The stress concentration at the main-branch intersection is a well-known concern in tee design, and this study provides quantitative data for engineers to evaluate the structural adequacy of extrusion tees. The finding that the maximum stress has a quadratic relationship with the inner transition radius (when the outer radius is fixed) is particularly useful for design optimization. It suggests that increasing the inner radius beyond a certain point yields diminishing returns in stress reduction, which has direct implications for material usage and manufacturing cost.

The empirical correlation formula proposed in the paper offers a practical tool for engineers to quickly estimate the maximum stress in extrusion tees without performing full finite element analysis for each design iteration. This is especially valuable during the preliminary design phase when multiple geometric configurations need to be evaluated rapidly. The study also highlights the importance of transition radius design in extrusion tee manufacturing, as the extrusion process parameters directly influence the achievable transition radii.

Study Insights and Reflections

This paper provides a valuable quantitative foundation for the stress assessment of extrusion tees, complementing the analytical approaches traditionally used in pressure vessel design codes. The finite element method allows for more accurate stress distribution mapping than simplified analytical models, particularly in the complex geometry of the main-branch intersection. The quadratic relationship between maximum stress and inner transition radius is a useful design guideline that can be incorporated into engineering practice for tee design optimization. However, it is important to note that finite element results are sensitive to mesh density, material model accuracy, and boundary condition assumptions. The validation against theoretical calculations strengthens the credibility of the results. For manufacturing engineers, the findings emphasize the importance of controlling transition radii during the extrusion process, as even small variations in radius can have significant effects on stress concentration. This work serves as a useful reference for the design and quality assessment of extrusion tee fittings in petrochemical applications.