Methodological Framework for Assessing Plastic Collapse Load in Full Encirclement Split Tee

Abstract Split tee fittings are recognized as the most effective solution for executing hot taps in pipeline systems. They are designed to remain securely in place while minimizing integrity risks and operational impacts. Full encirclement tee fittings, utilized for hot tapping and plugging (HT&P), are completely wrapped around, and welded to the pipeline. In accordance with the ASME Boiler & Pressure Vessel Code (BPVC) Section VIII, Division 2, Part 5, one of the design-by-analysis requirements is the protection against plastic collapse. Assessing the plastic collapse load of a split tee fitting requires consideration of the fitting, the welds, and the pipeline as a system, introducing significant complexity to the evaluation process. This paper presents a comprehensive and systematic framework for determining the plastic collapse load of split tee fittings in compliance with ASME BPVC Section VIII, Division 2, Part 5. The study begins with a thorough examination of the effects of various loads and boundary conditions using Finite Element Analysis (FEA). A detailed analysis of models incorporating pipelines with varying wall thicknesses is then conducted. Specifically, a method is proposed to determine the appropriate pipe wall thickness for the plastic collapse analysis of fitting assemblies . It provides critical insights for determining the plastic collapse load of split tee fittings. Finally, the accuracy and reliability of the proposed methodology are validated by comparing the calculated plastic collapse load of a 12 -in fitting assembly with empirical data obtained from a physical burst test. This comparison reinforces the reliability of the methodology presented and its applicability in real-world scenarios.