This study investigates the formability of seamless copper hollow T-joints with varied protrusion-to-base diameter ratios manufactured through tube hydroforming (THF) using finite element analysis. Three configurations were simulated in Abaqus/CAE: T1 (protrusion diameter smaller than tube blank diameter), T2 (protrusion diameter equal to tube blank diameter), and T3 (protrusion diameter larger than tube blank diameter). Formability was comparatively assessed through four critical metrics: operational fluid pressure range enabling effective material flow for protrusion formation, plastic strain components, wall thickness distribution, and achievable protrusion height. The findings establish scientific and practical foundations for optimizing THF processes to manufacture high-integrity monolithic pipe connectors.