Mechanical vibrations in industrial piping systems can generate severe dynamic conditions capable of causing fatigue failures in structural components, particularly in small-bore connections (SBCs). To address this issue, an integrated approach is proposed, combining experimental vibration measurements and harmonic numerical modeling. The method directly correlates the measured field velocities with the acting stresses at the weld toe through Frequency Response Functions (FRFs), allowing the estimation of stress spectra and fatigue life under real operating conditions. It also enables the definition of allowable RMS velocity limits adjusted to the geometry and desired reliability level, supporting damage-based inspections and predictive maintenance strategies. The results demonstrate that the proposed procedure effectively complements traditional normative vibration criteria, providing a more accurate and representative framework for structural integrity management in piping systems subjected to dynamic excitation.