Assessment of Vibration-Induced Stress in Small-Bore Connections Through Finite Element Frequency Response Functions and Experimental Vibration Data

Abstract Vibration-induced fatigue remains a persistent problem in small-diameter piping systems used in gas pipelines, particularly around drain valves and pressure taps. Although addressed by international standards and procedures, the vibration criteria tend to be broad and overly conservative, designed to accommodate a wide range of geometries and configurations. Additionally, the theoretical framework supporting these methodologies and the limits of their applicability are often omitted. This paper proposes the stress assessment through the implementation of an expert-level procedure for gas piping systems using typical compressors, such as reciprocating, centrifugal, or screw types. The structural analysis is conducted using the Finite Element Method, with frequency response functions for stress and displacement acquired through time-harmonic analysis under steady-state conditions. By correlating vibration levels measured in the field with the structural model, more representative stress spectra are calculated in the critical regions of the weld toe, assuming linear behavior. The resulting stress-induced damage can thus be calculated using fatigue life estimation methods applied in both the time and frequency domains. An experimental validation is conducted using a prototype piping system excited by a shaker driven by a white noise signal. The findings demonstrate that the proposed approach enhances the precision in assessing the stress from measured velocities, providing a balance between operational safety and reduced uncertainty.