Fatigue and Vibration Assessment
Fatigue and vibration assessment is an important component of facility integrity management because repeated cyclic loading can initiate and propagate cracks even when individual stress levels remain below the material yield strength. In oil and gas facilities, small-bore connections associated with pumps, compressors, control valves, instrumentation, drains, and vents can be particularly susceptible to vibration-induced fatigue due to local flexibility, attached mass, pressure pulsations, flow-induced excitation, and mechanical vibration transmitted from connected equipment.
- Assessment of small-bore connections, instrument take-offs, drains, vents, and branch connections susceptible to vibration-induced fatigue.
- Evaluation of vibration generated by pumps, compressors, reciprocating equipment, pressure pulsations, turbulence, flow disturbances, and transient operating conditions.
- Identification of potential resonance conditions where excitation frequencies approach the natural frequencies of piping or small-bore connections.
- Assessment of cyclic stress range, stress concentration, connection geometry, unsupported length, attached mass, and support stiffness.
- Evaluation of existing or suspected fatigue cracking to determine its significance, likely driving mechanism, and suitability for continued service.
- Fatigue assessments may be performed in accordance with applicable requirements of ASME B31.3, API 579-1/ASME FFS-1, ASME Section VIII Division 2, and recognized vibration guidance such as the Energy Institute Guidelines for the Avoidance of Vibration Induced Fatigue Failure in Process Pipework.
- Advanced assessments may incorporate finite element analysis, modal analysis, harmonic response, measured vibration data, and fatigue life calculations where screening methods are insufficient.
- Engineering assessment can support decisions related to continued operation, monitoring, support modification, bracing, connection redesign, repair, or replacement.
