Vibration Fatigue is a specific type of mechanical fatigue that is caused by the vibration of equipment during operation. Like other forms of fatigue, vibrations can initiate a crack which may lead to propogation of the crack and eventual failure of the equipment. The most commonly affected areas of vibration fatigue include areas around pumps, compressors, and rotating equipment.
The amount of damage is related to the magnitude and frequency of vibration and results in the form of brittle cracking. Cracking caused by vibration fatigue can be detected using surface nondestructive testing (NDT) techniques. However, inspection is not the most cost-effective or reliable method for locating and monitoring cracks caused by vibration fatigue.
Not all materials are subject to vibration-induced fatigue failures. Some materials, such as carbon and low alloy steels, have an endurance limit (sometimes called the fatigue limit). The endurance limit is the stress amplitude below which the material will never fail by fatigue, regardless of the number of fatigue cycles. For carbon and low alloy steels, the endurance limit is usually 40 to 50% of the tensile strength of the material. Materials such as the austenitic stainless steels (i.e. the 300-series) do not have endurance limits. Regardless of the stress amplitude, these materials will eventually fail if they are in a vibrating service for a sufficient length of time.
Mitigation Measures
The best defense against vibration-induced fatigue is in initial design, the use of supports, and vibration dampening equipment. Some important notes on mitigation:
- Material upgrades are usually not a solution.
- Small bore piping near pumps or compressors has higher risk to vibration-induced fatigue. Installation of gussets or stiffeners can mitigate small bore piping fatigue problems.
- Installation of restraints in the wrong places can aggravate the problem instead of mitigating it. Therefore, post-construction installation of restraint systems should be done by personnel qualified to judge where such restraint will be beneficial.
- Vortex shedding can be minimized at the outlet of control valves and safety valves through proper side branch sizing and flow stabilization techniques. Note that purpose-designed pressure reducing valves are available that are essentially immune to vibration-induced fatigue failure.
Related Topics
- Brittle Fracture
- Carburization
- Cavitation
- CO2 Corrosion
- Cooling Water Corrosion
- Corrosion Fatigue
- Corrosion Under Insulation (CUI)
- Cracking
- Decarburization
- Embrittlement
- Erosion Corrosion
- Fatigue (Material)
- Flue Gas Dew Point Corrosion
- Graphitization
- Green Rot
- High Temperature Hydrogen Attack (HTHA)
- High-Temperature Creep
- Hydrochloric (HCl) Acid Corrosion
- Hydrofluoric (HF) Acid Corrosion
- Hydrogen Embrittlement
- Hydrogen Stress Cracking
- Liquid Metal Embrittlement (LME)
- Metal Dusting
- Microbiologically Influenced Corrosion (MIC)
- Naphthenic Acid Corrosion (NAC)
- Phosphoric Acid Corrosion
- Pitting Corrosion
- Spheroidization (Softening)
- Stress Assisted Corrosion
- Sulfidation Corrosion
- Sulfuric Acid Corrosion
- Thermal Fatigue
- Wet H2S Damage
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