Vibration Analysis

A reliable and revealing indicator of many different problems, vibration is one of the most useful measurements for machinery troubleshooting. Likewise, it is a key element of rotating equipment health monitoring for problem identification before costly or catastrophic failure occurs.

Leveraging its end-user, manufacturer, and researcher background with its expertise in rotordynamics and bearing technology helps the BRG teamsolve the most complex of machinery vibration problems. BRG’s vibrational analysis training also helps our clients to resolve such problems themselves.

BRG conducts several different types of analysis to determine a machine’s vibration performance:

  • Field Measurement & Diagnosis

  • Modal Analysis

  • Finite Element Analysis

  • Balancing

Vibration Analyses

Field Measurement & Diagnosis

Accurate diagnosis of radial, torsional and axial phenomena often requires on-site measurements using existing or specially installed instrumentation. High speed, simultaneous acquisition of vibration signals as well as process and other machine instrumentation may be necessary. Baseline measurements for future reference can be recorded for transient operating conditions such as startup and shutdown.

Full clearance orbit during violent rotor instability in a cracked gas compressor

Waterfall plot of an integral gear compressor experiencing intermittent vibrations due to liquid carryover from a failed demister pad

Subsynchronous vibrations in a machine experiencing shaft whip rotor instability

Modal Analysis

Such testing may be necessary to identify and correct resonance situations within casings, baseplates and piping as well as rotor lateral and torsional critical speeds. External excitation is applied for measurement of the specific natural frequencies and mode shapes. To avoid self-excited vibrations such as shaft whip, advanced stability verification tests measure a particular rotor mode’s log decrement under various machine operating conditions.

Impeller testing of an open impeller to resolve a blade resonance problem

FRF measurements of a machine’s bearing pedestal along with identified model for use in rotordynamics analysis

Ring testing results of a rotor assembly to determine stiffening effects of components with shrink fits

Finite Element Analysis

Modeling complements field measurements for accurate diagnosis and resolution of vibration problems. To mitigate risk, such analysis permits evaluating design modifications before field implementation. Measurement and test condition limitations often necessitate FEA when dealing with various machinery components, in particular, turbine blades and impellers.

Pedestal frame mode causing resonance vibration problem for its motor driver in an air separation plant

Second nodal diameter mode of an integral gear compressor impeller

Balancing

A high quality shop balance is necessary to achieve reliable vibration performance of critical machinery. To help ensure successful commissioning, witnessing of shop low speed and/or high speed balancing is recommended. If balance degradation occurs during operation, in situ or field balancing may be an option to minimize vibration at the speed(s) of concern. Single or multiple plane corrections are accomplished using influence coefficient or modal balancing methods.

Balance weight installation on the coupling of an offshore platform’s 20,000 rpm compressor train

Balance repeatability check results for a high speed disc pack coupling

Witnessing the high speed balance of a 22,000 hp (16 MW) steam turbine for a refinery FCC unit