Vibration Analysis and Shaft Alignment for Rotating Equipment
Vibration analysis and shaft alignment are two important maintenance practices for keeping rotating equipment reliable. Vibration analysis helps identify developing mechanical and electrical faults, while precision shaft alignment ensures coupled machines operate with their shafts correctly positioned.
Used together, these techniques help reduce unexpected failures, bearing and seal wear, excessive vibration and unnecessary production losses. They are particularly important for pumps, motors, compressors, turbines, fans and other critical rotating equipment.
Key takeaway: Vibration monitoring can identify developing faults and establish machine condition, while precision alignment addresses one of the common causes of excessive vibration. Combining both with proper baseline and post-maintenance measurements provides a more complete approach to rotating equipment reliability.
What Is Vibration Analysis?
Vibration analysis is a condition monitoring technique used to measure and interpret the vibration produced by rotating machinery. Sensors capture vibration data, which is then analysed by size, frequency and pattern to identify conditions such as unbalance, misalignment, looseness and bearing deterioration.
Every rotating machine has a normal vibration signature. Changes from that baseline can provide an early indication that a component is developing a fault. This allows maintenance teams to investigate and plan corrective work before the problem develops into an unplanned shutdown.
What Does Vibration Analysis Measure?
Machine vibration can be measured as displacement, velocity or acceleration. Each measurement provides useful information for different types of machinery and faults.
- Velocity: Commonly expressed in millimetres per second RMS and widely used for assessing overall machine vibration severity.
- Acceleration: Useful for identifying higher-frequency conditions, including developing bearing faults.
- Displacement: Often used for evaluating shaft motion, particularly on machines equipped with fluid-film bearings.
What Is Shaft Alignment?
Shaft alignment is the process of positioning two coupled machines so that their rotating shafts are correctly aligned relative to their intended operating centreline. A common example is aligning an electric motor with a centrifugal pump.
Incorrect alignment can increase loads on couplings, bearings and seals. It can also contribute to increased vibration, heat generation and premature component wear.
There are three common forms of shaft misalignment:
- Parallel or offset misalignment: The shaft centrelines remain parallel but are displaced from each other.
- Angular misalignment: The shaft centrelines meet at an angle rather than remaining parallel.
- Combined misalignment: Both offset and angular errors are present, which is common in practical installations.
Why Do Vibration Analysis and Shaft Alignment Go Together?
Misalignment is one of the conditions that can contribute to excessive vibration, making vibration analysis useful both before and after an alignment activity. Vibration measurements can help identify whether further investigation is required, while post-alignment measurements provide evidence of the machine’s operating condition after corrective work.
A combined approach can follow a simple maintenance cycle: identify the condition, investigate the root cause, correct the problem and establish a new baseline. This can help maintenance teams move from reactive repairs towards condition-based maintenance.
| Activity | Purpose | Typical Outcome |
|---|---|---|
| Vibration survey | Identify abnormal machine behaviour | Fault indicators and maintenance priorities |
| Alignment inspection | Check shaft position and installation condition | Identification of alignment-related issues |
| Precision alignment | Correct shaft position | Alignment within the applicable tolerance |
| Post-work vibration check | Verify machine condition after maintenance | Updated operating baseline |
What Equipment Needs Vibration Analysis and Alignment?
Most coupled rotating equipment can benefit from vibration monitoring and precision alignment. The priority is generally higher for machines where failure could affect production, safety, equipment availability or maintenance costs.
- Centrifugal and positive displacement pumps
- Electric motors and generators
- Fans, blowers and cooling tower drives
- Compressors and turbines
- Gearboxes and speed reducers
- Extruders, mixers and conveyors
- Other critical coupled rotating equipment
How Does Vibration Analysis Work?
Vibration analysis begins by measuring vibration at selected points on the machine, commonly around bearing housings. The collected data can then be reviewed in both the time and frequency domains.
Results are compared with machine baselines, applicable alarm limits and known vibration patterns. Repeating the measurements over time allows maintenance teams to identify trends instead of relying only on a single reading.
Sensors and Instruments
Accelerometers are commonly used for general vibration measurements. Proximity probes can measure shaft movement directly on certain large turbomachinery applications, while velocity sensors may be used on selected machines.
Portable data collectors are suitable for route-based monitoring programmes, while permanently installed systems can provide continuous monitoring for critical or difficult-to-access machinery.
Vibration Analysis Techniques
- Overall vibration trending: Helps identify changes in machine condition over time.
- Frequency spectrum analysis: Helps identify frequencies associated with specific machine components or faults.
- Time waveform analysis: Provides additional information about the nature of vibration events.
- Phase measurements: Can help distinguish between different fault conditions.
- Orbit analysis: Useful for certain machines equipped with shaft proximity probes.
- Envelope analysis: Helps identify repetitive high-frequency impacts associated with developing bearing defects.
Route-Based vs Online Monitoring
| Monitoring Type | How It Works | Typical Application |
|---|---|---|
| Route-based monitoring | Technicians collect readings at defined intervals using portable instruments. | Large populations of general-purpose machines. |
| Online monitoring | Fixed sensors collect data continuously or according to a configured schedule. | Critical, inaccessible or fast-changing machinery. |
| Combined programme | Monitoring method is selected according to machine criticality. | Plants with a mixture of critical and general equipment. |
What Faults Can Vibration Analysis Detect?
Different machine faults can produce characteristic vibration patterns. However, a vibration indication should normally be assessed together with other machine information before corrective action is recommended.
- Unbalance: Often associated with a strong component at running speed, particularly in the radial direction.
- Misalignment: Can produce elevated running-speed components and increased axial vibration.
- Mechanical looseness: May produce multiple running-speed harmonics and, in some cases, sub-harmonics.
- Bearing defects: Can produce characteristic bearing defect frequencies and high-frequency envelope signatures.
- Gear problems: Can appear around gear mesh frequencies and associated sidebands.
- Resonance: Can occur when a structural or support natural frequency interacts with an operating frequency.
- Pump cavitation and flow problems: May create broadband and higher-frequency vibration.
- Electrical motor faults: Can generate vibration components associated with electrical and rotor conditions.
What Do ISO 20816 Vibration Limits Mean?
ISO 20816 is a series used for evaluating machine vibration. Depending on the applicable machine category, vibration severity can be assessed using defined zones that describe the general condition of a machine.
| Zone | General Interpretation | Typical Maintenance Consideration |
|---|---|---|
| Zone A | Typical condition for newly commissioned or reconditioned machinery. | Establish or maintain the operating baseline. |
| Zone B | Generally acceptable for unrestricted long-term operation. | Continue normal monitoring. |
| Zone C | Not generally suitable for long-term continuous operation. | Plan investigation and corrective action. |
| Zone D | Vibration is severe enough to potentially cause damage. | Immediate investigation and action may be required. |
Alarm limits should be selected for the applicable machine category rather than applying one generic value to every machine. OEM requirements, client specifications and applicable machinery standards may establish tighter limits.
How Does Laser Shaft Alignment Work?
Laser shaft alignment uses laser and detector units mounted on the shafts or suitable brackets to determine the relative position of coupled machines. The system calculates the required vertical and horizontal corrections based on the measured geometry and entered machine dimensions.
Plan and Isolate
Obtain the required permits and isolate the driver and driven equipment using the approved lockout and tagout procedure. Confirm that the equipment cannot start unexpectedly.
Inspect the Installation
Inspect the base, grout, hold-down bolts, shims and contact surfaces. Record the as-found condition before making adjustments.
Disconnect the Coupling
Disconnect the coupling or flexible element where required so the two shafts can be measured independently.
Check Soft Foot
Verify that the machine feet sit correctly on the base. Correct soft foot before carrying out the final alignment.
Check for Pipe Strain
Assess whether connected pipework is applying forces to the equipment. Correct pipe support or installation problems instead of compensating for them through machine shimming.
Mount the Laser System
Install the brackets, laser and detector units, then enter the relevant machine and coupling dimensions.
Take As-Found Measurements
Measure the shaft positions and record the existing alignment condition before making corrections.
Calculate Corrections
Use the measured data to calculate required vertical shim changes and horizontal machine movements, including any applicable thermal growth targets.
Adjust and Re-Measure
Move the machine, tighten the hold-down bolts and repeat the measurements until the alignment falls within the applicable tolerance.
Complete Final Checks
Reconnect pipework and other connections, verify that the machine has not moved during final tightening and confirm the final alignment condition.
Record As-Left Data
Save the final readings, shim information, alignment values and applicable tolerances in the equipment record.
Start Up and Verify
After commissioning or restart, take vibration and temperature readings and compare them with the established baseline and applicable limits.
Which Shaft Alignment Method Should You Use?
The main shaft alignment approaches include rim-and-face dial indicators, reverse dial methods and laser alignment systems. The appropriate method depends on machine configuration, tolerance requirements, accessibility and equipment criticality.
| Method | Advantages | Considerations |
|---|---|---|
| Rim-and-face dial indicators | Simple and relatively low cost. | Slower and more sensitive to bracket sag and reading errors. |
| Reverse dial indicators | Can provide improved measurement accuracy for many coupling arrangements. | Still depends on technician skill and rigid bracket installation. |
| Laser alignment | High-resolution measurements, live readings, automated calculations and reporting. | Requires appropriate equipment and trained personnel. |
What Are Soft Foot, Pipe Strain and Thermal Growth?
Correct shaft measurements alone do not guarantee that an alignment will remain stable during operation. Soft foot, pipe strain, thermal growth and poor base conditions can all affect the final machine position.
Soft Foot
Soft foot occurs when one or more machine feet do not sit properly on the base. Tightening the hold-down bolts can distort the machine frame and change shaft position. Soft foot should therefore be corrected before final alignment.
Pipe Strain
Pipe strain occurs when connected pipework applies forces to the machine casing. These forces can shift the equipment position and affect shaft alignment. Where significant movement is identified, the underlying pipe support or installation condition should be addressed.
Thermal Growth
Machines can change position as they reach operating temperature. Drivers and driven machines may expand at different rates, particularly on hot equipment such as steam turbines, compressors and high-temperature pumps. Where applicable, the OEM’s thermal growth information should be used to determine the required cold alignment offset.
Base and Foundation Condition
Cracked bases, deteriorated grout, loose anchor bolts and poor shim arrangements can affect alignment stability. These conditions should be inspected and corrected before relying on the final alignment measurement.
What Alignment Tolerances Should You Use?
There is no single alignment tolerance that applies to every rotating machine. The applicable tolerance depends on factors such as machine speed, coupling configuration, spacer length and machine class.
OEM requirements, client specifications and recognised standards should therefore be used to establish the applicable tolerance. ANSI/ASA S2.75 provides shaft alignment methodology and quality guidance, while API 686 includes machinery installation practices relevant to alignment and soft foot.
Important: Treat the applicable tolerance as a maximum allowable condition rather than a target. Where practical, completing the alignment comfortably within the specified tolerance provides additional margin against thermal movement, wear and small changes in the machine or base condition.
Standards and Guidelines for Vibration Analysis and Alignment
Vibration and shaft alignment activities can be governed by several international standards and industry practices. The exact requirements depend on the equipment, project, client and applicable engineering specification.
- ISO 20816 series: Evaluation of machine vibration.
- ISO 13373: Condition monitoring and diagnostics of machines using vibration.
- ISO 18436-2: Qualification and assessment requirements for vibration condition monitoring personnel.
- ISO 21940: Rotor balancing standards.
- API 610: Centrifugal pumps.
- API 617: Axial and centrifugal compressors.
- API 670: Machinery protection systems.
- API 686: Machinery installation practices, including alignment-related requirements.
- ANSI/ASA S2.75: Shaft alignment methodology, practices and tolerances.
UAE Considerations for Vibration Analysis and Shaft Alignment
Industrial maintenance work in the UAE needs to account for site conditions, permit systems, isolation requirements and client-specific engineering standards. These requirements should be confirmed before mobilisation.
Heat, Sun and Dust
High ambient temperatures and direct sunlight can influence machine temperatures and alignment measurements. Where practical, measurements should be taken under stable conditions, with equipment allowed to reach an appropriate temperature state. Instruments, sensors and cables should also be protected from excessive heat and dust.
Permits and Isolation
Alignment and vibration activities must follow the applicable site permit-to-work, isolation and lockout/tagout requirements. The specific requirements can vary by emirate, client and facility. Equipment should never be worked on unless the approved isolation procedure has confirmed that unexpected start-up cannot occur.
Client and Operator Requirements
Major operators and industrial clients may define specific vibration limits, alignment tolerances, monitoring procedures, documentation requirements and personnel qualifications. These requirements should be reviewed before the work is planned or equipment is mobilised.
How Do Vibration and Alignment Work Fit Into Shutdowns?
Vibration analysis and alignment can support shutdown planning before, during and after an outage. Pre-shutdown vibration surveys can help identify machines requiring attention, while as-found alignment readings provide useful information about the condition before disassembly.
- Carry out vibration surveys before the shutdown to identify abnormal machines.
- Use survey findings to prepare bearings, seals, couplings, shims and other required materials.
- Record as-found alignment before equipment disassembly.
- Perform precision alignment after overhaul, bearing replacement, seal replacement or baseplate work.
- Reconnect pipework and check for movement after final alignment.
- Take post-startup vibration readings and establish the new baseline.
- Plan hot alignment verification where thermal growth is significant.
Benefits of Vibration Analysis and Precision Alignment
A properly planned vibration and alignment programme can help maintenance teams identify developing faults earlier and reduce avoidable mechanical stress. It also creates better records for future condition monitoring and troubleshooting.
- Early identification of developing mechanical faults.
- Reduced bearing, seal and coupling wear.
- Improved rotating equipment reliability.
- Better maintenance planning and prioritisation.
- Reduced risk of unexpected equipment failure.
- Improved equipment condition records.
- Better support for root-cause analysis.
- More reliable shutdown and maintenance planning.
Common Vibration and Alignment Mistakes
Many alignment and vibration problems are caused by incomplete preparation, inconsistent measurements or failure to investigate the underlying condition.
- Performing alignment without properly checking soft foot.
- Ignoring pipe strain and compensating for it through shimming.
- Using generic alignment tolerances instead of the applicable OEM or client limits.
- Ignoring thermal growth on high-temperature machinery.
- Failing to inspect the base and foundation condition.
- Using inconsistent vibration measurement points or poor sensor mounting.
- Judging machine condition only from overall vibration levels without reviewing the frequency spectrum.
- Failing to record as-found and as-left measurements.
- Using personnel without the appropriate training or recognised qualifications.
- Treating alignment as a one-time activity rather than part of an ongoing maintenance programme.
How to Choose a Vibration Analysis and Alignment Provider in the UAE
When selecting a service provider, consider technical competence, equipment quality, reporting standards and experience with the machinery involved. The lowest quoted price does not necessarily provide the level of diagnostic or alignment capability required for critical equipment.
- Vibration analysts with recognised qualifications appropriate to the required diagnostic work.
- Calibrated vibration analysers and laser alignment systems.
- Traceable calibration documentation for measurement equipment.
- Experience with pumps, motors, compressors, turbines, fans and other relevant machinery.
- A documented alignment procedure covering soft foot, pipe strain and thermal growth.
- Reports showing measurements, applicable limits, findings and recommended actions.
- Suitable safety systems and the ability to work within site permit and isolation requirements.
- Capability to support planned shutdowns as well as urgent maintenance requirements.
Why Choose Tensor?
Tensor supports industrial, marine and oil & gas clients across the UAE with technical and maintenance services for rotating and mechanical equipment. Its service capabilities include mechanical services for equipment repairs and maintenance, instrumentation services for installation and calibration, and hydraulic pump repair and overhaul.
For vibration monitoring, shaft alignment and related rotating equipment requirements, the scope can be planned around the machine type, operating condition, shutdown requirements and applicable client specifications.
Need Vibration Analysis or Shaft Alignment Support?
Discuss your rotating equipment requirements with Tensor’s technical team and plan the appropriate inspection, alignment or maintenance scope for your facility.
Discuss Your ProjectFAQs
The interval depends on how critical the machine is and how quickly its faults develop. Many plants use online monitoring for their most critical machines, and route-based readings monthly or quarterly for other equipment. Machines with known problems or recent repairs are checked more often until they are stable.
It can show that a fault is developing, identify what it is and indicate how fast it is progressing, but it cannot give an exact failure date. Reliable trends need a baseline and regular measurements. The result is a planning window, so repairs can be scheduled before the fault becomes critical.
Yes, new machines should be aligned during installation and commissioning, because factory alignment is lost during transport, mounting and piping connection. Alignment should be checked again after grouting, after the piping is connected and after the first run at operating temperature. New machines also need baseline vibration readings for later comparison.
Unbalance is an uneven mass distribution on a rotor, which produces a strong 1× running-speed vibration, mainly in the radial direction. Misalignment is a disagreement between the centrelines of two coupled shafts, which typically produces elevated 1× and 2× vibration and often high axial readings. One can be correct while the other is not, so each is corrected separately, by balancing and alignment respectively.
A vibration baseline is a set of reference measurements taken when a machine is healthy, such as after commissioning, overhaul or alignment. Later readings are compared with it to spot changes early. Baselines are recorded at the same points and operating conditions each time so the comparison is fair.
No, correcting alignment requires the machine to be stopped, isolated and locked out, because the machine must be moved and shimmed. Vibration and temperature readings while running can show that misalignment is present, and hot alignment checks can be done soon after shutdown. The correction itself is always done with the machine at rest.
A vibration report should identify the machine, measurement points, instruments, operating conditions, overall levels against limits, spectra or diagnostics, findings and recommended actions. An alignment report should show as-found and as-left readings, the tolerance used, shim and adjustment details and any soft foot, pipe strain or thermal growth findings. Both should be dated, signed and stored with the asset record.
