Eliminating Excessive Vibration of Rotating Equipment: UNITEC-D Diagnostic Guide

1. Problem and Scope of Application

Excessive vibration of rotating equipment is a critical indicator of potential malfunctions that can lead to unplanned production stoppages, significant financial losses, degraded product quality, and most importantly, threats to personnel safety. This UNITEC-D manual is designed to systematically diagnose and eliminate the main causes of increased vibration covering a wide range of industrial rotating equipment, including pumps, fans, electric motors, compressors, gearboxes and turbines used in Ukrainian industry.

Classification of vibration severity according to DSTU ISO 10816-1:2004:

• Critical: Vibration level exceeding the upper limits of permissible values (Zone D) requires immediate equipment shutdown and troubleshooting.
• Significant: The level of vibration in zone C requires scheduled shutdown of the equipment for diagnosis and repair. Long-term operation in this area reduces the service life of the components.
• Minor: The level of vibration in zone B indicates the presence of a malfunction that may progress. Enhanced monitoring is recommended.

Timely and accurate identification of the root cause of vibration is the key to reliable and safe operation of the equipment.

2. Precautions

Before starting any diagnostic or repair work with rotating equipment, strict safety rules must be followed. Ignoring these precautions could result in serious injury or death.

STAFF SAFETY IS OUR PRIORITY

• Lockout/Tagout (LOTO): ALWAYS isolate and lockout all sources of power (electrical, hydraulic, pneumatic) to equipment. Use standard LOTO procedures in accordance with the company's internal regulations. Check for voltage and residual pressure.
• Stored Energy: Be aware of potentially stored energy in springs, hydraulic accumulators, flywheels, and pressurized gases. Make sure all these sources of energy are discharged or safely locked.
• Personal Protective Equipment (PPE): Use appropriate PPE: safety glasses (DSTU EN 166), gloves (DSTU EN 388), protective shoes (DSTU EN ISO 20345), hearing protection (DSTU EN 352).
• Hot Surfaces and High Pressure: Be careful when handling equipment that operates at high temperatures or pressures. Use thermal imaging cameras and pressure gauges to assess conditions.
• Rotating Parts: NEVER work near rotating parts without protective covers.
• Consult: If in doubt about safety, consult a senior engineer or occupational health and safety specialist.

3. Necessary Diagnostic Tools

Effective vibration diagnosis requires a certain set of tools. Their correct application allows obtaining accurate data for analysis.

4. Initial Evaluation Checklist

Before starting a detailed diagnosis, it is necessary to collect as much information as possible about the operating conditions and the history of the equipment. This will narrow down the range of potential causes.

5. Systematic Flow of Diagnostics

The diagnosis of vibration requires a systematic approach, starting with the measurement of the general level and proceeding to a detailed spectral analysis to identify the dominant frequencies.

1. Measure the overall level of vibration:
   • Use a vibration analyzer to measure the vibration velocity (mm/s RMS) on the bearing housings in three directions (horizontal, vertical, axial).
   • Compare the obtained values ​​with the permissible thresholds according to DSTU ISO 10816-1 for the corresponding machine class.
   • If the total vibration level exceeds zone B (minor fault) or C (significant fault): Go to step 2.
   • Otherwise: The problem is probably not related to mechanical vibration, or its level is negligible. Enhanced monitoring.
2. Perform spectrum analysis (FFT) and time signal analysis:
   • Collect vibration spectra (plot of vibration amplitude versus frequency) and time signal (plot of amplitude versus time) at each bearing assembly in all three directions.
   • Determine the rotational speed of the equipment (1X RPM) using a tachometer.
   • Analyze the spectra for the presence of dominant frequencies and their harmonics:
   • 1. IF is dominated by 1X RPM (rotor rotation speed) with high amplitude:
        • THEN Check for unbalance:
          • IF amplitude of 1X RPM is high in radial directions (horizontal/vertical) and varies proportionally with speed.
          • THEN Probable cause: Imbalance. Go to the diagnosis of imbalance (clause 7.1).
        • THEN Check for misalignment:
          • IF the amplitude of 1X RPM is high in the axial direction, or if 1X RPM and 2X RPM are both high in the radial directions.
          • THEN Probable cause: Inconsistency. Go to diagnostics of inconsistency (clause 7.2).
     2. IF is dominated by 2X RPM (twice the rotor speed) with high amplitude:
        • THEN Check for misalignment (angular/parallel):
          • IF amplitude of 2X RPM is much higher than 1X RPM in radial directions, or if 2X RPM is high in axial direction.
          • THEN Probable cause: Inconsistency. Go to diagnostics of inconsistency (clause 7.2).
     3. IF high harmonics (3X, 4X RPM and higher) or subharmonics (0.5X RPM) are present:
        • THEN Check for looseness:
          • IF harmonic amplitudes are nonlinear or subharmonics appear, as well as noise in the timing signal.
          • THEN Probable cause: Mechanical loosening. Go to the diagnosis of loosening (clause 7.5).
     4. IF characteristic bearing frequencies (BPFI, BPFO, FTF, BSF) or amplitude modulated high frequencies are present:
        • THEN Check for bearing defects:
          • Use shock pulse analysis (SPM, PeakVue) or ultrasonic detector to confirm.
          • THEN Probable cause: Defects in bearings. Go to diagnosis of defects in bearings (clause 7.3).
     5. IF high amplitude vibration at a frequency that is not a harmonic of the rotational speed, but is close to it or constant:
        • THEN Check for resonance:
          • Perform a run-up/coast-down test or shock test to determine natural frequencies.
          • THEN Probable cause: Resonance. Proceed to diagnostics of resonance (clause 7.4).

6. Matrix "Failure-Cause"

This matrix provides a quick overview of common vibration symptoms, their likely causes, and diagnostic tests.

7. Root Cause Analysis for Each Malfunction

7.1. Rotor imbalance

Why it occurs: Imbalance is an uneven distribution of the mass of the rotor relative to its axis of rotation. This can be caused by manufacturing defects, uneven build-up of contaminants (eg dust on the fan, scale on the pump rotor), material erosion or corrosion, and inaccurate repair or replacement of components without further balancing. For example, repairing a fan blade without restoring the original balance.

How to confirm: The primary indicator is a dominant vibration at 1X RPM in the radial direction, which increases proportionally with rotational speed. Phase analysis shows a stable vibration phase. Performing a trial run with the addition of a test mass and analyzing the change in vibration allows you to quantitatively determine the magnitude and angle of the imbalance.

Damage if not corrected: Prolonged imbalance results in increased stress on bearings and seals, which shortens their life, causes fastener failure, structural fatigue of the frame and base, and can lead to shaft failure and other catastrophic failures. Vibration of 15-20 mm/s RMS for standard mid-sized machines is already critical.

7.2. Misalignment of Shafts (Coupling)

Why it occurs: Misalignment is a deviation of the centers of the shafts or the angles of their axes from ideal alignment. It can be parallel (displacement of centers), angular (displacement of corners) or combined. Typical causes are: poor installation, deformation of the frame or foundation under load, thermal expansion of components during operation, "soft footing" (uneven contact between the support and the foundation), and settlement of the foundation.

How to confirm: The main indicators are high vibration amplitudes at 1X RPM and 2X RPM. Parallel misalignment is often dominated by 1X RPM in the radial direction, while angular misalignment is often dominated by 2X RPM in the radial direction and/or 1X RPM in the axial direction. Measuring with a laser leveling system (more accurate than watch-type indicators) allows you to quantify the deviation and type of misalignment. A deviation of more than 0.05 mm is unacceptable for most industrial machines.

Damage if not corrected: Misalignment causes cyclic loads on bearings, couplings and seals, leading to accelerated wear, overheating and premature failure. It also increases the energy consumption of the motor and can cause damage to the shafts.

7.3. Rolling Bearing Defects

Why it occurs: Bearing defects are one of the most common causes of vibration. They can be caused by material fatigue (spalling), incorrect installation (shock loads, misalignment), insufficient or excessive lubrication, contamination of the lubricant with foreign particles, electrical erosion (current passing through the bearing), excessive loading or overheating.

How to confirm: A characteristic feature is the appearance in the vibration spectrum of specific frequencies of bearing defects: BPFI (inner ring raceway defect), BPFO (outer ring raceway defect), FTF (separator defect), BSF (rolling body defect). These frequencies are calculated based on bearing geometry and rotational speed. For early detection, shock pulse analysis methods (SPM, PeakVue) or ultrasonic monitoring are effective, which detect high-frequency pulses generated when the rolling elements come into contact with defects. An SPM level of more than 15-20 dB from the baseline is alarming.

Damage if not corrected: Progression of bearing defects leads to increased vibration, overheating, separator failure, bearing seizing and, as a result, shaft or rotor failure.

7.4. Resonance

Why it occurs: Resonance occurs when the excitation frequency (eg operating speed, blade/tooth frequency, electrical frequency) matches one of the natural (natural) frequencies of the system or its component (frame, shaft, foundation). This leads to a significant increase in the vibration amplitude even with a relatively small excitation force. Reasons: change in stiffness or mass of the structure, incorrect choice of operating speed, change in dynamic characteristics of the foundation.

How to confirm: High amplitude vibration at a specific frequency that may be out of tune up to 1X RPM. For confirmation, a run-up/coast-down test is used, during which the equipment is smoothly accelerated or stopped, and the vibration is recorded. A significant vibration peak at a certain speed of rotation indicates the passage of the resonance frequency. An impact test (Impact Test) is also used to determine the natural frequencies of the structure.

Damage if not corrected: Resonance leads to rapid structural fatigue, failure of welds, fasteners, loosening of bolts, cracks in the frame and foundation, which can cause catastrophic equipment failure.

7.5. Mechanical Looseness

Why it happens: Mechanical loosening is a loss of stiffness or reliability of a component's mounting, allowing it to "knock" or vibrate non-linearly. This can be caused by loose mounting bolts (foundation, bearing assemblies, housings), cracks in the frame or foundation, worn bearing seats, or excessive clearances in plain bearings. It is often a consequence of other malfunctions (imbalance, lack of awareness) that have progressed.

How to confirm: Symptoms of shake in the vibration spectrum often include the presence of sub-harmonics (0.5X RPM), high harmonics (2X, 3X RPM and higher), and changes in vibration amplitude depending on the load. Analysis of the time signal shows pulse bursts or cut-offs in the signal. A visual inspection of fasteners, their tightening, and the use of a hammer impact test can help locate the source of loosening. A thermal camera can detect overheating in areas of increased friction.

Damage if not corrected: Loosening leads to progressive wear, deformation of components, failure of fasteners, misalignment of shafts and, as a result, failure of seals, bearings, shafts and other critical components.

8. Step-by-Step Troubleshooting Procedures

8.1. Elimination of Imbalance

1. Preparation: Isolate equipment (LOTO). Visually inspect the rotor for dirt, damage, and missing parts. Clean the rotor.
2. Measurement: Measure initial vibration at 1X RPM.
3. Balance: Apply dynamic balancing method in place (according to DSTU ISO 1940-1). For most industrial machines, quality class G6.3 is acceptable, for high-precision machines - G2.5 or G1.0.
4. Test run: Add test mass, measure the change in vibration.
5. Correction: Calculate the necessary correction mass and its position. Install the mass on the rotor.
6. Verification: Measure the vibration again. The vibration velocity level should be less than 4.5 mm/s RMS for a medium-sized machine (Class II).

8.2. Elimination of Unawareness

1. Preparation: Isolate equipment (LOTO). Clean the supporting surfaces, check the couplings for wear.
2. Soft Leg Check: Check all motor/pump legs using a dial indicator or laser system. If the deviation when tightening the bolt exceeds 0.05 mm, adjust the "soft paw" using calibrated spacers.
3. Alignment: Use a laser shaft alignment system to precisely adjust the position of the motor relative to the pump/gearbox. Observe the tolerances specified by the coupling manufacturer or recommended by the standards (for example, 0.02-0.05 mm for most couplings at 1500 rpm).
4. Verification: After alignment, tighten all bolts to the torque specified in the documentation and measure the vibration again. Amplitudes at 1X and 2X RPM in the radial and axial directions should be significantly reduced.

8.3. Elimination of Defects of Bearings

1. Preparation: Isolate equipment (LOTO). Ensure the cleanliness of the work area.
2. Disassembly: Carefully disassemble the bearing assembly using a specialized tool (pullers) to prevent damage to the shaft and housing.
3. Inspection: Carefully inspect the shaft, bearing housing, seats for wear, corrosion, burrs.
4. Installing a new bearing:
   • Use only original or certified UNITEC-D bearings.
   • Installation is carried out by heating (induction heater) or with a press, using special installation tools. NEVER hit the outer or inner race of a bearing without an appropriate mandrel.
   • Ensure correct radial and axial clearance according to the bearing manufacturer's recommendations.
5. Lubrication: Fill the bearing with the appropriate lubricant according to the manufacturer's recommendations (type, quantity). Use recommended syringes and dispensers.
6. Verification: After replacement and lubrication, start the equipment, monitor vibration and temperature. The level of vibration speed and shock pulses must correspond to normative values, the temperature must stabilize within the normal range (usually < 70°C).

8.4. Elimination of Resonance

1. Preparation: Isolate equipment (LOTO).
2. Determining the natural frequency: Perform an impact test (Impact Test) at various points of the structure to determine the natural frequencies.
3. Design modification:
   • Change of stiffness: Add or strengthen supporting elements, increase the thickness of the plates, install additional braces. The goal is to move the natural frequency away from the operating excitation frequency (minimum by 20%).
   • Mass Change: Add or reduce the mass of the resonating component. This will also change the natural frequency.
   • Changing the operating speed: If possible and economically justified, change the operating speed of the equipment to avoid overlap with the natural frequency.
4. Verification: After making the changes, repeat the impact test and the acceleration/coasting test to confirm the change in natural frequencies. Start the equipment and check the vibration level.

8.5. Elimination of Mechanical Shaking

1. Preparation: Isolate equipment (LOTO).
2. Localization: Using a vibration analyzer, impact test and visual inspection, pinpoint the source of the shake.
3. Tightening fasteners: Tighten all loosened bolts and nuts to the torque specified in the technical documentation (for example, 120 Nm for M16 bolts of strength class 8.8).
4. Damage repair:
   • If cracks are found in the frame/foundation: weld, strengthen the structure according to engineering calculations and standards.
   • If the bearing seats are worn: restore the seats (spraying, bushings) or replace the housing/shaft.
   • If the clearances in the slide bearings are excessive: adjust the clearances or replace the bushings.
5. Verification: Run the equipment and repeat the vibration measurements, paying special attention to the harmonics and the time signal. The vibration should correspond to the norm.

9. Preventive Measures

Preventive maintenance is the key to long and reliable operation of rotating equipment.

10. Spare Parts and Components

UNITEC-D GmbH is a reliable supplier of high-quality spare parts for rotating equipment. The use of certified components is critical to ensure the reliability and durability of the repair. Below are typical groups of spare parts.

Для замовлення та отримання детальної інформації про асортимент запасних частин UNITEC-D, відвідайте наш Електронний Каталог UNITEC-D.

11. Links

• DSTU ISO 10816-1:2004 Mechanical vibration. Evaluation of machine vibration based on the results of measurements on non-rotating parts.
• DSTU ISO 1940-1:2007 Vibration. Requirements for the quality of balancing solid rotors.
• DSTU ISO 15243:2009 Rolling bearings. Damages and waivers. Terminology, classification and illustrations.
• EN 15417-1:2008 Alignment of machines. Part 1: Methods and tolerances.
• Operation and maintenance manuals from equipment manufacturers (OEM).
• UNITEC-D internal standards for equipment diagnostics and repair.