Vibration Troubleshooting

What is Vibration Troubleshooting

Vibration troubleshooting is a systematic approach to addressing vibration issues. The primary goal is to identify the root causes of vibration and provide effective solutions. At CCPGE, a significant portion of our field measurements is dedicated to troubleshooting vibrations in reciprocating compressors and rotating pumps, which often present complex challenges, such as cracks in compressor suction bottles and damage to couplings and motor fans.

Why Perform Vibration Troubleshooting

Excessive vibration can lead to failures and damage in mechanical equipment, piping, and structures. Vibration troubleshooting helps identify the root causes of vibrations and resolve issues quickly, preventing further damage and minimizing downtime.

Vibration Troubleshooting Procedure

Below is a flowchart outlining the procedure for conducting vibration troubleshooting.

Pre-work preparation involves discussing and finalizing the troubleshooting plan with the client. Necessary field documentation, including the FLHA and work permit, will be completed, along with training and site orientation. Measurement instruments will be calibrated and prepared, and a comprehensive working plan will be delivered to the client prior to the site visit.

Understanding problems includes gathering site information to thoroughly understand the vibration issues. Key information typically includes:

The characteristics of the vibrations
The locations and conditions under which the vibrations occur
Whether the vibrations can be reproduced

Field measurements involves conducting field vibration measurements in consultation with site personnel. All necessary tests will be conducted under various operating conditions, particularly those under which the maximum vibration can be observed. The data will be collected and secured appropriately.

Problem diagnosis involves analyzing the collected data with focus on parameters such as vibration direction, amplitudes, frequencies, and the operating conditions during which maximum vibration occurs. Operational deflection shapes (ODS) obtained from measured vibration data can be quickly visualized to facilitate the diagnosis process.

On-site representation includes presenting the processed data to the client, and explaining the findings and underlying causes of the vibrations. If the data indicates a direct action is needed, initial recommendations will be provided after discussing them with the client. If the data indicates that immediate action is needed, initial recommendations will be provided after discussion with the client. Further studies, such as computational analysis, root cause analysis (RCA), or a follow-up site visit, may be proposed as necessary.

After-work delivery involves the completion of the vibration troubleshooting report, which includes field measurement results, diagnostic analysis, and recommended modifications to existing systems, ensuring client satisfaction.

Vibration Troubleshooting Example

An example of vibration troubleshooting for a 1200 kW, 1800 RPM Emergency Diesel Generator (EDG) set on an offshore platform is illustrated below. The EDG set has been experiencing high vibrations, particularly on the generator side. On-site vibration measurements were conducted to identify the root cause of the vibrations and to develop effective mitigation solutions.

Emergency Diesel Generator (EDG) Set

EDG Damping Pad

During the site inspection and measurements, it was determined that the current damping pads between the EDG set and the skid significantly influence the vibration levels of the EDG set. The CCPGE field team proposed replacing these soft damping pads with rigid connections to enhance the supporting stiffness of the EDG set, thereby improving overall structural integrity and reducing vibration levels to acceptable limits.

Vibration Measurements Before and After Change of Damping Pad

Notes on Vibration Troubleshooting

Analysis Diagnostic and Root Cause Analysis (RCA)

Analysis Diagnostic involves utilizing computational tools and techniques to systematically analyze data and diagnose issues within equipment and systems. This process includes modeling, simulations, data analysis, field validation, and predictions of system behavior. Meanwhile, Root Cause Analysis (RCA) systematically identifies the fundamental causes of failures. RCA uncovers the causes of events and problems after they occur, making it essential to conduct the analysis as early as possible to preserve evidence.

During vibration troubleshooting, Analysis Diagnostic and RCA are typically employed when vibration measurement data is insufficient to identify root causes or when complex issues may not be apparent through standard on-site troubleshooting tests. Conducting Analysis Diagnostic and RCA provides valuable insights into the primary causes of failures, enhancing problem-solving and decision-making. Additionally, Analysis Diagnostic is useful for predicting system responses after implementing mitigation solutions, thereby preventing future issues or failures.

CCPGE incorporates Analysis Diagnostic and RCA in its vibration troubleshooting efforts. Typical computational analyses employed for this purpose include pulsation analysis, mechanical analysis, flow-induced vibration analysis, torsional vibration analysis, and skid analysis. The results of these analyses, combined with field measurements, facilitate the quick identification of vibration causes and enable the development of effective mitigation solutions.

Below is an example of vibration and crack failure troubleshooting involving Analysis Diagnostic and RCA for a 4500 KW reciprocating compressor unit. A significant crack was discovered in the repad of the 3rd stage suction bottle nozzle within this unit. The figure below illustrates the observed crack.

Cracks Found on the Repad of Compressor Suction Bottle Nozzle

Using Analysis Diagnostic, including pulsation analysis to obtain the unbalanced shaking forces, and mechanical analysis to predict the vibration levels acting on the 3rd suction bottle, and three-dimensional thermal expansion analysis for the 3rd suction bottle installed on two cylinders, it was determined that the crack failure was resulted from the combined effects of dynamic compressor gas forces and thermal expansion stress, rather than vibration alone. This thermal stress was caused by the suction bottle being positioned on the cylinders on both sides of the compressor frame, despite this being a common design for many compressor models.

CCPGE recommended splitting the single 2-nozzle suction bottle into two separate suction bottles, each with one nozzle connected to a single cylinder. This change aimed to reduce thermal expansion stress without increasing vibration levels. This solution effectively resolved the crack failure issue. The figures below illustrate the pulsation, mechanical, and thermal expansion analysis models for this project.

Pulsation Analysis Model

Mechanical Analysis Model

Suction Bottle Thermal Analysis Model

Common Vibration Issues and Solutions

Several common issues can cause excessive vibration in machine systems, each requiring specific solutions:

Mechanical Looseness: Loose restraints, supports, clamps, or bent or broken bolts can alter the low-frequency resonance of piping spans, leading to excessive vibration. Regularly inspecting and tightening all bolts and fasteners with torque wrenches ensures proper tightness. Structural reinforcement, such as adding support brackets or reinforcing welds, may be necessary in areas with structural looseness.
Imbalance: Uneven weight distribution on rotating components often results in imbalance. Solutions include performing in-situ or shop balancing of rotors, and ensuring balance weights are correctly positioned. Additionally, inspecting for damage or buildup on rotors and removing any deposits that may cause imbalance is crucial
Misalignment: Misalignment between the compressor and its driver can lead to significant vibration issues. Utilizing laser alignment tools helps achieve precise alignment, addressing both angular and parallel misalignment. It’s also essential to correct soft foot conditions by ensuring the compressor base is flat and evenly supported.
Valve Issues: Worn or damaged valves can create abnormal vibrations. Regular inspections of valve seats, springs, and guides, along with ensuring that valves open and close at the appropriate times, can help prevent these issues. Adjusting valve timing is key to maintaining optimal performance
Bearing Wear: Deteriorated bearings can result in high vibration levels. Monitoring bearing condition through vibration and oil analysis, and replacing bearings that show significant wear or damage, is vital to preventing catastrophic failure.
Foundation Issues: Ensuring the compressor is mounted on a solid foundation is critical. Regularly inspecting the foundation for cracks, settling, or other stability concerns, and strengthening it if necessary, is essential for reducing vibration.