Step-Increase at 1x on Turbine-Driven Feed Water Pump:

A sudden step-increase in vibration levels observed on a turbine-driven feed water pump is a concerning indication of a potential machinery defect for any client. Furthermore, additional testing indicated the levels were continuing to increase, signaling a rapidly degrading process, heightening the risk of component failure. If left unaddressed, the impending failure of this critical component could necessitate a forced de-rate of up to 35% in the nuclear power plant’s generation.

Given the implications for plant performance and safety, prompt action is imperative. Conducting a thorough analysis to identify the root cause of the vibration anomaly is paramount. Possible causes may include mechanical wear, misalignment, imbalance, or resonance issues within the turbine-driven feed water pump assembly.

Once the root cause is determined, appropriate corrective measures should be implemented to mitigate the risk of failure and restore the equipment to optimal operating conditions. These measures may include repairs, realignment, balancing, or even replacement of damaged components.

By addressing the underlying issues proactively, the plant can minimize the likelihood of costly downtime, prevent safety hazards, and uphold operational reliability. Additionally, leveraging advanced monitoring techniques such as vibration analysis can help preemptively detect similar issues in the future, enabling timely intervention and proactive maintenance strategies.

Vibration Analysts Inc. | Case Studies

During testing, VAI collected and analyzed cross-channel phase data, which confirmed that the observed increase in vibration levels was attributable to an alignment issue affecting the turbine-driven feed water pump assembly. In response, we provided informal ODS (Operating Deflection Shape) training to the plant’s vibration engineer, empowering them with the knowledge and skills necessary to address the underlying alignment issue effectively.

Furthermore, recognizing the importance of ongoing monitoring and trend analysis, VAI installed a multi-channel vibration monitoring system at the plant. This system enables continuous monitoring of vibration levels across multiple points within the assembly, facilitating early detection of anomalies and proactive maintenance interventions.

By leveraging advanced analysis techniques and implementing robust monitoring solutions, VAI equipped the plant with the tools and expertise needed to safeguard against possible near-future issues, optimize equipment reliability, and ensure uninterrupted operation of the nuclear power plant.

The recommendations and data analysis services provided to the plant allowed them to continue operating until the next scheduled de-rate. At that time, they confirmed the problem was due to the loss of coupling lubricant, resulting in a bound coupling that adversely affecting the alignment.

Step-Increase on Gearbox After Increasing Flow:

The sudden increase in gearbox vibration levels observed when increasing pump flow to meet new test requirements was a critical issue that demanded immediate attention. The fact that the increase primarily occurred in the horizontal direction on the gearbox and at 4x diesel running speed further underscored the seriousness of the situation, particularly considering that it affected the plant’s #1 safety-related component.

Vibration Analysts Inc. | Case Studies

As soon as the pump flow was increased, the gearbox vibration levels increased from 0.15 to 0.90 IPS-Pk (at the highest point). Plant Engineering personnel reported that the maximum allowable levels were only 0.56 IPS-Pk (25% higher than allowed for the pump).

A review of work history revealed the pump’s as-left alignment was out-of-spec by 30 mils, however due to the short time allowed to make corrections, neither the diesel (or pump) could be moved due to all the structure and piping connections. Furthermore, if the gearbox was moved to correct the alignment on one side of the gearbox, the alignment on the other side would get worse. And to further complicate this problem, the gearbox had a newly found resonance at 4x diesel speed.

After reviewing the data and collecting additional data, VAI recommended the plant optimize the alignment between the gearbox and pump because the high gearbox levels coincided with 2x pump speed (4x diesel). This meant the gearbox was more sensitive to the misalignment between it and the pump, as compared to the gearbox and diesel.

VAI also recommended de-tuning the gearbox resonance by adding mass to the top of the gearbox. A stiffener was quickly ruled out because of the time required to engineer and approve a new stiffener, and because a new resonant frequency might be close to one of the diesel forcing frequencies.

By optimizing the alignment and detuning the resonance, vibration levels dropped from 0.90 to 0.44 IPS-Pk, which was well below the required 0.56 IPS limit.

The photo below shows the steel plates added to the gearbox.

Vibration Analysts Inc. | Case Studies

Vibration Levels on Vertical Shaft Bearing Increase:

A chemical plant monitored by VAI used six (6) reactors to produce their product. Each reactor utilized a vertical shaft rotating at approximately 60 RPM (1 Hz), a speed deemed too low to be analyzed using spectral analysis.

In the past, when a shaft bearing failed unexpectedly, not only would the customer lost their product, but it would also harden inside the reactor. This required expensive down time to remove the product and the plant reported each failure caused an estimated $1,000,000 lost.

To promptly detect and identify future bearing failures at very low levels, VAI implemented monthly waveform testing to monitor for increased impact levels. This analysis was performed monthly during which time VAI determined the normal waveform vibration levels (in Velocity) were approximately 0.05 IPS-Pk.  Sometime later, during one of our monthly walk downs, the level on one shaft were observed to be ~6x higher.  When displayed using amplitudes measured in Acceleration g’s-Pk, the waveform data clearly showed impacting at which time the client immediately performed an inspection determined our analysis was correct and that the issue was due to a degraded rolling element bearing.

Vibration Analysts Inc. | Case Studies

Based on VAI’s test plan and the subsequent data, the plant was able to replace the bearing and prevent a failure. By providing accurate and timely reporting of bearing faults, the customer was able to continue their operations and avoid the consequences of an untimely bearing failure.

Vibration Analysts Inc. | Case Studies

High Levels of a Non-Harmonic Frequency:

Collecting and analyzing data for new customers is always interesting because we invariably we find a component that is on the verge of failure and which could affect their plant operations.  One example which occurred at a Utah mining facility, happened after collecting and analyzing the initial data. During this initial analysis period, we saw high amplitude bearing fault frequencies (up to 0.4 IPS-Pk) on the outboard motor of one of the plant’s centrifugal air compressor (figure below).

Vibration Analysts Inc. | Case Studies

The plant immediately performed corrective maintenance and discovered the outer race of the bearing was spinning inside the bearing housing. Had this bearing issue not been accurately identified in a timely manner, the plant’s air compressor would have eventually failed, affecting plant operations.

Does your plant have a dependable vibration program? If not, call us at 815-742-1793 to get your program up and running!

Have a project for us?

Connect with us today to get your project underway. We’d love to discuss your particular challenge and begin the process of designing a solution today!
Contact Us Today!