Vertical pumps are especially susceptible to minor conditions that can result in elevated vibration amplitudes. The vertically suspended design and long stationary element lengths often combine into natural frequencies that are near forcing frequencies, such as running speed or even sub-synchronous faults. The complexity of these issues makes it difficult to diagnose and resolve persistent vibration issues with the type of data that is routinely available to the end users.
In-depth field testing paired with computational analysis provides a clear path to both an accurate diagnosis and a solution that has a high likelihood of success. The effectiveness of this methodology was proven for a Gulf Coast midstream company who was experiencing high vibration with their vertical freshwater pumps. By applying advanced field diagnostics, the end user was able to understand the underlying causes of the vibration and evaluate possible solutions in a theoretical environment prior to implementing them in the field.
Read the full case study, published in the May 2025 edition of Pumps & Systems magazine, here.
Read more case studies on vibration analysis and the work completed by Hydro Reliability Services here.
The importance of engaging with a facility that has strong engineering capabilities and subject matter expertise was proven during a series of boiler feed pump repairs for a Canadian biomass power plant. Like many biomass facilities, this plant had segmental ring boiler feed pumps, also commonly referred to as BB4 pumps. This is a complex design installed in a high energy, critical application, with numerous stacked and nested components that must be kept in alignment.
Upon disassembly, it became apparent that there were several critical issues that needed to be addressed to increase the reliability and mean-time-between-repairs for this equipment. The discharge head gussets were heavily eroded clear cracks and dislocation, which weakened the discharge head assembly and made is susceptible to high vibration.
Fit-ups of the stationary assembly were excessive with average fit-ups measuring in the range of 0.010 – 0.030”; for reference, Hydro’s typical acceptance criteria are 0.001 – 0.003”. Critical faces and bores were also found out of acceptable tolerance, with concentricity, parallelism, and perpendicularity measuring in the range of 0.005 – 0.015”, where acceptance is usually held less than 0.002”. Not only did the out of tolerance fits contribute to overall misalignment, they provided a leak path that resulted in erosion of the column pipes at the fit areas.
Excessive wear was also found on the impeller vanes and the impeller liner surface, indicating contact between these two components. This contact was likely caused by both the overly loose impeller fit and non-concentricity of the rotor and stator, as mentioned above. The impeller vane wear would have increased rotor imbalance, further increasing vibration. The opening of this clearance would have also reduced the pump efficiency, causing it to lose performance and require more energy to operate.
Modifications were designed to provide structural reinforcement to the discharge head and to eliminate the factors causing premature wear of the bearings and shaft sleeves. The eroded gussets were removed and replaced with thicker, more robust gusset to enhance the structural integrity of the components. The new gussets and lifting lugs were fabricated from carbon steel and installed using precision welding. A PT inspection was completed to ensure weld integrity. The eroded stuffing box was also repaired using weld restoration techniques.
Vertical pumps are especially susceptible to misalignment since they have a large number of stacked components. Large fit-ups between each component can easily stack-up to a large offset at the bottom of the assembly that exceeds the bearing clearance. By restoring recommended fits and tolerances, non-centerline compatibility between the stationary and rotating elements would be greatly decreased.