Optimizing Reliability Through Material Upgrades

centrifugal pump test

The 14-stage boiler feedwater pump installed for testing to ensure that the performance achieves desired operating conditions.

At a combined cycle power plant, a boiler feedwater pump was experiencing problems. Dr. Gary Dyson of Hydro, Inc. and Larry White of HydroTex discuss how major cost savings were provided through engineering analysis, material upgrades and testing for validation.

A combined cycle power plant in the Pan Handle region of Texas found themselves experiencing repeated failure on one of their 14 stage boiler feedwater (BB3) pumps. The pump had recently been modified by the supplier to provide a short-term solution. This in turn reduced the mean time between failure (MTBF) of the pump, requiring continued support and further analysis.

Combined cycle plants are comprised of both gas and steam power production technologies, capable of producing up to 50% more electricity than traditional simple-cycle plants. With the ever-increasing demand for energy, this technology is becoming increasingly relevant in throughout the pump industry. As such, it is highly important that these plants operate at peak efficiency.

Originally, the stationary inserts at several locations in the pump assembly were modified in such a way that increased the likelihood of friction and galling of the stationary and rotating parts of the pump assembly. The consecutive failures experienced on site were repeatedly of the same failure mode, which strongly points toward a pump design problem.

Authored by Gary Dyson, Ares Panagoulias, Larry White, and Chris Brown.
Source: worldpumps.com

An Engineered Battle Against Cavitation

Impeller Cavitation

With inlet backflow recirculation present, the impellers were experiencing horrific vane breakage and cavitation.

A power station’s cooling water pumps were constantly being repaired, costing the plant millions of dollars in costs and service time due to the severe operational disruption and logistics required to remove and transport such large equipment. Previous attempts made by the station to improve the reliability of the impellers through upgraded material selections had little impact on reliability.

It was clear that something had to change as the station’s pump reliability was now a major financial focus. The many vane cracks, cavitation and broken vane sections that were weld-repaired during inspections throughout the pumps’ life cycles prompted the station to investigate a more permanent solution to the issue.

During the last repair, the reliability engineer inspected the impellers and found the cavitation was similar to those reported during prior repairs. An engineering repair company that specializes in fluid dynamics was asked to investigate the root cause of the continuing pump issues. The team conducted an investigation on the system layout and operation parameters.

The results of the forensic analysis showed that the impeller blades were suffering cavitation to the low-pressure side of the vanes. Additionally, the cavitation and cracked vanes toward the eye also indicated that the sizing of the inlet and its associated blade angles may be active factors in the repeated failures.

Authored by Gary Dyson and Michael Cooper.
Source:pumpsandsystems.com

Pump Renovation Restores Balance

Vibration issues with a two-stage pump forced a major steel manufacturer to remove the pump from service. Due to incorrect weights welded on an impeller, a steel manufacturer called upon Hydro to repair and balance a two-stage pump.

Written by: Ken Babusiak (Hydro, Inc.)
Published by: World Pumps

The pump was experiencing the vibration during the spring and summer months of 2016. The steel company sent the pump to HydroAire’s Chicago, IL facility in September of that year. HydroAire was able to determine the cause of the vibration and created a solution that got the pump back in operating condition. The pump was installed and back in service by February, 2017.

The initial testing and analysis deter-mined that the impeller had large weights welded onto it. The steel company was concerned for many reasons, especially because the staff knew that using weights was not the correct way to balance an impeller. This caused the steel manufacturer to question the manner in which the pump had previously been repaired.

Weights added to impellers

Adding weights to impellers is generally not standard practice.

Where not to position the weights.

Where not to position the weights.

Continue reading

Using Latest Technology to Refurbish a 50-year-old Pump Element

Power pump performance improved with redesign of the first-stage, double-suction impeller and twin volute. 

This project has been divided into two articles. The first, published in the June 2017 Pumps & Systems; the second, published in September 2017 Pumps & Systems.

Written by: Dave Allard & Dr. Gary Dyson
Published by: Pumps & Systems

In the aftermarket business, part replication is not enough. Precision engineering combined with the latest technology are essential for manufacturing high-quality parts. A main boiler feed pump at a Midwestern United States power plant was built in 1967 using sand casting and wooden patterns, now considered outdated technology. Even though the pumps received refurbishment every six to eight years, the pumps continued to have low performance as well as vibration issues.

Using all its resources—including casting simulations, 3-D models, up-to-date foundry casting techniques and considerable engineering data—Hydro fully manufactured a complete element, performed sophisticated testing in the Pumps Test Lab Approved Program (PTLA) certified test lab, and returned the pump to operation within just 12 weeks.

This project involved the manufacture of a complete first stage twin volute and a description of the latent defects.

The pump suffered from ongoing vibration issues which were caused by pressure pulsations at vane frequency. To improve the vibration levels, hydraulic analysis and redesign were required to develop a new, improved design.

This project has been divided into two articles. The first is the manufacturing of the twin volute and the second is the design of a new impeller.

Twin volute stage piece

Image 1. A received bundle showing failure in the twin volute stage piece. Hydro received the internal element and casing (pump bundle, or element) of the pump. (Images and graphics courtesy of Hydro, Inc.)

The first-stage twin volute is a complicated casting, which failed during operation as a result of poor design.

Hydro re-engineered the casting by using sophisticated engineering and 3-D modeling, along with simulation software and 3-D sand printing.

In addition, Hydro identified the opportunity to improve the performance of the pump by redesigning the first-stage double-suction impeller. To improve vane passing frequency, the first-stage double suction impeller was redesigned with staggered and split vanes.

Hydro’s aftermarket services capability provided a completely new replacement element for this high-energy boiler feed pump and also redesigned the castings to eliminate the original latent defect in the casting design.

Hydro provided sophisticated hydraulic engineering improvements to increase the mean time between repairs (MTBR) of the newly manufactured element.

Continue reading

Hydro Middle East performs swift re-build on fire-damaged circulating pumps

Hydro Middle East, specialists in pump rebuilding, particularly in the oil and gas industry and other industrial markets was called in to assess the damage and redesign and rebuild the fire-damaged pumps. Hydro’s engineers first evaluate the causes of any pump damage or failure and then provide expert engineering analysis and a responsive field service.

Written by: Thomas Arakal (Hydro Middle East)
Published by: World Pumps

Two fire damaged pumps

Two fire damaged pumps arrive at the Hydro Middle East Service Centre.

Analysis & recommendations

In the case of the fire-damaged pumps, once the fire was under control, Hydro immediately sent a field engineer to the site to conduct a root cause analysis and make recommendations to ensure that the equipment would be restored within the very fast turnaround that the company required.

The engineers discovered that the fire had been so severe it had completely burned out all of the oil in the bearing housing. In addition, the baseplate was also warped because of the excessive heat. A turnaround of between two and three weeks for redesign and rebuild was proposed, subject to mechanical seal availability and the two hot oil circulating pumps, along with the baseplate and the motors were shipped to Hydro Middle East’s facility in Dubai, U.A.E.

Continue reading