Category Archives: Vertical Pump Shaft Bushing

Solving Vertically Suspended Barrel Pump Failures

Between 2011 and early 2012, a refinery suffered repeat failures of a pair of vertical pumps. Looking at the cross section, you can see this is not an ordinary pump. It is essentially a BB5 multi-stage diffuser pump mounted vertically.
The pumping conditions are also uncommon–0.61 specific gravity hydrocarbon running at 300 F (149 C). The vapor pressure is nearly 50 psi (3.3 bar), well into the range of a flashing hydrocarbon.
In short, not an easy application–a vertically mounted, multi-stage, barrel pump in a hot, light, flashing, low viscosity hydrocarbon.
Vertically Suspended Barrel Pump

Vertically Suspended Barrel Pump

 

 

Repeat Pump Failures

The pumps were failing due to seizure of the original metal parts, which were 12% chrome alloy with a hardness difference. At the point where the refinery contacted Boulden, the pumps had failed several times in the previous year.

The Upgrade

The engineers at the plant had heard that Vespel® CR-6100 wear parts would not seize. They discussed with Boulden that the material could handle the service conditions. The temperature limit for Vespel® CR-6100 is 500 F (260 C) and it resists all hydrocarbons without issue, so this application was well within the capabilities of Vespel® CR-6100. After several failures with the metal parts, the refinery decided to go forward with Vespel® CR-6100.
Vespel® CR-6100 wear rings, inter-stage rings, and throttle bushings were installed. Clearance at the wear rings was reduced to approximately 50% API recommended values for metal parts. A year later, the spare pump was also upgraded.

Results of Upgrading to Vespel® CR-6100

The first pump finally came out of service in early 2021 after nearly 9 years. From the look of the components, the Vespel® CR-6100 survived some really tough conditions. There was evidence of running dry, hard contact between rotating and stationary parts, and local temperatures well over 300 F (149 C). Yet, the pump never seized, and the Vespel® CR-6100 parts remained in usable condition all the way to the end of the run.
The MTBR for these pumps went from a few months to 9 years with a simple upgrade to Vespel® CR-6100. The investment in Vespel® CR-6100 has probably paid for itself 100 times over. The pumps clearly last longer, are easier to operate, and arguably much safer because they do not seize in this hot, flashing hydrocarbon service.

Conclusion

Do you have an application more difficult than this? Tell us about it.
Take your next repair as an opportunity to upgrade your pump. Boulden has a large inventory of material in stock and we can supply raw material or finished parts with very short lead times. We can provide all of the technical support required for you or your preferred workshop to make the upgrade a success.
Whatever the temperature, chemical, or operating conditions, it is likely that Boulden has a non-seizing, non-galling composite material to help you improve your pump reliability. Contact us today with the process conditions and we will let you know what we can do.

 

Comparing Pump Component Composite Materials

There is one material property that can tell you a lot about how a composite material is likely to perform in a pump: The coefficient of thermal expansion (CTE). If the value is too high, the material can deliver inconsistent results in challenging services.

Why CTE?
A low CTE is essential for reliable performance because components like wear ringsthrottle bushings, and vertical pump shaft bearings run with tight clearances. A low CTE allows the material to experience normal frictional heat generation during contacting conditions without significant deformation.

Conversely, it is difficult for a material with a high CTE to maintain a tight clearance. When exposed to normal frictional heat generation or higher temperatures, a high CTE can quickly cause the component to “grow” and close the clearance. When this happens, contact increases, frictional heat generation increases, and premature failure of the component can follow. This is likely what happened to the bushing in figure 1:

Failed vertical pump shaft bushing made from high CTE material

Figure 1: Failed vertical pump shaft bushing made from high CTE material

The difficulty from the user’s perspective is everyone selling materials for pumps claims that their material has a “low CTE.” What this often means is “low CTE relative to other plastics.”
How do you define low CTE?

At Boulden, we define “low CTE” to mean “equal to or lower than the CTE of the metal parts in the pump.” Common metals used to manufacture pumps are carbon steel, 400-series stainless, or 300-series stainless, so we want to be close to or below the CTE for these materials.

Boulden B-Series
Because we think CTE is so important, we developed our B-Series materials with this in mind. If you are currently using PEEK-based components, contact Boulden about upgrading to our B-Series materials. B-835 is our replacement for 30% carbon fiber filled PEEK; B-1050 is our replacement for “abrasive resistant” PEEK blends. B-920 is a non-PEEK proprietary blend, also for potentially dirty services.

CTE of composite materials

Material CTE (in/in/F) CTE (mm/mm/C)
Vespel CR-6100 3.1 5.6
B-920 3.5 6.3
B-1050 5.1 9.2
410 SS 5.5 9.9
Carbon Steel 6.0 10.8
B-835 8.7 15.7
316 SS 8.9 16
30% CF Filled PEEK 15 27

 

Conclusion

A low CTE is critically important to the performance of a composite wear part in a pump and one of the reasons Vespel® CR-6100 has proven so reliable over the past 20 years. Boulden-supplied materials also offer ease of machining, simple installation practices, and material availability. Boulden keeps the material you need in stock and can supply raw material or machined parts including our patented PERF-Seal® with rapid delivery.

If you want to make your pumps more reliable, easier to operate, safer, and more efficient, contact Boulden today. We can help you choose the best material for your application and provide detailed design assistance.