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.
A low CTE is essential for reliable performance because components like wear rings, throttle 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:
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.
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)|
|30% CF Filled PEEK||15||27|
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.
Last fall, a power plant needed to replace the vertical pump shaft bearings on their cooling water intake pump. They contacted Boulden to find a solution.
The cooling water intake pumps at the plant pump brackish water from the local harbor. The salty water creates corrosion issues, the silt in the water creates abrasion issues. The line shaft bearings are exposed to potentially high loads from the pump at an operating speed of 1500 rpm.
Boulden selected B-1050 for the application due to its excellent dimensional stability, resistance to abrasive wear in dirty water conditions, and high load carrying capability. Unlike most plastic or composite materials used for this application, B-1050 has a coefficient of thermal expansion less than carbon steel. Boulden has found that a coefficient of thermal expansion less than carbon steel is probably the most important material property for the reliable performance and ease of design of a composite bearing or wear ring. For a complete data sheet, contact Boulden today.
Some key properties of B-1050 are shown in Table 1:
Tough, wear resistant shaft bearings from Boulden
Boulden supplied the B-1050 bearings mounted in Duplex Stainless shells. The old bearing spiders were corroded and needed to be re-machined; therefore, the shells were machined to fit after the modification to the spiders. The bearings ran against a 7″ (180 mm) diameter shaft. One line shaft bearing design was 9″ (225 mm) long; the other was 11″ (270 mm) long. The components were manufactured in a few weeks, delivered and installed without issues.
If you are looking for better materials for your vertical shaft bearings, contact Boulden. Consider B-1050 for your cooling water pumps, waste water pumps or other services where you need the ability for the bearings to run in potentially dirty service plus survive off design conditions such as running dry. We have a portfolio of materials with B-Series and Vespel® CR-6100, so whatever your vertical shaft bearing application, we can help.
For consultation on the best material for your application or design assistance, contact Boulden today. We have the material you need in stock and can supply raw material or machined parts with rapid delivery.
Frequently Asked Question:
“Are the OEMs using Vespel® CR-6100?” is a question we hear every month. The answer is definitely, “yes.” All of the major API pump manufacturers use Vespel® CR-6100 for both new pumps and aftermarket upgrades.
A related question: “If Vespel® CR-6100 is so great, why don’t the OEMs include it as a standard material?”
To answer that, we need to look at how pumps are usually purchased…
Most pumps are sold into projects. The EPC contractor generally selects the pump with the lowest price which meets the bid specification. Therefore, if the bid spec allows bronze or cast iron wear rings, the OEM will probably quote bronze or cast iron because they are the cheapest materials. These materials might result in a higher life-cycle cost, but procurement personnel will not care if their decision is driven by the initial price.
Put it in the Bid Spec
If you want to maximize your pump reliability and efficiency, specify Vespel® CR-6100 for the stationary wear components in your next project. When it is part of the specification, the OEMs are happy to quote and supply Vespel® CR-6100.
If your company does not allow using brand names in the project specification, you can use the generic description for Vespel® CR-6100 from API610, Table H.3: PFA/CF reinforced composite, 20% mass fraction random X-Y oriented carbon fiber. For clarity, you can add the note “one example of which is DuPont™ Vespel® CR-6100.”
Direct Questions to Boulden
If there are any questions from the Project Engineer, EPC contractor, or OEM, please ask them to contact Boulden. We will be happy to answer any questions they have and make sure that the Vespel® CR-6100 is used correctly throughout the project.
In short, if you want Vespel® CR-6100 wear rings, vertical pump shaft bearings, or throttle bushings in your new pumps, all you have to do is ask–i.e. spell it out in the bid spec. Until next time, if you need any material for your pumps, we have a wide range of sizes in stock and ready for immediate shipment.
Part 3: Reduce Clearance – Improve Pump Efficiency
Welcome to Part 3 in our series on upgrading pumps with composite wear parts.
In the first part of this series, we discussed how upgrading your pumps with composite wear parts can help avoid galling and seizing. Because composite parts do not gall or seize like metal parts, this allows you to reduce the clearance at these components in your pump.
In Part 2, we discussed how reducing the clearance at the wear rings, throttle bushings, and center-stage bushings creates a stabilizing force in your pump called The Lomakin Effect. This force helps to reduce vibration and shaft deflection, leading to longer seal and bearing life in your pumps.
Today, we will discuss how reducing the clearance in your pump also improves pump efficiency.
Centrifugal Pump Background
According to a major centrifugal pump OEM, energy consumption accounts for 44% of the life cycle cost of a centrifugal pump. You can reduce this cost by upgrading the wear components to a composite material like Vespel® CR-6100 and reducing the clearance in your pump.
The specific components where you want to reduce the clearance are the pump wear rings, inter-stage rings, center-stage bushing, and throttle bushing. These components form the barriers between high-pressure and low-pressure areas within the pump. The differential pressure across these components creates internal recirculation within the pump, resulting in a loss of pump efficiency (Figure 1).
When you upgrade these components to Vespel® CR-6100, you can typically reduce the clearance by 50% compared to the API minimum for metal parts. If you reduce the clearance by 50%, you reduce the internal recirculation by approximately 50%, leading to a significant efficiency gain.
Which Pumps Produce the Biggest Gains?
If we consider only efficiency gains, horizontal multi-stage pumps usually offer the best return on investment from an upgrade to Vespel® CR-6100 with reduced clearance. These pumps have multiple leak paths across wear rings, inter-stage rings, center bushings, and throttle bushings. Because they have many stages, these pumps also tend to consume a lot of power. Consider the following cases where process plants have reduced the operating costs of their multi-stage horizontal pumps:
- A power station upgraded a 3MW boiler feed water pump with Vespel® CR-6100 along with the Boulden PERF-Seal™ design and reduced clearance and recorded a 7% efficiency gain compared to a newly rebuilt pump with original clearances.
- A refinery upgraded their hydrocracker charge pumps with Vespel® CR-6100 along with the Boulden PERF-Seal™ design and reduced clearance and recorded 4% more throughput to their hydrocracker-a hugely profitable upgrade.
- A product pipeline company upgraded their LPG shipping pumps with Vespel® CR-6100 and reduced clearance, resulting in a 4% efficiency gain.
Another area to consider is process pumps which are marginally undersized, requiring parallel pump operation to achieve 100% of the target process rate. Sometimes, a modification as simple as reducing the wear ring clearance can get you back to one-pump operation with a full-capacity spare pump.
To further increase the efficiency gain associated with reduced clearance, the components can be modified with the Boulden PERF-Seal™ design. Internal testing has shown that the PERF-Seal™ creates an additional reduction in flow across throttle bushings, center-stage bushings, and wear rings beyond what can be achieved with reduced clearance alone.
When you eliminate the metal-to-metal contact surfaces in your pumps and use Vespel® CR-6100 stationary wear components, you can then reduce the clearance. This reduction in clearance improves pump efficiency and lowers the operating cost of the pump. Numerous field examples exist where customers have saved tens of thousands of dollars on their annual pump operating costs with this simple upgrade.
If you have a pump where improved efficiency will save you money, contact Boulden today. We have a huge inventory of Vespel® CR-6100 standard sizes in stock ready for immediate shipment almost anywhere in the world.
For application and installation details, download the Boulden Installation Guide for Vespel® CR-6100.
Part 2: Reduce Clearance – The Lomakin Effect
Welcome back to our series on upgrading pumps with composite materials. In part 1, we discussed how using composite materials like Vespel® CR-6100 in your pumps allows you to eliminate the metal-to-metal contact points in the pump and minimize the risk of pump seizure:
- In the shop during assembly
- In the field during alignment
- During slow-roll, start-up, and shut down
- During off-design events like dry-running or low flow
Reducing Clearance – The Lomakin Effect
Minimizing the risk of seizure in your pump sets the stage for reducing the clearance at the wear parts in your pump. Reducing clearance can be a significant pump reliability upgrade due to a phenomenon known as the “Lomakin Effect“.
Your Wear Rings are Bearings
During pump operation, the flow created by differential pressure across the wear parts in the pump (wear rings, throttle bushings) creates a force called The Lomakin Effect. The force arises from an unequal pressure distribution around the circumference of the component during periods of rotor eccentricity. This force counteracts shaft deflection in the pump.
Figure 1 shows how shaft deflection creates this force. As the fluid enters the clearance between the rotor and wear component, it accelerates as it passes from the high pressure end to the low pressure end. Due to the eccentricity of the rotor, there is more clearance on one side of the wear part than the other. There will be more flow and a locally higher velocity on the side of the wear ring with more clearance and lower velocity on the side of the ring with less clearance. Higher velocity results in lower pressure; lower velocity results in higher pressure, creating a net corrective force which acts in the direction opposite of the shaft deflection.
In other words, when your pump experiences shaft deflection, there is a hydraulic “stiffness” (Lomakin Stiffness) which is generated to counteract the shaft deflection.
Using Vespel® CR-6100 you can typically reduce the clearance at the pump wear rings by 50% compared to the API recommended minimum for metal wear parts. The Lomakin Stiffness is inversely proportional to clearance; therefore, a 50% reduction in clearance doubles this force.
Potential benefits for your pumps include:
- Less shaft deflection
- Lower vibration levels
- Fewer mechanical seal leaks
- Longer bearing life
The Lomakin Effect is generally beneficial to all centrifugal pumps, but some pump types often show significant vibration reductions and reliability improvements with reduced clearance:
- Multi-stage horizontal pumps
- Older overhung pumps with long, thin shafts (high L/D ratios)
- Two-stage overhung pumps
Reducing the clearance at the wear components can be a major reliability upgrade for your pumps. The reduced clearance increases The Lomakin Effect which improves pump rotor stability. The net result is a pump which runs with potentially lower vibration, fewer seal leaks, and longer bearing life.
Reducing the clearance also increases pump efficiency, which we will discuss in Part 3.
Until then, if you are working on a pump with a long, thin, flexible rotor, contact Boulden to discuss upgrading the wear parts to Vespel® CR-6100 and reducing the clearance. We have a huge stock of Vespel® CR-6100 standard sizes in the USA, Europe, and Singapore available for immediate delivery to your workshop.
For application and installation details, download the Boulden Installation Guide for Vespel® CR-6100.
If you increase the clearance, the long-term reliability and efficiency of the pump will suffer.
We hope you have had a chance to enjoy your summer holidays. From New Orleans to Narvik, it’s hot out there, so be safe, and wear sunscreen.
In our messages, we frequently highlight how Vespel® CR-6100 does not seize and therefore allows you to reduce the clearance at the wear parts in your pumps: wear rings, inter-stage rings, throttle bushings, and center bushings.
Today we want to look at things from another perspective–negative effects which can happen to your pump when you increase the clearance at the wear parts.
What can happen when you increase clearance?
If a process plant has a problem with a pump seizing during operation or galling during commissioning, the traditional response has been to increase the clearance at the wear parts.
Although increasing the clearance might make the pump operable in the short term, there are several negative consequences from increased clearance.
|Hydraulic Effects||Mechanical Effects|
|Lower head||Reduced rotor stability|
|Lower flow||Potentially higher vibration|
|Lower efficiency–increased power consumption||Potentially higher shaft deflection|
|Higher NPSHR–greater risk of cavitation||Increased risk of shaft breakage|
|Higher motor load||Potentially shorter seal life|
|Need to run steam turbines at higher speed||Potentially shorter bearing life|
|Higher likelihood of needing to run pumps in parallel||Higher risk of motor over-heating or tripping from excessive load|
So, while you don’t want your pumps to seize, increasing the clearance can create some major issues. At a minimum increased clearance drives up the operating cost of the pump and likely compromises the long term reliability of the machine.
The Poster Pump
A while back, one of our clients had an 11-stage horizontal pump which was originally supplied with metal wear components. The pump seized soon after start-up, and the recommendation from the OEM was to increase the clearance. The pump seized again. The second recommendation was to use a “non-galling” metal alloy to address the problem. The pump seized again. The clearance was increased one more time. When the pump was started again, the overall pump vibration levels were beyond alarm limits. The multiple increases in clearance had resulted in a loss of rotor stability to the point that the pump was no longer operable.
The end of the story will be in our next email…
Until next time, if you have a pump in your shop which has galled or seized, contact Boulden to discuss an upgrade to Vespel® CR-6100. We will be happy to work through the details of the upgrade with you and we have material in stock and available for immediate shipment.
Helpful Links for Vespel and Pump Case Studies:
DuPont™ Vespel CR-6100 resists seizing, can run dry, has high impact resistance, and a low wear rate for a long life under a wide range of process conditions.
Vertically Suspended Pumps
Vertically suspended pump types (API types VS1-VS7) use long, flexible shafts which are supported by a series of product-lubricated shaft bearings. Vespel® CR-6100 is a great upgrade for these components.
Typical Vespel Services
Vertically suspended pumps can be divided into two general categories: discharge through column (API Types VS1, VS2, VS3, VS6, and VS7) and separate discharge (VS4 and VS5).
Discharge through column pumps tend to be used in light, flashing products like butane, LPG, and natural gas liquids, or in water condensate or cooling water intake service. In flashing services, it is not uncommon for these pumps to run dry temporarily at start up, which can be a challenge for the shaft bushings. In many of these pumps the flexible shaft can create very large loads, leading to high wear rates of traditional materials.
Separate discharge pumps tend to be used as sump pumps. In API Type VS4 pumps, the shaft bearings can run dry at start-up until the flushing fluid arrives. Sometimes, the external water flush is turned off; sometimes the flush lines from the process fluid are plugged; sometimes the bearing grease is insufficient. In a chemical sump, the mix of chemicals can cause corrosion issues.
Vespel® CR-6100 Replaces Traditional Materials
Most vertical pump shaft bearings are made from either bronze/cast iron, carbon/graphite based materials, or stainless steel alloys. Bronze/cast iron bearings can have a high wear rate. Carbon/graphite bearings can break. Stainless steel bearings can seize.
Vespel® CR-6100 can replace all of these materials in process conditions from cryogenic to 500 F (260 C). Vespel® CR-6100 is low friction with a low wear rate. It is durable and impact resistant so it resists breakage during installation, transport, and operation. Plus, Vespel® CR-6100 does not seize like metal parts and is capable of surviving the run dry conditions which can occur with the flashing process fluids.
Consider the results from a long term study at an oil refinery. The plant upgraded 22 vertical pumps to Vespel® CR-6100 wear parts. The pumps were operating in light hydrocarbons, flare knock out drum, and several stop/start services like product transfer, comprising many “bad actors” in the plant. Looking at the number of repairs within this population for 5 years before Vespel® CR-6100 and 5 years after, the plant found the following.
|22 Vertical Pumps||Number of Pump Repairs||MTBR for the Population|
|5 Years Before
|5 Years After
Next time you are rebuilding a vertically suspended pump, consider upgrading the shaft bearings to Vespel® CR-6100. Contact Boulden with your process conditions and we will be happy to let you know if Vespel® CR-6100 is a good fit for your pump.
The Vespel® CR-6100 installation guide will walk you through the installation process. Vespel® CR-6100 is easy to machine and install, and Boulden is always happy to help if you have any questions. Finally, we have large quantities of Vespel® CR-6100 in stock and ready for immediate delivery in North America, Europe, and Southeast Asia.
Helpful Vespel Links:
Setting the final dimensions of your DuPont™ Vespel CR-6100 component
We have discussed how to measure your pump, prepare the metal parts, and establish the press fit for your Vespel® CR-6100 installation. The final two dimensions you need to establish are the part length and the clearance.
The Part Length
Vespel® CR-6100 has an extremely low coefficient of thermal expansion in the radial plane (perpendicular to rotation). This is one of the principal reasons it performs so well in centrifugal pump components. The low coefficient of thermal expansion is achieved through the use of radially-oriented, long carbon fibers.
Conversely, the coefficient of thermal expansion along the axis is relatively high. Therefore, the part length for a Vespel® CR-6100 component should account for the axial thermal expansion at operating temperature. Table 4 of our installation guide provides the details on how to make this adjustment.
The clearance for the part is set depending on the diameter and component type. Tables 2a and 2b in the installation guide show the clearance recommendations for horizontal pump components such as pump wear rings, throttle bushings, center bushings, inter-stage rings, balance bushings, and throat bushings.
Tables 3a and 3b show the clearance recommendations for vertical pump components like vertical pump shaft bearings, wear rings, and throat bushings.
The best way to set the clearance is to press the component into place, and then final machine the bore to the desired clearance. This is shown in steps 5a-7a in our installation guide, pages 8-9.
Where final machining after the press fit is not practical, you can design the component to have the correct clearance after the press fit. For most component geometries, you can assume the Vespel® CR-6100 will reduce at a 1:1 ratio with the press fit. This method is shown in steps 5b-7b in our installation guide, page 9.
Some sites have implemented a hybrid method. They measure the inside diameter of the Vespel® CR-6100 case wear ring after installation, and then machine the metal impeller wear ring to set the desired clearance.
Installing Vespel® CR-6100 is an easy upgrade to make your pumps more reliable, safe, and efficient. Follow the steps in our installation guide and you can make your pump even better than the day it was new. If you need material, Boulden carries inventory of stock sizes in the USA, Europe, and Singapore.
The interference fit value for DuPont™ Vespel CR-6100
We have discussed how to measure your pumps and prepare the metal parts. The next step is to machine the DuPont™ Vespel® CR-6100 part to have the correct dimensions.
Remember, Vespel® CR-6100 is used for stationary wear parts like wear rings, throttle bushings, and vertical pump shaft bearings. The rotating components running against the Vespel® CR-6100 remain metal. The Vespel® CR-6100 components are installed with an interference fit (aka “press fit”).
Installation Guide for Vespel CR-6100
The Boulden Installation Guide for Vespel® CR-6100 Tables 1a (Imperial) and 1b (Metric) outline the interference fit values for a Vespel® CR-6100 component based on diameter and the pump operating temperature.
If you only want the right value, follow the guide. You can stop reading and contact Boulden whenever you need material or if you would like to request a quote. If you want to know how we arrived at the values, continue reading.
Low Coefficient of Thermal Expansion
Vespel® CR-6100 has an extremely low coefficient of thermal expansion–about 60% lower than carbon steel in the radial plane. This property is one of the reasons Vespel® CR-6100 can survive pumps running dry and avoiding seizure.
The low coefficient of thermal expansion is a main factor in the interference fit value. At elevated temperatures, the metal parts will thermally expand more than the Vespel® CR-6100 parts. Therefore, as pump operating temperature increases, the interference fit increases.
Vespel CR-6100 Low Modulus of Elasticity
Vespel® CR-6100 parts press in relatively easily due to a very low modulus of elasticity. Vespel® CR-6100 can be used in temperatures up to 500 F (260 C). At maximum operating temperature, the recommended interference fit can be quite high. Due to the low modulus, the material generally presses in without issue.
Small Pilot Fit
To facilitate the large interference fit, machine a small pilot or “step” on the leading edge (Figure 1) of the Vespel® CR-6100 component. This will help the part sit squarely in the bore as it is being pressed in (Figure 2).
Figure 1: Pilot Fit on leading edge to facilitate press fit
Figure 2: Press fit operation
No Pins or Screws Required
Once Vespel® CR-6100 is installed with a press fit and a shoulder to retain the part against differential pressure, no further retention of the components is required. There are thousands of pumps running for many years with Vespel® CR-6100 components without retaining pins or screws.
If you insist on using retaining pins with Vespel® CR-6100, contact Boulden and we will discuss the possible designs given your part geometry.
When installing Vespel® CR-6100, make sure you are using the correct interference fit. Download our installation guide for the full installation procedure. If you need material, Boulden carries inventory of stock sizes in the USA, Europe, and Singapore.
If you need any material or have any questions. Please contact us today. Until next time.
Grand Canyon, Arizona USA
Boulden Company – Conshohocken, PA, USA | 1-610-825-1515
Boulden International, S.ar.L – Ellange, Luxembourg | +352 26 39 33 99