Pump Magazine On-Line

INDUSTRIAL DIGEST

Article #62 MATERIALS

This section  is dedicated as depository of information on materials and collection of the feedback from the pump end users, pump manufacturers, materials manufacturers, and other experts. These entries are posted as discussions, named "Entroids" - we hope you will find them informative and useful.

Entroid-1 - Question:

From: Posey, Lee Lee.Posey@valero.com
Sent: Sunday, October 10, 2010 1:53 PM
To: DrPump@PumpingMachinery.com
Subject: Recent Pump & Systems Article

Dear Dr. Nelik,

I enjoyed your recent article about using a specialty material to help improve the efficiency and reliability of a multistage pump.  I was interested in your selection of the Graphalloy material.  I have used Vespel CR6100 to reduce running clearances for efficiency gains and rotor stability improvements.  Do you have experience using Vespel?  If so, what comparisons can you make between this and Graphalloy?  When would you recommend one over the other?  Any experiences you can share would be greatly appreciated.

Best Regards,

Lee M. Posey

Entroid-1 - Answer:

Lee, - you are asking a difficult question. There is a great multitude of materials that can be used for pump bushings, including metals (bronze, hardened steels), hard coatings (which can be applied by many methods: fused deposition (cold or hot methods), laser treatment, nitriding, carburizing, etc.), non-metals (thermoplastics, thermosets, composites), ceramics. All of them have benefits and shortcomings, such as resistance to temperature, thermal or mechanical shock, machinability, galling resistance, dimensional stability, swelling, chemical resistance, abrasive resistance, etc., and also of course cost.

It would be good to have a 3-dimensional tabulation listing these materials on one column (say, horizontal), versus properties on the other (vertical), and application (pumped fluid) inside the table, for some sort of visual “pick-and-choose” guide, - but I am not aware of such table.

In practice, it is difficult to select a truly all-around best choice, for many reasons, mostly due to, frankly, unfamiliarity of the end users with the multiple products that exist, and users being cautious against over-zealous salesman trying to sell them a bushing material for their application which may or may not be appropriate for what they pump. By the time the problem surfaces, the salesman may already have moved to another job – selling, with vigor, something he previously just as vigorously used to be talking the end user against buying.

Pump manufacturer have a somewhat less biased approach to this, because they are willing to apply any material that the end user asks for (of course reflective in price), and/or their own experience with (usually a limited number of) material(s) they apply – and if they do not hear anything bad about the material from the field, - good enough (no news is good news!), it probably indicates to them it works.

To truly know, one needs to have a good survey of the cross-section of interested parties: material manufacturers, pump supplier, and end users, to produce and compile such tabulation. Back in my days with Goulds Pumps Engineering, we produced such tabulation, trying to reflect our experience and knowledge, and, although it was also limited, provided us with some degree of judgment when applying this or that material to this or that application. Other pump companies probably have similar internally generated selection guides, but very little is actually published, because, to be truly unbiased, such compilation would have to include, as I mentioned,  a wide spectrum of parties, with often unavoidably biased commercial interests.

My personal choice of Graphalloy, as presented in the article you read (for exmple:

www.pump-zone.com/pumps/centrifugal-pumps/specialty-materials-help-improve-pump-reliability-and-save-energy.html), was based on what I knew from my own experience working with it, while, in truth, also with limited knowledge of alternatives, some of which perhaps could work just as satisfactory, but unfortunately simply not known to me, other than superficially from the brochures and claims “we-the-best”, i.e. not from personal knowledge of the actual design(s) I had done. Back in my younger days with Ingersoll-Rand, graphalloy was also used, for example, for liquid CO2, at multi-stage pumps, with high pressures and low temperatures, obviously with very poor lubricity and viscosity. There was a paper published on that application some 20+ years ago, although I do not remember its title anymore. Knowing it handles CO2 (tough staff) makes it a good enough starting reason for me to review its potential for other applications. And that is how it works for most people: we use what we know works.

I will ask the Pumps & Systems editors to post this discussion at one of the issues, and will collect the feedback. I have started a section to reflect this feedback at:      www.pumpingmachinery.com/pump_magazine/maintenance/maintenance.htm (section: Materials) which will be used to collect such feedback(s), and available for the end users as information depository. As started, it is still in its infancy, but, as the information develops, it might evolve into a useful materials comparison resource.

Thank you for your question. Perhaps you have started a good information exchange on materials.

Lev Nelik, Ph.D.,  P.E.

President / Technical Director

Pumping Machinery, LLC

Atlanta, GA

Tel. 770-310-0866

Fax. 770-350-9311

email DrPump@PumpingMachinery.com

web www.PumpingMachinery.com

Feedback #1A (DuPont, USA)

Dear Lee,

I am one of the applications engineers with the Kalrez® & Vespel® business of DuPont.  
Your inquiry on Vespel® has been forwarded to us by Dr Nelik.

I would like to take this opportunity to send you some of our literature (was attached with Mr. Lunardi email), while trying to help answer some of your questions. Among the different families of Vespel® products, CR-6100 is the one specifically recommended for use in centrifugal pumps. Its key performance attributes are:

1. Nearly universal chemical resistance, being able to work in a wide range of acid and alkaline environments (pH range from about 0.2 to 14);

2. It is a non-porous material;

3. Excellent in water or steam services;

4. Easily machinable/lapped to surface finish <16 RMS. It does not generate dust when machined;

5. It is non-brittle, tough under impact;

6. It has high tensile & compressive strength (in its x-y plane);

7. Excellent stiffness and creep resistance under high  loads;

8. Adequate thermal conductivity thanks to overlapping carbon fibers;

9. Non-galling properties;

10. Self Lubricating, dry run capabilities;

11. Broad temperature range capability ( - 423 °F to + 550 °F);

12. Radial thermal expansion close to the CTE of steel shafts, which maintains the interference fits of bushings and wear rings over its temperature range capability;

13. Allow use of reduced running clearances to reduce equipment vibration and improve pump efficiency

14. Lower coefficient of friction than other materials;

Feedback #1B (Boulden International / DuPont Vespel, Europe)

Dr. Nelik,

 First, thank you for encouraging the dialogue about non-metallic materials. I have been working with DuPont™ Vespel® CR-6100 for the past 13 years—for 4 years as one of the first customers when I was a rotating equipment engineer at a refinery in California, and for the past 7 years representing Vespel® CR-6100. I currently represent Vespel® CR-6100 in EMEA (Europe Middle East Africa).

 The most important thing is for users to recognize the value of installing non-metallic wear rings with reduced clearance. Even after 20 years of experience with non-metallic wear rings, 98% of the pumps used in industry continue to use metal wear rings with larger clearances. These pumps with metal rings run with lower reliability, lesser efficiency, and are not as safe as pumps fitted with non-metallic wear rings. So, my input is to encourage users to recognize the value of non-metallic wear ring upgrades for their pumps, learn about the various options, and select the material they believe will provide them with the best reliability.

 As for providing users a guide of which materials to chose, I would point to API610 11^th Edition, Table H.3. It includes the most commonly used composite materials for industrial pump applications: Vespel® CR-6100 (under the cumbersome, non-commercial description of “PFA/CF reinforced composite 20% mass fraction random x-y oriented carbon fiber”), polyetheretherketone (PEEK) based composites, and impregnated graphite materials. The table provides acceptable operating conditions in terms of temperature and differential pressure. These limits are based upon feedback from the pump users community and the API committee is working to expand and improve the table with each successive edition of the standard.

 Beyond the temperature and pressure limits in table H.3, users should consider the following material characteristics:

 * Coefficent of thermal expansion

 * Chemical compatibility

·        * Limiting PV (pressure-velocity ratio)

·        * Creep Resistance

·        * Wear Rate

·        * Impact Resistance

·        * Thermal Shock Resistance

·        * Machining and Installation Characteristics

·        * For composite plastics, glass transition temperature

For a specific application, other properties may come into play, but the above list should be a good starting point for most centrifugal pump applications. Furthermore, users need to consider the full range of properties as the long-term performance of non-metallic materials is not driven by one or two factors, but a combination of a wide range of properties.

One final note, in your original response to the user, you suggest that users look to the pump OEM as an unbiased source of information. In some cases, this will be true, but not always. There are some pump OEMs who have commercial incentive to recommend certain materials. These commercial relationships are not always disclosed to the customer.

Best Regards,

Robert Aronen

Boulden International

27 Z.A.E. Le Triangle Vert

L-5691 Ellange

Luxembourg

+352 26 39 33 99 (Phone)

+352 24 61 16 62 (Fax)

+352 621 29 4321 (GSM)

robert@bouldencompany.com

Feedback #2 (Graphalloy)

Dear Lee,                                  

Dr. Nelik fowarded your response to his article in Pumps & Systems to me and also a Dupont email about Vespel.  I’d like to share some additional information about Graphalloy with you and especially to compare it to Vespel and other plastics.

As you are aware, Graphalloy has been used by Valero facilities for many years for various applications including pumps for boiler feed service, hydrocarbons, liquid gases and vacuum tower bottoms.

Compared to plastics, Graphalloy has some key advantages:

•      Excellent dimensional stability and heat-transfer capabilities.  Graphalloy is not just dimensionally stable in one or two directions - really dimensionally stable. No creep even under high loads!

•        Self-lubricating, superior run-dry capabilities.  Graphalloy outperforms plastics as it is a run-dry material that survives “loss of pumpage” operation for prolonged periods without either damage or preventing pump restart.

•       Non-galling.

•       Graphalloy has a constant coefficient of friction - our testing has shown that competitive materials including carbon fiber reinforced plastics and teflons experience degraded results when run dry at pump speeds.  (Testing for some of the published data about competitive products was performed at speeds  much lower than pumps experience.)

•       Clearances using Graphalloy can be greatly reduced to lower vibration levels and reduce cavitation with no risk of galling.

•       Graphalloy does not swell or cold flow (in any direction) and can be submerged in liquids.

•       Graphalloy has a wider temperature range than any plastic: Graphalloy performs in cryogenic temperatures, and is used in pump applications to 750 F (and much higher in non-oxidizing environments).

•       You can also choose to have Graphalloy machined to your specifications or semi-finished sizes to minimize subsequent machining.

•       Over 50 years of experience in multistage pumps, moving fluids from super critical ethylene to heater drain condensate to bottoms pumps.

 
If there is any other information we can provide you, including case histories, please contact us.