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Difference between revisions of "Graphalloy"

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* Hard Carbons: These are the same materials used commonly to make seal faces.  They are very hard and often used in either abrasive services or pumps where dry-running is not expected to occur.
 
* Hard Carbons: These are the same materials used commonly to make seal faces.  They are very hard and often used in either abrasive services or pumps where dry-running is not expected to occur.
 
* Metals such as chrome or bronze.  These are the most traditional of the pump wear parts. Due to their tendency to gall, they are used in pumps where dry running is not expected to occur.
 
* Metals such as chrome or bronze.  These are the most traditional of the pump wear parts. Due to their tendency to gall, they are used in pumps where dry running is not expected to occur.
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'''References'''

Revision as of 13:23, 2 January 2020

Graphalloy is a trade name for a family of proprietary graphite-metal alloys used to make product-lubricated pump bushings, often in the oil and gas processing industry.  

Introduction:

Graphite is one of the two most common dry lubricants used in industry today[1] (the other being Molybdenum Disulfide). Graphite has unique properties that make it useful as a material for bushings when the risk of pump upset conditions rule out the use of traditional sleeve bushing materials.  Graphalloy is an alloy of Graphite and metal that takes advantage of the friction properties of Graphite while gaining the strength and thermal conductivity of metal.

Graphite Structure:[2]

Graphite is a carbon allotrope.  It is made up of layered sheets of hexagonally arranged carbon atoms.  The sheets themselves are called Graphene and bonds between each sheet are weak. The loosely bonded sheets of Graphene are what allows Graphite to be a good dry lubricant – Sheets will ablate from the Graphite surface to the rubbing surface, coating it and reducing friction. 

Graphalloy Structure:

Graphalloy is a graphite-metal alloy bushing material.  This alloy is produced through a combination of extreme temperature and pressure[3]. The result is that the natural pores in the graphite are filled with filaments of metal.  By weight, this alloy is typically 25-35% metal and 65-75% graphite or carbon-graphite. Because of this unique mixture, many of the benefits of metal and graphite materials are maintained, while eliminating the risks associated with using them alone: With metal bushings, Galling (adhesive wear or welding) due to dry-run is one of the biggest risks. 

Uses:

Graphalloy is often used to make bushings and wear rings for centrifugal pumps[4] and dampers in refineries and for pumps used in midstream transmission activities. The reason it is so widely used in pumps is the impact it has on reliability of equipment.  Due to its non-galling properties, Graphalloy parts can be designed with tighter running clearances than with using metallic wear parts[5]. These tighter clearances allow pumps to be run more efficiently and result in energy savings[6]. Graphalloy is also able to go to higher temperatures than other materials listed in the API 610 Standard under “non-metallic wear part materials”[7]. Graphalloy’s self-lubricating properties lead to better survival of dry running without causing damage to the pump itself.  This means less frequent repairs to pumps – and increases in MTBR/MTBF.

Limitations:

Although the material can withstand extreme temperatures from -450F to over +1000F, it is not usually used in heavy abrasive services.  Most chemicals are compatible with most grades of Graphalloy. 

Alternatives / Traditional Bushing Materials:

The main alternatives to Graphalloy materials as pump wear parts are in three categories:

  • Thermoplastics: The most common thermoplastics are PEEK (Polyether ether ketone), a thermoplastic material that API recommends for service up to 275F[7] and PFA/CF reinforced composite, another thermoplastic material that API says can be used up to 450F[7]. These materials do not gall, and therefore can withstand some limited dry running.
  • Hard Carbons: These are the same materials used commonly to make seal faces.  They are very hard and often used in either abrasive services or pumps where dry-running is not expected to occur.
  • Metals such as chrome or bronze.  These are the most traditional of the pump wear parts. Due to their tendency to gall, they are used in pumps where dry running is not expected to occur.

References

  1. [1] https://en.wikipedia.org/wiki/Dry_lubricant Accessed 12/27/2019
  2. https://en.wikipedia.org/wiki/Graphite
  3. https://www.graphalloy.com/html/features.html
  4. SPE 122415 – “Multistage Centrifugal Pumps for Drilling and Production Waste Injection Operations” Newman, McCosh, Woolsey, Boodhay. 2009. https://www.onepetro.org/conference-paper/SPE-122415-MS
  5. ANSI/API STANDARD 610. ELEVENTH EDITION (September 2010), page 38, Note at bottom of page. 
  6. “Specialty Materials Help Improve Pump Reliability and Save Energy” Dr. Lev Nelik, P.E. APICS. Published in Pumps & Systems magazine, December 17,2011.  Accessed on 12/27/2019 at https://www.pumpsandsystems.com/topics/pumps/centrifugal-pumps/specialty-materials-help-improve-pump-reliability-and-save-energy
  7. 7.0 7.1 7.2 ANSI/API STANDARD 610. ELEVENTH EDITION (September 2010), page 145