2. Polymer Bearings Paper List
a. Surface Analysis of Fluoroelastomer Bearing Exposed to Geothermal Environment,
covers information on hydrothermal degradation mechanisms of the Viton elastomers
after being exposed for 4 months to geothermal environment. 6/2000
b. Hydrothermal Oxidation of Fluoroelastomer Bearings after a year-lon Exposure to
Geothermal Environments, which was under taken in Program No. 3.5.2 (Hightemperature
Polymeric Elastomers) aimed at identifying the potential Elastomeric
materials for use in bearing systems in down-hole pumps. 3/2001
c. Post-test results of the Ethylenepropylene-diene-terpolymer (EPDM) Elastomer
bearing that was used for 6months in Mammoth Pacific geothermal power station.
d. Elastomer testing/information –Viton ETP-500/ETP-900, September 2003
e. Candidate for Elastomer Bearing in Geothermal Down-hole Pumps, Brookhaven
3. Summary of Quarterly Progress Reports
QUARTERLY PROGRESS REPORT FOURTH QUARTER 1998
This quarter's work continued on the project design phase and began the procurement phase. The
evaluation of the concept bearing design was completed with the exception of the lubrication
system. The bearing design is to insert (vulcanize) high temperature rubber polymer (ZETPOL
2000 with a peroxide cure) bearings into larger inner diameter copies of the bronze bearings
manufactured out of carbon steel to increase tensile strength. The material ZETPOL 2000 was
chosen for heat resistance. This design allows use of the current lube string and line shaft design.
It was determined that the bearing design would allow for both lubricating flow paths
envisioned. This allowed an order to be placed for rubber bearings and some of the lube string
parts required for the modification of one test pump.
Additional design work and information gathering was undertaken on the lubricating water flow
path, control schemes, instrumentation and stuffing box bearing design.
The work proceeded with the remaining technical requirements that were not addressed last
quarter. These were as follows:
1. Design should review the required thickness and surface area of rubber bearing to allow
for a ten year lifetime, including suitability of a bearing every five feet.
2. Design should review required clearance of rubber bearing to that of line shaft and the
resulting clearance after thermal growth of all members.
3. Design should review changes to natural resonance of the line shaft due to changes in
bearing clearances or rigidity.
4. Design should review any significant changes in starting or running torque and resulting
effects on motor.
These issues were addressed one by one with both Johnston Pump and Palmer Products.
As discussed in the last quarterly report, there are pros and cons for competing lubricating water
flow paths. A flow path from pump discharge up through the lube string is the option that is most
seriously being pursued. The decision is being delayed while more input is being gathered from
A basic control scheme has been developed. This includes a flow meter of the annubar type to
measure lubrication water flow. The flow indication will provide input into protective logic to
shutdown the pump in the event of a loss of lubricating water flow to prevent bearing damage.
Additionally, an allowance for automatically reversing flow, to top down, in the event of a pump
trip is being studied. This will ensure lubricating flow during pump spin down.
To adopt a bottom up flow path, a method of returning the water back to the well at depth is
required. This is most likely going to be a capillary tube from the surface through the annulus to
a sufficient depth to prevent flashing and resultant scaling of the tube. The size of the tube should
be sufficient for the required flow rate, but small enough to prevent excessive flashing at the
throttle point. This sizing requirement is being worked on currently.
The pump stuffing box bearing is currently a pressed in bronze bearing. This will have to be
converted to rubber. This bearing is currently being designed.
Work proceeds to complete the design phase. The procurement
bearings that occurred during the initial test. Two bearings were submerged in a section of our
hot brine system to verify no chemical attack. After one week there was no attack or degradation
at all, but after six weeks the bearings exhibited the same expansion and extrusion of the rubber
that was evident during the pump test. This shows a reaction with the brine that is transforming
the rubber. The original test only subjected the bearings to approximately two days submergence
in hot brine, but expansion and extrusion occurred, while over seven days were required during
the static test. This indicates another influence involved such as friction or pressure.
The rubber manufacturer does not yet understand the mechanism of the rubber's transformation.
Because of this, work proceeds on several other fronts. Two bearings were manufactured out of a
viton based rubber versus a nitrile based rubber. These were submerged in a section of our hot
brine system for testing. The test has been ongoing for 8 days now.
Alternate bearing designs have been developed and evaluated, including modified hex, modified
octagon and partial arc (cross sections are attached). These allow more lubricating flow and less
contact than the standard hex design. This will allow less critical tolerances for heat expansion.
A prototype partial arc design has been manufactured.
Work has progressed on a silicon based bearing impregnated with graphite. The material, trade
name AFLAS, has excellent heat properties, but poor resistance to tearing. Impregnating with
graphite will make it a more suitable candidate for a bearing material.
A silicone coating applied to the bearing immediately after milling to fill the natural pores has
been discussed as a way to prevent entry of brine into the material.
In summary, testing will continue until the transformation is understood and/or a more suitable
bearing material or manufacturing process is selected. The material will be statically tested
successfully and at that time another pump will be modified and tested.
Attached are several reports:
INEEL assisted us in checking the thermal growth patterns and tensile effects on the lube string
to ensure this had not caused the loss of clearance. A report is attached.
Palmer Products issued two reports after the initial test. These are attached.