elastomer types vta
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8/12/2019 Elastomer Types Vta
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ElastomersElastomers
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Stator ElastomersStator Elastomers
Three basic types of elastomers extensively used:
Nitrile Rubbers (NBR), two common grades
Medium High (ACN), Buna
Ultra High (ACN), High NitrileHydrogenated or Fully Saturated Nitrile Rubbers
Flurocarbon Elastomers
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Nitrile RubbersNitrile RubbersThe majority of elastomers in PC pumps are
classified as nitrile rubbers (NBR)Emulsion copolymerization of butadiene with
acrylonitrile (ACN)
List of about 20 other ingredients, plasticizers, fillers,curatives, carbon black
Sulfur or peroxide cured
Least expensive and easiest to moldBest mechanical properties
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Acrylonitrile Effects on NBR Acrylonitrile Effects on NBRNBR material properties effected primarily by varying
the ACN contentMedium-high ACN (30-40%) content commonly
referred to as Buna N
Ultra-high ACN (>40%) content commonlyreferred to a High Nitrile
ACN increases polarity and improves resistanceto non-polar oils and solvents
I.e: Aromatics are non-polar
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Fully Saturated Nitrile RubbersFully Saturated Nitri le Rubbers
Butadiene portion of butadiene-acrylonitrile polymer
hydrogenated (fully saturated)Improved properties over NBR with respect toHeat resistance (150OC, 300OF)
H2S resistanceMore difficult to manufacture
Typically four times the cost of NBR
Typically designated as HNBR
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Flurocarbon ElastomersFlurocarbon ElastomersTrade name “Viton”
Excellent resistance to heat
Excellent resistance to oils, solvents and
chemicalsExtremely poor mechanical properties
Hard to mold
Expensive
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Elastomer Properties TableElastomer Properties Table
Characteristics
Buna High Nitrile Hydrogenated Viton
Mechanical Properties Excel lent Good Good Poor
Abrasiv e Resistance Very Good Good Good Poor
Aromatic Resistance Good Very Good Good Excel lent
H2S Resistance Good Very Good Excellent Excellent
Water Resistance Very Good Good Excellent Excellent
Tempertuare Limit ** 95 C (203 F) 105 C (221 F) 135 C (275 F) 150 C (302 F)
Elastomer Type
** The temperature at the pump must be 20- 30 C below this l imit to
accommodate the friction heat generated by the interference fit
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Material PropertiesMaterial PropertiesElastomer performance is dependent on its mechanical and
chemical properties
Compounding and Vulcanization also important
Primary mechanical properties are (ASTM):Liquid or Swell Resistance
Tensile StrengthTear ResistanceFatigue and Flex Cracking ResistanceHeat Resistance
Abrasion ResistanceHardnessElasticity (resilience)
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Fluid SwellFluid SwellElastomer is a permeable membrane
Swell is the result of fluid absorption by diffusion into theelastomer
Swelling takes place until equilibrium is reached throughoutthe elastomer
Oilfield fluids that commonly cause swell:higher API gravity oils that contain aromatics
aromatics: Benzene, Toluene, Xylene
Water, gas
Different elastomers have varying degrees of compatibilitywith a particular fluidI.e. Oils that contain aromatics will cause high swell in Bunaand
lower swell in High Nitrile elastomers
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Effects of Fluid SwellEffects of Fluid SwellSwelling can cause an excessively tight rotor/stator
interference fitTight fits may lead to a rapid hysteresis failure
Badly swollen stators exhibit high pump friction torque and
poor volumetric efficienciesPumps with minor swelling can generally be fit with a smaller
rotor and reused
Swell results in the deterioration of mechanical and chemicalproperties
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Thermal SwellThermal Swell
Heat causes overall expansion
Temperature resistance is dependent on chemicalstructure, base polymer etc.
Heat can break down the chemical structure resulting in a
deterioration of material properties
Heat can affect the adhesive bond between the elastomer
and stator tube
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Gas SwellGas Swell
Gas will permeate into an elastomer by diffusion
Permeation rate is determined mainly by the gas size,shape and polarity
Permeation is a diffusion process governed by:
temperature
pressure differential
thickness of elastomer
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Gas SwellGas Swell
Solubility determines the quantity of gas that will absorb into
the elastomer Gas solubility increases as the molecular weight of the gas
increases
CO2 & H2S more soluble than CH4
Elastomers with a high diffusivity value allow gas to escape
from elastomer when subjected to rapid pressure drops
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Elastomer BlisteringElastomer Blistering
Blistering is one result of Explosive Decompression (ED)
ED is when an elastomer compound is exposed to highpressure for a period sufficient for gas molecules to diffuseinto the compound, subsequent rapid reduction in pressurecan cause internal fracturing in the form of cracks or blisters
Elastomers exposed to CO2 is leading cause of ED failures
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ED contED cont
’’dd
Common causes of rapid pressure reductions:
Retrieving pump to surfaceRapid fluid equalization between casing and tubing in pumped off
wells. The deeper the well the more pronounced the pressuredrop.
Majority of damage at pump discharge Permeation is a diffusion process governed by:
temperature
pressure differential
thickness of elastomer
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Elastomer Fluid Swell /Elastomer Fluid Swell /
Thermal Expansion PhenomenonThermal Expansion PhenomenonThe amount of swelling or expansion can be expressed as a
percentage of the elastomer thickness
the thicker the elastomer, the more significant the swellTherefore the amount of change is dependent on the cross-
sectional profile of the stator elastomer
Since the stator cross section is non-uniform, resultantswell/expansion is also non-uniform
resulting in altered stator geometry and ultimately lowerpump efficiencies
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Single Lobe 1:2Single Lobe 1:2
Thicker elastomer cross-section, therefore greater
swell/expansion…lower pump mechanical efficiency
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Elastomer ThicknessElastomer Thickness
Tierra Alta design
engineering:Minimize the amount of
elastomer in the tube
Minimizes the effects
due to chemical/thermal
swell
Optimized Design
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Optimized Elastomer VolumeOptimized Elastomer Volume
Less dimensional fluid and/or temperature swell
Elastomeric rubber is an insulator
Thicker elastomer = more insulated heat
Thinner elastomer = more dissipated heat
Swell is measured as a % of the elastomer thickness
Thicker elastomer = more dimensional swell
Thinner elastomer = the less dimensional swell
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Elastomer SofteningElastomer Softening
Chemicals in the produced fluid attack the elastomer and
cause it to softenI.e. Amine based corrosion inhibitors
Aromatics will also cause softening
Softening results in the deterioration of the elastomerschemical and material properties
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Elastomer HardeningElastomer Hardening
Curatives (I.e sulfur) plus heat, pressure and time initiate thevulcanization process
Wellbore environments can contain all of the above
Wells that contain H2S may cause advanced vulcanization
HNBR (hydrogenated) elastomers have been speciallyformulated to reduce effects
Hardening results in the deterioration of mechanicalproperties
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Elastomer ShrinkageElastomer Shrinkage
Lower molecular weight parrafins (C3-C30) will extractplasticizers from NBR and cause shrinkage
Extraction of plasticizers results in an overall reduction inelastomer volume
Shrinkage will reduce rotor/stator interference fit
Wells that have wax problems correlate with elastomershrinkage
Shrinkage results in the deterioration of mechanical
properties
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Tierra Alta ElastomersTierra Alta Elastomers
M6 –Medium Nitrile Soft
Best elastomer for PCP
Soft durometer to improve abrasion resistance
H1 –High NitrileHigh Performance formulation
Best resistance to aromatic/chemical swell
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