Elastomer Types Vta

8/12/2019 Elastomer Types Vta

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ElastomersElastomers



w w w . t i e r r a a l t a . c o m

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




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




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




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




Flurocarbon ElastomersFlurocarbon ElastomersTrade name “Viton”

Excellent resistance to heat

Excellent resistance to oils, solvents and

chemicalsExtremely poor mechanical properties

Hard to mold

Expensive




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




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)






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




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




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




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




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




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




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




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




Single Lobe 1:2Single Lobe 1:2

Thicker elastomer cross-section, therefore greater

swell/expansion…lower pump mechanical efficiency




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




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




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




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




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




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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Elastomer Types Vta