singapore presentation 2015 new
TRANSCRIPT
SEALS AND SEALING TECHNOLOGY
ByThomas W. Ray
T W R CONSULTANTS
Education SymposiumJuly 2015
Introduction• All potential causes of seal failure must be controlled. • Any of the following scenarios, if overlooked, can cause
premature seal failure:– Incorrect seal design; I.e., the environmental stresses exceed
the limits of the material.– Loss of strength due to shelf-aging
• Improper seal installation.• Improper choice of elastomer for the environment to be
sealed.• Poor quality assurance in manufacturing.
Introduction
Material selection is based on service conditions (temperature, pressure, and environment), customer requirements, and involves the total seal system.
Introduction - Continued• Two basic categories of seals
• Static• Dynamic
• Static seals should be zero-leakage• Seal must be resilient enough to flow and fill any small
irregularities on surface being sealed• Resist extrusion into gap between sealing surfaces• Both requirements must be long term• Dynamic requirements are somewhat conflicting and call
for a compromise• Good contact pressure with minimum friction
Basic Seal Mechanics
Prone To Extrusion Or Overstressing
• O-rings — simplest and most versatile type of seal Wide range of applications both static and dynamic Some of the basic mechanics of seal design using o-
rings are illustrated in the next slides.
Basic Seal MechanicsExtrusion / Overstress / Prevention - Static Seal
Extrusion / Overstress / Roll
Prevention - Dynamic &
Pressure Reverse Seal
Shaped Back-Up Ring
Working Pressure and Groove Design
Notes:
Basically controlled by clearance gap, temperature of system, and hardness of the ring.
Clearance gap can change in working environment due to expansion and contraction of metal parts.
Extrusion of 95 Shore A O-ring
9000
9500
10000
10500
11000
11500
12000
12500
13000
13500
14000
150 200 250 300 350 400
6 MILS
8 MILS
10 MILS
12 MILS
(66) (93) (121) (149) (177) (204)
(97)
(93)
(90)
(86)
(83)
(79)
(76)
(72)
(69)
(66)
(62)
Test Conducted w/o Back Rings Under Status Conditions
Temperature (°F)(°C)
Pres
sure
(PSI
)(M
Pa)
Working Pressure and Groove Design - Continued
• Low-temperature operation can use a shallow groove, whereas high-temperature uses a deeper groove to allow for expansion.
• Typical o-ring groove design should have :– A radius of 0.50 to 0.75 mm (0.020 to 0.030 inches) in the bottom
corners. – Top edge 0.12 mm to 0.25 mm (0.005 to 0.10 inches) to eliminate a
cutting edge.• Groove finish is important as it affects the wear and life of
the seal.• A finish of better than :
– 0.75 m (37 inches) is recommended for static – and 0.4 m (16 inches) is recommended for dynamic
Working Pressure and Groove Design - Continued
Notes to Remember1. Remember - Elastomers are
incompressible2. In general, the compression for static o-
ring should be 15 to 30%, depending on the cross-section
Working Pressure and Groove Design - Continued
Reduction in cross-section due to stretch
Squeeze should never be below 5%
Diametral Stretch, %
Red
uctio
n in
Cro
ss S
ectio
n Sq
ueez
e %
Vee-Packing· Also known as “chevron” rings.· Used in both static and dynamic applications.· Pressure rating and low temperature sealing capability can
be increased by using two or more rings together.
· Failure Mode: Extrusion into clearance gap.· Fiber filler gives a very slight improvement in extrusion
resistance.
DOUBLE MALE ADAPTER
METALRING
SOFTRING
HARDRING
BACKUPRING
Back-Up Ring Hard Ring
Soft Ring Retainer Wire
Double Male Adapter
Mandrel
CN
0150
8Seal Assembly
· Variety of seal types are needed
· HP/HT designed to move
· Vee-rings designed to have initial interface with seal bore
· Pre-loaded seal-Retainer Wire
Seal FailuresCompression SetProbably the most common cause of o-ring failure• A continuous “Seal Line” between sealed
surfaces must be maintained to prevent leakage• Proper selection of gland or groove design and
cross-section of the ring will give correct squeeze or compression
• Compression set is reported as the percent of deflection by which the elastomer fails to recover after a fixed time under a specified squeeze and temperature.
Seal Failures - ContinuedCompression Set - Continued
Causes of compression set– Some materials inherently have poor compression set– Excessive temperature– Incomplete curing– Fluid incompatibility
• Desirable to have low compression set values
Seal Failures - ContinuedSpiral Failure• O-Rings are not
particularly suitable for slow speed reciprocating seals
• The amount of squeeze is very important - too much promotes spiral failure
• Spiral failure usually caused by conditions which allows some part of the ring to slide and the other to roll
Explosive Decompression• Rubber is not 100% dense material.• Molecular void or air space make up 3-4% of a
seal’s volume.• Gases under pressure enter these void sites.• Three problems can occur
• Blistering• Rupture or fracture• Explosion
• Blistering is characteristic of materials having• Low Hardness• Low Cross-link Density• High Elongation
• Rupture is characteristic of materials having• High Durometer• High Cross-link Density• Low Elongation• Undersized O-Ring Groove
• In the past, explosive decompression was characteristic of high performance materials such as:
• Chemraz• KalrezBut improvements in compounding and the base polymer has greatly improved their resistance to explosive decompression.
• Preventing Explosive Decompression• Avoid Testing with Gas - CO2 is probably the most destructive• All gases will cause some problems• Very slow bleed-down is recommended
• Below 1500 psi• 20 psi per minute• or 100 psi; wait 10 minutes; another 100 psi• Continue to atmospheric pressure
• Testing on surface with gas can cause damage to seals before equipment is placed in service if bleed-down procedure is not followed.
Explosive Decompression - Cont’d
Explosive Decompression
Example of surface cracks caused by explosive decompression.
Explosive Decompression
WhereG = shear modulusv = Poisson’s ration 0.5
Cannot change critical pressure and flaw size easily.Shear modulus can be altered by changing the cross-link density or adding reinforcing filler to the rubber.
• Three major factors controlling seal resistance to these types of failures:• Critical Pressure is defined as
5E 6
• Flaw Size: 3-4% of Volume of Seal• Shear modulus of rigidity is defined as
G = E/2(1+v)
where E = Young’s modulusE = Tensile Stress (σ)/Tensile Strain ()
shear stressshear strain
s
s
Causes Of Seal Failure
Maintenance
GlassTransitionTemp Too High
Slow ElastomerRecovery
O-ring NotLubricatedAt Assembly
Abrasion
Too Rough/TooSmooth SurfaceFinish
PoorLubrication
HighTemperature
FluidContamination
MiscCauses
WeatherOzoneCracking
PlastigizerExtraction
Gas ExpansionRupture
Failure ofBack-up Ring
PressureSurges
Extrusion of Back-Up Rings
ThermalCharge
SpiralFailure
Proper CrossSection Not Used
Effects OfStroke Speeds
Uneven Dispensionof Lubricant
UnevenSurface Finishes
SideLoads
InstallationDamage
ManufacturingDefects
DifficultAccess
ID Too LargeOn Piston Seal
Too LittleElongationRod Seals
OD Too SmallOn Piston Seal
Sharp CornersThreads
InsufficientLead In Chamfer
Out OfDimensions
Excessive Flash
Poor KnitLines
InadequateQ.C.
Inclusion OfElastomerContaminants
No Back-UpRings
PressureToo High
O-ring “Bonds” To Mating Surface
Low TemperatureContraction
Should Not BeUsing Elastomer Seal
Low TemperatureBrittleness
Improper Elastomer
ImproperDesign
GlassTransitionTemp Too High
Slow ElastomerRecovery
InsufficientElongation
ImproperCompounding
CompressiveModulus Too Low
Tensil ModulusToo Low
InadequateSqueeze
ExcessiveStretch
RetrofitConstraints
ImproperSurface Finish
Improper VolumeIncrease Allowance
Extrusion /Nibbling
O-Ring Softened/Swelled by fluid
O-ringToo Soft
ClearanceToo Large
Clearance DecreasesUnder Pressure
CornersToo Sharp
PressureSurges
ExcessiveSwell
Ref Fluids NotRepresentative Of Service Fluid
Service Fluid /Rubber Incompatibility
PreservationFluid Effect
AggressiveAdditive
Compression Set (Stress Relaxation)
Improper HighSet Compound
InadequateCure
Hardening
TimeEffect
Temp TooHigh
ExcessiveSqueeze
Too SmallCross Section
• Mechanical properties should be examined in terms of temperature
• Illustrates change in shear modulus on cooling
Mechanical Properties
• Note the transition region is arbitrarily taken at 100 MPa shear modulus
• Material no longer has any rubbery properties - now stiff and brittle
• Hardness of 95 Shore A gives a shear modulus of 10 MPa• Very little rubbery properties left
Mechanical Properties – (Cont’d)
SHEAR MODULUS vs. HARDNESS
ShearModulus-G
MPa
10
3
1
0.3
0.1
0 20 40 60 80 100
Durometer
SHORE A
IRHD
NITRILE (NBR) ELASTOMERS
Used in Completion Products and Completion Service Tools
NITRILE (NBR) ELASTOMERS• Polymer of Butadiene and Acrylonitrile• Workhorse elastomer of the oilfield• Good resistance to oil swell• Nitrile seals (all types) are used in the
majority of wells worldwide• Useable from -20F (-29C) to 275F (135C) in
standard service• Good explosive decompression resistance if
compounded correctly
NITRILE (NBR) ELASTOMERSSuitable for Use In:
• Crude Oil• Brines• Sweet Gas• Most Water-Base Drilling Muds (Testing is
advised before use in oil-base mud.)• Methanol Injection• Water Injection• Water Base Inhibitors• CO2 Injection
NITRILE (NBR) ELASTOMERSTemperature Range:
• From -20F (-29C) to 275F (135C) long term application and where seal movement is required
• Up to 325F (163C) short term application and where no seal movement is required
• Peroxide cured material should be used for higher temperature
NITRILE (NBR) ELASTOMERSCautions / Limitations:DO NOT USE IN:
• Sour service• Oil based organic amine corrosion
inhibitors• Zinc and Calcium Bromide (contact
elastomer group)• Aromatic Solvents• Explosive decompression can be controlled
with proper bleed-off if procedure is followed
• Back-up rings are suggested for o-rings if temperature exceeds 225F (107C) and 3000 psi
NITRILE (NBR) ELASTOMERS
Nitrile / Buna-N - Continued
Types of Seals Temperature Range
• Elements Retrievable 275°F (135°C)• Permanent 350°F (176.7°C)• O-Rings 275°F (135°C)• Molded Seals 275°F (135°C) • Vee-Packing 275°F (135°C)
Not recommended• H2S • Zinc Bromide • Calcium Bromide • Xylene • Inhibitors –Oil
Soluble • Hydrochloric/
Hydrofluoric Acids • Calcium
Hypochlorite (Packer Fluid)
• CO2 – Some Swell• Methane – Some
Swell• Alcohols – OK• Inhibitors – Water
Soluble – OK• Diesel – Some Swell• Brine – OK• Sweet Oil & Gas –
OK
Environments
HNBR (Highly Saturated Nitrile Elastomers)
Used in Completion Products and Completion Service Tools
HNBR (Highly Saturated Nitrile Elastomers)
• Polymer of standard nitrile (butadiene and acrylonitrile) with added chemistry.
• Better resistance to H2S than standard nitrile
• Higher temperature use than standard nitrile
• Not as good in explosive decompression as standard nitrile
HNBR (Highly Saturated Nitrile Elastomers)
Suitable for Use In:• Crude Oil• Brines• Methane• Methanol Injection• Water Injection• Water Base Inhibitors• CO2 Injection• Ethylene Glycol Fluids• Sour Service, H2S less than 5%
HNBR (Highly Saturated Nitrile Elastomers)
Temperature Range:• From -20F (-29C) to 325F (163C) with
sulfur cured material and 350F (177C) with peroxide cured material
• Up to 350F (177C) with sulfur cured material if no seal movement is required
Note: The specification for HNBR should state “if material is sulfur or peroxide cured.”
HNBR (Highly Saturated Nitrile Elastomers)
Cautions/LimitationsDO NOT USE IN:
• Oil base inhibitors• Aromatic solvents• Zinc or calcium bromide (contact elastomer
group)• Sulfur cured compounds have better
extrusion resistance than peroxide cured materials.
HNBR (Highly Saturated Nitrile Elastomers)
Cautions/LimitationsDO NOT USE IN:
• Sour service when the H2S content exceeds 5%.
• With oil based inhibitors, zinc or calcium bromide, or with aromatic or halogenated solvents.Harder compounds (90+ Duro) will not have as much swell in CO2 as softer compounds. This also applies to explosive decompression situations.The sulfur-cured materials have better extrusion resistance than peroxide-cured ones.
Notes
HNBR (Highly Saturated Nitrile Elastomers)
Highly Saturated Nitrile
Type Of Seals• C02 - Some Swell• Alcohols - OK• Sweet Oil & Gas -
OK• Brine - OK• Inhibitors - Water
Soluble - OK• No Molded Seals Or Vee-Packing
Tested At This Time
• Elements
RetrievablePermanent
355°F (176.7°C)375°F (190.6°C)
Not Recommended• H2S — Fair• Zinc Bromide • Aromatic
Solvents (Xylene)
• Inhibitors - Oil Soluble
Temperature Range
Environments
VITON® & FLUOREL® Fluorocarbon Elastomers
Used in Completion Products and Completion Service Tools
VITON® & FLUOREL® Fluorocarbon Elastomers
• Polymer of Vinylidene Fluoride and Hexafluoropropylene
• Improved temperature rating over standard nitrile
• Resistant to acids (HCL and HF) if compounded correctly
• Good resistance to aromatic solvents• Fluorel has good explosive decompression
resistance
VITON® & FLUOREL® Fluorocarbon Elastomers
Suitable for Use In:• Sour Service• Standard Service• Some Drilling Muds (Testing is Advised)• Aromatic Solvents• Zinc and Calcium Bromide
VITON® & FLUOREL® Fluorocarbon Elastomers
Temperature Range:• Viton from -20F (-29C) to 325F
(163C) for long term application or where seal movement is required
• Fluorel -20F (-29C) to 400F (204C) for long term application or where seal movement is required
VITON® & FLUOREL® Fluorocarbon Elastomers
Cautions / Limitations:DO NOT USE IN:
• Steam• Organic Acids (such as Acetic or Formic)• Methanol Injection• Organic Amine Corrosive Inhibitors • High pH Fluids (pH 8 or greater)
Note: Back-up rings are recommended at temperatures above 250F (121C) and 5000 psi.
VITON® & FLUOREL® Fluorocarbon ElastomersFluorocarbon Elastomers
Environments Types Of Seals Temperature Range
• Glutaraldehyde (Biocide)
Not Recommended• Organic Amines
(Inhibitors) • Methanol Injection
• Steam
• Formic & Acetic Acids
• Dimethyl / Disulfide(DMDS)
• High pH Fluids
(Xylene) - OK
(Usually < 10%)
Acid (Caution) - OK
• H2S - OK
• Zinc Bromide - OK
• Calcium Bromide - OK
• Aromatic Solvents
• C02 - Some Swell
• Hydrochloric / Hydrofluoric
• Sweet Oil & Gas - OK
• Retrievable (Viton) (Fluorel)
• O-Rings(Fluorel)
(Viton)
• Molded Seals(Fluorel)
• Vee-Packing(Filled)
(UnFilled)
• T - Seals
350°F (176.7°C)400°F (204°C)
325°F (162.8°C)400°F (204°C)
400°F (204°C)
350°F (176.6°C)325°F (162.8°C)
400°F (204°C)
COMPOUNDED WITH LEAD OXIDE
COMPOUNDED WITHOUT LEAD OXIDE
FLEXIBLE
BRITTLE
VITON® & FLUOREL® Fluorocarbon Elastomers
VITON® & FLUOREL® Fluorocarbon ElastomersCOMP: C
Time: 24 hr
Sol: Amine w/Diesel
Press: 6000 psi
Temp:330°F
VITON - ETP
Used in Completion Products and Completion Service Tools
VITON - ETP
• A premium fluorocarbon elastomer being investigated for long-term downhole applications
• Polymer of ethylene, tetrafluoroethylene and perfluoromethylvinyl ether
• Good resistance to high pH fluids• Good resistance to most oil-base
drilling muds• This compound is now available for
seals
VITON - ETP
Suitable for Use In:• Sour Crude• Oil-Base Drilling Muds• Potassium / Cesium Formate Fluids• High pH Fluids• Brine Solutions• Zinc and Calcium Bromide• Hot Diesel with Inhibitors• Aromatic Solvents
Note: In all the above tests, Viton-ETP gave outstanding results.
VITON - ETPTemperature Range:
• From -20F (-29C) to 400F (204C)
• Vee-Packing tested to 400F (204C) and 15,000 psi
VITON - ETPCautions / Limitations:
• Back-Up Rings are recommended as with all Fluorocarbon Elastomers
• This material now has field history with outstanding results
AFLAS ® - FLUOROCARBON
ELASTOMER Used in Completion Products and
Completion Service Tools
AFLAS® - FLUOROCARBON ELASTOMER
• Polymer of Tetrafluoroethylene and Propylene
• A 100 H Polymer has been used successfully in downhole applications
• First used in South Texas in deep hot well in mid 1980’s
• Packers are still in the holes with no problems
• Packers tested to 450F (232C) and 13,000 psi differential
• Held temperature and pressure for 20 hours• Test completed - No Leaks• Temperature Range 100F (38C) to 450F
(232C)
Suitable for Use In:• Standard Service• Sour Service (H2S)• Zinc and Calcium Bromide• High pH Fluids• Organic Amine Corrosion Inhibitors• Organic Acids
AFLAS® - FLUOROCARBON ELASTOMER
Cautions / Limitations:DO NOT USE IN:
• Aromatic Solvents• Oil-Base Drilling Mud - Testing is
advised• Hot Diesel Completions
Note: Back-up rings are recommended above 250F and 6000 psi.
Note: Aflas® seals should not be used below 100F (38C) because of the glass transition temperature.
AFLAS® - FLUOROCARBON ELASTOMER
Aflas®
• CO2
• H2S RESISTANCE• Zinc Bromide• Calcium Bromide• Corrosion Inhibitor
( All Types)• Sweet Oil & Gas Production • Brines• Dimethyl \ Disulfide
( DMDS )
Some Swell ( Usually < 10% )Good
Very Good
Very Good
Very Good
Good Very Good
Very Good
Environments Types Of Seals Temperature Range
• Packer Elements Retrievable Permanent
400 O F (204 O C)450 O F (232 O C)
• O-Rings• Vee-Rings
( ATR ) • Molded Seals
400 O F (204 O C)
450 O F (232 O C)
400 O F (204 O C)
AFLAS® - FLUOROCARBON ELASTOMER
Physical Property vs Temperature
1000
100
10
1.0
0.1
Hard Glass
Glass Transition
Transition (Leathery)Regions
Rubbery
Viscous
ShearModulus, GMPa
Temperature
Aflas® seals are good in explosive decompression if they have been compounded correctly.
AFLAS® - FLUOROCARBON ELASTOMER
PerfluoroelastomersKALREZ® & CHEMRAZ®
Used in Completion Products and Completion Service Tools
Perfluoroelastomers KALREZ & CHEMRAZ
• Perfluoroelastomer• Chemically very stable• Can be reinforced with fibers• KTR (Kalrez, Teflon, Ryton) Seals were
used in hot sour well in late 1970’s. Some of these same seals are still in producing wells.
• In the early use of this material it was poor in explosive decompression resistance, but advances in compounding has improved its resistance to explosive decompression.
Perfluoroelastomers KALREZ & CHEMRAZ
• Standard Service• Sour Service• Aromatic Solvents• High pH Fluids• Acidizing Solutions• Sulfur Solvents
Suitable For Use In:
Perfluoroelastomers KALREZ & CHEMRAZ
Temperature Range:
• Kalrez from 100F (38C) to 450F (232C) as o-rings and up to 450F (232C) as vee-packing with a proper back-up system
• Chemraz from 40F (4C) to 450F (232C) as o-rings and up to 450F (232C) as vee-packing with a proper back-up system
Perfluoroelastomers – KALREZ & CHEMRAZ
Cautions / Limitations:• Proper bleed-down must be used in
order to avoid explosive decompression with both Kalrez and Chemraz.
• Kalrez should never be used below 100F (38C) because of the glass transition temperature.
Chemraz – Registered Trademarks of Green-Tweed Co.Kalrez – Registered Trademarks of DuPont Co.
Chemraz• Minimum Use Temperature 40 F (5 C)• Maximum Use Temperature 450 F (232 C)• Corrosion Inhibitor Resistance – Good• Solvent Resistance - Good• Gas Resistance (CO2, Methane, H2S) – Some Swell• Explosive Decompression Resistance – Good• Acid Resistance – Good• Backup Rings must be used
Type of Seal
• O-Rings
• Vee-Rings
• CTP
Temperature Range
• 40 F 450 F(5 C 204 C)
• 40 F 450 F(5 C 232 C)
• 40 F 450 F(5 C 232 C)
Kalrez• Minimum Use Temperature 100 F (38 C)• Maximum Use Temperature 450 F (232 C)• Corrosion Inhibitor Resistance – Good• Solvent Resistance – Good• Gas Resistance (CO2, Methane, H2S) – Some Swell• Explosive Decompression Resistance – Fair• Acid Resistance – Good• Backup Rings must be used
Type of Seal
• O-Rings
• Vee-Rings
• KTR
Temperature Range
• 100 F 450 F(38 C 204 C)
• 100 F 450 F(38 C 204 C)
• 100 F 450 F(38 C 232 C)
Perfluoroelastomers KALREZ & CHEMRAZ
Elastomers vs. Plastics in SealsElastomers· Resistant to Creep· Resilient / Compliant in Seals· Flexible for Easy Fitting into Grooves etc.· Capable of Recovery/Good Stress Relaxation
Plastics and Thermoplastic Elastomers· Creep (Cold)· Temperature Dependent· Lower Extensibility Making Fitting Difficult· Poor Compression Set Under Constant Deformation· Shaft Fretting in Mechanical Seals· Poor Compliance to Imperfect Finishes
High PerformanceThermoplastics
Used in Completion Products and Completion Service Tools
Thermoplastic Materials
Ryton
• RTR Seal Unit — 200° F (98 C) 350 F (177 C) at 15,000 psi
• RTR Seal Unit — 200 F (98 C) 450 F (232 C) at 10,000 psi
• Chemical Resistance — Good
• Broad Temperature Range
• Blends well with Glass and Teflon
• Good Mechanical Properties
• Impact Strength — Poor
• Elongation — Poor
PEEK
• PTP Seal Unit — 200 F (98 C) 450 F (232 C) at 20,000 psi
• PTP Seal Unit for Steam injection— 200ÞF (98 C) 550 F (288 C) at 3000 psi
• Chemical Resistance — Good
• Blends well with Glass and Teflon
• Broad Temperature Range
• Outstanding Thermal Resistance
• Good Elongation (up to 30%)
• Impact Strength — Good• Retention of Properties at Temperature
Seals have been tested to 600 F and 2000 psi
• Excellent Back-up Material for O-Rings and Vee-Packing
High PerformanceThermoplastics
Teflons
25% Glass Filled • Standard Material in Packer Seal Unit• Chemical Resistance — Good• Elongation — Good• Recommended for Standard or Corrosive Service• Hard Back-up Rings must be used with Teflon Vee-Packing• Can be used as Back-up Rings for O-Rings
40% Glass Filled • Used in PTP Seal Units for Steam Injection• Chemical Resistance — Good• Elongation — Good• Can be used as Back-up Rings for O-Rings• Recommended for Standard or Corrosive Service
Teflon Containing Molybdenum Disulfide• Back-Up Rings Must Be Used With This Material Under All Conditions• Chemical Resistance — Good• Impact Strength — Good• Extrusion Resistance — Poor
High PerformanceThermoplastics
Elastomer Storage
Used in Completion Products and Completion Service Tools
Storage (To Obtain Maximum Shelf-Life)
· Ambient Temperature Should Not Exceed 120F (49C).
· Protect from UV light such as the sun and fluorescent lights.
· Do not store near electrical equipment or welding machine. These produce ozone.
· Store in opaque package materials.
The End