Singapore Presentation 2015 new

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


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


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

Tom

start here

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


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%


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.”


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.


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


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



• 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


Suitable for Use In:• Sour Service• Standard Service• Some Drilling Muds (Testing is Advised)• Aromatic Solvents• Zinc and Calcium Bromide


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


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 ElastomersCOMP: C

Time: 24 hr

Sol: Amine w/Diesel

Press: 6000 psi

Temp:330°F

VITON - ETP


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


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®

• 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)


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.


PerfluoroelastomersKALREZ® & CHEMRAZ®


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.


• Standard Service• Sour Service• Aromatic Solvents• High pH Fluids• Acidizing Solutions• Sulfur Solvents

Suitable For Use In:


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)


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


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


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


Elastomer Storage


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

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