Np_short_course_a

SESSION ON DRY GAS SEALS GE Nuovo Pignone Florence, October 1st and 2nd

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FLOWSERVE Dortmund GmbH & Co KG

Seal Basics

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GASSEAL Principle Layout Compressor Housing

Atmosphere

Stationary Face

Housing

Product

Springs

Retainer

Rotating Mating Ring

Thrust Ring Shaft

Sleeve

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Dry gas seal technology

• Non contacting mechanical seal design. • Faces are separated and lubricated by a thin gas film.

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Generating the gas film STATIC • Aerostatic forces separate the seal faces at pressures above 30psi (2bar).

DYNAMIC • Aerodynamic forces separate the faces above 6ft/sec (2m/s), e.g. 3inch (125mm) shaft at 200 rpm.

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Groove Geometries

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Circumferential gas packing

Inward pumping Flow Solutions Division BW Seals Durametallic Seals Pacific Wietz Seals Pac-Seal

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BI-DIRECTIONAL GROOVE DESIGN

T - Groove Phoenix - Groove

Christmastree Groove

U - Groove

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UNI-DIRECTIONAL GROOVE DESIGN

APG - Groove

Spiral - Groove V - Groove

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Benefits of dry running gas seals Feature

Benefit

• Bi-directional running

• Less spare parts required

• Lower leakage rates

• Less product loss

• Higher maximum operating pressure

• Simplified seal design & application

• Higher maximum operating speed

• Better seal standardization

• Stable seal performance under • Consistent reliable performance varying operating conditions

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Seal Types

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SINGLE SEAL = GASPAC S

Clean Gas

Clean Gas Leakage

PROCESS

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SINGLE SEAL = GASPAC S • Used for non-toxic and / or non-hazardous gases • Short in length • Low weight of the rotating mass • Pressurized by clean and dry gas • Moderate pressure range, up to 100 bar

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DOUBLE SEAL = GASPAC D Barrier Gas

Barrier Gas Leakage

Barrier Gas Leakage

PROCESS

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DOUBLE SEAL = GASPAC D • Used for toxic and / or hazardous gases • Short in length • Low weight of the rotating mass • Pressurized by an Inert Gas ( approx. 2-4 bar positive pressure differential to Product pressure) • Pressure range limited to 40 bar Product pressure

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TANDEM SEAL = GASPAC T

Clean Gas

Clean Gas Leakage

Clean Gas Leakage

PROCESS

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TANDEM SEAL = GASPAC T

• Prooven system up to 250 barg • Short in length • Low weight of the rotating mass • Full pressure differential sealed across one sealing gap only • Full pressure capability of the outboard seal

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TANDEM SEAL WITH INTERSTAGE LABYRINTH = GASPAC L Inert + Clean Gas Leakage

Inert Gas

Clean Gas

Inert Gas Leakage

PROCESS

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TANDEM SEAL WITH INTERSTAGE LABYRINTH = GASPAC L

• Same features as Tandem seal • The Inert Gas flow through the Interstage Labyrinth avoids Product Gas migrating to the Atmosphere

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Triple Seal

Clean Gas

Clean Gas (Half Pressure)

Clean Gas Leakage

(Full Pressure)

Clean Gas Leakage

PROCESS

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Triple Seal • System used by competitors in high pressure applications • Needs more axial space • Higher weight of the rotating mass • Full pressure differential can not be sealed across one sealing gap only • No full pressure capability of the outboard seal • No safety seal function possible Flow Solutions Division BW Seals Durametallic Seals Pacific Wietz Seals Pac-Seal

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Advantages of Bi-directional Lift off patterns

• Full interchangeable for both ends of the compressor • Fool save installation • Less spare parts • Reverse running of compressor without seal damage possible

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Standard Application Range

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GASPAC Application Range Standard • Static Sealing Pressure

High Pressure

120 bar

250 bar

• Dynamic Sealing Pressure 120 bar

230 bar

• Circumferential Speed

200 m/s

150 m/s

• Temperature Range

-80°C to +180°C

-80°C to +210°C

• Shaft Diameter

30 to 250 mm

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Gas Seal Application Range 400

pressure [bar]

300

200 High Pressure - Standard

120

Standard 50

100

150 Shaft Diameter [mm]

350 Flow Solutions Division BW Seals Durametallic Seals Pacific Wietz Seals Pac-Seal

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Change of Operating Parameters %

350 Druck Pressure

300

Geschwindigkeit Speed

61700 bar m/s ~ + 210 %

pxV

425 bara ~ +120 %

250 200

145 m/s ~ + 40 %

150 100 1994

1995

1996

~ 20000 bar m/s ~ 110 m/s ~ 200 bara

1997

1998

1999

2000

2001

2002

2003

Jahr Year

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Special Limits

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Gas Seal Special Condition Limits

High Speed and Low Pressure Differential • Outboard Seal in Tandem Arrangement Low Speed • Ratchet Slow Roll • Continuous Slow Roll

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Low pressure differential / High speed Film damping vs. speed for seal size 55

Film damping [Ns/µm]

80

1,2 bara; // - Gap 1,0 bara; // - Gap 1,0 bara; V - Gap 1,0 bara; A - Gap

75 70 65 60 55 50 5000

10000

15000

20000

Speed [rpm] Flow Solutions Division BW Seals Durametallic Seals Pacific Wietz Seals Pac-Seal

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Low pressure differential / High speed

Film stiffness [N/µm]

Film stiffness vs. speed for seal size 55 130 120

1,2 bara; // - Gap 1,0 bara; // - Gap 1,0 bara; V - Gap 1,0 bara; A - Gap

110 100 90 80 70 60 5000

10000

15000

20000

Speed [rpm] Flow Solutions Division BW Seals Durametallic Seals Pacific Wietz Seals Pac-Seal

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Slow Roll Capability • Rachet slow roll < 1 m/s • Differential pressure up to operation pressure • unpressurized up to 0.3 m/s • Speed appr. 2 m/s for continuous slow roll Shaft-ø > 100 mm: Pressure differential 0.2 bar Shaft-ø < 100 mm: see diagram Flow Solutions Division BW Seals Durametallic Seals Pacific Wietz Seals Pac-Seal

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Slow roll capability continued

sealing pressure [bara] p1 at OD

7 Kz 31 Kz 35 Kz 47 Kz 41

6 5 4 3

required sealing pressure for achieving an 1-1.2µm working gap width at 1.8 m/s speed

2 1 1

1,2

1,4

1,6

1,8

2

2,2

back pressure [bara] p2 at ID Flow Solutions Division BW Seals Durametallic Seals Pacific Wietz Seals Pac-Seal

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Theoretical Background I) Pressure distribution

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Calculated Influences Seal Faces: Taper, Groove geometry Atmosphere: Backpressure

Productside: Gas, Pressure, Temperature

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Static equilibrium of forces Gap opening force

Pressure Force

Gap opening force Friction

Friction Spring Force Pressure Force

Gap opening Force = Pressure Force + Spring Force +/- Friction Flow Solutions Division BW Seals Durametallic Seals Pacific Wietz Seals Pac-Seal

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Calculation Tools Gasdynamic • CFD developed by University of Braunschweig within a Turbomachinery sponsored research program • Assumption of isothermal conditions in the sealing gap (laminar or turbulent flow) • Calculation of local Machnumbers • Calculation of high speed and high pressure possible • Interface with FE program Flow Solutions Division BW Seals Durametallic Seals Pacific Wietz Seals Pac-Seal

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Groove depth

Calculated Area

Se a

Inner Diameter

lin

gd

Outer Diameter

am

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Boundary Conditions

Speed

Sealing pressure, Temperature, Kind of gas

Inside Pressure Flow Solutions Division BW Seals Durametallic Seals Pacific Wietz Seals Pac-Seal

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3-D Pressure Field

Size Shaft- Ø Sealing Pressure p Inside Pressure p Speed n Medium

: Kennz. 55 : 130 mm : 5 bara : 1 bara : 11000 min-1 : Air

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Calculation of the Integral Pressure Distribution

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Theoretical Background II) Deflection

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Calculation Tools

Deflections, Temperature-Influence: • Finite Elemente Method (ANSYS) • Coupled with gasdynamic-program • Also used as stand alone calculation tool

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FE - Model

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Coupling of the pressure distribution with the face distorsion • Compiling the pressure lines from the 3-D pressure field to an integral, representative pressure distribution • Transfering the pressure distribution to the Finite Element Program • Calculation of the face distorsion with the pressure distribution • Restart calculation of the pressure distribution with the calculated face distorsion • Further steps of the iteration, until the pressure distributions in accordance with the face distorsion Flow Solutions Division BW Seals Durametallic Seals Pacific Wietz Seals Pac-Seal

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V-Gap

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V-Gap

• Higher pressure at the Inner Diameter • Lower pressure at the Outer Diameter • Inertial moment with the tendency to create an A-Gap

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A-Gap

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A-Gap

• Higher pressure at the Outer Diameter • Lower pressure at the Inner Diameter • Inertial moment with the tendency to create a V-Gap

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Iterationloop

This Iterationloop will be calculated until the interaction between the face distorsion and the integral pressure distribution is synchronized.

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Leckage

V

Leckage-Behaviour for different Gap Geometries

Design Pressure

V-Gap Optimum A-Gap

Sealing Pressure

p

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Stationary face distorsion in Y- direction at 100bar sealing pressure

- .213E-03 - .1087 E-03 -.00255 E-03 .1027 E-03 .2079 E-03 .3131 E-03 .4183 E-03 .52355 E-03 .62877 E-03 .734 E-03

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Further Calculation Results

• Working gap width under calculated pressure differentials and speeds • Filmstiffness • Filmdamping • Powerloss

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Theoretical Background III) Gas Film

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Working Gap Width Size : Kennz. 55 T-Groove Shaft-Ø : 135 mm

Gap width [µm]

8

n= 11000 min-1 n= 7400 min-1 n= 3700 min-1

7 6 5 4 3 2 1 0 0

50

100

150

200

250

Pressure differential [bar] Flow Solutions Division BW Seals Durametallic Seals Pacific Wietz Seals Pac-Seal

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Filmstiffness

Filmstiffness [kN/mm]

4000

Size : Kennz. 55 T-Groove Shaft-Ø :135 mm

n= 11000 min-1 n= 7400 min-1 n= 3700 min-1

3500 3000 2500 2000 1500 1000 500 0 0

50

100

150

200

250

Pressure differential [bar]

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Damping Size : Kennz. 55 T-Groove Shaft- Ø : 135 mm

Damping [kNs/mm]

1000

n= 11000 min-1 n= 7400 min-1 n= 3700 min-1

750

500

250

0 0

50

100

150

200

250

Pressure differential [bar]

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Summary Gasfilm Model

Spring / Damper System

• The damping coefficient must be positive to maintain the gas film • The film stiffness is strictly related to the gap width, the smaller the gap width, the higher the film stiffness • The adapted gap width is mainly related to the balance ratio. The result of a higher balance ratio is a smaller gap width. Flow Solutions Division BW Seals Durametallic Seals Pacific Wietz Seals Pac-Seal

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Summary • The Stationary Face must follow the movements of the Rotating Face without overpressing the gasfilm. In any case the gasfilm must carry the loads created by the springs and the friction of the secondary sealing element. • Additional loads will be created by axial vibrations (accellerations). Example: The maximum vibrationlevel acc. VDI 2063 is 4*g • The mass of the stationary face is 0,08 kg • With an assumed accelleration of 4*9,81 m/s²= 39,24 m/s² the axial force equals : F=m*a= 0,08 kg*39,24 m/s²= 3,124 N • The measured friction of the secondary sealing element is 5 N, which is resulting in an additional total axial force of appr. 8,2 N. • A gas film with a stiffness of 100 N/µm will be squeezed with this axial force by appr. 0,08 µm. Flow Solutions Division BW Seals Durametallic Seals Pacific Wietz Seals Pac-Seal

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500

Gap width [µm]

Filmstiffness [N/µm]

Influence of axial vibrations on the gasfilm n= 11000 1/min n= 7400 1/min n= 3700 1/min

400 300 200 100 0

8 7 6 5 n= 11000 1/min n= 7400 1/min n= 3700 1/min

4 3 2

0

5

10

15

Pressure differential [bar]

20

0

5

10

15

Pressure differential [bar]

20

The filmstiffness of 100 N/µm exists at appr. 2,5 bar pressure differential. The gap width will change at n= 11000 min-1 from 7,5 µm to 7,5 µm - 0,08 µm = 7,42 µm Flow Solutions Division BW Seals Durametallic Seals Pacific Wietz Seals Pac-Seal

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Theoretical Background IV) Groove Geometry Comparison

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Comparison of different Groove Geometries The boundary conditions for the following comparison between T-Grooves and APG-Grooves are identical • Seal Size • Balance Ratio • Damwidth • Groove to Land Ratio • Spring Force Flow Solutions Division BW Seals Durametallic Seals Pacific Wietz Seals Pac-Seal

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Balance Ratio Seal Face area

k=

Pressure loaded area

Pressure loaded area Seal Face area

The Balance Ratio determines the main load on the gasfilm Flow Solutions Division BW Seals Durametallic Seals Pacific Wietz Seals Pac-Seal

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Static equilibrium of forces Gap opening force

Pressure Force

Gap opening force Friction

Friction Spring Force Pressure Force

Gap opening Force = Pressure Force + Spring Force +/- Friction Flow Solutions Division BW Seals Durametallic Seals Pacific Wietz Seals Pac-Seal

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Groove Geometries APG - Groove

Dam

Land

Groove

T - Groove

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Lift - Off - Speed 250

5

500

1000

1500

2000

Size : Kennz. 49 Speed Shaft-Ø : 115 mm [1/min]

Gap width [µm]

4 3 2

SMT 0 barg SMT 2 barg SMT 4 barg APG 0 barg APG 2 barg APG 4 barg

1 0 2

4

6

8

10

12

14

16

18

20

Circumferential speed [m/s] Flow Solutions Division BW Seals Durametallic Seals Pacific Wietz Seals Pac-Seal

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Filmstiffness comparison Size : Kennz. 49 Shaft-Ø : 115 mm Speed n : 11.000 min-1 Medium : Air

400

Filmstiffness [kN/mm]

350

APG-Groove

300 250 200

SMT-Groove

150 100 50 0 0

1

2

3

4

5

6

Pressure [bara]

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Gap width comparison Size : Kennz. 49 Shaft-Ø : 115 mm Speed n :11.000 min-1 Medium : Air

Gap width [µm]

9 8 7

SMT-Groove

6 5 4 3

APG-Groove

2 1 0 0

1

2

3

4

5

6

Pressure [bara]

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Isobarlines for APG- Grooves Pressure [barg] 3,08 2,85 2,62 2,39 2,16 1,93 1,69 1,46 1,23 Size Shaft-Ø Speed n Sealing Pressure p Medium

: Kennz. 49 : 115 mm : 50 min-1 : 3 barg : Air Flow Solutions Division BW Seals Durametallic Seals Pacific Wietz Seals Pac-Seal

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Isobarlines for T- Grooves Pressure [barg]

Size Shaft-Ø Speed n Sealing Pressure p Medium

: Kennz. 49 : 115 mm : 50 min-1 : 3 barg : Air

3,08 2,85 2,62 2,39 2,16 1,93 1,69 1,46 1,23

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Theoretical Background V) Gas Comparison

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Comparison of different gases Size Shaft-Ø Speed n Circumferential Speed u Gas Air

: Kennz. 66 : 180 mm : 7900 min-1 : 110 m/s

Dyn. viscosity Gasconstant Standard density η ∗10 −4 [Pas] R [J/kgK] [kg/m³] 1,82 287 1,29

H2

0,89

4124

0,09

He

1,96

2077

0,179

CO2

1,49

Processgas

0,982

188,9 1138

1,98 0,102 Flow Solutions Division BW Seals Durametallic Seals Pacific Wietz Seals Pac-Seal

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Calculated filmstiffness for different gases Air H2 He CO2 Processgas

Filmstiffness[kN/mm]

4000 3000 2000 1000 0 0

5

10

15

20

25

30

35

Pressure differential [bar] Flow Solutions Division BW Seals Durametallic Seals Pacific Wietz Seals Pac-Seal

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Calculated gap width for different gases

Gap width [µm]

4,5

Air H2 He CO2 Processgas

4

3,5

3

2,5 0

5

10

15

20

25

30

35

Pressure differential [bar] Flow Solutions Division BW Seals Durametallic Seals Pacific Wietz Seals Pac-Seal

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Calculated leakage rates for different gases

Leakage [l/min]

30

Air H2 He CO2 Processgas

20

10

0 0

5

10

15

20

25

30

35

Pressure differential [bar]

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Comparison of calculated values with measurements 30

Leakage [l/min]

Air Calculated Air Measured 20

10

0 0

5

10

15

20

25

30

35

Pressure differential [bar] Flow Solutions Division BW Seals Durametallic Seals Pacific Wietz Seals Pac-Seal

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Material Selection

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Basics for the layout of a Gasseal

• Stability of the parts High strength materials High thermal conductivity of the face materials FEM supported design • Low friction secondary sealing elements

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Material selection

• Stationary face

: Silicon carbide with DLC layer

• Rotating mating ring

: Silicon nitride or Silicon carbide

• Secondary sealing elements

: Viton or PTFE

• Metal parts

: High alloys

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Distorsion behaviour Distorsion of the stationary face at 250 bar pressure differential Carbon Youngs Modulus = 26500 N/mm²

182 µm

14 µm

Silicon carbide Youngs Modulus = 350000 N/mm²

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Thermal Face Deflection Tungsten Carbide / Carbon

SIC / SIC

93.3 93.7 94.1 94.5 94.8 95.3 95.6 96.0 96.4 96.8

73.0 76.7 80.4 84.1 87.8 91.5 95.2 98.9 102.6 Heat input Temp. gradient Total Face Deflection

= 1 kW = 29.6°C = 21 µm

Heat input Temp. gradient Total Face Deflection

= 1 kW = 3.5°C = 1.3µm

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Material Properties

Density Youngs Modulus Tensile Strength Thermal Expansion Thermal Conductivity [kg/m³] [g/cm³] [kN/mm²] [psi] [N/mm²] [psi] [µm/mK] [µin/in°F] [W/mK] [Btu/s ft °F] Silicon Carbide 3070 3,07 350 24115 170 11,713 4 2,22 120 7,48 Silicon Nitride 3200 3,2 300 20670 450 31,005 3,2 1,78 30 1,87 Carbon Antimony Fille 2150 2,15 26,5 1825,9 50 3,445 3,4 1,89 8,4 0,52 Tungsten Carbide 14500 14,5 600 41340 540 37,206 4,5 2,50 80 4,98 Stainless Steel 1.4006 7850 7,85 220 15158 550 37,895 11 6,11 15 0,93

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Secondary Seal Elements

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O-RING DESIGN

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SPRING ENERGIZED O-RING

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O-Ring explosive decompression

Natural voids in O-ring

High pressure gas Flow Solutions Division BW Seals Durametallic Seals Pacific Wietz Seals Pac-Seal

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Dynamic Seal Technology (continued) Dynamic J-Ring: •

PTFE material is not susceptible to explosive decompression

•

Extends chemical resistance beyond elastomers

•

Extends temperature range (-100°C to 230°C)

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High Pressure dynamic gasket system

• Excludes gap extrusion by minimizing gap dimensions • Insures functionality over the full pressure range from 0 to 425 barg • Achieves resistance against explosive decompression • Approaches temperature range from -80°C to +230°C • High chemical resistance Flow Solutions Division BW Seals Durametallic Seals Pacific Wietz Seals Pac-Seal

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PTFE GASKETS

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