Seals
TOSI Giampiero
Compressor Sealing
Balancing Drum
Shaft End Seal Shaft End Seal
Balancing Line
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OIL SEALS vs DRY GAS SEALS
Advantages Advantages
• Widely Used for HP applications • Simplified System
• Positive Impact on rotordynamics • Total Lower Cost
Critical Issues • No Oil Contamination
• Very Sensitive to H2S content Critical Issues
• Rotor-dynamic
3
Nomenclature
Primary vent (leakage from inbord seal Secondary vent (leakage from Outbord seal
+ intermediate buffer gas - to flare) STREAM 2 + separation gas - atmospheric) STREAM 4
Interm. buffer gas
(N2 or Purified Seal Separation Gas (N2)
Gas) STREAM 3 STREAM 5
Seal Gas STREAM 1
Atmosphere
(Bearing Chamber)
Inboard Seal
Carbon Rings
Product side
Face
Seat Face
Seat
Secondary Seal Intermediate Labyrinth Outboard Seal Separation Seal
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Gas Seal Operation
Dry Gas Seal - Components
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7
Running clearance ~ 3 micron
Carbon ring
Human
Hair groove depth = 10 micron
diameter
50-70
microns
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Dry Gas Seal: Seal Ring picture showing grooves
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Dry Gas Seal Operation
Process Side
Dynamic behavior
Spring thrust
Static pressure
Discharge
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With 1 Atm pressurization,
a tip speed of 6 m/sec is enough
to develop a pressure able
to obtain the two discs separation
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Gas Seals for Low Pressure
Elastomer
secondary
seals
Softening
resistance
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Gas Seals for High Pressure
Carrier for primary ring and
secondary seal
Polymer secondary seals
Extrusion resistance
Temperature resistance
High decompression rates
Chemical resistance
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Type 28 AT (o-ring)
The disc carrier is over
the disc in order to keep
it in case of rupture
O - ring
Small plate to compensate
the non uniformity of
thermal dilatations due
to different steel types
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Criticals
Type 28 AT:
Reverse Static Pressurization
O-Ring
extrusion
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Clearance Between Carbon Ring
and Spring Carrier
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Clearance: effects on “O” ring due to rings movements
such effect impacts on the “O” ring life
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“O” ring criticity
O- rings limitations:
“O” ring seems a simple element, but it requires a deep selection
to avoid machinery leakages and production shortage due to its
failure.
The followings aspects have to be considered
• Limited life
• Limited pressure
• Limited temperature (~ 100°C)
• Suspect to chemical attack (material)
• Sticktion (Quality)
• Explosive decompression (Q.C.)
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Explosive decompression
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Sticktion
Deposits on the product and/or atmosphere side of
the mechanical seal can lead to loss of axial mobility
(blocking) of the spring-backed seal face.
A distinction is drawn between mechanically induced
and thermally induced deposits.
Deposits from leakage
on atmosphere side
Sealing is lost and moisture
can pass through
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New design Change the “O” ring type for better
resistance to decompression and sticking
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Components
Dry Gas Seal: sectional view
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Dry Gas Seal: assembled parts ready for installat.
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Dry Gas Seal: disassembled parts
T 28 XP
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Dry Gas Seal: disassembled fixed parts
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Dry Gas Seal: Ring with single direction grooves
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Dry Gas Seal: Ring with double direction grooves
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Seal types availability
TANDEM SEALS
Labyrinth Tertiary seal
Contact Ring Pressurised Tertiary seal
TRIPLE SEALS
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Tandem Seals
Job seals
Tested at 350 bar
Dynamic
11.000 RPM
Tertiary seal
labyrinth
or
pressurised type
Carbon contact
rings
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Tertiary Seal Type 82 Contact Seals
Springs
Carbon
Hardened sleeve on Shaft
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When leakage increases,
To 2nd Differential Pressure
vent lowers below 0,5 bar. N2 Supply
Leakage detection can be
monitored by a PDT.
Bearing
side
0,5 Bar
Seal
side
N2 release N2 release
Hardened sleeve on Shaft
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Nitrogen Primary Clean Gas
Buffer Vent Injection
Tandem Seal
with
intermediate
labyrinth
(new goal)
Development Plan for
430 bar Dynamic
13.000 RPM
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Triple Gas Seal
Pressure Filtered
Outboard Intermediate Control
Vent Vent (if required)
Process
Gas
TRIPLE
SEALS
Experienced up to
290 bar Dynamic
and 310 bar Static
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Materials
Materials
Metal parts X12Cr13
17/4 PH
Carbon Steel
Face Graphite
Cranite
Silicon Carbide
Seat Tungsten Carbide
Silicon Carbide
Secondary Seals Elastomer
Spring Energized Polymer
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Materials
Metal parts ASTM A276, Gr.420
(DIN 1.4122)
UNS S42400
(DIN 1.4313,
DIN 1.4313S (NACE))
Primary Ring carbon graphite
Seat tungsten carbide,
silicon carbide
Secondary Elastomer
sealing Metal spring
elements energized
polymer rings
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Auto-buffer
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External Buffer Source
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Dry Gas Seal P&I Diagram
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Oil Seals
Oil Seal arrangement
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Oil Pressure Diagram in the Rings
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Schematic
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Oil Seal Assembly
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Oil Seal P&I Diagram
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Labyrinth Seals
Labyrinth Seals
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Avional Labyrinths (Compresor Interstage)
This type of Labyrinth is
normally employed, on
the diaphragms
(stationary component
as part of the bundle),
as mechanical barrier to
gas passage between
two following impellers.
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