Mech.seal Hpcl
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Transcript of Mech.seal Hpcl
TOPICS TO BE COVERED
Why at all a Mechanical Seal?How does a Mechanical Seal work?
Types / Classification of seals.Materials of Construction.Environmental conditions.
Equipment condition.Trouble Shooting & Failure Analysis.
CENTRIFUGAL PUMPS – HORIZANTAL
CETRIFUGAL PUMPS – VERTICAL
AXIAL FLOW PUMPS
MIXED FLOW PUMPS. / JET PUMPS.
POSITIVE DISPLACEMENT PUMPS.
RECIPROCATING PUMPS / PISTON PUMPS
DIAGHPRAM PUMPS
SCREW PUMPS – SINGLE / DOUBLE / TRIPLE. / VANE
VACUUM PUMPS
SUBMERSIBLE PUMPS
TYPICAL END SECTION PUMP
Front End view of Pump.
Typical Stuffing box with Compression Packing
Impeller Stuffing Box
Compression Packing
(Gland Packing)Packing Pusher
(Gland)
Fastner
DISADVANTAGE OF PACKING.
Power Consumption is high. The Ratio of Power Consumption of Mechanical Seal to
Compression is 1: 8
Leakage is very high and unpredictable. Varies with the compression on the packing. The Ratio of Leakage of
Mechanical seal to compression Packing is 1 : 600
No automatic wear compensation.Fretting on Sleeve or Shaft.
Typical Mechanical Seal & Leakage Path.
Rotary Stationary
1. Gland to Pump face- Sealed with a Gasket. 2.Over the top
of the seal-’O’Ring
3. Along the Shaft
4. Under the Seal Ring 5. BETWEEN THE SEAL FACES
Stuffing Box PressureThe pressure acting on the stuffing box which must be sealed.
IT IS A FUNCTION OF PUMP IMPELLER DESIGN AND THE PRESENCE OR CONDITION OF WEAR RINGS.
•Impeller design and Stuffing box pressure–Back vanes - Open impeller
•Suction + 25% of differential = Stuffing box pressure
–Balance Holes - Closed impeller•Suction + 10% of differential = Stuffing box pressure
–Double Suction•Suction pressure = stuffing box pressure
Viscosity – Generally the higher the viscosity, the better the lubricating characteristics
–A product with a viscosity of 20,000 SSU (5000 cp) can be sealed with standard seals
–Beyond 5000 cp, the drive unit has to be beefed up to compensate for the increased shear occurring at the sealing faces.
–For high viscous applications:
•Single seal with external flush
•Double seal with external flush
–The viscosity & lubricity of water decrease with increased temperature. Above 82C (viscosity 0.35 cp) seal faces can contact each other and wear rapidly, unless specially designed
Specific Gravity
–Specific Gravity = Density of a substance
Density of Water at 4C
–Specific gravity is used to estimate the lubricity of light hydrocarbons
–Specific gravity below 0.68 (Heptane), require one face as carbon and special seal face design with higher balance to contain fugitive emissions
Vapour Pressure –THE PRESSURE AT WHICH A LIQUID WILL FLASH INTO VAPOR AT GIVEN TEMPERATURE
–If seal generated heat causes the sealing liquid to boil in seal chamber pressure, the liquid film between the seal faces will vaporize.
–Solution :
•Increase seal chamber pressure with proper bypass flush line and throat restriction device.
•Cooling the seal chamber. Seal chamber should be kept at least 15C below the boiling point of the product at the seal chamber pressure
Cavitations OPERATED UNDER CAVITATING CONDITIONS FOR SUFFICIENT LENGTH OF TIME:* Pitting of impeller vanes and pump volute
* Short bearing life and heavy loading
*Shaft breakage and other fatigue failures in the pump
Damages to mechanical seals can be :
•Short seal life•Worn pins and pin slots
•Broken springs•Shaft fretting
•Chipping of carbon faces
High speed video shows that seal face temperature excursions occurred when gases were drawn across the seal faces and by the formation of gas bubbles in the seal chamber near the seal faces during pump cavitation.
Seal Performance during cavitation :Zones Normal Pump
OperationPump Cavitation
Mode
Seal chambertemperature (C)
65 65
Shaft sleevevibration, mils p-p
1.9 2 to 8.4
Seal facevibration, mils p-p
<2.0 13 to 35
Seal facetemperature ( C )
67 to 74 166 to 427
Nomenclature of a Typical Seal
CollarSet Screw
Spring Pins
SpringsDrive Pins
Compression Ring
Compression Unit
Gland Ring
Insert Mounting
Insert
Seal Ring
Shaft Packing Gland Gasket
TYPES OF SEALSBased on mounting Outside seal
(Single sealInside seal
Based on arrangement
Single seal Double seal Tandem seal
Based on design
Balanced Unbalanced Special seal
Based on constructionPusher type
(spring design)
Stationary bellow
Bellow design
Metal bellowTeflon bellowElostamar
bellowSingle coil spring
Rotary bellow
Multispring
Dry running sealHigh pr seal
Gas seal
Custom built sealSlurry seal
Single Out Side Seal
EFFECT OF PRESSURE ON SEAL
BALANCED SEAL DESIGN FOR HIGH PR.
TANDEM SEAL
METAL BELLOW SEAL
MATERIALS OF CONSTRUCTION
300 Series Stainless Steel like SS 316, SS 316L
400 Series Stainless Steel like SS 410
Duplex Stainless Steel
Alloy – 20
Hastalloy B & C
Monel
Inconel
Nickel
Titanium
Seal Hardware Materials.
SEAL FACE MATERIALS
Other General Seal Face Materials
StelliteNi-ResistBronze
Secondary Packing Materials
Pure Graphite -400 C
Environmental Control
• Environmental control is a key factor for the proper functioning of Mechanical seal.
• (I.e) flushing / quenching / Cooling or heating / Jacketing / etc.,
API Plan – 02 (Jacket)
Flushing of Seal.
API Plan – 12
API Plan – 13 API Plan – 13 Re-circulation from Seal Chamber to SuctionRe-circulation from Seal Chamber to Suction
API Plan – 21 Bypass Flush through Heat ExchangerBypass Flush through Heat Exchanger
Close
Clearance
Bushing
Orifice (when specified)Heat Exchanger
API Plan 23 -- Heat ExchangerRe-circulation through Heat ExchangerRe-circulation through Heat Exchanger
Single Inside SealSingle Inside Sealwith Pumping Ringwith Pumping Ring
Pumping Ring
Circulating Device
API Plan - 31
API Plan – 32 External FlushExternal FlushSingle Inside SealSingle Inside Seal
Close
Clearance
Throat
Restriction /
LIP SEAL
Flow
MeterPressure Gauge
External
Flushing
Source
LIP Seal Assembly
API Plan - 51Vent Connection
API Plan - 52
API Plan - 53
API Plan – 54
API Plan - 61
API Plan - 62Flush and QuenchFlush and Quench
EQUIPMENT CONDITION
Shaft Whip -- Best limit 0.004” Check Condition of Radial Bearing
New Shaft Thrust bearing location.
Best Limit 0.004”
Care has to be taken while removing front casing.Max. 0.003”
Care has to be taken while removing the sleeve
Max 0.004”
Causes of Seal Failure
Failure Analysis
Failure due to Chemical Attack
Fretting Corrosion
Failure Due to Mechanical Action
High Spots
Seal Face Deflection
‘O’-Ring Extrusion
Anti Extrusion Ring.(with GFT)
Erosion
Drive Pin Wear
Failure Due to Heat Build up
Heat Checking
Vaporization.
BLISTERING
SPALLING
Oxidation & Coking
2PM 41D
11PM 6A
11P 10A
11PM 3B
11PT 2B
12PM 1B
16PM 4A
16PM 4A
42PM 17A
42PM 17A
12PM 1B
16PM 4A
CASE STUDYUnit: MEROXPump Item No. 16 P 04 A Amine Sump Pump.Pump make KSB – WKT 50 / 2Fluid handled: Acid Condensate / H2S / NH3& solvents.Operating Temp. 70o CMax. Discharge Pr. 8.0 Kg/ cm2Seal Size & Type 1.750” RA Outside sealSeal Faces Tung.Car / CarbonPacking Viton.Flushing Plan 11 & 13Due to urgent need and since there was no pump was available for the service, HPCL had a spare Hot Well pump, which met the operating parameters was installed.After few days of running the seal has failed. The pump was opened and the internals were checked. The main attack was to the secondary packing. Due to damage of packing the Carbon face also damaged.Remedial action was taken by modifying the seal and the packing were revised to Kalrez. The revised seal was installed about a week back, and the performance is being monitored.
MECHANICAL SEAL CHECKS
Check seal flushing, steam purging & stuffing box cooling for high temperature services.
Ensure flushing oil flow in the seal flushing line by sensing the temperature of the line. It should have the same temperature as that of the pump casing (incase no cooler is provided).
Ensure flushing line is insulated for hot services.
Incase seal is smoking, check for proper cooling water circulation to stuffing box, flushing flow is adequate.
Ensure LP dry steam to seal chamber as quench steam. Flow to be adjusted so that steam does not impinge on bearing housing
Contd
Ensure proper insulation to quench steam lines.
Incase of seal puffing, check for condensate in purging steam, contamination in product, inadequate flushing at seal, periodic vapor locking of pump. If no problem detected, inform rotating section for further check.
INTERACTIVE SESSION.
Use of Mech. Seal or Packing.
Can we convert packing to seal vis-a vis.
Carbon face to be Rotary or Stationery
Selection of seal type.