•What is it?
–According to API-682:
•A flush is a fluid which is introduced into the seal chamber on the process fluid side in close proximity to the seal faces and typically used for cooling and lubricating the seal faces
•A flush plan is a configuration of pipe, instruments and controls designed to route the fluid to the mechanical seal
–General Interpretation:
•A mechanical seal flush plan is a system that improves the mechanical seal reliability and performance by modifying the environment around the mechanical seal.
 

•Why are they used?
–To keep the sealing faces clean and cool
•Wash the seal to keep dynamic parts clean
•Flush the seal chamber to remove heat generated by the seal (turbulence and friction)
•Lower the fluid temperature
•Clean the process fluid
•Control the leakage on the secondary/atmospheric side of seal
Provide adequate vapor margin (or vapor suppression)
•50 psi vapor margin required for products with specific gravities < 0.6
•25 psi vapor margin required for products with specific gravities > 0.6
 

•What codes and standards apply?
–API-682 - Shaft Sealing Systems for Centrifugal and Rotary Pump
–API 610 - Centrifugal pumps for petroleum, petrochemical and natural gas industries
–ISO 21049 Pumps - Shaft sealing systems for centrifugal and rotary pumps
–ASME B73 - Specification for Sealless Horizontal End Suction Metallic Centrifugal Pumps for Chemical Process
–Flowserve best practices - FTA157_Piping_Plan_R2.pdf
–Customer best practices - RS-TO-MAT-GDL-316-0003 Seal Guideline rev 1.pdf ; BP Whiting seal selection sheet.doc
 

•Primary Flush Arrangements
(API-682 appendix A4 list the flush plans with a short description)
–01,02 Pump feature Flush Plans
API-682 Type A, Arrangement 3
–11,12*,13,14 Bypass Flush Plans - flush plans intended to keep the seal area clean, remove seal generated heat, and build pressure in the seal chamber; throat bushing clearance must be known to calculate the flush rate
–21,22*,23 Cooling Flush Plans - flush plans intend to cool the seal area
–31,32 Slurry Flush Plans - flush plan intended to keep the slurries (particles) away from the sealing area
–41* a combination plan for cooling and slurry flush plan

Secondary/Atmospheric Flush Arrangements (API-682 appendix A4 list the flush plans with a short description)
API-682 Type A, Arrangement 3
–51*,52,53A/B/C,54 Dual Seal Flush Plans – flush plans intended to lubricate the sealing faces and contain and dilute the leakage
–61,62,65 Atmospheric Flush Plans - to provide for a suitable atmosphere outside the seal area or behind the primary seal faces
–71,72,74,75,76 Gas seal or Containment Flush Plans - to provide for a suitable atmosphere behind the primary seal faces

What is it?
•Internal seal chamber flush from pump discharge
•Operates similar to a bypass flush (API-11)
Why is it used?
•Seal chamber heat removal
•Seal chamber venting on horizontal pumps
•Reduce risk of freezing or polymerizing fluid in exposed bypass piping plan (API-11)
Where is it used?
•Custom seal chamber, most likely an ASME/ANSI pump
•Clean, moderate temperature fluids
•Used with single seals, rarely used with dual seals
Advantages/Disadvantages?
•Flush typically can not be directed over the sealing faces
•Heat removal is limited
•Calculate flush flow rate based on impeller design, head loss through internal porting, and throat bushing clearance

What is it?
•Dead-ended seal chamber with no flush
Why is it used?
•Simplicity – no environmental controls
Where is it used?
•Large bore or open throat seal chambers in moderate temperature services
•Top-entry mixers or agitators with dry seals
Advantages/Disadvantages?
•Process must have adequate vapor margin to avoid vaporization at the sealing faces (maintain seal chamber pressure at least 30% above product vapor pressure or maintain a 20C (36F) product temperature margin)
•Dirty product stream where the particle density is at least 2x density of carrier fluid
•Cooling fluid in seal chamber jacket may be needed at all times in hot services
•Often used in combination with steam quench

What is it?
•Seal flush from pump discharge (or high pressure source) through orifice
•Default single seal flush plan
Why is it used?
•Seal chamber heat removal
•Seal chamber venting on horizontal pumps
•Increase seal chamber pressure and fluid vapor margin
Where is it used?
•General applications with clean fluids
•Non-polymerizing fluids
Advantages/Disadvantages?
•Use an orifice with a minimum 0.125” (3 mm) diameter
•Calculate flush flow rate to size orifice based on impeller design, flush piping loss, and throat bushing clearance (rate controlled to < 20 fps)
•Increase boiling point margin with proper orifice and throat bushing sizing
•Flush should be directed over seal faces with piping inlet at 12 o’clock position
•Cost to recirculate product

What is it?
•Recirculation from seal chamber to pump suction through orifice
Why is it used?
•Continuous seal chamber venting on vertical pumps
•Seal chamber heat removal
Where is it used?
•Standard flush plan on vertical pumps or any application where the seal chamber pressure is higher than suction pressure
•Moderate temperature fluids with moderate solids where the particle density is at least 2x the density of the carrier fluid
•Non-polymerizing fluids
Advantages/Disadvantages?
•Vent flush piping loop prior to starting vertical pumps
•Use an orifice with a minimum 0.125” (3 mm) diameter
•Calculate flush flow rate based on impeller design, flush piping losses, and breakdown bushing clearance
•Reduce seal chamber pressure with proper orifice and throat bushing (breakdown bushing) sizing
•Cost to recirculate product
 

What is it?
•Seal flush from pump discharge and recirculation to pump suction with orifices
•Combination of Plan 11 and Plan 13.
Why is it used?
•Continuous seal chamber venting on vertical pumps
•Seal chamber heat removal
•Increase seal chamber pressure and fluid vapor margin
Where is it used?
•Standard flush plan on vertical pumps
•Clean, non-polymerizing, moderate temperature fluids with moderate solids where the particle density is at least 2x the density of the carrier fluid
Advantages/Disadvantages?
•Vent piping loop prior to starting vertical pumps
•Use an orifice with a minimum 0.125” (3 mm) diameter
•Calculate flush flow rate based on impeller design, flush piping losses, and breakdown bushing clearance
•Control seal chamber pressure with proper orifice and throat bushing (breakdown bushing) sizing
•Cost to recirculate product

What is it?
•Seal flush from pump discharge through orifice and cooler
•Cooler in Plan 11 flush increases heat removal
Why is it used?
•Seal cooling
•Reduce fluid temperature to increase fluid vapor margin
•Reduce coking around sealing faces (<300ºF)
Where is it used?
•High temperature service, typically less than 350ºF (177
ºC) due to cooler fouling
•Hot water over 180ºF (80ºC)
•Clean, non-polymerizing fluids
Advantages/Disadvantages?
•Seal cooler and piping must have vents at highest elevation; vent before starting
•When using API-682 seal cooler, pipe with series flow to maximize heat transfer
•Use an orifice with a minimum 0.125” (3 mm) diameter
•Calculate flush flow rate based on impeller design, flush piping losses, and breakdown bushing clearance
•Control seal chamber pressure with proper orifice and throat bushing (breakdown bushing) sizing
•Cost to recirculate product

What is it?
•Seal flush from internal pumping device through cooler
•Standard flush plan in hot water services
Why is it used?
•Efficient seal cooling with low cooler duty
•Reduce fluid temperature to increase fluid vapor margin
•Improve water lubricity
•Reduce coking around sealing faces (<300ºF)
Where is it used?
•High temperature service, hot light hydrocarbons
•Boiler feed water and hot water over 180ºF (80ºC)
•Clean, non-polymerizing fluids
Advantages/Disadvantages?
•Seal cooler piping must have vents at highest elevation – vent before starting
•When using 682 Seal Cooler, pipe with parallel flow to minimize head loss
•Seal chamber requires close clearance throat bushing to isolate process fluid
•Tangential seal gland taps should enter at bottom and exit at top
•Regularly monitor cooler inlet and outlet temperatures for signs of plugging or fouling
•Process fluids with iron should flow through magnetic separator before cooler (BFW service)

What is it?
•Seal flush from pump discharge (or higher pressure) through cyclone separator
•Centrifuged solids are returned to pump suction
Why is it used?
•Seal chamber heat removal
•Solids removal from flush and seal chamber
Where is it used?
•Dirty or contaminated fluids, water with sand or product streams with particles
•Non-polymerizing fluids
Advantages/Disadvantages?
•Cyclone separator works best on solids with a particle density of at least 2x the density of the carrier fluid
•Seal chamber pressure must be nearly equal to suction pressure for proper flows (assume a 50/50 split overflow to underflow); Cyclone separator.TIF
•Piping should not include an orifice and is not expected to vent the seal chamber
•Flush piping to seal must have vents at highest elevation; vent before starting
•Cost to recirculate product

What is it?
•Seal flush from an external clean source at a higher pressure
Why is it used?
•Seal chamber heat removal (usually a clean, cool flush fluid)
•Process and solids removal from seal chamber
•Increase seal chamber pressure and fluid vapor margin
Where is it used?
•Dirty or contaminated fluids, paper pulp, tower bottoms
•High temperature service
•Polymerizing and/or oxidizing fluids
Advantages/Disadvantages?
•Injection fluid must be compatible with process fluid
•Use throat bushing sized to hold pressure or maintain flow velocity
•To restrict dirty process fluid, regulate injection flow rate (15 fps rule at throat bushing to size flush rate)
•To increase fluid vapor margin, regulate injection pressure
•Cost to recirculate product

What is it?
•Unpressurized buffer fluid circulation through reservoir
•Fluid is circulated by a pumping ring in the dual seal assembly
Why is it used?
•Outboard seal acts as a safety backup to the primary seal (designed to take full process pressure)
•Zero to very low process emissions
•No process contamination from the buffer fluid is allowed
Where is it used?
•Used with dual unpressurized seals
•High vapor pressure fluids, light hydrocarbons
•Hazardous or toxic fluids
Advantages/Disadvantages?
•Seal pot vent must self-vent to vapor recovery/flare system near atmospheric pressure
•Flush piping loop must self-vent to reservoir located at highest elevation
•Process vapor pressure is generally greater than reservoir pressure
•Buffer fluid must be compatible with process leakage
•Primary seal leakage is indicated by increased seal pot pressure or reservoir level gauge

What is it?
•Pressurized barrier fluid circulation through reservoir
•Fluid is circulated by a pumping ring in the dual seal assembly
Why is it used?
•Isolate process fluids
•Zero process emissions
Where is it used?
•Used with dual pressurized seals
•High vapor pressure fluids, light hydrocarbons
•Hazardous or toxic fluids
•Heat transfer fluids
•Dirty, abrasive or polymerizing fluids
•Mixers or agitators
•Vacuum service
Advantages/Disadvantages?
•Barrier fluid must be compatible with process
•Flush piping loop must self-vent to reservoir located at highest elevation
•Pressurize reservoir at all times
•Reservoir level gauge indicates both IB and OB seal leakage

What is it?
accumulator
•Fluid is circulated by a pumping ring in the dual seal assembly
Why is it used?
•Isolate process fluid
•Zero process emissions
•Handle higher pressures than Plan 53A
Where is it used?
•Used with dual pressurized seals
•High vapor pressure fluids, light hydrocarbons
•Hazardous or toxic fluids
•Heat transfer fluids
•Dirty, abrasive or polymerizing fluids
•Mixers or agitators
•Vacuum service
Advantages/Disadvantages?
•Barrier fluid must be compatible with process
•Flush piping loop must self-vent at highest elevation
•Piping loop must be fully vented before starting
•Accumulator must be pressurized at all times, usually by gas charge
•Regularly monitor barrier pressure –manually add barrier fluid when pressure decays

What is it?
accumulator
•Fluid is circulated by a pumping ring in the dual seal assembly.
Why is it used?
•Isolate process fluid
•Zero process emissions
•Higher pressure than Plan 53A
•Dynamic tracking of system pressure
Where is it used?
•Used with dual pressurized seals
•High vapor pressure fluids, light hydrocarbons
•Hazardous or toxic fluids
•Heat transfer fluids
•Dirty, abrasive or polymerizing fluids
•Mixers or agitators
•Vacuum service
Advantages/Disadvantages?
•Barrier fluid must be compatible with process
•Flush piping loop must be fully vented at highest point
•Piping loop must be fully vented before starting
•Reference line must tolerate process contamination without plugging
•Reservoir level gauge indicates both inboard and outboard seal leakage

What is it?
•Pressurized barrier fluid circulation by an external system
at a higher pressure
Why is it used?
•Isolate process fluid
•Zero process emissions
•Seal cannot induce circulation
•Clean source is available in unit
Where is it used?
•Used with dual pressurized seals
•Hot low vapor pressure fluids, heavy hydrocarbons
•Hazardous or toxic fluids
•Heat transfer fluids
•Dirty, abrasive, or polymerizing fluids
•Mixers or agitators
•Vacuum service
Advantages/Disadvantages?
•Barrier fluid must be compatible with process
•Piping loop must be fully vented before starting
•Circulating system must be pressurized and energized at all times
•Circulation system level gauge indicates both inboard and outboard seal leakage
•Flush will not flash to vapor at product temperature
•Cost to recirculate barrier product

What is it?
•External quench on atmospheric side of seal
•Quench fluids typically steam, water or nitrogen
Why is it used?
•Prevent solids buildup on atmospheric side of seal (coking or crystallizing)
•Prevent icing on light hydrocarbon seal applications
Where is it used?
•Mainly used with single seals
•Oxidizing fluids or fluids that coke
•Hot low vapor pressure fluids, heavy hydrocarbons (> 300ºF)
•Crystallizing fluids or fluids that salt out (caustics, amines)
•Heat transfer fluids
•Cold fluids less than 32ºF (0 ºC).
Advantages/Disadvantages?
•Quench inlet should be on top of gland with drain/outlet on bottom
•Quench pressure should be limited to 3 psi (0.2 bar) or less
•Use throttle bushing on atmospheric side of seal to direct quench flow to seal drain
•Monitor regularly, checking for closed valves, blocked lines, and steam trap condition

What is it?
•Unpressurized buffer gas control system
•Containment seal support typically with nitrogen buffer gas
Why is it used?
•Zero to very low process emissions
•Safety backup to primary seal
•Dilute primary seal leakage or sweep leakage into a closed system
Where is it used?
•Used with dual unpressurized containment seals (gas containment seal)
•High vapor pressure fluids, light hydrocarbons (non- condensing products)
•Hazardous or toxic fluids
•Clean, non-polymerizing, non-oxidizing fluids
•Used in combination with Plan 75 and/or Plan 76
Advantages/Disadvantages?
•Clean, reliable, low pressure gas must be supplied to seal at all times
•Bottled gas supply is not recommended except as part of an emergency backup system
•Primary seal leakage is indicated by pressure in the vent line
•Vent or drain are usually connected to low pressure vapor recovery/flare system

What is it?
•Pressurized barrier gas control system
•Gas seal support typically with nitrogen barrier gas
Why is it used?
•Isolate process fluid
•Zero process emissions
Where is it used?
•Used with dual pressurized gas seals
•High vapor pressure fluids, light hydrocarbons
•Hazardous or toxic fluids
•Services that do not tolerate barrier fluids
•Clean, non-polymerizing fluids
•Moderate temperature fluids
Advantages/Disadvantages?
•Clean, reliable, pressurized gas must be supplied to seal at all times
•Barrier pressure is typically at least 25 psi (1.75 bar) above seal chamber pressure
•Barrier flow meter indicates both inboard and outboard seal leakage
•Bottled gas supply is not recommended except as part of an emergency backup system
•Venting the seal chamber and pump may be required prior to startup and operation to avoid gas accumulation in pump case

What is it?
•Drain from containment seal cavity to liquid collector and vapor recovery
Why is it used?
•Leakage collection for zero to very low process emissions
•Safety indicator for primary seal
Where is it used?
•May be used alone or with Plan 72 on containment seals
•Fluids that condense at ambient temperature
•High vapor pressure fluids, light hydrocarbons
•Hazardous or toxic fluids
•Clean, non-polymerizing, non-oxidizing fluids
Advantages/Disadvantages?
•Collection reservoir must be located below seal drain and downward-sloped piping
•Continuously vent collection reservoir to low pressure vapor recovery/flare system
•Drain collection reservoir to liquid recovery system as needed (typically set up to pressurize in order to move liquids to recovery system)
•Primary seal leakage is indicated by increased vent pressure
•Monitor regularly for liquid level, valve settings, and low vent pressure

What is it?
•Vent from containment seal cavity to vapor recovery system
Why is it used?
•Leakage collection for zero to very low process emissions
•Safety indicator for primary seal
Where is it used?
•May be used alone or with Plan 72 on containment seals
•Fluids that do not condense at ambient temperature
•High vapor pressure fluids, light hydrocarbons
•Hazardous or toxic fluids
•Clean, non-polymerizing, non-oxidizing fluids
Advantages/Disadvantages?
•Continuously vent to low pressure vapor recovery/flare system
•Vent piping should include a condensate drain and connect to the top of the flare header
•Primary seal leakage is detected by increased vent pressure
•Monitor regularly for valve settings, blocked lines, and low vent pressure

Other Primary Seal Flush Plans
•Plan 12–Flush through a strainer
•Plan 22–Flush through a strainer and seal cooler
•Plan 41-Flush through a cyclone separator and seal cooler
Other Secondary/Atmospheric Seal Flush Plans
•Plan 61–Porting to atmospheric side of seal plugged for future use
•Plan 65–Collection of atmospheric liquid leakage (new in ISO 21049 / 682 3rd edition)
•Plan 71–Porting to containment seal cavity plugged for future use

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