Piping Plans for Dual Mechanical Seals
Purpose of Piping Plans
�Create a more favorable environmentfor the mechanical seal
• Flushing to remove heat
• Lowering fluid temperature
• Altering the seal chamber pressure
• Cleaning the process fluids
• Control atmospheric side of seal
Purpose of Piping Plans
�Provide a means of detecting andcontrolling seal leakage
• Capture and/or prevent leakage
• Detect leakage
• Route leakage to appropriate collection
or disposal system
• Provide fluid other than process fluid for
the seal environment
Requirements of Mechanical Seals
�Liquid seals
• Stable fluids
• Good lubricating properties
• Fluids do not flash or vaporize in seal
chamber
• Free from contamination and solids
• Moderate viscosities
Requirements of Mechanical Seals
�Gas seals
• Gas or vapor suitable for sealing
• Constant supply of external buffer/barrier
gas
• Process fluids free from contamination
from both liquids and solids
• Process fluids which are not adversely
affected by gas leakage
Methods of Achieving Goals
�Piping or routing of process fluids
�Introduction of external fluids
�Auxiliary equipment
• Seal coolers
• Cyclone separators
• Reservoirs
�Instrumentation
Plan 52What• Unpressurized buffer
fluid circulationthrough reservoir.
• Fluid is circulated bya pumping ring in thedual seal assembly.
Plan 52Why• Outboard seal acts
as a safety backupto the primary seal.
• Zero to very lowprocess emissions.
• No processcontamination isallowed.
Plan 52Where• Used with dual
unpressurized seals(“tandem”).
• High vapor pressurefluids, lighthydrocarbons.
• Hazardous or toxicfluids.
• Heat transfer fluids.
API 682 Type A Arrangement 2
2CW-CW
Plan 52Preventative
Maintenance
• Piping loop mustself-vent to vaporrecovery/flaresystem nearatmosphericpressure.
• Process vaporpressure is generallygreater thanreservoir pressure.
• Buffer fluid must becompatible withprocess leakage.
Plan 52Preventative
Maintenance
(continued)• Primary seal leakage
is indicated byincreased ventpressure.
• Reservoir level gageindicates outboardseal leakage.
Plan 53AWhat• Pressurized barrier
fluid circulationthrough reservoir.
• Fluid is circulated bya pumping ring in thedual seal assembly.
Plan 53AWhy• Isolate process
fluids.
• Zero processemissions.
Plan 53AWhere• Used with dual
pressurized seals(“double”).
• High vapor pressurefluids, lighthydrocarbons.
• Hazardous or toxicfluids.
• Heat transfer fluids.
• Dirty, abrasive orpolymerizing fluids.
• Mixers or agitators.
• Vacuum service.
API 682 Type C Arrangement 33CW-FB
Plan 53APreventative
Maintenance
• Piping loop mustself-vent to reservoirlocated at highestelevation.
• Pressurize reservoirat all times,maximum gascharge 150 - 200 psi(10 - 14 bar)
• Barrier fluid must becompatible withprocess.
• Reservoir level gageindicates both IB andOB seal leakage.
Plan 53BWhat• Pressurized barrier
fluid circulation witha bladderaccumulator.
• Fluid is circulated bya pumping ring in thedual seal assembly.
Plan 53BWhy• Isolate process fluid.
• Zero processemissions.
• Higher pressure thanPlan 53A.
Plan 53BWhere• Used with dual
pressurized seals(“double”).
• High vapor pressurefluids, lighthydrocarbons.
• Hazardous or toxicfluids.
• Heat transfer fluids.
• Dirty, abrasive orpolymerizing fluids.
API 682 Type C Arrangement 3
3CW - BB
Plan 53BPreventative
Maintenance
• Piping loop must befully vented beforestarting.
• Accumulator must bepressurized at alltimes, usually by gascharge.
• Barrier fluid must becompatible withprocess.
• Regularly monitorbarrier pressure –manually add barrierfluid when pressuredecays.
Plan 53CWhat• Pressurized barrier
fluid circulation witha pistonaccumulator.
• Fluid is circulated bya pumping ring in thedual seal assembly.
Plan 53CWhy• Isolate process fluid.
• Zero processemissions.
• Higher pressure thanPlan 53A.
• Dynamic tracking ofsystem pressure.
Plan 53CWhere• Used with dual
pressurized seals(“double”).
• High vapor pressurefluids, lighthydrocarbons.
• Hazardous or toxicfluids.
• Heat transfer fluids.
API 682 Type A Arrangement 33CW - BB
Plan 53CPreventative
Maintenance
• Piping loop must befully vented beforestarting.
• Reference line musttolerate processcontaminationwithout plugging.
• Barrier fluid must becompatible withprocess.
• Reservoir level gageindicates bothinboard andoutboard sealleakage.
Plan 54What• Pressurized barrier
fluid circulation by anexternal system.
Plan 54Why• Isolate process fluid.
• Zero processemissions.
• Seal cannot inducecirculation.
Plan 54Where• Used with dual
pressurized seals(“double”).
• High vapor pressurefluids, lighthydrocarbons.
• Hazardous or toxicfluids.
• Heat transfer fluids.
• Dirty, abrasive, orpolymerizing fluids.
• Mixers or agitators.
API 682 Type C Arrangement 3
3CW - BB
Plan 54Preventative
Maintenance
• Piping loop must befully vented beforestarting.
• Circulating systemmust be pressurizedand energized at alltimes.
• Barrier fluid must becompatible withprocess.
• Circulation systemlevel gage indicatesboth inboard andoutboard seal leakage.
Plan 72What• Unpressurized buffer
gas control system.
• Containment sealsupport typically withnitrogen buffer gas.
Plan 72Why• Zero to very low
process emissions.
• Safety backup toprimary seal.
Plan 72Where• Used with dual
unpressurizedcontainment seals(“tandem”).
• High vapor pressurefluids, lighthydrocarbons.
• Hazardous or toxicfluids.
• Clean, non-polymerizing, non-oxidizing fluids.
• Used in combinationwith Plan 75 and/orPlan 76.
API 682 Type A with Containment
2CW - CS
Plan 72Preventative
Maintenance
• Clean, reliable, lowpressure gas must besupplied to seal at alltimes.
• Bottled gas supply isnot recommendedexcept as part of anemergency backupsystem.
• Primary seal leakage isindicated by pressurein the vent line.
Plan 72Preventative
Maintenance
(continued)
• Vent or drain areusually connected tolow pressure vaporrecovery/flare system.
Plan 74What• Pressurized barrier gas
control system.
• Gas seal supporttypically with nitrogenbarrier gas.
Plan 74Why• Isolate process fluid.
• Zero processemissions.
Plan 74Where• Used with dual
pressurized gas seals(“double”).
• High vapor pressurefluids, lighthydrocarbons.
• Hazardous or toxicfluids.
• Services that do nottolerate barrier fluids.
• Clean, non-polymerizing fluids.
• Moderate temperaturefluids.
Plan 74Preventative
Maintenance
• Clean, reliable,pressurized gas mustbe supplied to seal atall times.
• Barrier pressure istypically at least 25 psi(1.75 bar) above sealchamber pressure.
• Flow meter indicatesboth inboard andoutboard seal leakage.
Plan 74Preventative
Maintenance
(continued)
• Bottled gas supply isnot recommendedexcept as part of anemergency backupsystem.
Plan 75What• Drain from containment
seal cavity to liquidcollector and vaporrecovery.
Plan 75Why• Leakage collection for
zero to very lowprocess emissions.
• Safety indicator forprimary seal.
Plan 75Where• May be used alone or
with Plan 72 oncontainment seals.
• Fluids that condense atambient temperature.
• High pressure fluids,light hydrocarbons.
• Hazardous or toxicfluids.
• Clean, non-polymerizing, non-oxidizing fluids.
API 682 Type A with Containment
2CW - CS
Plan 75Preventative
Maintenance
• Collection reservoirmust be located belowseal drain anddownward-slopedpiping.
• Continuously ventcollection reservoir tolow pressure vaporrecovery/flare system.
• Drain collectionreservoir to liquidrecovery system asneeded.
Plan 75Preventative
Maintenance
(continued)
• Primary seal leakage isindicated by increasedvent pressure.
• Monitor regularly forliquid level, valvesettings, and low ventpressure.
Plan 76What• Vent from containment
seal cavity to vaporrecovery.
Plan 76Why• Leakage collection for
zero to very lowprocess emissions.
• Safety indicator forprimary seal.
Plan 76Where• May be used alone or
with Plan 72 oncontainment seals.
• Fluids that do notcondense at ambienttemperature.
• High vapor pressurefluids, lighthydrocarbons.
• Hazardous or toxicfluids.
• Clean, non-polymerizing, non-oxidizing fluids.
API 682 Type A with Containment
2CW - CS
Plan 76Preventative
Maintenance
• Continuously vent tolow pressure vaporrecovery/flare system.
• Vent piping shouldinclude a condensatedrain.
• Primary seal leakage isdetected by increasedvent pressure.
• Monitor regularly forvalve settings, blockedlines, and low ventpressure.
Good Piping Practices
�Minimize line losses
�Large diameter tubing
�Upward sloping lines
�Long radius bends
high point vent
Vertical
Equipment
Horizontal
Equipment
18 - 24 in.
(0.45 - 0.6 m)
3 ft. (0.9 m) max
low point drain
Plan 23 Example
Good Piping Practices
�Minimize line losses
�Large diameter tubing
�Upward sloping lines
�Long radius bends
Vertical
Equipment
Horizontal
Equipment
18 - 24 in.
(0.45 - 0.6 m)
4 ft. (1.2 m) max
low point drain
Plan 53A Example
Review
�Intended to create a more favorableenvironment for the seal
�Collect and detect seal leakage and providesafety backup
�Documented in several API, ASME, and ISOstandards
�May require auxiliary equipment or externalsources of fluids
�Necessary to improve seal reliability/Safety
Questions?