Page 526 - Subyek Teknik Mesin - Forsthoffers Best Practice Handbook for Rotating Machinery by William E Forsthoffer

Pump Mechanical Seal Flush Best Practices Best Practice 8 .12
nance best practice’ requires that the flush system be com-
Take a sample to determine if debris is present pletely checked (including the throat bushing clearance) each
If seal fluid is not water or product fluid (which must meet time a seal is changed. Note that this recommendation applies to
product specifications) have sample analyzed all seal configurations: single, tandem (dual un-pressurized) or
Send sample results to seal vendor
double (dual pressurized).
Fig 8.11.12 Seal fluid check guidelines
Coordination with the seal vendor
representative

After all mechanical seal and flush system condition parameters
Orifice condition
Seal 4 have been measured, coordination with the seal vendor repre-
Throat bushing clearance sentative and/or in-house seal vendor engineer is necessary. A
Cooler condition ‘team’ approach is very effective and is being used by all seal
Strainer condition vendors today in large gas plants, refineries and chemical plants.
Cyclone separator condition
This approach provides immediate seal condition monitoring
Buffer fluid condition (tandem seal) and troubleshooting assistance as well as on site manufacturing
Buffer fluid level (tandem seal)
capability. Suggested seal vendor field information is presented
Pumping ring condition
Buffer fluid pressure (tandem seal) in Figure 8.11.14.

Fig 8.11.13 Seal reliability as a function of flush system component
condition is based upon:
The following field seal information is suggested to be exchanged
with the seal vendor for seal reliability issues:
- If the pump is operating in the EROE (provide curve)
Variance in seal chamber pressures and temperatures, if the - Seal chamber temperature
pump is operating in the EROE, are most likely to be caused by - Seal chamber pressure
malfunction of components in the flush system. Figure 8.11.13 - Seal fluid sample results
defines the flush system components which can affect seal - Seal flush system component operation confirmation
chamber pressures and temperatures. - Throat bushing clearance confirmation
Based on the seal flush plan used, the flush system compo- - Seal jacket temperature change (if applicable)
nents should be checked in the logical order e starting with the - Seal quench fluid pressures, temperatures and condition
beginning of the flush system and ending with the throat bush- (if applicable)
ing. (The exception is flush Plan 13 which begins with the throat
bushing and ends at the pump suction pipe.) FAI ‘seal mainte- Fig 8.11.14 Seal vendor field information

Best Practice 8.12Practice 8.12
Best

All flush Plan 52s (un-pressurized tandem seals) must be In addition, a short ‘mini information’ presentation by site rotating
continuously vented to flare or safe point to ensure that the machinery specialists has been effective in making operators aware of
seal pot is not contaminated with the inner seal process this potential safety hazard.
fluid which will expose the plant to a process fluid release
through the outer seal. A laminated warning sign is Lessons Learned
recommended at each application of this kind. Most plants have experienced a release of process fluid
Un-pressurized dual seals (formerly called ‘tandem’) require an from dual un-pressurized (tandem) seal systems when the
open path to flare or high point safe location to remove all seal fluid vent line had been improperly closed off.
vapors (usually flammable and/or toxic) from the seal pot and direct Lack of awareness of dual un-pressurized (tandem) seal system
them to a safe location. operational principles has resulted in flammable and toxic fluid re-
A valve closure and/or restriction in the seal pot vent line will leases in many plants.
prevent removal of the process fluid, contaminate the seal pot safe
barrier fluid and expose the plant and its personnel to a flammable or Benchmarks
toxic fluid release in the event of an outer (atmospheric side) seal This best practice has recommended since the mid-1980s. Since that
failure. time, this best practice, when implemented by plant operations, has
It is recommended that a local, laminated, warning sign be posi- resulted in optimum dual un-pressurized (tandem) seal safety and re-
tioned at the pump. liability (MTBFs > 48 and as high as 80 months).

497