Page 543 - Subyek Teknik Mesin - Forsthoffers Best Practice Handbook for Rotating Machinery by William E Forsthoffer

Be st Practice 9 .3 Dry Gas Seal Best Practices

Fig 9.2.1 Double dry gas seal

Best
Best
Best Practice 9.3Practice 9.3Practice 9.3
Monitor both primary and secondary tandem seal condi- In 2007, a number of secondary seal failures forced all compressor
tions to ensure plant and personnel safety. vendors to become more aware of the lack of secondary seal moni-
Many tandem dry gas seal systems do not incorporate a means of toring, and to issue directives to their clients to always have a means of
monitoring the condition of the secondary (atmospheric) seal. secondary seal condition monitoring.
In addition, many applications do not include the injection
of intermediate nitrogen between the primary and secondary seals. Benchmarks
Not using intermediate nitrogen to buffer the seal chamber between This best practice has been used since 2005 after investigation of
the primary and secondary seal exposes the seal to a certain process a secondary seal failure after a prolonged period on turning gear
gas release in the event of a secondary (atmospheric) seal failure. (compressor/steam turbine train in a chemical plant).
Methods to monitor secondary seal condition include: Since that time, it has been FAI standard practice to monitor sec-
Monitoring high secondary vent pressure ondary seal condition in all tandem seal applications.
Monitoring low separation gas to secondary vent differential pressure
Monitoring low primary vent pressure (where primary vent pressure
is kept higher than flare header pressure by a backpressure device)

Lessons Learned
Failure to monitor the secondary tandem seal has resulted
in plant safety issues (loss of plant assets and lost time
accidents).

B.P. 9.3. Supporting Material arrangement) and the separation seal to a safe location. Most
importantly, conditions in this vent can provide information on
the health of the outer seal (secondary seal for tandem ar-
Vent systems between the DGS cartridge rangements and atmospheric seal for double seals) and the
and separation seal separation seal. The majority of installations do not specifically
monitor the condition of the secondary or outer seal. Un-
Usually referred to as the secondary vent, its purpose is to direct detected failure of the secondary or the outer seal exposes the
the gas that is present between the DGS (tandem or double plant to a process gas release in the event of primary or inner seal

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