Page 308 - Subyek Teknik Mesin - Forsthoffers Best Practice Handbook for Rotating Machinery by William E Forsthoffer

Be st Practice 5.9
Steam Turbine Best Practices Best Practice 5 .10
Condition monitoring of the system vacuum is essential to predictive maintenance practices. ‘THINK SYSTEM’ and
maintaining moisture-free lubrication oil. Many a turbine check all components of the seal system frequently.
bearing has failed because of poor seal system preventive and

Best Practice 5.9

Use dual gland condenser systems in special purpose Installation of two vacuum eductors will allow a faulty eductor to
turbines to positively prevent contamination of lube oil and be switched over and repaired on-line (just like a cooler or filter in an
to optimize steam seal MTBF. oil system).
Considering that seal systems in any type of rotating equipment are
the number one failure component, it is most surprising that steam seal Lessons Learned
system reliability is usually neglected. Most special purpose turbine gland vacuum sealing sys-
Most special purpose turbines use a vacuum, eductor gland, con- tems fail during a continuous run of 4-5 years, and are not
denser system to pull a 2-4 cm (5-10") vacuum in the last set of gland repaired on-line, resulting in oil system contamination and
packing, to buffer the seal with atmospheric air in order to prevent exposure to bearing failures.
steam condensate entering the bearing housing.
Since lube and seal systems used in special purpose (un-spared) Benchmarks
equipment trains always use dual elements (pumps, filters, coolers, This best practice has been used for new projects since 2005, when
etc.), the same philosophy should be used for steam seal systems to numerous reliability issues were experienced with faulty vacuum
ensure their proper operation at all times. eductor systems that were not repaired on-line.

B.P. 5.9. Supporting Material
Please refer to material in B.P. 5.8.

Best Practice 5.10Practice 5.10Practice 5.10Practice 5.10
Best
Best
Best
Always shop test special purpose steam turbines in spite The initially attractive option of field testing to correct manufactur-
of schedule delays, but do consider a spare rotor high ing schedule delays has proven time and again to be a false hope,
speed balance machine test, to minimize total factory ac- which leads to longer delays in field start-ups than would have resulted
ceptance test (FAT) time when the delivery is behind from a delayed FAT.
schedule.
Schedule delays can prompt some vendors to offer field mechan- Benchmarks
ical tests as an alternative to specified shop tests. This best practice has been used since the 1980s to ensure on time
Field testing exposes turbines to situations not encountered in FAT start-ups and steam turbine field operation of the highest possible
testing (piping and foundation stresses, etc.) which lead to decision reliability (99.7%þ).
delays and possible acceptance of less than reliable equipment.
Lessons Learned
Field testing exposes the end user to many issues that can
lead to endless discussions regarding acceptability and
corresponding start-up delays. The necessity to correct
identified field issues can delay start-ups by months.

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