Page 424 - Subyek Teknik Mesin - Forsthoffers Best Practice Handbook for Rotating Machinery by William E Forsthoffer

Lube, Seal and Control Oil System Best Practices Best Practice 7 .15
failure. Operators should observe valve stem travel and pressure into the lube system. Most plant utility lines contain pipe scale
gauges to confirm valve actuator condition. In the event of ac- that could easily plug systems and cause significant critical
tuator failure, the control valve should be designed for isolation equipment damage.
and bypass while on-line. In addition, the following reliability factors should be noted
This design will permit valve or actuator change out without (refer to Figure 7.14.2):
shutting down the critical equipment. During control valve on-
line maintenance, an operator should be constantly present to - Be sure to install a check valve upstream of the accumulators
monitor and modulate the control valve manual bypass as to ensure all accumulator oil is delivered to the desired
required. components.
- Accumulators should be checked periodically (monthly)
for proper pre-charge and bladder condition by
Accumulator considerations isolating and draining the accumulator. Note that the
accumulator pre-charge pressure cannot be determined
Concerning accumulators, checks should be made when unit is while on line.
shut down for accumulator bladder condition if supplied with - When refilling the accumulators, care must be taken not to
bladders. One area which can cause significant problems in suddenly open the supply valve. Best practice is to install an
auxiliary systems is accumulators that are supplied with a con- orificed bypass valve to be used for filling the accumulator.
tinuous charge e that is, charge lines (nitrogen or air) which - Best practice is also to install two (2) full size accumulators to
come directly from a plant utility system. Any rupture of a di- ensure that one accumulator is always on line during monthly
aphragm will provide a means for entry of charge gas directly checks.

Best
Best
Best Practice 7.15Practice 7.15Practice 7.15
Use SS oil coolers and filters to allow maximum bearing, Lessons Learned
seal and turbine control component MTBFs (120 Filters, although positioned downstream of the coolers, do
monthsD). experience bypassing and expose critical machines in-
Shell and tube oil coolers typically have the water in the tubes and stalled in large plants to extended downtime for compo-
oil in the shell and are made of carbon steel for cost reasons. nent replacement (3e5 days) which results in lost revenue
Oil filters are therefore usually positioned downstream of the oil
in the millions of USD.
coolers to prevent carbon steel (iron sulfide) particles from entering the
In addition, a complete stainless steel oil system will greatly reduce
machinery components and causing pre-mature wear/failure.
oil flush time and offer the opportunity for increased unit revenue.
However, it is rare that filters do not experience bypassing around
the seals which will expose machine components to early wear and/or Benchmarks
failure.
Considering the daily revenue for critical units today (2010), the use This best practice has been used since 2000 when daily revenues for
of stainless steel coolers and filters can easily be justified and will medium sized process units exceeded $1,000,000 USD, making it
ensure maximum machine component life. viable to install dual stainless steel coolers and filters in oil consoles
used for critical (un-spared) units.

incorporated in the system. The function of providing cool oil
B.P. 7.15. Supporting Material
is naturally that of the coolers. As will be discussed in this
Referring to the generic definition of an auxiliary oil system, section, coolers can be supplied in many different types and
configurations. The function of the filters is to supply clean
the function of the coolers, filters and transfer valves is ‘to
oil. They must continuously ensure that all fluid supplied to
continuously provide cool, clean fluid to the critical equipment
components’.Withinthis definition, ‘continuously’ requires the critical equipment is within the system specification of
that components be dual main and spare filters and coolers. In cleanliness.
addition, a means for on-line transfer of one bank of coolers
and filters to the stand-by bank is required. This transfer must
be accomplished without any significant pressure fluctuations, The sub-systems
or flow disturbances in the auxiliary system. In order to
ensure pulsation-free transfer, all components involved must Coolers and filters actually are a part of the cooling and filtration
be purged of air and must be full of auxiliary fluid. This re- subsystems in any auxiliary system. The cooling sub-system
quires that properly sized vent, bleed and fill lines be consists of the transfer valves, the temperature control valves,

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