Page 457 - Subyek Teknik Mesin - Forsthoffers Best Practice Handbook for Rotating Machinery by William E Forsthoffer

Be st Practice 7 .27
Be st Practice 7 .28 Lube, Seal and Control Oil System Best Practices

Best Practice 7.27Practice 7.27
Best
Perform an oil system site audit if the subject system has Lessons Learned
caused critical machinery unit shutdowns in the past that Continuing critical machinery unit oil system reliability
have resulted in lost product revenue. issues need to be evaluated in terms of lost revenue costs
Use the original equipment manufacturer (OEM) or a qualified to justify an oil system site audit to discover root causes
consultant to review past problems and conduct a site audit to cover and corrective action.
the following items as a minimum:
Determine the present operating condition of each system Benchmarks
component
I have performed site auxiliary system audits since 1990 for the reso-
Verify that all set points are as specified in the instruction manual
lution of long term reliability issues that have lost the end user large
Check component selection, where required and verify proper
amounts of revenue. This procedure has resulted in oil system and
component sizing
machinery unit reliabilities of 99.7%þ.
Define a remedial action plan which in addition may include:
Off-line testing at the first opportunity
Requests for additional component sizing information from the
OEM
Modifications to the operating procedure for this oil system

B.P. 7.27. Supporting Material

See B.P: 7.5 for oil system component audit information
guidelines.

Best
Best Practice 7.28Practice 7.28
Be sure to require all oil system interconnecting supply and Lessons Learned
drain piping to have maximum oil velocities set to prevent Lower than anticipated unit reliability and safety issues
excessive pressure drops, which will affect control valve (plant fires) have resulted from improper sizing of inter-
sizing and expose bearing brackets to flooding (possible connecting oil piping.
split line oil leaks). The use of smaller than required interconnecting oil supply pipes
The maximum velocity values are: has resulted in backpressure (bypass) valve replacement due to the
Supply piping e Maximum 6 ft/second higher pressure necessary to force the oil up to the unit and corre-
Drain piping e Maximum 1 f/second sponding low valve opening causing valve noise and/or wear and or
Our best practice recommendation is therefore to include inter- instability.
connecting oil piping design and manufacture in the machinery vendor Additionally, fires have been experienced in steam turbine appli-
scope of supply. cations on the steam inlet end, when bearing bracket oil leaks were
Oil system vendor backpressure and supply valve sizing is based caused by drain oil piping being smaller than required, which raised the
on assumed interconnecting oil pressure drops. oil levels in the bearing bracket to the split line.
If the interconnecting piping is not sized properly and has greater
pressure drop than anticipated during the selection of the control Benchmarks
valves, the control valves may not be properly sized. This best practice has been used since the mid-1980s when I was
Improper control valve sizing will affect valve transient response involved with the start-up of a large petrochemical plant. Allowing the
and stability leading to lower than anticipated unit reliability. contractor (EP&C) to select and manufacture the interconnecting
In addition, higher than anticipated interconnecting drain pipe supply oil piping resulted in having to throttle the backpressure control
pressure drop can raise the level of oil in the bearing bracket and cause valve inlet block valve to prevent valve noise, wear and instability, until
split line oil leaks that can expose the machinery and environment to the valve could be resized for a smaller trim at the first turnaround
fires in hot service areas (steam turbine surfaces and pipes). (three years of exposure to unnecessary unit trips caused by improper
valve response during transient conditions). Since that time, this best
practice has been used on all new projects to ensure maximum unit
reliability (99.7% or greater).

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