Page 52 - Improving Machinery Reliability

24 Improving Machinery Reliability

Auxiliary Systems for Turbomachinery: The Systematic Approach

Malfunction of auxiliary systems (e.g., speed governors, lube and seal-oil supply
consoles, etc.) is responsible for a large portion of unscheduled downtime for turbo-
machinery. This is a fertile field for improvements in specifications, post-order relia-
bility audits, pre-commissioning checkouts, and post-S/U maintenance.
To ensure that the specification is written for maximum equipment reliability, the
specifying engineer must generally go beyond the industry’s standard specification.
He must know what it is he is specifying and how the system, subsystem, or even
how a given component functions and performs. If he is not sufficiently qualified to
make the decisions that necessarily lead to the procurement of highly reliable
machinery, he should seek the advice of experienced plant engineers or consultants.
While it is beyond the scope of this text to rewrite or pre-define entire specifica-
tions for process plant machinery, it is important to make the preceding points as
forcefully as possible. Using compressor lube and seal oil systems as an example, we
want to see how the systematic examination of even a generally acceptable industry
standard specification can lead to revisions and amendments that will make the
equipment easier to operate and more maintainable, reliable, or accessible.

Specifying Lube and Seal Oil Auxiliaries

Lube oil or seal oil supply systems provide required quantities of lubricating or
sealing oil to machinery bearings, gears, and/or seals. The oil has to be filtered,
cooled (or preheated in some ambients), and pressurized. It has to be stored, purified,
delivered, returned, metered, bypassed, degassed, switched through different head-
ers, and blocked in. All of these functions require hardware, and while the purchaser
may elect to leave the selection of hardware to the machinery manufacturer, the pur-
chaser nevertheless must identify and specify the desired systems configuration.
API Standard 614,* “Lubrication, Shaft-Sealing, and Control Oil Systems for Spe-
cial-Purpose Applications,” can serve as a skeleton specification for lube and seal oil
systems. However, to ensure reliable operation, a number of supplementary require-
ments should be specified by the purchaser. Referring to Figure 1-14, we would add
to or modify the reservoir as follows:

The filter-breather should be extended 6 or more feet (2 m) above the reservoir top
to encourage oil vapors to condense inside the extension piece rather than escaping
to the atmosphere. Furthermore, during periods of gas leakage past the compressor
seals, we want the gas to escape well above grade.
For better heat transfer and reduced corrosion risk, the steam-heater cavity at the
reservoir bottom should be filled with a heat-transfer oil or perhaps discarded lube
oil. A filler standpipe and breather cap should be provided.

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“API Standard 614, “Lubrication, Shaft-Sealing, and Control Oil Systems for Special-Purpose
Applications,” Third Edition, 1992, repiinled by courtesy of the American Petroleum Institute.