Page 265 - Improving Machinery Reliability

236 Improving Machinery Reliability

-On steam turbine driven compressors the “trip oil” dump valve should be modi-
fied to allow isolation in order to permit on-the-run testing of all trips and alarms.
-On motor driven compressors the “tripping relay” should have isolation provisions
to achieve the same testing function as on steam turbine driven compressors.
-On steam turbines, following any shutdown in which alarm or tripping circuit
instrumentation could have been affected or after compressor repairs or turn-
arounds, the turbine should be tripped once on “slow roll” to assure the operation
of the tripping circuit.
Lube oil analysis procedures might generally be adequate, but not up to the stan-
dards used by leading plants. In these plants, in addition to testing for H20, flash
point, viscosity and appearance, testing includes oxidation inhibitor and acid num-
ber in order to help assure longer life of bearings and seals.

Similarly, a few examples of “machinery impact” observations and recommenda-
tions typically documented by an audit team are highlighted next:

Disc-pack couplings provided on pumps may not have a means for on-line inspec-
tion. Provisions for hinged covers or the retrofitting of expanded sheet metal win-
dows is recommended for the coupling guards of disc-pack couplings. Hinged or
expanded sheet metal covers facilitate visual inspection of couplings under opera-
tion through the use of a strobe light to “freeze” the coupling allowing observation
of disc “bowing” or other malfunctions that manifest themselves at speed and load.
Compressor trains are occasionally found with gear-type couplings that can limit
extended plant operation. A systematic program of planning for future conversion
to low-maintenance, high reliability dry-type couplings is sometimes advocated.
Pump failure experience at petrochemical plants always merits close review. Mea-
sures to upgrade mechanical seal selection and rolling element bearing procurement
are usually explained and an implementation schedule mapped out for the plant.
Based on field experience elsewhere, an audit team may consider hydro-pneumatic
governors installed on large steam turbines a threat to long-term reliability of
major machinery. The technical reasons would have to be explained and electronic
governor retrofits recommended for future consideration. The cost basis for retrofit
application of electronic governors must be provided as part of the audit follow-up.

As a means of determining how the plant pursues chronic problems, an audit team
should use actual problems, when possible. This not only provides immediate assis-
tance, but also provides a means of demonstrating failure analysis concepts to an
audience “primed” for the results.
Addressing organizational means for improving machinery reliability usually con-
stitutes the third phase of an audit. To further re-enforce the technical capability of a
client’s staff, audit teams often recommend and adapt to the needs of a specific facil-
ity three key techniques:

A detailed role statement typically is developed for the position of Equipment
Reliability Engineer. Experience shows that without this statement, the perceived
role is going to differ widely from person to person. While the individual slated for