Page 353 - Intro Predictive Maintenance

344 An Introduction to Predictive Maintenance

specific machine-trains. If the rate of change of a specific machine indicates rapid
degradation, you should either repair it or at least increase the monitoring frequency
to prevent catastrophic failure.

The recommended data acquisition frequencies are the maximum that will ensure pre-
vention of most catastrophic failures. Less frequent monitoring will limit the ability
of the program to detect and prevent unscheduled machine outages.

To augment the vibration-based program, you should also schedule the nonvibration
tasks. Bearing cap, point-of-use infrared measurements, visual inspections, and
process parameters monitoring should be conducted in conjunction with the vibration
data acquisition. Full infrared imaging or scanning on the equipment included in the
vibration-monitoring program should be conducted on a quarterly basis. In addition,
full thermal scanning of critical electrical equipment (e.g., switch gear, circuit break-
ers) and all heat transfer systems (e.g., heat exchangers, condensers, process piping)
that are not in the vibration program should be conducted quarterly.

Lubricating oil samples from all equipment included in the program should be taken
on a monthly basis. At a minimum, a full spectrographic analysis should be conducted
on these samples. Wear particle or other analysis techniques should be used on an
as-needed basis.

15.5.2 Setting Up Analysis Parameters
The next step in establishing the program’s database is to set up the analysis para-
meters that will be used to routinely monitor plant equipment. Each of these parame-
ters will be based on the specific machine-train requirements that we have just
developed. For nonmechanical equipment, the analysis parameter set usually consists
of the calculated values derived from measuring the thermal profile or process para-
meters. Each classification of equipment or system will have its own unique analysis
parameter set.

15.5.3 Setting Boundaries for Signature Analysis
All vibration-monitoring systems have finite limits on the resolution or ability to
graphically display the unique frequency components that make up a machine’s vibra-
tion signature. The upper limit (F max) for signature analysis should be set high enough
to capture and display enough data so that the analyst can determine the operating
condition of the machine-train, but no higher. Most vibration-based predictive main-
tenance systems are capable of resolutions up to 12,000 lines; the tendency is to
acquire high-resolution signatures as part of the routine monitoring sequence.
Although this approach is technically viable, the use of high-resolution signatures (i.e.,
1,000 lines or higher) dramatically increases the memory required to store acquired
data. Because most of the data collectors have limited memory, this will limit the
number of signatures that can be stored without uploading them to the host computer.
The time lost because of the combined use of high-resolution signatures and the