Chemical Engineering April 2022 - 32

Facts At Your Fingertips
Predictive Maintenance Methods
Department Editor: Scott Jenkins
P
redictive maintenance (PdM)
programs can provide advanced
warning of equipment
problems and potential failures. This
one-page reference provides brief
descriptions of six common predictive
maintenance methods.
Infrared thermography
Continuous monitoring of equipment
temperature over
diminishes
time has
the potential to identify both normal
and abnormal temperature profiles.
Running equipment at elevated
temperatures
lifetime,
and is an early symptom of equipment
damage or malfunction. For
example, heat generated from friction
in mechanical equipment or heat
from electrical resistance in electrical
components can be precursors to
larger problems.
Infrared (IR) thermography instruments
use a special camera to detect
IR electromagnetic radiation that
is emitted from equipment surfaces.
Higher-temperature areas emit more
IR radiation. A lens in the camera focuses
the IR radiation onto a thermal
sensor. Different pixel configurations
in the sensor determine the resolution
of the camera. The IR energy
is converted into a visual image in
which pixels are color-coded according
to temperature, and a " heat
map " of the object is generated (Figure
1). IR thermography can be used
to monitor bearing temperature,
identify deteriorating or overloaded
circuits, analyze process temperature
and detect leaks.
Ultrasound
analysis
FIGURE 1. Infrared thermography
uses infrared
radiation from surfaces
to make a heat map
32
Many failure
conditions and
damage processes
tend to
produce detectable
levels
of ultrasound
before they are
severe enough
to be audible to
humans. These
processes include
pressure leaks (of compressed
air or steam, for example), electrical
discharge and deterioration of bearings
and other machinery. Ultrasonic
equipment detects airborne
and structure-borne sounds that
are normally inaudible to the human
ear and electronically " transposes "
them into audible signals
that a technician can hear and view
on a display. Ultrasound technology
can detect certain mechanical and
electrical faults by sensing subtle
changes in ultrasonic amplitude.
For example, ultrasound is adept at
finding early-stage bearing faults.
Motor-current signature
Developing faults can cause distortions
in the current drawn by an electric motor.
Motor-current-signature analysis
(MCSA) detects impending problems
by measuring the current drawn by
the motor and analyzing distortions
to the current's waveform. Analyzing
a frequency spectrum of the current
waveform can reveal distortions
that appear as peaks on a frequency
spectrum, located at frequencies that
are characteristic of the phenomenon
causing the distortion. By assessing
the size of the peak and its frequency,
users can deduce the probable cause
of the distortion and assess its severity.
MCSA can be used to detect developing
defects in rotors, such as rotor
bar cracking.
Oil analysis
Contamination can hinder the ability
of machinery lubricants to perform
their required task. When that occurs,
machinery components can
wear quickly and equipment surfaces
can degrade, contributing to machinery
failures. Oil analysis monitors and
analyzes lubricant oils for characteristics
such as contamination, chemical
content and viscosity. An understanding
of changing lubricant properties
can increase both uptime and extend
the lifetime of equipment.
Partial discharge monitoring
Partial discharges (PD) are small
electrical sparks that do not comFIGURE
2. Vibration analysis uses data on the vibration
signature along three axes
pletely bridge the electrodes. They
occur within the electrical insulation
of medium- and high-voltage electrical
assets, such as cables, transformers,
switchgears and windings
found in large motors. Discharges are
the result of an electrical breakdown
of an air pocket within the insulation,
and give off energy in different forms,
which can be detected by sensors.
Partial discharges are an early indicator
of insulation deterioration.
Vibration analysis
Vibration analysis monitors the vibratory
signature of a system over
time and looks for anomalies to
the established pattern (Figure 2).
Machine-mounted accelerometers
gather data about the vibration signature
along three axes (vertical,
horizontal and axial) and quantify the
magnitude of the vibration in terms of
displacement (total distance moved
by vibrating part), velocity (speed of
the vibrating mass) and acceleration
(rate at which velocity is changing).
Machine vibration comes from
many sources, and even small amplitudes
can have severe effects on the
overall machine vibration, depending
on the transfer
and resonances.
function, damping
n
References
1. Froelich, J.M., More than Meets the Eye: Tackling Invisible Threats
with Infrared Thermography, TUV Sud, whitepaper, 2019.
2. Pareschi, D., Rotating Machines: Digital Technologies to Enable
Predictive Maintenance, Chem. Eng., March 2018, pp. 32-37.
3. Custeau, K., Maintenance Strategies in the Era of IIoT, Chem.
Eng., May 2019, pp. 42-46.
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
APRIL 2022
http://WWW.CHEMENGONLINE.COM
Chemical Engineering April 2022

Table of Contents for the Digital Edition of Chemical Engineering April 2022
