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8/3/2019 Maintenance Assignmnt

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THERMOGRAPHYThermography is a predictive maintenance technique that can be used to monitor the condition of plant

machinery, structures, and systems. It uses instrumentation designed to monitor the emission of infrared

energy, i.e., temperature, to determine their operating condition. By detecting thermal anomalies, i.e.,

areas that are hotter or colder than they should be, an experienced surveyor can locate and define incipient

problems within the plant.

Infrared technology is predicated on the fact that all objects having a temperature above absolute zero

emit energy or radiation. Infrared radiation is one form of this emitted energy. Infrared emissions, or

below red, are the shortest wavelengths of all radiated energy and are invisible without special

instrumentation. The intensity of infrared radiation from an object is a function of its surface temperature.

However, temperature measurement using infrared methods is complicated because there are three

sources of thermal energy that can be detected from any object: energy emitted from the object itself,

energy reflected from the object, and energy transmitted by the object. Only the emitted energy is

important in a predictive maintenance program. Reflected and transmitted energies will distort raw

infrared data. Therefore, the reflected and transmitted energies must be filtered out of acquired data

before a meaningful analysis can be made.

The surface of an object influences the amount of emitted or reflected energy. A perfect emitting surface

is called a blackbody and has an emissivity equal to 1.0. These surfaces do not reflect. Instead, they

absorb all external energy and reemit as infrared energy. Surfaces that reflect infrared energy are called

graybodies and have an emissivity less than 1.0. Most plant equipment falls into this classification.

Careful consideration of the actual emissivity of an object improves the accuracy of temperature

measurements used for predictive maintenance. To help users determine emissivity, tables have been

developed to serve as guidelines for most common materials. However, these guidelines are not absolute

emissivity values for all machines or plant equipment.

Variations in surface condition, paint, or other protective coatings and many other variables can affect the

actual emissivity factor for plant equipment. In addition to reflected and transmitted energy, the user of

thermographic techniques must also consider the atmosphere between the object and the measurement

instrument. Water vapour and other gases absorb infrared radiation. Airborne dust, some lighting, and

other variables in the surrounding atmosphere can distort measured infrared radiation.

Since the atmospheric environment is constantly changing, using thermographic techniques

requires extreme care each time infrared data are acquired.

Most infrared monitoring systems or instruments provide special filters that can be used to avoid the

negative effects of atmospheric attenuation of infrared data. However, the plant user must recognize the


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specific factors that will affect the accuracy of the infrared data and apply the correct filters or other

signal conditioning required to negate that specific attenuating factor or factors.

Collecting optics, radiation detectors, and some form of indicator comprise the basic elements of an

industrial infrared instrument. The optical system collects radiant energy and focuses it upon a detector,

which converts it into an electrical signal. The instruments electronics amplifies the output signal and

processes it into a form which can be displayed. There are three general types of instruments that can be

used for predictive maintenance: infrared thermometers or spot radiometers, line scanners, and imaging

systems.

ULTRASONIC MONITORINGThis predictive maintenance technique uses principles similar to vibration analysis. Both techniques

monitor the noise generated by plant machinery or systems to determine their actual operating condition.

Unlike vibration monitoring, ultrasonics monitors the higher frequencies, i.e., ultrasound,

produced by unique dynamics in process systems or machines. The normal monitoring range for vibration

analysis is from less than 1 to 20,000 Hz. Ultrasonics techniques monitor the frequency range between

20,000 and 100 kHz. The principal application for ultrasonic monitoring is in leak detection. The

turbulent flow of liquids and gases through a restricted orifice, i.e., leak, will produce a high-frequency

signature that can easily be identified using ultrasonic techniques. Therefore, this technique is ideal for

detecting leaks in valves, steam traps, piping, and other process systems. Two types of ultrasonic systemsare available that can be used for predictive maintenance: structural and airborne. Both provide fast,

accurate diagnoses of abnormal operation and leaks. Airborne ultrasonic detectors can be used in either a

scanning or a contact mode. As scanners, they are most often used to detect gas pressure leaks. Because

these instruments are sensitive only to ultrasound, they are not limited to specific gases as are most other

gas leak detectors. In addition, they are often used to locate various forms of vacuum leaks. In the contact

mode, a metal rod acts as a waveguide.

When it touches a surface, it is stimulated by the high frequencies (ultrasound) on the opposite side of the

surface.

This technique is used to locate turbulent flow and/or flow restriction in process piping. Some of the

ultrasonic systems include ultrasonic transmitters that can be placed inside plant piping or vessels. In this

mode, ultrasonic monitors can be used to detect areas of sonic penetration along the containers surface.

This ultrasonic transmission method is useful in quick checks of tank seams, hatches, seals, caulking,

gaskets, or building wall joints.

In a typical machine, many other machine dynamics will also generate frequencies within the


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bandwidth covered by an ultrasonic instrument. Gear meshing frequencies, blade pass, and other machine

components will also create energy or noise that cannot be separate from the bearing frequencies

monitored by this type of instrument. The only reliable method of determining the condition of specific

machine components, including bearings, is vibration analysis. The use of ultrasonics to monitor bearing

condition is not recommended.

Intelligent CBM

The term intelligent implies a CBM system is capable of understanding and making decisions

without human intervention. Technologies making this possible include: sensors with built in

intelligence (SMART Sensors) capable of transmitting relatively rich, high grade information [11];

re-programmable on-line sensors [12], designed to be reconfigured with new rules in the event that

detectable recognisable patterns change; algorithms, fuzzy logic and neural networking, designed to

analyse trends within recovered sensory data, and produce decisions on the likelihood of failure of

monitored plant items [12]; artificial intelligence algorithms capable of providing proxy data as a

substitute for failing or a failed sensor, whilst the malfunctioning sensor is repaired [13].

Further intelligence is possible through integration of a CBM system with a companys

computerised purchasing system, thus automating parts ordering [11].

As technological advancements have fed into CBM so the method of deploying CBM systems and

integrating them with other business systems has changed. Two recognised deployments are:

Localised CBM, and Remote CBM.

Localised CBM

Localised CBM is an independent predictive maintenance practice, likely to be undertaken within

immediate proximity of the components being monitored, by a maintenance engineer (technician)

or operator. A typical procedure involves taking and recording CBM data at periodic intervals in

order to determine the condition of the component being monitored, and then deciding whether the

condition of the component is acceptable or not.

Remote CBM

Remote CBM systems can be either standalone or networked to another business system/s. Remote

CBM involves monitoring the condition of a component at a location away from the immediate

vicinity of the component in question. Monitoring will be undertaken automatically or manually

depending upon the systems capabilities at intermittent time periods. Diagnosing the condition of

the component may be either automatic or manual, again depending upon the systems capabilities.


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Wireless sensors present opportunities for placing sensors in difficult-to-reach locations,

electrically noisy environments, and mobile applications where wire cannot be installed. Discussion

on the latest developments in wireless sensors is presented by F. Zorriassatine [14].

Presenting CBM information through web pages accessible by Internet browsers, is given the name

Internet CBM, or E-Monitoring Machine Health System. Internet CBM takes remote CBM to

another level, i.e. providing global remote capabilities. Since browsers reside on many platforms,

Internet CBM systems may be accessed by multiple users working on any type of operating system.

This presents the opportunity for employees to monitor their machinery whilst away from the

factory, i.e. overseas on business calls. Unauthorised access to an Internet CBM system is

prevented with the inclusion of user name and password access on the index web page (first page)

for the web site. User name and password access may also be used to control access rights onto

specific web pages and degree of user system interaction.

V.R. Kennedy [15] explains how interaction between users and the Internet CBM system is performed

using Active Server Pages (ASPs). ASPs, programmed using VBScript and JavaScript working behind

the scenes within the Web server, offer flexibility to system designers. They carry out programmed

instructions within the web server, define how the HTML is assembled and presented to users, providing

users with the power to interact with the user interface and make choice selections. As an example, Lloyd

Dewey Lee [16] explains how vibration or process levels may now easily be transmitted over the Web

and presented to the end user as gauges, reporting the condition of the remote machine in real time.

Further examples presented by Rolf Orsagh et al. [13], include displaying graphs showing performance

trends, and tables of performance parameters, anomalies, and diagnosed faults.

OIL DEBRY ANALYSIS

When analysing oil from a machine, there are a number of techniques that can be used or applied to look

at the chemical composition of the oil and foreign materials in it.

Ferrography and magnetic chip detection examine iron based wear, and can help pinpoint the specific

component that is wearing.

Spectrometric oil analysis measures the presence and amounts of contaminants in the oil through atomic

emission or absorption spectrometer. It is useful for determining not only iron, but also other metallic and

non metallic elements, which can be related to the composition of the various machine components, such

as bearings, bushings, piston rings, washers, and so on. It is useful when wear particles initially being

generated in the early stages of failure, as those particles are small.

Chromatography measures the changes in lubricant properties, including viscosity, flash point, pH, water

content, and insoluble fraction, through selective absorption and analysis.


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CORROMETER TEST

There are several tests for corrosion using a simple electric circuit monitored by varying degrees of

sophisticated instrumentation. The corrator uses the electrochemical polarisation method in a vessel

with corrosive liquid. The Corrometer uses the electrical resistance across a probe inserted in the

active environment (e.g. refinery process equipment).

The Corrometer is a new corrosion "sensor" designed to respond and advise of deterioration in

electronic components and other susceptible equipment. The operating principle is straightforward:

over the same distance travelled, as corrosion increases so does electrical resistance.

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