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Unit 50: Condition Monitoring and Fault DiagnosisOn successful completion of this unit a learner will:Understand the concepts of condition monitoringUnderstand the nature and use of condition monitoring techniquesBe able to locate faults in engineering systemsBe able to analyse the cause and effect of faults in engineering systems

Intended Learning OutcomesOn successful completion of this unit a learner will:Understand the concepts of condition monitoringUnderstand the nature and use of condition monitoring techniquesBe able to locate faults in engineering systemsBe able to analyse the cause and effect of faults in engineering systems

Unit ContentUnderstand the concepts of condition monitoringUnderstand the nature and use of condition monitoring techniquesBe able to locate faults in engineering systemsBe able to analyse the cause and effect of faults in engineering systemsConditionMonitoringFaultDiagnosis

Unit Content1. Understand the concepts of condition monitoring

Failure and breakdown: degradation due to corrosion, cracking, fouling, wear, ageing, maloperation, environmental effects, operational and maintenance considerations; statistical analysis of failure rates on plant and equipment

Monitoring: arrangements and measured parameters (online and offline monitoring, fixed and portable monitoring equipment, continuous and semi-continuous data recording, stress analysis)

Data analysis: data analysis eg computerised systems, data acquisition techniques, use of generic computer software (such as spreadsheets, databases), fault analysis/diagnosis, plant down time analysis, data storage techniques, high-speed data capture, trend analysis, expert systems, condition monitoring integrated within normal plant and machinery control and data acquisition systems

Unit Content2. Understand the nature and use of condition monitoring techniques

Vibration: broad band defect detection; frequency spectrum analysis; shock pulse method; high-frequency analysis techniques

Leak detection: acoustic emission and surveillance; moisture sensitive tapes; radiotracer/radio-chemical methods

Corrosion detection: chromatography; eddy currents; electrical resistance; tangential impedance meter; IR spectroscopy; potential monitoring; thermograph; lasers

Crack detection: ultrasonic methods; optical fibres; lasers; strain gauges; electrical potential method; eddy currents; acoustic emission; thermography

Temperature: thermography; thermometry; thermistors; thermocouple devices; RTDs; optical pyrometers; IR pyrometers; lasers

Scheme of work and assessment planDateTopicAssessment17:45h - 19:15h19:30h - 21:00h03/02Introduction to UnitFailure and breakdown10/02Failure and breakdownMonitoring24/02MonitoringUnit 24 Assignment ReviewOut03/03Data analysisData analysis10/03Condition monitoringVibration17/03Leak detectionCorrosion and Crack detection24/03TemperatureAssignment Review31/03Easter break07/04Easter break12/04Assessment submission deadline (via Moodle)In14/04Fault Analysis starts16/04Feedback

Moodle

http://moodle.swindon-college.ac.uk

Assignments are to be submitted via Moodle/Turnitin

What is Condition Monitoring?Condition monitoring (or, colloquially, CM) is the process of monitoring a parameter of condition in machinery (vibration, temperature etc.), in order to identify a significant change which is indicative of a developing fault.

It is a major component of predictive maintenance. The use of conditional monitoring allows maintenance to be scheduled, or other actions to be taken to prevent failure and avoid its consequences.

Condition monitoring has a unique benefit in that conditions that would shorten normal lifespan can be addressed before they develop into a major failure.

Condition monitoring techniques are normally used on rotating equipment and other machinery (pumps, electric motors, internal combustion engines, presses), while periodic inspection using non-destructive testing techniques and fit for service (FFS) evaluation are used for stationary plant equipment such as steam boilers, piping and heat exchangers.

Standards and relevant referencesBS ISO 13372: "Condition monitoring and diagnostics of machines. Vocabulary" (2012)

ISO (2011). ISO 17359:2011, Condition monitoring and diagnostics of machines - General guidelines. The International Organization for Standardization (ISO)

BS ISO 13374: "Condition monitoring and diagnostics of machines. Data processing, communication and presentation (parts 1-3)" (2012)

BS ISO 13381-1: "Condition monitoring and diagnostics of machines. Prognostics - General guidelines" (2004)

Simon R. W. Mills (2010). Vibration Monitoring and Analysis Handbook - (INST397). The British Institute of Non-Destructive Testing. ISBN 978-0-903132-39-8

Charles W. Reeves (1998). The Vibration Monitoring Handbook. Coxmoor Publishing Co. ISBN 978-1-901892-00-0

Trevor M. Hunt & John S. Evans (2008). Oil Analysis Handbook. Coxmoor Publishing Co. ISBN 978-1-901892-05-5

Condition monitoring technologyThe following list includes the main condition monitoring techniques applied in the industrial and transportation sectors:Vibration condition monitoring and diagnosticsLubricant analysisAcoustic emissionInfrared thermographyUltrasound emissionMotor Condition Monitoring and Motor current signature analysis (MCSA)

Most CM technologies are being slowly standardized by American Society for Testing and Materials (ASTM) and International Organization for Standardization (ISO)

Rotating equipmentThe most commonly used method for rotating machines is called a vibration analysis. Measurements can be taken on machine bearing casings with accelerometers (seismic or piezo-electric transducers) to measure the casing vibrations, and on the vast majority of critical machines, with eddy-current transducers that directly observe the rotating shafts to measure the radial (and axial) displacement of the shaft. The level of vibration can be compared with historical baseline values such as former start ups and shutdowns, and in some cases established standards such as load changes, to assess the severity.

Interpreting the vibration signal obtained is an elaborate procedure that requires specialized training and experience. It is simplified by the use of state-of-the-art technologies that provide the vast majority of data analysis automatically and provide information instead of raw data.

One commonly employed technique is to examine the individual frequencies present in the signal. These frequencies correspond to certain mechanical components (for example, the various pieces that make up a rolling-element bearing) or certain malfunctions (such as shaft unbalance or misalignment). By examining these frequencies and their harmonics, the CM specialist can often identify the location and type of problem, and sometimes the root cause as well.

Rotating equipmentExamples:High vibration at the frequency corresponding to the speed of rotation is most often due to residual imbalance and is corrected by balancing the machine.

A degrading rolling-element bearing will usually exhibit increasing vibration signals at specific frequencies as it wears. Special analysis instruments can detect this wear weeks or even months before failure, giving ample warning to schedule replacement before a failure which could cause a much longer down-time. Beside all sensors and data analysis it is important to keep in mind that more than 80% of all complex mechanical equipment fail accidentally and without any relation to their life-cycle period.

Rotating equipmentMost vibration analysis instruments today utilize a Fast Fourier Transform (FFT) which is a special case of the generalized Discrete Fourier Transform and converts the vibration signal from its time domain representation to its equivalent frequency domain representation.

However, frequency analysis (sometimes called Spectral Analysis or Vibration Signature Analysis) is only one aspect of interpreting the information contained in a vibration signal. Frequency analysis tends to be most useful on machines that employ rolling element bearings and whose main failure modes tend to be the degradation of those bearings, which typically exhibit an increase in characteristic frequencies associated with the bearing geometries and constructions.

Depending on the type of machine, its typical malfunctions, the bearing types employed, rotational speeds, and other factors, the CM specialist may use additional diagnostic tools, such as examination of the time domain signal, the phase relationship between vibration components and a timing mark on the machine shaft (often known as a keyphasor), historical trends of vibration levels, the shape of vibration, and numerous other aspects of the signal along with other information from the process such as load, bearing temperatures, flow rates, valve positions and pressures to provide an accurate diagnosis.

Rotating equipmentThis is particularly true of machines that use fluid bearings rather than rolling-element bearings. To enable them to look at this data in a more simplified form vibration analysts or machinery diagnostic engineers have adopted a number of mathematical plots to show machine problems and running characteristics, these plots include the bode plot, the waterfall plot, the polar plot and the orbit time base plot amongst others.

Handheld data collectors and analyzers are now commonplace on non-critical or balance of plant machines on which permanent on-line vibration instrumentation cannot be economically justified. The technician can collect data samples from a number of machines, then download the data into a computer where the analyst (and sometimes artificial intelligence) can examine the data for changes indicative of malfunctions and impending failures.

For larger, more critical machines where safety implications, production interruptions (so-called "downtime"), replacement parts, and other costs of failure can be appreciable (determined by the criticality index), a permanent monitoring system is typically employed rather than relying on periodic handheld data collection. However, the diagnostic methods and tools available from either approach are generally the same.

Rotating equipmentRecently also on-line systems have been applied to heavy process industries such as pulp, paper, mining, petrochemical and power generation. These can be dedicated systems like Sensodec 6S or nowadays this functionality has been embedded into DCS.

Performance monitoring is a less well-known condition monitoring technique. It can be applied to rotating machinery such as pumps and turbines, as well as stationary items such as boilers and heat exchangers.

Measurements are required of physical quantities: temperature, pressure, flow, speed, displacement, according to the plant item. Absolute accuracy is rarely necessary, but repeatable data is needed. Calibrated test instruments are usually needed, but some success has been achieved in plant with DCS (Distributed Control Systems).

Performance analysis is often closely related to energy efficiency, and therefore has long been applied in steam power generation plants. Typical applications in power generation could be boiler, steam turbine and gas turbine. In some cases, it is possible to calculate the optimum time for overhaul to restore degraded performance.

Sensodec 6S - for predictive maintenance in tissue machinesThe Sensodec 6S online condition, runnability and oil lubrication monitoring system provides you with an integrated, cost-efficient tool for process and machinery monitoring. It helps your maintenance people, machine operators, production personnel and process engineers solve problems in a proactive and preventive way. With its flexible modular design, Metso Sensodec 6S allows you to start with present needs and budgets, and extend to cover the future needs of millwide monitoring later on.

Based on advanced, yet easy-to-use analysis tools, the Metso Sensodec 6S tissue machine condition monitoring system ensures that machine operators and maintenance peopleare alerted well before any mechanical problems in the machinery occur. It pays to haveearly warning in dynamic processes like papermaking, where mechanical conditions can deteriorate rapidly and where it is especially vital to recognize the early warning signs of faults.

Sensodec 6S - for predictive maintenance in tissue machinesAvoid unplanned downtime Early failure detection helps avoid unplanned machine downtime, and effectively solves runnability problems. Rolls, bearings, gears and other drive train components produce low-level signals at an early stage when a fault is developing, but is not yet apparent to operators or maintenance personnel.The Sensodec 6S system can immediately detect even these early signs of defects with sensitive high-quality vibration sensors designed for monitoring in a paper machinery environment. Fast measurement cycles, speed-adaptive alarm handling and advanced analysis tools make these signs fully apparent to the personnel. As a result, maintenance actions can be scheduled on time and for the right reasons.

Case study: Norilsk NickelFollowing the delivery of a Metso Sensodec 6S condition monitoring system, remote diagnostic support provided by Metso has proved to be an invaluable aid to predictive maintenance.

Situated in southwest Finland, the Norilsk Nickel Harjavalta operation produces nickel metals and chemicals from raw materials that come from as far as Australia and Brazil as well as Finland. Commissioned in 1959 and expanded in 1995 and 2002, today the plant is the seventh largest nickel refinery in the world with an annual capacity of 65,000 tonnes of nickel. As part of the productivity, machine availability and maintenance development activities the plant invested in a Metso Sensodec 6S for continuous condition monitoring of key process machinery. Today the system monitors 4 ball mills, 3 nickel briquetting machines and two large process fans.

An important part of the condition monitoring is a monthly report prepared by Metso specialist, Aarno Kernen, using data from the Sensodec system he acquires via a secure remote link.

Case study: Norilsk Nickel

Overview shows that a warning (yellow) in two points in one of the briquetting machines. The 24 month trends show that vibration level in 1000-3000 Hz range has slowly risen compared to the red alarm limit line.

Metso specialist Aarno Kernens analysis of this spectrum showed why the vibration level has increased, there are clear bearing fault harmonics around 1300-1900 Hz.

Other techniquesVisual inspectionsThermographyScanning Electron MicroscopeSpectrographic oil analysisUltrasound Shock Pulse MethodHeadphonesPerformance analysisWear Debris Detection Sensors

Criticality IndexThe Criticality Index is often used to determine the degree on condition monitoring on a given machine taking into account the machines purpose, redundancy, cost of repair, downtime impacts, health, safety and environment issues and a number of other key factors. The criticality index puts all machines into one of three categories:Critical machinery Machines that are vital to the plant or process and without which the plant or process cannot function. Machines in this category include the steam or gas turbines in a power plant, crude oil export pumps on an oil rig or the cracker in an oil refinery. With critical machinery being at the heart of the process it is seen to require full on-line condition monitoring to continually record as much data from the machine as possible regardless of cost and is often specified by the plant insurance. Measurements such as loads, pressures, temperatures, casing vibration and displacement, shaft axial and radial displacement, speed and differential expansion are taken where possible. These values are often fed back into a machinery management software package which is capable of trending the historical data and providing the operators with information such as performance data and even predict faults and provide diagnosis of failures before they happen.Essential Machinery Units that are a key part of the process, but if there is a failure, the process still continues. Redundant units (if available) fall into this realm. Testing and control of these units is also essential to maintain alternative plans should Critical Machinery fail.General purpose or balance of plant machines These are the machines that make up the remainder of the plant and normally monitored using a handheld data collector as mentioned previously to periodically create a picture of the health of the machine.

Failure and breakdown

Failure and breakdownDegradation due to:CorrosionCrackingFoulingWearAgeingMaloperationEnvironmental effectsOperational and maintenance considerations

Statistical analysis of failure rates on plant and equipment

Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen. Formation of an oxide of iron due to oxidation of the iron atoms in solid solution is a well-known example of electrochemical corrosion, commonly known as rusting. This type of damage typically produces oxide(s) and/or salt(s) of the original metal. Corrosion can also occur in materials other than metals, such as ceramics or polymers, although in this context, the term degradation is more common.

In other words, corrosion is the wearing awayof metals due to a chemical reaction.

www.ventiq.com/corrosion

Degradation due to corrosion

"Rust and dirt" by Roger McLassus. Licensed under CC BY-SA 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Rust_and_dirt.jpg#mediaviewer/File:Rust_and_dirt.jpg

"Galvanic corrosion of aluminum and steel in seawater" by Webcorr - Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Galvanic_corrosion_of_aluminum_and_steel_in_seawater.jpg#mediaviewer/File:Galvanic_corrosion_of_aluminum_and_steel_in_seawater.jpg

"Crevice corrosion of 316 stainless steel in desalination" by Webcorr - Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Crevice_corrosion_of_316_stainless_steel_in_desalination.jpg#mediaviewer/File:Crevice_corrosion_of_316_stainless_steel_in_desalination.jpg

Many structural alloys corrode merely from exposure to moisture in the air, but the process can be strongly affected by exposure to certain substances. Corrosion can be concentrated locally to form a pit or crack, or it can extend across a wide area more or less uniformly corroding the surface. Because corrosion is a diffusion controlled process, it occurs on exposed surfaces. As a result, methods to reduce the activity of the exposed surface, such as passivation and chromate-conversion, can increase a materials corrosion resistance. However, some corrosion mechanisms are less visible and less predictable.Degradation due to corrosion

It will never happen to me

"Opel engine X14NZ-rusty block near the water pump" by Kychot - Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Opel_engine_X14NZ-rusty_block_near_the_water_pump.jpg#mediaviewer/File:Opel_engine_X14NZ-rusty_block_near_the_water_pump.jpg

Corroded Transmission Gear from BMW R80 ST Motorcyclehttp://www.advrider.com/forums/showthread.php?t=435511Degradation due to corrosion

Metals (and their alloys) can be arranged in a galvanic series representing the potential they develop in a given electrolyte against a standard reference electrode. The relative position of two metals on such a series gives a good indication of which metal is more likely to corrode more quickly. However, other factors such as water aeration and flow rate can influence the process markedly.

Degradation due to corrosion

Degradation due to corrosionCorrosion Prevention

Selection of materials: Use of the standard corrosion references to select the appropriate material for the environment

Changing the character of the environment: Lowering temperature, velocity or concentration of the fluids

Using inhibitors: These are substances that when added in low concentrations to the environment decreases its corrosiveness. The inhibitor depends on both the alloy and the corrosive environment. They are used mainly in closed systems: e.g. car radiators, steam boilers

Using physical barriers: Films and coatings applied to the surface. There is a large diversity of metallic and non-metallic coatings with a high degree of surface adhesion

Cathodic Protection: Very effective. It involves supplying from an external source electrons to the metal to be protected, making it a cathode

Degradation due to cracking

Degradation due to cracking

Degradation due to crackingFigure 4-7: Microscopic examination of a cross section of the inner raceway revealed surface cracks consistent with the spalling observed.Figure 4.8: Etching the sample revealed a homogeneous macrostructure of a tempered martensite matrix with undissolved carbides present.Figure 4.9: Microscopic examination of a quartered ball bearing also revealed surface cracks.Figure 4-10: A large crack extending towards the centre of the bearing was also found.Figure 4-11: The large surface crack ties along a border of the heterogeneity.

Degradation due to foulingFouling is the accumulation of unwanted material on solid surfaces to the detriment of function.

The fouling material can consist of either living organisms (biofouling) or a non-living substance (inorganic or organic). Fouling is usually distinguished from other surface-growth phenomena in that it occurs on a surface of a component, system or plant performing a defined and useful function, and that the fouling process impedes or interferes with this function.

Other terms used in the literature to describe fouling include: deposit formation, encrustation, crudding, deposition, scaling, scale formation, slagging, and sludge formation. The last six terms have a more narrow meaning than fouling within the scope of the fouling science and technology, and they also have meanings outside of this scope; therefore, they should be used with caution.

Fouling phenomena are common and diverse, ranging from fouling of ship hulls, natural surfaces in the marine environment (marine fouling), fouling of heat-transfer components through ingredients contained in the cooling water or gases, and even the development of plaque or calculus on teeth, or deposits on solar panels on Mars, among other examples.

Degradation due to fouling

Degradation due to fouling

Degradation due to wearAbrasive Wear: Particles generated as a result of abrasive wear are "work hardened;" they become harder than the parent surface and, if not removed by proper filtration, will recirculate to cause additional wear.

Here's how it happens:Particles enter the clearance space between a component's two moving surfaces, bury themselves in one of the surfaces, and act like cutting tools to remove material from the opposing surface. The particle sizes causing the most damage are those equal to and slightly larger than the clearance space. Ultimately, abrasive wear will result in dimensional changes, leakage and lower efficiency. Left uncontrolled, more particles will be generated which will result in a chain reaction of abrasive wear -- a chain reaction that will continue and cause premature system component failure unless adequate filtration is implemented to break the chain. To protect components from abrasive wear, particles of approximately the dynamic clearance size range must be removed.

Degradation due to wearErosive Wear: Erosive wear is caused by particles that impinge on a component surface or edge and remove material from that surface due to momentum effects. This type of wear is especially noticed in components with high velocity flows, such as servo and proportional valves. Particles repeatedly striking the surface may also cause denting and eventual fatigue on the surface. The damaging effects of erosive wear can be seen in dimensional changes to equipment, leakage, lower efficiency, and the generation of additional particles, which leads to further contamination and wear throughout the system.

Adhesive Wear: Excessive load, low speed, and/or reduction in fluid viscosity can reduce oil film thickness to a point where metal-to-metal contact occurs. Surface asperities are "cold welded" together and particles are sheared off as surfaces move.

Fatigue Wear: Bearing surfaces are subjected to fatigue failures as a result of repeated stress caused by particles trapped between the two moving surfaces. At first, the surfaces are dented and then cracking begins. These cracks spread after repeated stress by the bearing load, even without additional particulate damage, and eventually the surface fails, producing a spall. Contamination reduces bearing life significantly through fatigue, abrasion and roughening or degradation of operating surfaces.

Degradation due to wear

Degradation due to ageing

Degradation due to ageingAgeing is not about how old your equipment is; it is about its condition, and how that is changing over time. Ageing is the effect whereby a component suffers some form of material deterioration and damage (usually, but not necessarily, associated with time in service) with an increasing likelihood of failure over the lifetime.

Ageing equipment is equipment for which there is evidence or likelihood of significant deterioration and damage taking place since new, or for which there is insufficient information and knowledge available to know the extent to which this possibility exists.

The significance of deterioration and damage relates to the potential effect on the equipments functionality, availability, reliability and safety. Just because an item of equipment is old does not necessarily mean that it is significantly deteriorating and damaged. All types of equipment can be susceptible to ageing mechanisms.

Overall, ageing plant is plant which is, or may be, no longer considered fully fit for purpose due to deterioration or obsolescence in its integrity or functional performance. Ageing is not directly related to chronological age. There are many examples of very old plant remaining fully fit for purpose, and of recent plant showing evidence of accelerated or early ageing, e.g. due to corrosion, fatigue or erosion failures.

Degradation due to ageing

Degradation due to maloperation

Degradation due to environmental effects

"Rust and dirt" by Roger McLassus. Licensed under CC BY-SA 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Rust_and_dirt.jpg#mediaviewer/File:Rust_and_dirt.jpg

Degradation due to operation and maintenance considerationsPreventative Maintenance

Corrective Maintenance

Predictive Maintenance

MonitoringArrangements and measured parameters:online and offline monitoringfixed and portable monitoring equipmentcontinuous and semi-continuous data recordingstress analysis