The Pump Condition Monitoring Engineering Essay
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To avoid unplanned downtime, realize energy savings or other considerations, pump users require a method or tool to determine the appropriate time for overhaul of a pump.
This method or tool is used by engineers in managing assets to provide capacity for production and energy efficiency to save operating expenses or even to minimize greenhouse impact. This optimization method can be applied to all items where deterioration results in equipment breakdowns or loss of efficiency.
Pumps like any rotating machine tend to rotate in response to excitation forces like residual rotor unbalance, turbulence in liquid flow, pressure pulses, cavitations and wear of pump. If vibration frequencies and natural frequencies match, resonance occurs, amplifying the vibrations. This is a sufficient cause to damage pump components
Why Pump Condition Monitoring is important: (Source http://www.pumpmonitor.com)
Pumps are used at about 20% of the world's most electrical power generating companies.
about 7% of the world's green houses gas productions.
power and preservation usually covers more than 50% of Life sequence expenses.
Statistics show that 20% or more of the energy devoted by pumping systems could be saved throughout equipment and control alters.
Pumps are frequently considered critical mechanism of a process. Plant reliability is best possible when they are maintained on a regular basis or nonstop state monitoring.
Performance based maintenance costs are considerably lesser than a schedule based costs.
Hence it becomes very important to Condition Monitor the pumps.
Chapter -2: Aim & Objectives
The object of this research study is to critically study Condition Monitoring of both, Centrifugal and axial pumps. That will include most important aspects like:
Condition Monitoring and its Part in Maintenance
Pump Performance and the Effect of Wear
Performance Analysis and Testing of Pumps for Condition Monitoring
Performance Analysis and its Application to Optimise Time for Overhaul
Other Methods of Performance Analysis for Pump Condition Monitoring
Vibration Analysis of Pumps
Other Uses of Condition Monitoring
Other Condition Monitoring Methods
Positive Displacement Pumps
Chapter -3: Project plan
Attached with this report
Chapter -4: Introduction
Pumps are used to add energy to fluids. Generally it is done by using a rotating blade to force a fluid in a given direction.
Classification of pumps:
Positive Displacement Pumps
Radial Flow Pumps
Axial Flow Pumps
Progressive Cavity Pumps
[Figure-1: Different types of Pumps]
a) Positive Displacement pumps: A positive displacement pump, as the name suggests, pushes a fluid by containing a fixed amount of it and then displacing the entire contained volume into the pipe. Positive displacement pumps produce a constant flow at any given speed and hence are called "Constant Flow Machines". These are used for pumping fluids other than water.
Following types of mechanism are used to displace the fluid:
a1) Reciprocating Type: Reciprocating pumps are plunger pumps or diaphragm pumps. Diaphragm valves.
Recently used for slurries treatment in plants, and are used to force dangerous, toxic materials.
a2) Rotary Type: These pumps use rotation principle. These are mostly used in, oil burners, soaps, cosmetics, sugars, syrup, and molasses, as well in dyes, ink, bleaches, vegetable and mineral oils.
Gear pump: Two gears rotates in a closely fitted casing. A common application of the gear pump is the engine oil pump in car engines.
[Figure-2: Gear Pump]
Progressing cavity type pump: These are applied for pumping sewage sludge contaminated with large particles. Helical shaped rotor is used.
[Figure-3: Progressive Cavity Pump], (Image Source: http://www.highflowpumps.com/)
Lobe Pumps: Fluid is passed between the rotors teeth and the volute chamber.
[Figure-4: Lobe Pump]
Screw Pumps: Screw pump transmits fluid into the spaces between the screw gears.
[Figure-5: Screw Pump]
b) Centrifugal pump: They are widely used in general piping systems. These are used for pumping water in industry and constitute 75% of pumps installed
b1) Radial Flow Pump
In a Radial Flow pump, fluid is discharged in a direction perpendicular to the direction of intake or suction. The fluid flowing into the pump first makes contact with a spinning impeller. This deflects the fluid away from it. The fluid is pushed out through a circular casing around the impeller. In this case fluid pressure increased not the speed.
Fluid is sucked into the pump along the axis of rotation of the impeller. It is accelerated in a perpendicular direction into a diffuser chamber. From here it is discharged into the outlet pipe. Centrifugal pumps are applied where there is small head and large discharge is required. These have high hydraulic efficiency.
These are used in waste treatment plants. Screw type centrifugal pumps are very effective in sludge handling , comprising of fibrous elements and for handling sludge with up to 10% dry matter .
[Figure-6: Centrifugal Pump] (Image source : http://www.thomasnet.com/articles/image/centrifugal-pump.jpg)
b2) Axial flow pumps: In an axial pump, the discharge and suction are both in the same direction. Flow is along the axis of the blade. Axial pumps are used to increase of speed of fluid flow without increase of pressure. They have high flow rates and can operate at very low pressure.
[Figure-7:Axial Flow Pump]
Chapter -5: Maintenance and Condition Monitoring:
The intention of performing maintenance is to provide optimum capacity of production at the lower cost. Maintenance should be preferred for reliability and not as repair.
There are 4 Types of Maintenance, which are given below:
(a) Preventive Maintenance: This type of maintenance prevents failure from occurring. It comprises of scheduled periodic maintenance checks. Such maintenance prevents breakdowns and ensures delay free functioning.
The advantages of preventive maintenance include:
Enhanced systems dependability.
reduces cost of substitute.
cuts system downtime.
Better standby account management.
(b) Corrective Maintenance: Maintenance performed to correct an error after a failure has occurred is corrective maintenance. The failed component may require restoration , repair or replacement.
(c) Breakdown Maintenance: If a machine breaks down or malfunctions , breakdown maintenance is performed to return it to normal functioning. This is done by replacing or repairing parts.
(d) Predictive Maintenance: This type of maintenance consists of methods of observing the condition of in service machines and thus predicting when maintenance is required to be performed. This method reduces costs as compared to preventive maintenance as tasks are only performed when necessary.
Condition monitoring is a type of predictive maintenance. It involves prediction of condition of a machine by on monitoring its performance, statistical process control or equipment behaviour to detect defects at an early stage and rectify them, which could otherwise result in delays leading to unnecessary expenditure.
Maintenance is performed while the machine/ equipment is in operating regularly , with little or no interruption in its functioning. The methods for detection of errors include infrared thermographs, circuit analysis, analysis of vibrations etc. Predictive Maintenance or Condition monitoring a smart way to reduce downtime and reduce cost.
The fundamental purpose of maintenance is to contribute for profit objectives, by maximizing the production and safety of people and plant.
This report will explore how maintenance should be used as a tool to keep pumps working to its optimum level.
Condition based maintenance:
Definition of Condition Monitoring:
Condition monitoring is part of maintenance, not something done by experts from outside (Beebe, 2001)
Signs of degradation are detected in operational equipment by monitoring the equipment through continuous inspection. Data collected is analysed , and a prediction is made for the duration in which a machine can run safely without failure.
Condition Monitoring is the art of monitoring of the equipment's health by taking
simple measurements of the machine performance. It works the same as a
Doctor checks (measure) the health by checking pulse, temperature,
blood pressure etc of a person.
If we measure the current draw and the outlet flow of a pump and find out that that the current draw was increasing while the outlet flow was decreasing, as compared to the previous months measurements, there are very good chances that the condition is deteriorating and that some maintenance was due for the pump,
The scheduling of the monitoring is decided by the size of plan, ease of data collection etc. This may be done everyday, once a month or on an annual basis.
Advanced technology may be used for condition monitoring. It may not be limited to
Motor Current Analysis
Pump life cycle costs
Pump life cycle cost is defined as the sum of the commissioning cost, maintenance cost, running cost and decommissioning cost for the period of a pump's service life.
Complete understanding of the pump's lifecycle cost helps us to radically reduce the energy consumed , thus greatly reducing the pumps environmental impact
PLCC = Cin + Cins + Cpo + Cop + Cm + Cd + Cen + Cdc
PLCC = life cycle cost
Cin = initial costs, purchase price (pump, system, pipe, other services)
Cins = installation and commissioning cost (including training)
Cpo = power consumed costs
Cop = operation costs
Cm = maintenance and repair costs (routine and predicted repairs)
Cd = delay costs (loss of production).
Cen = environmental costs (contamination from pumped liquid )
Cdc = decommissioning (counting renovation of the home Environment)
Maintenance Cost of a Pump in its Life Cycle:
[Figure-8: Maintenance Cost] (Image Source: http://www.waterworld.com)
The costs for maintenance are dependent on the actual equipment involved , records can be consulted to make cost estimates. The annual cost has to include the following:
Value of spare parts used.
Charge for any third party work.
Normally Maintenance cost of a Pump within its life cycle is estimated 20%.
Pump selection reliability factors
Reliability of machines, has been increasingly debated in recent years . Low reliability of commonly used centrifugal pumps has been a focal point of this debate.
Pump selection is very important its reliability. But it is not the only factor for reliable pump operation.
Other critical installation parameters are also important. The main factor for enhanced reliability is selecting the right pump.
The first step in pump selection is deciding the pump parameters. The head and capacity required have to be calculated. There are three major conditions related to reliability which affect selection; operating speed (FR), impeller diameter (FD) and flow rate (FQ).
Operating Speed - RPM (FR) Wear based on operating speed caused due to friction in rubbing contact surfaces like mechanical seals and shaft seals affects the reliability. Life of bearings and heat generated in bearings is another cause for lack of reliability. For all the above mentioned conditions wear has a linear relationship with the operating speed of the pump.
Impeller Diameter (FD) The impeller exerts a significant load on the shaft and bearings . This directly affects the reliability of the pump. Two types of loads are produced; one is due to the non uniform pressure distribution in the casing, the second is due to the interaction between the blades of the impeller and the discharge.
This second effect is extremely hazardous as it forces the seal faces to move away from each other repeatedly during each revolution. The intensity of this movement may be greater than steady deflection. There is a cubic proportionality between these loads and the impeller diameter.
Flow Rate (FQ) The flow rate of a centrifugal pump is the best efficiency point or BEP. Pumps are designed in such a way that they are most reliable only at a given flow rate for a specific operating speed and impeller diameter. The loads exerted on impeller at this flow rate are minimised. If the flow rate is more or less than the BEP than the load intensity increases and there is turbulence in the rotation of the impeller. Such unpredictable loads share the same effects on reliability as the impeller/discharge loads discussed above. Pumps are examined to check the ability to withstand the effects of these impacts. The main parameters of the tests are:
Pump shaft to motor alignment.
Reliability Index (RI) The Reliability directory is shaped as a product of three factors:
RI = FR x FD x FQ
Values vary from zero to one; the higher the value the better the dependability is.
Techniques of Condition Monitoring
Vibration Monitoring Analysis: is commonly used as a Monitoring analysis. It helps to determine the structural stability in a system. It is best suitable for rotating machines like pumps. Vibration measuring instruments are used for measurement.
The frequency of the vibrations are mapped. If a defect is present a particular frequency will be detected. Analysis made previously on existing equipment can be compared to analysis on new equipment. This data will give the condition of the equipment.
Visual Inspection: Devices like mirrors, TV Camers are used for Visual inspection.
Visual inspection in its most basic form may also be done by experienced inspectors and maintenance technicians. Causes of failure like cracks, leaks and corrosion can be detected and prevented. This is the cheapest form of condition monitoring. It also adds a sense of attachment between the equipment and the people who work on it.
Only visual inspection technique is not enough. It should be augmented by other techniques.
Performance Monitoring and Analysis: Analysis is done on usage of energy, as more energy usage means deteriorating condition of the machine. Performace can bne measured with parameters like Pressure, flow rate or temperature etc.
Analysis of wear particles in lubricants or contamination of process fluid: This process gives advance warning than many other predictive maintenance methods.
[Figure-10: Contamination of Process Fluid]
Spectrographic oil analysis may be used to test the chemical composition of the oil. Chemical analysis of oil is carried out for appearance, density, viscosity, moisture
content, mechanical impurities. High silicon content points to a presence of contamination of grit.. etc, and high iron levels indicate to tiring components. Independently, elements give reasonable indications, but when used together they can accurately determine the failure modes, e.g. for internal combustion engines, the presence of iron/alloy, and carbon would indicate damaged piston rings. (Source: http://en.wikipedia.org/wiki/Condition_monitoring)
Ferrous and non ferrous particles in the lubricant may be detected by wear debris detection sensors which can give a warning if the condition of the equipment deteriorates. This system prevents failure in machines like gearboxes , turbines, pumps etc.
Ultrasonic Analysis: Time and frequency data from ultrasonic tests can reveal a lot on the health of a machine.
Portable ultrasonic testing equipment is now a common tool for noticing leaks, testing steam traps, finding cavitations, bearing condition testing and toughness testing.
What are Ultrasound Signals?
Ultrasound refers to noise of frequency beyond the range of the human ear. For detecting airborne leaks, the frequency at which the most sound is produced by an unstable leak is 38.4 kHz. There are instruments, which listens to this frequency to detect leaks.
Electronics processing is required to make ultrasound audible. This is done filtering of frequencies.
Why Record Ultrasound Signals?
Judgment, Trending, verification of analysis.
Guidance of Maintenance observers.
Examination of low speed bearings.
Investigation of electrical defects.
Inspecting of steam traps.
Analysis of reciprocating compressors.
How to Record Ultrasound Signals?
Regulates rise of detector.
Corrects level of recording device.
Spins Auto Gain Control .
Records the signal and transfer to PC.
Opens signals in computer for laboratory analysis.
The classic time signal for a bearing defect gives a goldfish envelope like this:. (Thomas J. Murphy)
[Figure-11:Ultra sound signals]
Temperature is the best indicator of the state of a machine. One can check the temperature of any surface and determine the condition of a machine..
Infrared Thermography is an inspection technique which gives accurate, reliable and correct temperature outline of any material exterior without getting in touch with the surface.
The essential perceptive of thermography is that every object produces certain amount of Infrared energy and the intensity of this radiation is a task of temperature, hence by measuring infrared radiation, temperature of surface can be calculated. (Garnaik)
Infrared thermography is a fast and secure way of detecting imperfections in different conditions. Infrared cameras can be used to detect increases in temperature that indicate latent problems. These may increase the temperature of electrical contacts or insulators. IR thermography can easily be carried out during normal operation of equipment as it is non contact. This reduces downtime.
Advantages & Disadvantages of IR Thermography
Following are advantages and disadvantages of this technique.
â€¢ It is a non-contact type technique, and modern Infrared camera can be used .
â€¢ It is Fast, reliable & accurate output.
â€¢ Time required to measure large surface area is very less.
â€¢ The output can be presented in visual & digital form.
â€¢ Since the output can be presented in visual form, there is little skill required for monitoring.
â€¢ Instrument cost is very high.
â€¢ This technique is used to work out the temperature of surface. It is unable to detect the inside temperature...
Noise level are taken every month at designated locations.
Steps for implementation of Condition Monitoring Technique for Pumps
Selection of equipment
Selection of parameters / probe
Selection of monitoring frequency
Preparation of schedule
Preparation of database.
Actual monitoring and analysis
Selection of monitoring frequency
Daily (for critical equipments)
Fortnightly (for sub critical equipments).)
[Figure-12: Condition Monitoring Steps]
Benefits of Condition monitoring
Condition monitoring has become a proven method and has become essential part of industries as companies has proven its cost benefits.
Condition monitoring gives early detection of wear out/damage.
Condition Monitoring people tour the plant and picks up developing faults
Deterioration is detected in time and repairs are scheduled.
It minimises unnecessary shutdown and opening up of plant
Cost of labour, material and loss of production is saved
More satisfying work of maintenance, less effect of errors because of direct feedback of quality work.
Judicious use of Condition monitoring can yield 10 to 20 times the initial outlay within first year - (IK Dept trade & Industry report, maintenance to late 1990s')
Condition monitoring reassurance of safe continued operation(and vary effective when "nursing on" plant to a suitable maintenance opportunity)
Condition Monitoring saves cost - reduce spare usage and lower insurance.
Cost Savings from Condition Monitoring
A Quick cost saving estimate is made to calculate the cost saving easily. Quick cost saving estimate at each inspection saves delays. For example, a coupling is found broken and approximate to cause about 2 hours of delay leads to an unplanned maintenance job.
Cost A: If the coupling broke down without warning:
Delay * Cost of Delay/hr + Direct maintenance cost (unplanned & Unscheduled) + Potential damages
Cost B: Maintenance during scheduled shutdown.
Actual cost of maintenance: Delay (if any - should be fixed in scheduled shutdown) * Cost of Delay/hr + direct maintenance cost (planned & scheduled) + Damages(= 0) .
A- B = Cost saving, which may be as high as thousands of Dollars
Following is a Case study of Qatar Petroleum, which shows a huge saving of costs because of Condition Monitoring:
141. K0302 FLUE GAS FAN
Current Drawn before balancing the Fan: 83 Ampere
Current drawn post balancing the fan : 76 Ampere
Net Current reduction: 7 Amps
Power Saving = âˆš3 x V x I x Cos ¢
âˆš3 x 11 x 7 x 0.85
Annual Cost Savings = 113.3X0.081X24X365
(Power Cost = 0.081QR/Kwh) = 80393 QR/Year
Last Six Months Predicted Failures at Qatar Petroleum
Standards used for condition monitoring (Source: http://www.iso.org)
ISO 13381-1:2004 provides guidance. The basic purpose is to:
Let the clients, manufacturers of condition monitoring and diagnostics systems to share general thoughts in the fields of machinery error analysis.
Allow users to determine the essential information, characteristics and behaviour necessary for accurate estimate.
Outlines an appropriate approach to predict development.
Introduces predictions concepts in order to ease the development of future systems and training.
ISO 18436-6:2008: Condition monitoring and diagnostics of machines -- Prognostics -- Part 1: General guidelines
ISO 18436-6:2008 states the needs for qualification and evaluation of personnel who perform machinery condition monitoring and diagnostics using acoustic production. A certificate or declaration of conformity to ISO 18436-6:2008 will provide credit of the qualifications and ability of individuals to perform acoustic production measurements and analysis machinery condition monitoring using acoustic emission equipment. This procedure may not apply to particular equipment or other explicit situations. ISO 18436-6:2008 specifies a three class classification programme.
ISO 18434-1:2008 provides an introduction to the application of infrared thermography (IRT) to machinery condition monitoring and diagnostics, where "machinery" includes machine auxiliaries such as valves, fluid and electrically powered machines, and machinery-related heat exchanger equipment. In addition, IR applications pertaining to machinery performance assessment are addressed.
ISO 18434-1:2008: introduces the terminology of IRT as it pertains to state checking and diagnostics of machines; explains the types of IRT procedures and their qualities; provides leadership on establishing cruelty appraisal criteria for anomalies identified by IRT; outlines methods and requirements for carrying out IRT of machines, including safety suggestions; provides information on data understanding, and appraisal criteria and reporting requests; provides measures for determining and compensating for reflected obvious temperature, emissivity, and attenuating media.
ISO 18434-1:2008 also includes testing procedures for determining and recompense a reflected obvious temperature, emissivity, and attenuating media when measuring the exterior temperature of an aim with a quantitative IRT camera.
ISO 18436-3:2008: Condition monitoring and diagnostics of machines -- Requirements for qualification and assessment of personnel -- Part 3: Requirements for training bodies and the training process
ISO 18436-3:2008 defines the requirements for operating training programmes for personnel who carry out machinery condition monitoring, recognize machine faults, and propose corrective action. Procedures for training of condition monitoring and diagnostic personnel are specified.
ISO 18436-7:2008 : Condition monitoring and diagnostics of machines -- Requirements for qualification and assessment of personnel -- Part 7: Thermography
ISO 18436-7:2008 specifies the requirements for qualification and assessment of personnel who perform machinery condition monitoring and diagnostics using infrared thermography. An official document or declaration of conventionality to ISO 18436-7:2008 will provide recognition of the qualifications and competence of individuals to do thermal measurements and investigate machinery condition monitoring using moveable thermal imaging equipment. This procedure may not apply to particular equipment or other precise situations. ISO 18436-7:2008 specifies a three category classification programme.
ISO 13373-1:2002 : Condition monitoring and diagnostics of machines -- Vibration condition monitoring -- Part 1: General procedures
ISO 13373-2:2005 : Condition monitoring and diagnostics of machines -- Vibration condition monitoring -- Part 2: Processing, analysis and presentation of vibration data
ISO 13373-2:2005 recommends actions for dealing out and presenting vibration data and analysing vibration signatures for the reason of monitoring the vibration state of rotating machinery, and performing diagnostics as suitable. Different methods are described for different applications. Signal improvement techniques and analysis methods used for the investigation of exacting machine dynamic phenomena are included. Many of these techniques can be applied to other machine types, as well as reciprocating machines. Example formats for the parameters that are commonly plotted for valuation and diagnostic purposes are as well given.
ISO 13373-2:2005 is divided basically into two essential approaches when analysing vibration signals; the time domain and the frequency domain. Some approaches to the modification of diagnostic results, by changing the operational circumstances, are also covered.
Pump Performance and the Effect of Wear
Pumps wear as they are used but their efficiency can be maintained by
Condition monitoring and accordingly refurbishment:
[Figure-13: Effect of wear on pump characteristics]
Source: http://re.jrc.ec.europa.eu/solarec/index.htm (European commission Joint Research Center)
[Figure-14: Average wear trends for maintained and unmaintained pumps]
Source: http://re.jrc.ec.europa.eu/solarec/index.htm (European commission Joint Research Center)
Effect of internal wear on pump performance
The effect of Internal wear on pump is dependent on type of Pump . Slurry pumps are Designed to cope with erosive liquids. Total operating cost can be reduced by improving wear life. Wear is increased by High Velocity, large solid size and high concentration.
Chapter -6: Performance Analysis and Testing of Pumps for Condition Monitoring
The aims of testing a system's pump performance are to:
Record system pumps performance.
Verifying the impeller size at present installed in the pump.
Launch the system curve for the pumping system.
Establish the operating point of the pump; i.e. the point where the pump's impeller curve intersects the system curve with the discharge valve throttled and with the discharge valve fully open.
Measures the match between "full flow" flow delivered by the pump with the discharge valve fully open and the real plan flow requirement.
Considers the implications of throttled discharge valves and opportunities to open discharge valves and adjust pump performance by means of trimming the impeller, changing the motor to get an incremental motor/pump speed change or installing a VFD to change the motor/pump speed to a non-incremental value. The objective of all of these modification techniques is to provide design flow without the head forced by the throttled valve. As a consequence, the system will advantage from reduced pump energy use and operating costs.
Considers the flow variations produced in the system as different active elements are repositioned by their control processes.
becomes aware of and make a diagnosis of other control or performance problems.
Performance analysis needs performing data
[Figure-15: Pumps in System and relationship to Condition Monitoring]
Chapter -7: Performance Analysis and its Application to Optimize Time for Overhaul
The head test at Duty Point
Like it is known that condition monitoring is used as a tool for Predicting maintenance requirements of pumps. The Head Flow examination is the essential way can be used to inspect assumed poor performance. (http://www.engineeringnet.be)
Head flow measurement is a useful type of condition monitoring because it checks pump deterioration and also shows flaws in system resistance.. (Heinz P. Bloch)
It is easier to determine the head. alter in volume according to the time can be easily measured if an appropriate vessel is available in the system. A tank having uniform dimensions can be used for this purpose. Valves are arranged in such a way so that changes in fluid level can be measured, using which flow rate can be calculated.
If the measurement is to done from the suction side of the pump an allowance is to be taken . As the tank which is on the suction side, empties, the head will decrease. This value of suction head would be considered as negligible if the discharge head is high in sum, as long as an enough NPSH or Net positive suction head is preserved. The above method can be used for open tanks with water at atmospheric conditions.
Standard pressure gauges, with electronic transducers can be used to measure head.
Performance monitoring and examination is frequently applied to pumps to be familiar with and control the amount of interior wear. Out of different methods available, that of Head Flow is ideal (Beebe, 2004) as it exposes the state of the pump and also of the system it works on. Other methods may also be suitable, such as vibration investigation to check bearings, looseness, unbalance and alignment.
Filed tests might give different results as compared to provided by the supplier. This is because of actual site condition for flow and pressure measurement is unlike as compared to different standards for pump testing.
Information received from Head test results can be used to prioritise pump overhaul.
Chapter -8: Pump Condition Monitoring using other methods of performance analysis:
The shut-off Head method
Measuring head at Zero flow is a simple test. This is only possible in cases where it can be tolerated, which is not the case for the high-energy of high-pressure pumps, where power at shut-off is greater than at duty point. (Heinz P. Bloch).
When the discharge valve is completely closed for no more than 30 seconds, suction and discharge pressure are measured when stable. The temperature of liquid is also engaged to find out the density, this assists in converting pressure reading into values of head.
Since the head-flow curve in case of a worn pump moves toward zero flow axis, the wear in vane outer diameter can be easily detected. If the core is relatively steep, it shows sealing war ring degradation.
Figure below shows degradation of pump over three years. This is usually derived from head-flow tests near duty point, but can also be obtained using the shut-off head test.
The Thermodynamic Method
The Next means of pump monitoring is to determine the change in temperature of the liquid passing throughout the pump. increase in temperature represents the inefficiency of the pump. Temperature is measured carefully as the differential is vey small.
The measured inlet temperature, differential temperature and head of the pump is used to calculate the efficiency of the pump. A plot between efficiency and head measurement is well used to evaluate the data which is varying with time.
Tapings at suction and discharge must be two times the diameter away from pump flanges, for the installation of pressure/temperature probes. Motor power is checked by tong-type detectors. Pump effectiveness is then found from the accurate measurement of the head and temperature increase throughout the pump. By inspecting the motor loss, the power absorbs is considered. Using all the given data pump flow can be calculated.
The thermodynamic means would be more cost-effectively possible if no special tapping indicators were necessary.
Measurement of Balance Flow
A balance disk or drum is present in multistage pumps with impellers facing in same direction. This balance disk is placed in such a way that the discharge pressure at the final stage counteracts the axial thrust on the shaft. A second way for condition monitoring is to determine the leak off from the equilibrium device. If there is a boost in wear in the annular space to the balance disk, which is found by increased leak flow then the interstate clearance are furthermore worn. The leak off line is small as compared to the major flow pipe, a permanent flow gauge is very cheap.
Optimization of Pump Overhauls
It is very important to find out when is the optimum time to overhaul a pump, when degradation is detected . The best economic time is dependent on many factors.
If the deterioration is constant over a given period of time, then the company has to calculate the cost of overhaul and return from the overhaul.
In case the deterioration is increasing over a period of time then best time refurbish will be when
Accumulated cost of electricity use = Cost of refurbish (Ray Bee)
If the overhaul cost is not much in percentage to the cost of lost production, then refurbish is the best option.
One needs to compare extra hours of running the pump and in-turn the electricity consumption to check if the overhaul is required.
Chapter -9: Vibration Analysis of Pumps
Causes of Pump Vibration
Vibration can be known as the cyclical motion of an object about a balance point or in other words oscillation. In simple words a point which moves forward and backwards is supposed to be vibrating. Pendulum of a watch is an example of vibration, which is required and desired form for vibration. However in case of centrifugal pump, vibration is unwanted and guide to part breakdown.
All pumps vibrate at some attitude, which may be normal vibration. But there are vibration which may be harmful. Vibrations are a sign of a pump's state. Vibrations that exceed certain laid down satisfactory levels and can shorten a pump's life. Vibration investigation can be used as a instrument for troubleshooting and preventative maintenance.
What Causes Vibration?
Vibration is caused by an excitation force. Repetitive forces cause unwanted vibration troubles most generally linked with centrifugal pumps. The main cause of vibration are imbalanced, misaligned rotating components of the pump. Worn components also cause vibration.
How is Vibration Measured ?
[Figure-16: Checking Vibration of a Pump-1]
(Image -1) (Source: http://hpac.com/mag/causes-pump-vibration-0409/)
As shown in the figure-1, measurements for checking vibrations are measured at the inboard and outboard bearings housing of a pump and motor in 3 directions : alongside the axis, horizontally and vertically. If extra detailed testing is required, measurements should also be taken at several places on the pump base. Electronic probes or vibration sensors are attached at each of these locations, sending electronic signals to a vibration analyzer. The necessary measurements have to be taken when the pump is at operating speed for steady speed drives and at varying speeds for pumps on varying speed drives.
Example of some of the companies providing Pump Vibration measurement services are:
Max Flow Pump Service (www.maxflopump.com) sells equipments to measure the Pump Vibration.
Max-Flo provides tests pump vibrations for:
Pump Amplitude and Frequency
Total Pump Vibration Analysis
Direct Readout of the Predominant Frequency of the Pump Vibration
Strobe light Vibration Analysis
Vibration Analysis for all H.P. pumps
Industry Up Time (www.industryuptime.com)
Our pump vibration examination check provides necessary information concerning machine errors, serving plant staff make knowledgeable decisions to address "anxious" equipment. Does the pump require to be pulled? Does the unit need to be shut down? Can the equipment be mending in the field? Pump Vibration examination can give an industry proven basis for the answer.
How is Vibration Defined?
[Figure-17: Checking Vibration of a Pump-2]
Vibrations are converted into equivalent electrical signals by vibration analysers . These electrical signals can be measured by using specially designed algorithms. The spectrum created from this data shows each vibration as values of frequency, amplitude and phase. The information is analysed to notice the origin reason of the pumps vibration. verification of a vibration source is significant to any main corrective action based on a range.
Frequency is known as the rate of fluctuation of the vibrations or in other words the speed at which an object vibrates. It gives the number of total series that happen in a particular period of time, such as cycles per second (cps) also measured in hertz (Hz) or cycles per minute (cpm). The unit cpm is generally appropriate as it can be connected to the speed of the pump which is in revolutions per minute. think about a pump running at a speed of 1,800 rpm, and vibration frequency is 1,800 cpm, frequency can be calculated as:
1 Ã- rpm
If pump speed is 1,800 rpm and vibration frequency is 3,600 cpm, frequency can be articulated as:
2 Ã- rpm
The rotating frequency of a pump normally is referred to as the system's basic frequency. lots of vibrations simply are a multiple of basic frequency.
Chapter -10: Key trend for Condition Monitoring (Sandy Dunn)
Condition Monitoring is a technique, which is developing further and if not used properly, its costs are very high. Technological advances are taking place slowly as new technical discoveries are prepared, established and useful.
Here are some of trends to help condition monitoring further efficient:
The growth of clever systems, able of understanding and making decisions without human interference. Technologies making this promising including: sensors with built in cleverness (SMART Sensors) able of transmitting fairly rich, high grade information, re programmable on line sensors. Low cost on line watching systems that will authorize the charge effective nonstop monitoring of key equipment items
The increasing condition of built in vibration sensors as standard features in huge motors, pumps, turbines and other large equipment .
more and more complicated state monitoring software, with fast developing specialist diagnosis capabilities. specialist systems using artificial intelligence algorithms.
The acceptance of Condition Monitoring within the "typical" of Operations and Maintenance, with Production operators increasingly utilising Condition Monitoring technologies as part of their day to day responsibilities.
rising integration, and acceptance of ordinary principles for interfacing Condition Monitoring software with CMMS and Process Control software
A rising focus on the business implications and applications of Condition Monitoring technologies, leading to the use of Condition Monitoring technologies to improve equipment dependability and performance, better than to just predict component breakdown.
A decrease in the cost per point of applying Condition Monitoring technologies perhaps guides to more extensive use of these technologies.
Appendix -1: Case Studies
Case Study-1: SKF condition monitoring technology averts plant failure at major UK paper mill.
Case Study -2: Condition Monitoring as a Tool to Increase Availability of Multiphase Pumps
Online condition monitoring system helps Environment Agency to manage remote pumping station in the Humber Estuary from www.schaeffler.co.uk
Machine-Condition Monitoring Using Vibration Analysis - A case study from Nuclear Power Plant. By D. N. Brown and Bruel & Kjaer.
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