ONLINE AND MANUAL (OFFLINE) VIBRATION MONITORING OF EQUIPMENT FOR RELIABILITY CENTERED MAINTENANCE

BY Sheetalnath Mahalungkar, Reliability Engineer, Holcirn (US) Inc

Mike Ingrarn, Integrated Condition Monitoring Entek (Rockwell Automation)

Abstract:

As the cement industry evolved, keeping equipment running without failure became crucial. Loss in production due to equipment failure was no longer affordable due to the increasing demand. In the cement industry, maintenance is a costly and at the same time controllable expense. The initial concept of equipment maintenance was reactive maintenance. Scheduled or preventive maintenance replaced reactive maintenance, resulting in better equipment availability. Even with scheduled preventive maintenance unprecedented failures occur. Now the focus in the industry is shifting from scheduled maintenance to the new technology of constantly observing machine condition and predicting the condition in advance. This is predictive maintenance. The source of equipment abnormality is identified and corrected which prevents the failure in the future. This is reliability based maintenance. More concentration is focused on providing advance warning of signs of trouble to prevent sudden failure. Predictive maintenance is the current trend in the manufacturing Industry. Condition monitoring through vibration monitoring and oil analysis is the latest technique of maintenance to achieve higher equipment availability.

Holcim has evolved in last decade from preventive maintenance to reliability centered maintenance through condition monitoring. Condition based maintenance is the center of maintenance activity at the Holcim Portland Plant in Florence, Colorado. The plant has been in operation since May 2002. As part of the condition monitoring program, the plant has installed online vibration monitoring systems on all critical equipment. The online transducers are connected to the centralized control room through PLC’s. The equipment has settings for alarm and shutdown in case of excessive vibration. Another vibration monitoring tool being utilized by the plant is an online surveillance system. This combines both continuous monitoring as well as Fast Fourier Transform analysis. The plant also has offline vibration monitoring routes where the data is collected manually by field technicians and then analyzed.

This technical report presents information about the function of online and offline vibration monitoring. Brief information is presented about the current vibration monitoring system being used at the Plant. A case study is presented to show the cost justification analysis of implementing a vibration program. The report gives a brief comparison between online and offline monitoring showing the advantages and limitations of both. The investment required for the system installation as well as cost savings as a result of early prediction of equipment operation issues are presented.

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Holcim Overview

HolcimTM (Formerly HolnamTM) started production of cement in 1912 with one plant in Switzerland in the town of Holderbank. The company now operates in 70 countries around the world with 120 cement manufacturing units and achieved record sales of USD $10.4 billion in the year 2002. Developments in technology, increases in product quality, and decreases in sales price have driven the need for new methods to run equipment more reliably and at a lower cost. Many technologies are being utilized by the company to standardize this process. Enterprise resource planning tools are being used for activities like planning and managing resources. A process software package is being used to improve the process performance. The company has been very proactive about equipment reliability and has been investing in the latest technologies available to monitor and predict the possible failure of equipment. The company has a well developed preventive maintenance program and has been moving towards condition based maintenance in the last decade.

, Development from Breakdown Maintenance to Scheduled Maintenance to Predictive Maintenance to Reliability Centered Maintenance.

The journey of Breakdown Maintenance to the current Reliability Centered Maintenance can be traced through the last 6 decades. Before the Second World War the cement industry was not highly mechanized. The equipment being used was highly over-designed and simple to maintain. There was no need for any systematic maintenance other than lubrication, cleanup and servicing. Breakdown was not a big concern. The tendency was to fix it if it breaks. This was the first generation of maintenance or breakdown maintenance (Mourbay 2000).

During and after the Second World War the cement industry went through a revolution in machinery design. The limited manpower and increasing demand for material forced the industry to invent different methods of preventing downtime of equipment. This resulted in the evolution of Preventive Maintenance. The equipment was shut down at regular intervals and overhauled, thus improving the availability of equipment.

With increased competition and increased demand, companies are forced to improve performance. At the same time, to reduce cost, manufacturing companies are focusing on concepts such as Just in Time. Any sudden downtime of equipment results in lost production, unprecedented maintenance cost and interrupted customer service, creating questions about the credibility of the manufacturer. This has forced industry to research better methods for predicting equipment condition.

These needs led to Predictive Maintenance techniques such as condition monitoring, where characteristics of the machine are collected periodically and trended to determine machinery condition. Vibration analysis, Oil Analysis and infrared Thermography can be used to predict the failure of a bearing or a problem with a drive well in advance of failure.

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Additional developments have led to Reliability Centered Maintenance techniques such as designing equipment to have higher reliability and better maintainability and the use of decision support tools such as root cause failure analysis, failure mode effect analysis, and expert systems.

Holcim and Supplier relationship

Holcim (US) has been effectively implementing preventive maintenance programs for last two decades. Still, a few failures in bearings and gears go undetected in the regular preventive maintenance program. The solution to this issue was answered in the new condition monitoring techniques made available by the development in technology. Vibration analysis, oil analysis and infrared thermography can predict the failure of a bearing or problem with a drive well in advance.

Different plants in Holcim (US) had different condition monitoring equipment being used to predict the equipment health. Holcim (US) Portland plant was one of the first plants in Holcim group that decided to move towards implementing a full fledged two phase Condition Monitoring (CM) program. The production capacity of Portland Kiln is approximately 1.6 million tons of clinker per year. The plant has been utilizing automation since the startup in May 2002. The motors are being monitored using vibration and temperature sensors which shut the equipment down before any catastrophic failure occurs. This surveillance system, though sufficient to prevent permanent damage to the equipment, cannot predict the cause of high vibration or temperature levels.

This resulted in demand of an advanced system to monitor equipment health through analysis. A survey was conducted for the available suppliers in the market and the equipment that is most suitable and cost effective for the application was selected as a partner in development of the CM program at Holcim (US) Portland plant. The factors used to select the instrument supplier included available technology, service, and cost. The program is in the first phase of implementation and is already showing savings. It is being successfully implemented at Portland plant and has helped improve availability of equipment. This practice is being replicated at other Holcim Plants in the US.

Cost of failure

A kiln the size of Portland plant, if shut down due to equipment failure, can cause losses in the thousands of dollars per hour in lost clinker production. At the same time it creates strain on the supply chain due to reduced cement production and in turn inventory. This is the lost cost in production. There is also an added cost of maintenance due to sudden failure of equipment and unplanned maintenance. This cost includes material cost and overtime labor cost. The cost for damaged equipment has to be considered as well.

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Case study for Impeller Failure (estimated numbers)

Figure 1 - Failed impeller detected on vibration readings.

Equipment: Slurry Pump

Failure Mode: Impeller Worn

Annual Cost of the failure mode: $60,000 in lost production for repair provided the parts are available (6 hour's production).

The plant has a PM applied to this equipment for vibration monitoring. The vibration analysis is considered to be 80% effective in detecting a worn impeller prior to failure. The cost for detecting this type of problem through vibration analysis implementation is $50,000 per year. Considering the failure cost and the effectiveness of the vibration program $60,000 per failure x 80% effective = $50,000 in benefit less the cost of $50,000 provides a return of $0. There are other failure modes as well. The monthly vibration analysis can provide benefits such as predicting bearing failure or worn gear teeth in a gear box, misalignment, unbalance etc. If the inspection is considered 50% effective against predicting a worn bearing (a $20,000 failure) that would equate to $10,000 in additional benefits.

As it can be observed in the above cost evaluation, the vibration analysis can be effective against more than one cause of failure, thereby justifying the investment. The impeller shown in Figure 1 was detected on time and the scrubber operation was bypassed to keep the kiln running. The study shown is not only for increasing reliability of equipment but also can create a safe working environment by detecting a problem earlier that can cause catastrophic failure. Trained personnel with tools like vibration data collection, Thermography, Oil Analysis and visual inspection can help prevent unforeseen maintenance and safety issues.

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Vibration as a tool for predicting failure

For the Holcim Portland Plant with a capacity in excess of 1.6 million tons of cement production per year, the maintenance cost is approximately 20% of total production cost. For this cost even one failure if prevented can result in reduced maintenance cost. This savings can be related to increased production by preventing downtime and cost saved by preventing unprecedented maintenance cost. Any increased production quantity and reduced maintenance cost can be related to the increased profit. Considering this cost savings, investment made to monitor the equipment health is extremely important. Also, a problem detected in advance can be fixed with better planning and without disturbing the production schedule. Condition monitoring has proven to be the best tool to monitor equipment health for the above reason. Vibration data collection and analysis is a very useful part of the condition monitoring program. If vibration analysis is used efficiently and supported by condition monitoring tools like Oil Analysis, Thermography, and Root Cause Analysis, it can prevent losses to the manufacturer.

Vibration analysis is extremely effective in detecting a wide range of problems in rotating machinery, including imbalance, mechanical looseness, misalignment, gear defects and motor problems. The vibration related failures have a behavior trend. The failure can be related to multiple steps as shown in Figure 2 and Figure 3.

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Figure 2 - Failure mode in equipment with gradually increasing vibration.

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Figure 3 Equipment Life cycle

Advantages of frequency content versus analog values

Amplitude Measurements:

The amplitude of the vibration in the machine is a measure of how much motion is occurring and is proportional to the force acting on the bearings. The amplitude of the vibration tells us whether there is a problem. The amplitude readings can be used to trigger the alarm for high vibration and shut the equipment down if the vibrations exceed the safe limits. The 2 wire transmitter converts the analog signal to a 4-20 mA signal and transfers it to the PLC. The system acts as a failure protection system. Even though this system protects the equipment from permanent failure it is not capable of predicting the cause of high vibration amplitudes.

Frequency Measurements:

The frequency of the vibration tells at what rate the motion is occurring. More importantly, based on experience, frequency tells us what force is acting on the system to cause the vibration. For example, unbalance always occurs at a frequency equal to the running speed of the machine (IxRPM). The frequency of the mechanical vibrations are of two types, Synchronous (Multiple of rotation speed) vibration and asynchronous (non multiple of rotational speed) vibration.

Online Protection Vibration System

The implementation of a vibration monitoring program (data collection method and type of monitoring) is highly influenced by the size of plant and the amount of equipment (data collection points). The setup of data collection machinery points and routes is very important and can be a cumbersome job. Along with these issues, the criticality of the equipment to be monitored, rate of failure of different

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equipment, and the time to failure from the point the high vibration starts, all influence the selection of permanently installed online sensors.

Description of Process Software I PLC

The process software organizes and presents information about the process so plant personnel can use it to improve performance. It delivers data collected by a sensor and stored in relational databases to the desktop, where managers, engineers, and operators can apply it in making better decisions. The process software has process schematics to illustrate current or historical conditions and trend charts which can be used to study the process changes over time.

The process software is helpful in routine engineering tasks, such as examining and comparing process data. The process software can display the vibration readings from the PLC, which can be used to study the variation of equipment condition and respond if necessary.

Description of Sensor I 2-Wire Transmitter

The vibration transducer shown in Figure 4a is a seismic self-generating velocity pickup. It responds effectively to the machinery defect frequencies expected from the fans that are monitored. The output of the transducer is processed in a 2-wire transmitter to supply a 4-20 mA signal to the DCS system.

mitter

The 2-wire transmitter shown in Figure 4b simplifies the interface between the vibration transducer and process control computers (programmable logic controllers PLC, or distributed control systems DCS). The 2 wire transducer gives a 4-20 mA output signal which is proportional to the overall vibration amplitude. The output from 2-wire transmitter is connected to the Analog Inpuffoutput card of the PLCIDCS. There is a loop power supply from the Analog 110 card that provides isolated capability to drive the two wire transmitter.

The need for a vibration monitor between the sensor and the process control computer is eliminated by the 2-wire transmitter. The PLC's and the DCS's are sophisticated systems with the ability to make decisions based on inputs from

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process control equipment. The input amplitude can be compared with set alarm values. Based on this comparison, when the vibration signal exceeds the alarm value a task, i.e. shutting down the equipment, can be performed. This helps in protecting the equipment from permanent damage in the case of high vibration or temperature.

In the Portland plant, the sensors have helped detect issues like high vibration. caused by material buildup on fans and have given a warning signal. This has prompted the plant personnel to stop the equipment and perform inspections, thereby avoiding critical failure.

Description of Vibration database

The Vibration database allows for the trending of the machinery characteristics that enable predictive maintenance and condition monitoring. Condition Monitoring enables users to effectively implement the strategy of performing only that maintenance which is necessary based on system performance and indicated operating condition.

Figure 5 - Integration of Management and Condition Indicating Information

Historically, “condition monitoring and evaluation” systems have been thought of as vibration based ”predictive maintenance systems.” These systems have progressed to the point where they have incorporated additional condition monitoring technologies to support the condition indicating diagnoses. Unfortunately, the mere integration of multiple surveillance based condition indicating technologies is no longer enough in today’s globally competitive marketplace. Effective enterprise asset health management requires information which extends beyond each of the three disciplines by integrating their data to provide the complete picture of the operational and maintenance histories along with the historical and current condition indicating data. This integration of

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information can be used to dynamically adjust plant operational and maintenance philosophies and procedures, enhancing informed enterprise production and maintenance business decisions. Condition monitoring and evaluation integrated with control and maintenance information enables asset health managers to respond to diagnosis and prognosis with the most appropriate action.

Walk-around Vibration System

Description of Hand Held Data Collection Equipment:

Figure 6 shows a maintenance technician collecting data using hand-held data collection equipment on a motor. Commercially available hand held data collection equipment is available with different features ranging from displaying the vibration magnitude to helping in performing preliminary analysis of the data. The cost varies depending on the functions available in the hand held vibration data collection equipment. The Portland Plant has portable data collectors for monitoring and analyzing the condition of equipment which are similar in many industries such as power generation, petrochemical, pulp and paper, and primary metals.

Figui .e 6 - I =ield d i

Features of this data collector are a large LCD display, online context- sensitive HELP for all applications, storage capacity via PCMCIA cards and Off-route data collection. Most hand-held data collection equipment is capable of performing basic vibration data, including amplitude, frequency, and time waveform. Higher- end data collectors are capable of functions such as; Two-Plane Balancing, Frequency Response Function, and Start-up/Coast-down data collection.

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Costs of Walk-around (Offline) Data Collection Equipment

Required data collection equipment includes hand held data collection equipment (USD 15,000), Transducers, a computer system (USD 2000) for downloading the data and analysis software to upload the routes and perform analyses on the collected information (USD 20,000), and miscellaneous parts (USD 5000). Total cost is approximately USD 42,000.

Surveillance Vibration System

Distributed Control System (DCS) Characteristics

The advantages of using DCS’s are 1) High-speed data collection and signal conditioning 2) Vibration analysis algorithms 3) Dynamics identification algorithms [Nguyen and Nelson].

Online Surveillance System

An online surveillance system is useful for monitoring the condition of equipment, which needs constant attention due to higher equipment cost or the impact of failure of the equipment on production. It bridges the gap between portable data collectors with slow periodic update capabilities and continuous monitoring systems. An online surveillance system can be integrated seamlessly with the machinery information system to fully automate any condition monitoring program.

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Figure 7 - Surveillance system

An online surveillance system unit utilizes the existing Ethernet local area network (LAN) to transfer information. The machines distributed throughout the

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plant can be monitored at periodic intervals using an online surveillance system. This saves the time and money for data collection.

Remote machinery diagnosis can be performed with the aid of software for any equipment in alarm. Information from any channel of a specified online surveillance unit can be transferred, processed and displayed on a PC workstation for live-mode monitoring of spectra, time waveforms, trends, spectral maps and polar plots of data. Internet access makes troubleshooting of equipment possible from anywhere in the world.

Figure 8 beiow shows a planetary gear box with different locations where the transducers are installed to monitor the vibration using the surveillance monitoring system.

* Motor Monltodng - Reducer Monlforlng - Rotation measurement - Motor Current (out olPLC)

* Temperature (out of PLC)

- Dftferentlal pressure (out of PLC)

Figure 8 - Transducer installed on a planetary gear system for remote vibration monitoring

The presentation tool shown in Figure 9 is an excellent tool, which can display the plant on screen with links that can be utilized as a quick access system to check the status of different machine components. The data from the offline data collection and online surveillance system can be viewed in the window.

The Online Surveillance System provides an intuitive visual display of the plant status at a glance using the presentation tool. The unique alarm notification enables plant personnel to keep in touch with machinery status through automatic email notification when alarm thresholds have been exceeded.

Information can be acquired from important machinery in the plant more frequently than is cost-effective using portable instrumentation. The Online surveillance unit enables data to be acquired from inaccessible and dangerous locations. Its compact size allows it to be installed close to the machine under surveillance, which reduces cost by allowing shorter transducer cable runs.

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Costs of Online Surveillance System

This includes Transducers, Online monitoring equipment, offline switchbox, cable, etc. and installation cost. Total cost is approximately USD 35,000. The installation cost is a variable cost depending on the number of points and the negotiated price for each point installed.

Personnel:

The maintenance technicians in charge of the data collection get paid according to their contract, which is part of the maintenance department cost. This is the major cost of implementing the vibration program. Trained personnel who can perform vibration data collection as well as simultaneously performing visual inspections can achieve an excellent level of success by detecting vibration related issues as well as those issues which cannot be detected by vibration monitoring. Examples of these issues are wear of belts, pulleys, ducts, chutes etc.

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Case History #I

441-FN1 Kiln ID Fan (Figure IO)

This case history is presented to illustrate how the overall vibration can show that there is a problem, but not indicate the source of the problem. Figure 11 shows the overall amplitude of vibration recorded from the permanently mounted pickups as displayed on the process software system in the control room. It was found that when the fan was operated at full speed, the vibration was excessive on the fan. So at this point all we knew was the vibration was high for some reason. It was necessary to collect data with the hand-held data collector to pinpoint the looseness present in the bearings. This data is shown in Figure 12 and indicates severe looseness. The fan was taken offline and cleaned, which removed the source of the exciting force for the looseness and the bearings were scheduled for inspection at the next outage.

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Figure 11 - Process software showing overall trends.

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Figure 12 -Vibration data collected with hand-held data collector

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Case History #2

451-FN1 Precalciner Burner Fan

This case history illustrates a loose bearing due to installation errors. The vibration level was high, but may not have been noticed without a walk-around data collection system to point out the looseness present. Figure 13 shows the reading indicating looseness present in the fan bearing.

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Figure 13 - Data taken showing looseness present.

The bearing was removed and replaced. looseness still present but vibration levels are much lower as seen in Figure 14.

There appears to be some slight

Figure 14 - Data taken after replacement of fan bearing.

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Conclusion:

With the available technology and the developments in analysis techniques, increasing accuracy is possible in the prediction of machinery failure. Every available tool and technology for monitoring equipment health has its own advantages and disadvantages depending on the depth of information which can be collected using that particular tool. All the available condition monitoring tools like thermography, oil analysis and vibration analysis combined together can help improve the reliability of equipment to a greater extent. These tools are now an undivided part of a well established maintenance program in any industry. Even though the exact time of failure can not be predicted, these tools help to prevent large scale damage or failure by detecting the root cause. If required, the condition based maintenance job can be well planned in advance reducing the production loss. Regular inspections and condition monitoring, if used hand in hand, will give improved reliability of equipment and allow the achievement of higher production volumes and longer equipment life.

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References:

[l] John Mourbay, “Reliabilitv Centered Maintenance”, May 2000 2”d Edition, Industrial Press, Inc.

[2] Victor Wowk, “Machinew Vibration, Measurement and Analvsis”, 1991, McGraw Hill

[3] Solomon Baumgartner, (Holcim Group Support) “Condition Monitorina of Critical Eauipment“.

[4] Troy V. Nguyen and Harold W. Nelson, “A System Approach to Machinew Condition Monitorinq and Diaanostic.”

[5] www.holcim.comTM

[6] www.entek.cornTM (References for Data collector, online surveillance system)

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