Archive | 1997

258

9:27 pm
November 1, 1997
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Qualifying Motor Repair On Line

Motor repair shops, whether in the plant or commercial facilities outside the plant, should be able to furnish vibration data on repaired motors for use in condition monitoring or predictive maintenance programs. A requirement for such data is being included in motor repair specifications by an increasing number of maintenance and reliability professionals.

vibration_analyst

Customers can witness motor qualification on monitor where spectra can be called up on demand or examined live with time waveforms.
motor_qualification

Gary Herr, vibration analyst at Demaria Electric, uses a Microlog CMVA55 balancing wizard to determine motor unbalance.

Demaria Electric Motor Services Inc., Wilmington, CA, uses on-line monitoring to augment hand held data collectors in its motor repair operations. Its electric motor test stands now use multi-parameter vibration data collection technology tied to a local area network (LAN) to assure industry standard quality control. The technology, typically used to monitor critical industrial machinery, is easily adapted to the motor test cell environment.

When faulty motors arrive at the repair facility, they are tested to confirm mechanical or electrical problems. Spectral signatures are analyzed to determine incoming bearing condition, balance tolerance, and rotor bar condition. After motors are repaired, quality is confirmed at a test stand.

Multi-parameter monitoring allows all aspects of the motor frequency spectrum to be analyzed for quality assurance. Before and after repair reports contain a percent of change column to justify repairs and give credence to the customer’s predictive maintenance program. Test data are archived for historical reference, giving proof to the motor’s condition of operation upon shipment.

Demaria Electric incorporated the on-line monitoring system to augment its use of hand held data collectors for motor qualification. The system consists of an SKF Condition Monitoring CMMA320 local monitoring unit (LMU), a 32-channel NEMA enclosed vibration monitor with a front panel switch assembly with BNC connectors to access buffered signals and tachometer speed pulses.

The data acquisition device (DAD) is mounted on the wall next to the motor supply test panel which can power motors up to 3500 hp and up to 4160 V. A hinged 90 deg bend of conduit was fabricated and mounted on the motor test panel to allow the transducers to swing freely over the motor under test with 20 ft of lead length. A BNC connector at the end of the conduit gland fitting provides for optical phase reference input.

Six SKF Condition Monitoring integral lead accelerometers equipped with magnets are used for sensor inputs. System software allows for motor point configuration on a personal computer to be downloaded to the DAD which collects the data and communicates directly to the host computer over the LAN.

Accelerometers are placed in horizontal, vertical, and axial planes on both inboard and outboard bearings. Sixteen vibration points are collected on each motor. A complete set of data measurement points typically takes 6 min. Spectral signatures are collected at 1600 lines of resolution and two averages to allow for detailed frequency analysis.

Horizontal parameters include peak velocity at 10 times running speed of the motor under test, peak acceleration at 100 times running speed, acceleration enveloping, and high frequency detection (HFD).

Vertical and axial measurements include velocity and acceleration parameters.

Velocity measurement allows observation of running speed balance condition, 2 times line frequency electrical condition, lower order bearing condition, seal installation, and rotor rub condition.

Acceleration measurement gives an indication of higher order bearing frequencies and rotor bar frequencies. Envelope demodulation will confirm a bearing problem as repetitive frequencies are accentuated.

HFD provides a reliable indication of bearing installation quality, lubrication, and metal-to-metal contact, as it offers a higher frequency overall measurement from sensor resonance which acceleration spectra might not detect. SKF Spectral Emitted Energy (SEE) technology is used to confirm lubrication problems.

Motor test vibration data are sent directly to the analysis computer, running PRISM software. Spectra are updated continuously as the motor under test is exercised. Customers who elect to witness motor qualification can observe the real time aspects of the motor operation indicated on a monitor. Spectra may be called up on demand or examined live with time waveforms. Rolling element bearing condition may be monitored using the software frequency analysis module. BPFO, BPFI, BSF, and FTF frequency overlays on the spectrum point out any bearing fault frequencies.

Rolling element bearing motors are typically run for 30 min to 1 hr to allow for trend development to judge the integrity of the repair.

Large journal bearing motors are run from 1 to 2 hr to allow for proper stabilization of bearing temperatures and to understand how heat influences the rotor balance condition. This condition will determine whether the rotor will be balanced in place at running speed. If this is the case, the motor may be balanced with the company’s SKF Microlog CMVA55 hand held data collector-analyzer at the motor. The motor may also be balanced using the DAD’s buffered outputs.

Motors also may be monitored using existing eddy current probes in large sleeve bearing motors which can be connected to the system. The eddy current probe outputs also may be used for balancing. Polar vector plots make it easy to track phase angle changes over time for confirming unbalance.

System software is easily accessible to everyone in the shop. Motor parameters are derived according to running speed. Templates for a motor under test are easily created and downloaded to the DAD according to the job number. The software has been customized for a wide variety of motor applications. The operator enters a four-digit job number and motor RPM to create the machinery point parameters.

The database hierarchy is based on customer name with the motor shop reference job number residing within its respective set. Each motor point identification includes the motor job number. The software also allows for adding customer machine number, plant name, purchase order, and other helpful information. Notes may also be taken and saved to the particular motor data set.

Large motors (1000 hp and higher) typically are followed out to the field for installation. Only one attribute of the DAD points needs to be changed to allow for downloading shop data motor points to the data collector for on site data collection and baseline comparison.

Motors are run on the base uncoupled to prove sound operation. After alignment, another set of data is collected for on site baseline reference as well as the driven equipment. Data are often collected on a weekly basis (primarily for sleeve bearing motors) to insure proper working condition.

The on-line system has proved to be a valuable resource for the shop and its customers. If a vibration problem exists in the field, shop baseline data may be easily checked. The reporting capabilities of the software prove motor shop compliance with customer motor vibration specifications. Expert system PRISM4 Pro software can be used in conjunction with the system to provide before-and-after motor repair reports with analysis of incoming and outgoing condition. MT


Information furnished by SKF Condition Monitoring, 4141 Ruffin Rd., San Diego, CA 92123-1841; (619) 496-3400; Internet http://www.skfcm.com.

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362

8:15 pm
November 1, 1997
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A Successful Approach To Implementing A CMMS

Defining what the system should manage and planning the implementation are two keys to a successful computerized maintenance management system.

Information is the key ingredient in meaningful decisions on reducing maintenance costs. A computerized maintenance management system (CMMS) is a tool that can provide valuable information about how a maintenance department is performing.

Sandia National Laboratories purchased a CMMS to make good maintenance business decisions through data acquisition and to provide a mechanism for reducing maintenance costs. In order to achieve this goal, a phased implementation was conducted to transition from an old CMMS (and way of thinking) to a new CMMS (and way of managing maintenance). The CMMS was successfully implemented at Sandia because of two important factors: defining what the CMMS should manage, and phasing in the applications of the system in an order consistent with the work control process.

Selection
Determining the purpose of the CMMS is the first step in deciding which system to select. If the system is going to be used only to document work being done, then almost any CMMS will do. But if the system is going to manage maintenance activities through data acquisition and analysis, then the choice of CMMS narrows considerably. Sandia took the latter approach in selecting a system that would allow for data gathering and ease of analysis.

A joint application development (JAD) team was given the responsibility to develop and document the requirements for managing maintenance activities. The team consisted of maintenance personnel from managers to craftsmen as well as information systems personnel. The team documented the existing work control process and then looked for ways to improve the process (including all regulatory requirements). Hardware and network requirements were also defined.

The importance of defining the maintenance process and then looking for ways to improve it prior to selecting a CMMS cannot be emphasized enough. A maintenance department has the opportunity to improve maintenance effectiveness when converting from an old system to a new system. Sandia viewed this time as an opportunity to improve the work control process and find a system that would support such an improvement.

Test and review
The implementation of the CMMS began with the development of a detailed plan which stated the order of implementation of each work control process (including training requirements). The plan was developed by the implementation team who had the sole responsibility of replacing the existing CMMS with the new CMMS (work control, hardware, software and network). The team consisted of work control users, information system programmers, network administrator, and computer support personnel.

Other teams were assembled to test, evaluate, and make recommendations to modify specific applications prior to implementation. They were:

Test team—responsible for testing and evaluating the new CMMS against all JAD requirements.

Warehouse and procurement team—responsible for testing, evaluating, and implementing the system’s Inventory and Purchasing modules.

Work control team—responsible for integrating the existing work control process with the Work Order module.

Work request team—responsible for integrating the Work Request application with the way work is received.

Decision team—responsible for deciding on specific maintenance topics relevant to the new CMMS to improve the work control process.

The decision team addressed the issues listed in the box on the first page of this article.

By having many teams evaluate different applications of the system, potential problems were identified and corrected prior to the actual implementation. This methodology of reviewing and testing provided a high level of acceptance by users having a major part in the modification of the system. Without this system acceptance, this project would have failed at implementation.

Implementation
The actual implementation of the CMMS was performed in two parts: warehouse and procurement process, and work control process. During each conversion, a partial changeover was not considered. On a Friday the old system was being used and on Monday the new CMMS was being used by all core users. This total conversion worked only because of the modifications made to the system by each team prior to implementation and because all training was conducted prior to the actual implementation.

Implementing a CMMS is a systematic process of evaluating the correct order of application implementation. This process can be conducted if the knowledge base of the new CMMS is well known along with the knowledge of current and future maintenance operations. Therefore, the first step in implementing a CMMS is to take all available training classes (user and system administrator) to become an “expert” on how the system works and can potentially be modified. Next, a phased implementation has to be developed, reviewed, modified, and accepted by management. Sandia used the following phased implementation:

1. Test and validation. The CMMS was tested against all established JAD requirements to assure that it would perform all maintenance processes. The entire work control process (with all appropriate data loaded) was tested to understand how the new CMMS administered work from one application to another.

2. Decisions. After a thorough understanding of the system (through training) and a general understanding of how the CMMS administers work was achieved, decisions had to be made to merge the old system and set up the new system. The biggest decision was how to define and set up the equipment assemble structure (EAS). The EAS is the foundation of a CMMS, and a good deal of time was spent defining maintenance tracking levels. All installed facilities systems were defined to the lowest level of equipment maintenance that was to be tracked. This defined what equipment records Sandia was going to keep in the database. The greatest contribution of the EAS is the ability to track maintenance costs at the equipment level (then roll-up them to the system level) in order to perform optimal replacement analysis.

3. Modifications. Every application in the CMMS was reviewed for its applicability to the existing work control process. Each team learned every application, evaluated its functionality, and made recommendations to modify the application (field modifications or additional table requirements) to better fit Sandia’s process. Modifications were then made to the application. This approach insured that the existing work control process was included in the CMMS prior to implementation.

4. Training. Training of all users was developed and conducted by in-house Sandia personnel because they had the system knowledge combined with the work control process knowledge (both current and future). The training program was broken into two groups: inventory and purchasing, and work control. The inventory and purchasing group consisted of all users responsible for procuring and storing maintenance materials (excluding work control flow through the CMMS). The implementation team trained all planners and supervisors on work order flow through the CMMS (excluding inventory and purchasing). Users learned the application and then learned how the application was going to be used at Sandia.

5. Warehouse and procurement. The Inventory and Purchasing modules were the first to be implemented because the CMMS is set up to check for materials before a work order can be moved to in-progress status. All stored material data was converted into the inventory database and procurement personnel started submitting purchasing orders to the Sandia Purchasing Department. Most inventory “bugs” were worked out prior to full implementation of the work control process.

6. Work control. The work control implementation consisted of a comprehensive use of most of the applications in the CMMS . Sandia’s work control flow through the CMMS consisted of work order generation, receival of new work order, detail of work order, assignment of work order, posting of craft daily time, completion of the work order, and closing of the work order.

7. Equipment. The equipment application is the foundation of a CMMS and great care should be taken to correctly set up this application. All equipment data was converted from the old CMMS to the new CMMS equipment application. Each piece of equipment was then placed into the correct location of the defined EAS with the appropriate priority assigned to it. Then the correct equipment specification screen was assigned to the equipment for additional name plate data acquisition.

8. Job plans. Generic preventive maintenance (PM) job plans were written for all equipment types that require PM . These job plans would serve as a template when the PM masters were to be created. The objective was to build a library of job plans that could be used in future PM development.

9. Preventive maintenance. Preparing a PM master in a CMMS takes a great deal of effort, but yields many benefits. A PM master will automatically generate work orders when they are due and specify appropriate operations, materials, labor, and specialty tool requirements. The warehouse will always know what materials are needed for PM and when they are needed. Sandia is in the process of generating PM masters for all equipment requiring PM by using the EAS equipment priority.

10. Failure analysis. Tracking why equipment failed and how to fix it is the final leg of the implementation project. Sandia plans to use technical teams (mechanical and electrical) to define the most common failures for equipment types and define permanent repairs.

The implementation of a CMMS at Sandia has been going on for 2 years and should be completed by the end of this year. The success of the implementation was due to the primary definition of what Sandia wanted the new CMMS to do—allow us to make good maintenance business decisions through data acquisition and analysis. We are now in a position to start generating performance indicator reports to show how Sandia is doing as a maintenance department. Implementing a CMMS is not easy or cheap, but a well set up system will generate the information required for good business decisions for reducing maintenance costs. MT

Bobby Baca is the maintenance engineer at Sandia National Laboratories, P. O. Box 5800, Albuquerque, NM 87185; (505) 844-9057; e-mail bgbaca@sandia.gov.

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254

2:53 am
October 2, 1997
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Building a Solid Foundation for Maintenance Operations

Maintenance strategies, as I suggested in a previous article, should be developed in three stages:

  • Determine the maintenance requirements of each asset in its operating context
  • Decide what resources are needed to fulfill those requirements
  • Decide what systems are needed to manage the resources.

This process was compared to building a house where maintenance requirements are the foundation, the resources needed to fulfill the requirements are the walls, and the systems needed to manage the resources are the roof.

It was also mentioned that if the assessment of maintenance requirements focuses on what each asset does rather than what it is, the way in which the requirements are perceived is completely transformed. In other words, such an assessment changes the size, shape, and location of the foundation upon which the maintenance enterprise is built. If this review is carried out correctly, the foundation is also usually smaller than it would be otherwise. A smaller foundation means that the entire structure (resources and systems) built on that foundation is also smaller.

Of course, as every builder knows, the integrity of any structure depends first and foremost on the integrity of its foundation. So if we want to build a maintenance enterprise that is robust enough to satisfy all the expectations of its customers, we must ensure that its foundation is always the right size and shape, in the right place, and sufficiently solid to bear all the loads placed upon it.

Building a solid foundation means that the building project must be planned properly, the ground must be prepared correctly, the foundation must be properly designed, the right materials must be used, and the foundation must be built by people with appropriate knowledge and skills.

Planning the project means that clear objectives must be established, resources allocated, and a plan prepared.

Preparing the ground means that everyone in the organization served by the maintenance enterprise must clearly understand what maintenance can and cannot achieve, and what he or she must do to help achieve it.

Designing the foundation and selecting the right materials means systematically defining the functions and required performance standards of each asset, deciding what failure modes are reasonably likely to cause it to fail, assessing the effects and consequences of each failure, and selecting a failure management policy that deals appropriately with the consequences of each failure.

Using appropriate people means that the exercise must be performed by groups of people who have a thorough understanding of each asset in its operating context, working under the guidance of someone who profoundly understands the process being used to assess the maintenance requirements and who has a long-term vested interest in the success of the project.

In terms of this structural analogy, it is worth noting that many maintenance enterprises spend immense amounts of time, energy, and money on maintenance management systems (roofs) and on tools such as condition monitoring (part of the walls) but spend little or nothing on clarifying perceptions about what must really be done to cause the assets to continue to do what their users want them to do (the foundation).

The result is elegant roofs and walls built over a foundation that is the wrong shape and size, in the wrong place, and not nearly strong enough to support the loads imposed upon it. The end result is a maintenance enterprise that is not nearly as effective as it should be.

This is not to suggest that we don’t need computerized maintenance management systems or condition monitoring. Of course we do, in the same way that nearly every building needs a roof and walls. However, the roof and walls must fit their foundation, and the foundation must be able to support the rest of the structure.

In essence, the only way to develop a truly viable, long-term maintenance strategy is to invest an appropriate amount of time and energy in every element of the process. In particular, you must avoid the temptation to concentrate too heavily or too soon on maintenance technologies and systems without first ensuring that everyone shares a clear, common, and correct understanding about what must really be done to ensure that every asset continues to do what its users want it to do. MT

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237

2:36 am
October 2, 1997
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Structuring Reliability Training

Industrial companies are addressing plant capacity improvement in many ways. The cornerstone of these processes is often overall equipment effectiveness, which includes both equipment and process reliability. Several terms are used to describe programs that are structured to improve equipment reliability, including reliability-centered maintenance, reliability-based maintenance, total productive maintenance, and condition-based assessment.

The common thread for successful implementation of all of these initiatives is the applied knowledge and skills of the maintenance craft workers and operations personnel.

As competition drives companies to optimize plant capacity and reduce maintenance costs, some important work force performance issues must be considered:

  • How to boost employee morale by giving employees the skills and knowledge to do the job right the first time
  • How to save energy costs through efficient operations and well-executed maintenance plans
  • How to increase the company’s independence from vendors and their costly services
  • How to decrease the probability of personnel errors
  • How to reduce the number of surprise downtime incidents
  • How to benefit from consistency and accuracy in job activities through the joint participation of maintenance and operations departments

The Integrated Technologies Group of Fluor Daniel addressed these issues as part of its business enterprise optimization services for clients and to prepare its own workforce for contract maintenance activities.

The material presented here outlines our approach. It can be used as a basis for assessing your training needs and developing a program, or as a basis for developing specifications for a training program or materials to be supplied by others.

The primary objective of this initiative was to create a cost-effective method of delivering specialized skills for a selected group of employees to enable them to mitigate equipment failures.

Knowledge and skills transfer for maintenance personnel
The scope and content of the reliability training component of our program is based on an analysis of the classical reliability-centered maintenance (RCM) analysis process model.

Instructional Model For Maintenance

Fig. 1. Instructional model for maintenance personnel covers the main elements of reliability-centered maintenance.

Our analysis was accomplished by a team of reliability engineers and training specialists. The team focused on the definition of the knowledge and skills that facilitate maintenance craft worker participation in the corrective engineering and maintenance task implementation activities. Five topics, as well as the prerequisite knowledge for learning these topics, were identified, Fig. 1.

The basic building blocks, or prerequisites, for technical skills development can be found in existing craft training materials, vendor programs, or instructional materials designed for site or equipment-specific applications. However, the materials developed for equipment-specific training should reflect the results and recommendations of the RCM process, because these recommendations form the basis of maintenance.

A crucial step in the maintenance task implementation component of RCM is to determine the training and the special tools required to carry out the tasks. Procedures must be developed or revised to document the steps involved in performing difficult tasks. The documentation should be amply detailed to identify proper training requirements. Measurements must be used to gauge the results of the programs.

In addition, because the workforce also must be educated in the fundamentals of RCM and their roles in supporting the process, we developed a series of print-based and interactive media programs (computer-based training) to support this need. Topics covered to support the instructional model for maintenance personnel include the following:

  • Introduction to reliability
  • Selecting and performing preventive and predictive techniques
  • Identifying and explaining approaches to root cause failure analysis
  • Implementing root cause failure analysis
  • Identifying and explaining failure modes and effects analysis
  • Identifying and explaining wear and failure points
  • Identifying and explaining prevention or mitigation tasks

Knowledge and skills transfer for operations personnel
As companies move toward the elimination of traditional organizational lines between the production and maintenance departments, they often use elements of total productive maintenance (TPM). The five pillars of TPM call for

  • Maximizing equipment effectiveness
  • Involving operators in daily maintenance
  • Improving maintenance efficiency
  • Training to improve skill levels
  • Emphasizing maintenance prevention.

Operators in many companies are assuming responsibility for cleaning, routine inspection, and selected fundamental maintenance tasks. In addition, operators can provide valuable predictive or diagnostic support because of their familiarity with the equipment and their awareness of changes in the condition of a machine or a process. Operator feedback can provide valuable information for the root cause failure analysis process.

Instructional Model For Operations

Fig. 2. Instructional model for operators begins by introducing personnel to basic maintenance concepts.

Our skills enhancement program for operations personnel is outlined in Fig. 2. The building blocks necessary for advanced knowledge and skills development include a working knowledge of plant systems and equipment, safety and regulatory parameters, and equipment-specific skills. These training requirements are typically provided by equipment vendors, consultants, and inhouse subject matter experts.

 

We found there is a void relative to training products that are used to provide operators with the fundamentals of predictive technologies and preventive strategies and that also support the development of core maintenance skills at a technical level appropriate for operations personnel. Routine maintenance skills for operators was the first area we addressed in the development of the operator-performed maintenance (OPM) section of our program.

We developed 21 training modules covering mechanical, electrical, instrumentation and electronics, and general maintenance topics (for example, Introduction to Walk-Down and Inspection Programs).

The OPM modules were developed at an introductory level of maintenance technology appropriate for operators and nonskilled maintenance personnel. We also provided recommendations on how personnel can use their senses to determine equipment performance deviations and problems. Information about what an operator should look, feel, smell, or listen for is provided in module activity sheets.

The OPM modules were followed by a series covering the principles of RCM. Whereas the routine maintenance skills training facilitates the expansion of operator roles, the reliability-related modules enable production personnel to participate in equipment diagnostics and fault resolution. Each course should include an effective blend of classroom knowledge transfer and structured on-the-job training.

Because most companies have reliability programs that are specific to their industry and facility design, their training needs vary accordingly. Training programs and materials designed to support a broad range of equipment maintenance requirements can usually be tailored to support site-specific needs.

Most materials can be supplemented with more detailed equipment-specific courses or seminars that are consistent with the technical knowledge and skills of the incumbent work force and promote overall program objectives. MT


Michael E. McGrey is senior director at Facility and Plant Services, Inc., a Fluor Daniel Co., 100 Fluor Daniel Dr., Greenville, SC 29607-2762; (864) 281-4400.

 

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190

1:28 am
October 2, 1997
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Advanced Maintenance Technologies Help Solve Robotics Problem

Infrared thermography and waveform analysis identify mechanical failure and highlight increased duty cycle concerns in robotic work cell.

Root cause investigation of a single fault on a piece of critical production equipment at Accuride’s Henderson, KY, plant uncovered multiple hidden problems. Solving those problems resulted in increased productivity.

The investigation began shortly after an operator noticed a hunting and surfing motion in the work station’s Motoman K150 robot as it loaded a press. When excess following error increased and caused the machine to fault regularly, the staff decided to replace the reduction gear assembly on the affected axis.

The manufacturer was asked to send a technician to assist in the assembly replacement. Repairs were made, the axis was exercised with no load, and it showed no apparent faults, noises, or unusual vibration.

The reduction gear was disassembled to locate the cause of the failure, and a badly deteriorated bearing was found.

When the unit was placed in production the next day, setup personnel commented on the extreme heat of the repaired axis servo motor. This open dialogue between the plant’s maintenance and production teams allows flexibility in problem solving, which greatly facilitates the company’s maintenance objective.

How hot is hot?
When the motor encoder assembly was scanned with a Cincinnati Electronics infrared camera, it showed a temperature 20 deg F above the temperature of the same axis on another K150, Fig. 1. The reduction gear on the hot axis was found to be extremely worn.

The installation of a new unit appeared to correct the extra play or looseness in the system. The motor, which had logged 24,000 hours of production, also was replaced to eliminate concern that it might deserve a rebuild. The robot is in use 24 hours a day, 7 days a week, so testing, troubleshooting, and replacement are done at the expense of production.

Was this a poor repair?
Was the new $8000 reduction gear defective? Was something overlooked, or were there multiple problems? The plant’s experience in motion control indicated that the most obvious causes of overheating in pulse-width modulated servo systems are oscillation due to tuning or noise, overload, and phase unbalance.

Duty cycle and load are primary considerations. Because they are typically addressed at the design stage, they were assumed to be satisfactory at this stage of the investigation.

A balanced load on all three phases was quickly verified using a digital multimeter that measured true rms current. Oscillation and following error were stable and there were no major or minor faults. Testing of the cable harness and brake circuit proved inconclusive.

Waveform analysis
The staff continued the investigation of the problem by checking speed and torque curves with a dual trace Fluke 105 Scopemeter. They found that the torque curve was roughly parallel to the speed curve. Ordinarily, torque decays as speed levels off because maintaining speed requires less effort than acceleration or deceleration. Testing before disassembly showed a fairly normal torque curve with no load and abrupt changes to the unusual parallel pattern when a working load was applied.

Two weeks passed before production schedules would allow the time to disassemble any major components. The Motoman technical support technician returned to assist in identifying the cause of excess heat. Oscillation and unbalanced loads were eliminated before he arrived, so it became a matter of disassembling minor mechanical components. One tapered roller bearing out of four on the cantilever arm had disintegrated and parts were wedged between frame members.

After repairs were completed, additional tests showed a very clean speed waveform and rapidly decaying torque curve. This repair appeared to be a resounding success, but new infrared images showed only a small overall decrease in radiant heat. At this point the waveforms were again checked and found to compare favorably to those of another robot doing a similar task.

Further investigation revealed a rapid sequence of torque spikes related to programming procedures. There were more start-stop sequences than needed in cycle programming. Removing three stop-start cycles, and merging two positions, reduced the demand on the robot by 32 full-torque moves per minute and reduced radiated heat 15 deg F.

Because inrush current during startup is 200 percent or more of running current of the axis motor, it is likely that the more efficient program will result in significant reduction in stress to the unit. An unexpected benefit was a 2 second cycle time increase.

Project results
As bottlenecks inhibiting production were resolved, the duty cycle of the machine increased. Continuous improvement of the process and equipment have pushed this unit, one of the more reliable production cells, to the limit. Engineering had recently increased the working speed and position of this material handler; this increase probably precipitated the problem.

What had been the quickest part of the process has now become a concern of reliability and capacity. Yes, the robot can maintain this level of production, and there are still gains to be made. However, programming practices have become more critical, along with the need for more diligence in monitoring the condition of every system. A new opportunity exists to utilize the time gained, increasing productivity with minimum expense.

This investigation illustrates the value of thorough fault analysis. A single fault without clear resolution led to the identification of a series of problems whose resolution produced gains. These gains then may stress other parts of the machine train. Their resolution may then spotlight another opportunity. Continuous improvement resembles a cat chasing its tail: the target keeps moving but the goal remains the same. Collected data may be difficult to interpret without previous experience, but each effort will generate a record for future reference. MT


Bill Cunningham is a senior maintenance planner at Accuride Corp., Henderson, KY, a division of Phelps Dodge Industries. He has over 20 years’ maintenance management and hydraulics expertise and was instrumental in establishing predictive technologies at this facility. Kevin Harrison is an industrial electrician with 16 years’ experience at the plant. He is a licensed master electrician and a certified infrared thermographer. Continue Reading →

217

12:01 am
October 2, 1997
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Back In The Good Old Days, Part II

bob_baldwinLast month when I discussed two massive monuments to a bygone industrial era, the Cornish pumping engine and the Quincy mine steam hoist, I noted that the romantic good old days were not all that good. But people still wish for simpler times when the industrial scene was less complicated.

Not so long ago, machinery reacted reasonably well to the application of an acetylene torch or a sledge hammer. Today, the torch and hammer approach will destroy precision components such as antifriction bearings. Similar change has taken place in the electrical area where there is concern about harmonics and waveforms.

But these changes are only differences in parts, tools, and techniques. What people really miss, I think, is the protection of the old mass production mentality which was simple and straight forward. Technology was applied to allow workers to work harder and faster. Today, we are being asked not only to work harder and faster, but also smarter and to tighter tolerances. The tools and technology are up to the new challenge but I’m not sure about some business management practices.

In the good old days, inventory was your friend–a buffer that could accommodate the inevitable breakdowns.

Today, inventory is the enemy–a drag on investment, and there is no longer such a buffer to cover mistakes.

In the good old days, maintenance personnel could just focus on fixing things when they broke.

Today, maintenance personnel must manage the equipment and attend to it before it breaks. If it does break, they must find out what happened and reduce the risk of it happening again.

In the good old days, maintenance managers worked on improving repair efficiency. They were measured on how fast they could get the equipment back on line.

Today, maintenance managers must also focus on reliability and work on improving maintenance effectiveness. Mean time between failure is now a part of the matrix for measuring performance.

In the good old days, management furnished maintenance with torches and hammers.

Today, management is still making sure maintenance has a good supply of torches and hammers. But what about advanced technology and training? On the other hand, maybe this is as good as it gets. Perhaps maintenance managers back in the good old days had to go to the mat and fight for every torch and hammer they got.

Thanks for stopping by,

rcb

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562

8:13 pm
October 1, 1997
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Using a CMMS To Support RCM

A modern computerized maintenance management system should have the functionality to support a reliability-centered maintenance effort. Here is how they can work together.

Asset optimization at minimum cost is a fundamental principle of modern business management. It translates into getting the maximum uptime and hence the value from any asset or equipment. Most plants have a preventive maintenance (PM) program in place. Usually, equipment condition is assessed each time PM is performed. After a number of PM actions have been performed and recorded on the same equipment, sufficient data can be available to determine whether the equipment needs more or less frequent PM work and how PM frequency should be adjusted.

Reliability-centered maintenance (RCM) is the method that best addresses the requirement for maximum reliability at minimum cost, or more pragmatically, doing the right maintenance at the right time. RCM results in a maintenance program that focuses PM on specific probable failure modes only. It has a strong bias toward condition monitoring and trend analysis of equipment performance.

Nonintrusive condition monitoring, such as vibration monitoring and oil analysis, can reveal deterioration in performance and warn of impending loss of equipment functionality or failure. When sufficient data are available, trending can be used and maintenance can be performed when measurements stray out of a predetermined safe operating range.

Benefits of RCM
RCM is an engineered approach for determining the right proactive maintenance to achieve design reliability at minimal direct maintenance cost. The process recognizes that some failure modes are preventable, some are predictable, and some are entirely random. RCM targets all these failure modes with proactive maintenance activities that prevent, predict, or watch for signs of incipient failures.

Traditional maintenance approaches rely on the recommendations of equipment suppliers or on historic precedence. Although well intentioned, both of these approaches have serious drawbacks. Suppliers usually write only one maintenance manual for their equipment and provide it to all users. Equipment failure can produce widely different environmental, safety, production, or maintenance consequences, depending on equipment location and application, and yet, maintenance recommendations from the equipment manual will be the same for all.

The traditional “we’ve always done it this way” approach is similarly flawed for its lack of focus on failure mechanisms, causes, and effects. It also fails to eliminate historic maintenance activities that may be unsuited to the nature of the failure modes.

Failure of equipment such as a pump has both causes and failure mechanisms. The failure mechanisms are “how” the failure progresses to the point at which equipment function has stopped. These chains of events have an unfortunate and usually predictable conclusion, such as “stopped pumping.” If each component in the equipment is examined closely, it becomes apparent that it has a finite, and often small, number of failure mechanisms unique to the component or to its operating environment. RCM seeks to identify these mechanisms and then addresses either their cause through preventive maintenance or the conclusion of the failure mechanism by predicting when it will happen and taking appropriate steps to prevent the failure of the equipment function.

Performing the appropriate maintenance just in time can produce significant cost savings, in addition to increased equipment uptime. RCM is a powerful tool for optimizing just-in-time maintenance actions. RCM targets only preventable failure causes with actions intended to prevent them, predictable failure mechanisms with actions that take advantage of the predictability of the mechanism, or the tell-tale signs that show the failure mechanism is in its early stages so that steps can be taken to prevent the functional failure. RCM does not result in over maintaining the equipment with actions that do not address specific failure modes.

RCM programs produce the greatest return when applied during the design stages for equipment additions, plant modifications, and new plants. Once a PM program has been established, there is often a great deal of reluctance to change it. In all fairness, RCM will result in a number of maintenance tasks that are identical to those traditionally performed. Nevertheless, many plants are over maintained and many are under maintained. If breakdowns account for more than 20 to 25 percent of the total maintenance workload, a plant can benefit from RCM. A plant that experiences very few breakdowns but suffers from what may be excessive downtime for maintenance or excessive maintenance costs is likely being over maintained.

RCM can result in significant reductions in direct maintenance costs. In one recent application of RCM, the number and frequency of maintenance tasks were reduced by almost 50 percent while availability increased 10 percent. In the aircraft industry, where RCM had its genesis, heavy inspection and overhaul workloads have been reduced by orders of magnitude while aircraft availability and safety performance have increased. In both cases, before RCM was applied, over maintaining was the result of doing things the traditional way.

Achieving optimized maintenance
RCM combines a thorough evaluation of critical equipment to identify failure modes and their effects with a logical process of determining the right maintenance actions focused on the least intrusive methods first. RCM first focuses on determining what is most critical to an operation, assuring that the most benefits are realized as soon as possible. After equipment or systems have been identified and ranked by criticality, the rigorous failure modes and effects analysis process is applied to identify the failures, failure modes, and effects of those failures. Then the analyst has sufficient knowledge of each failure to apply RCM task identification logic and derive applicable and effective maintenance tasks and frequencies.

A rigorous RCM program can take considerable time and effort to put in place. Methods have been developed that guide the user through the steps to determine which equipment needs to be monitored or “registered” in the RCM program. Required data include the operating function and performance specifications. After the types of failures and failure modes that can occur have been determined and the effect of these failures has been evaluated, maintenance procedures to reduce the incidence of failure can be recommended.

The discussion that follows outlines the RCM approach and reviews the type of information support a properly configured computerized maintenance management system (CMMS) can bring to the process. It is based on the authors’ experience with the RCM process and CMMS software supplied by their respective companies.

1. Select equipment and locations to be reviewed
The CMMS database should be three dimensional, with information on the physical asset (or equipment or component), the equipment type, and the location of the asset.

The physical assets database should contain detailed equipment specification data that includes not only nameplate data but also any other physical attributes that the user requires. It could have a critical parts list as well as a list of standard PM tasks and other applicable jobs. A history of costs incurred, symptoms, cause codes, failure modes, and corrective action codes can be accumulated by the CMMS together with a description of the actual work performed, and parts and materials required to complete that maintenance. These data are then available to the planner, the craftsperson, and the manager.

The location database describes the plant’s facilities and physical process locations. Specifications, including operating conditions, can then be maintained for any location. All history data are stored by location as well as by equipment. Costs can then be rolled up the location hierarchy as required. In addition, downtime can be tracked for each location.

The equipment type database contains key data such as parts lists, specifications, and standard maintenance procedures to be stored only once for many pieces of equipment of that type.

It is not necessary and it is often too expensive to set up an RCM program for all equipment and locations in the plant. An analysis of criticality of the equipment is necessary to determine which equipment need not be analyzed or can be deferred to later in the program.

The equipment and locations to be first registered in the program are those that are critical to safety, the environment, and the operation of the process or plant, and that contribute significantly to lost production. Also included are equipment with high maintenance cost, high repair frequency, or low mean time between failures, and equipment that has the most downtime. A modern CMMS should identify equipment or locations that meet any of these criteria and produce reports showing the top 20 items for review.

Once equipment or locations are selected, they can be registered in the reliability program and the database. Registration can then trigger the display of typical symptoms associated with that location or equipment when a work request is created. Additional reliability information can be entered when work orders for registered equipment or locations are completed.

2. Define equipment functions and performance standards
RCM requires definition of primary, secondary, and protective functions of registered equipment. A versatile CMMS should include a facility for defining specifications for equipment and locations. These specifications will typically include operating characteristics and performance standards such as temperatures and pressures, as well as other measurements. The combination of specifications and measurements defines the performance standards for the equipment.

Defining equipment functions requires a thorough review of equipment purpose, both in the process or primary function (such as to pump fluid at a specific range of flows, pressures, and temperatures under specified suction conditions) and in the secondary and protective functions (such as to contain fluid, to prevent reverse flow of fluid from discharge to suction, and to provide visual indication of seal failure). The definition of equipment functions should be specific and detailed and include limits on operating parameters for satisfactory equipment function in its intended role.

3. Determine functional failures
The reliability team evaluates all possible failure modes for each piece of equipment in the RCM program and the failure types for each failure mode. Once determined, these failure types can be entered in a CMMS data table as descriptive information along with an appropriate failure code. This procedure serves the dual function of moving the RCM analysis forward as well as providing valuable information for the ongoing reliability analysis. The failure codes are captured by the equipment and location history function in the CMMS, thus enabling statistical analysis.

Detailed operating parameters were specified when equipment functions were defined. Functional failures occur when equipment performs outside these operating parameters. These off-specification operations, often seen by equipment operators and used as complaints about the equipment or descriptions of equipment failure, are failure types.

Determining all possible symptoms associated with each equipment type provides a further benefit. After the values are entered, they can be displayed when a work request is created for equipment or locations registered for reliability. Selecting these failure descriptions gives the work request description more meaningful information than simply “Fix pump P-101.” RCM will result in the identification of failure types that can be used as failure codes.

4. Identify failure modes and root causes
The failure mode and root cause of any failure is often identified only after a multidisciplinary approach to reviewing failure data. The root cause could be poor maintenance, unstable operating conditions on startup, operation outside the design standards, incorrectly specified equipment, poor engineering design, etc.

The root cause determination is a key step in the RCM analysis for preventable failure modes. Knowledge of the failure modes enables the analyst to identify failure effects that may be detectable with condition assessment technologies such as vibration analysis, oil analysis, and infrared thermography.

In addition to the root cause, there may be contributory causes. Most failures are caused by a combination of events that trigger a specific failure mechanism. For example, a noncontact oil seal combined with the use of a water hose to clean process equipment will result in oil contaminated with water and eventual failure of the bearings. Contributing causes are often reviewed as part of the root cause determination.

A CMMS data table can store a number of “cause codes” for each equipment type. Although contributing causes are not necessarily root causes, they do allow the operator or mechanic to enter any number of known con~tributing causes for a work order. This information is then stored as part of the equipment and location history.

5. Assess failure effects and consequences
It is important to recognize the consequences of potential failures, and recognition implies an understanding of the criticality or significance of the failure.

When the failure mechanisms are analyzed, some of the failure effects become evident. Local or equipment effects are usually obvious. The analysis then progresses up the equipment hierarchy to determine effects at the system and plant levels.

For example, a failed relay contact in a cooling tower fan starter may prevent the fan from starting, which in turn prevents the cooling tower from providing sufficient process cooling, which in turn results in the shutdown of part of the plant because of overheating of the process at certain critical heat exchangers. In this case, in which cooling is critical, failure of a seemingly insignificant relay can have significant operating consequences. Knowledge of the relay’s condition is now recognized as being important, and monitoring relay condition through infrared thermography or regular cleaning of the contacts becomes a worthwhile task. Now assume that the relay in this example results in the shutdown of only one of two fans, each of which can supply sufficient tower capacity for the process. The relay is now far less important, and it may be appropriate to simply wait until it fails and then fix it. Knowledge of the effects of the failures can therefore be important in making decisions on appropriate proactive steps.

6. Define maintenance strategies
Maintenance strategies to avert the probability of failure are determined on the basis of the foregoing analysis. These strategies have two components: what maintenance will be performed and when it will be performed. RCM provides a series of questions in a logical progression using the knowledge of the failure effects as an input to determining appropriate maintenance actions.

The question sequence first looks for hidden failures, failures with no obvious signs or effects that alert operators to the presence of the failure. If hidden failures have safety consequences, a failure finding task is appropriate if the failure cannot be prevented or predicted. If failures are not hidden, those having safety, environmental, production loss, or maintenance cost impacts are defined, in descending order of importance. It is important to determine whether it is possible to

Monitor for the presence of the failure before it has progressed to a total loss of functional performance
Prevent the failure through a time or usage-based action such as an oil change
Prevent failure consequences by replacing the failing item at some predetermined time or usage-based interval
Take default action

Default actions are based on the consequences of failures. A failure mode having unacceptable safety or environmental consequences should be designed out of the system or equipment, or it will be necessary to take contingency action to avert the consequences of the failure when it eventually occurs. Similarly, if the impact on production is severe, redesign may be warranted, but if the impact is minor, run to failure may be acceptable.

Through its focus on specific failure modes, RCM avoids the use of maintenance tactics that do not address the failure modes the equipment experiences. Rarely will an overhaul result from RCM because up to 65 percent of all failure modes are random in nature and do not respond to time-based overhaul actions.

Overhauls are typically appropriate only when equipment has a large number of time or usage-sensitive failure modes such as component wear caused by frequent start and stop cycles. In such cases, an overhaul is appropriate to collect component replacement actions into a single combination task. Overhauls that include much inspection work can usually be replaced with condition monitoring. Most overhaul work is followed by a series of smaller problems immediately after startup. These problems can be avoided.

7. Implement and refine the maintenance tactics
No maintenance system is effective without ongoing feedback and reviews. As work orders are completed, additional data can be collected. This practice enables capture of any failures that occurred, and codifies the corrective or preventive actions taken. Up to four codes are captured for all work orders on any equipment or location: failure code, symptom code, cause code, and action code. Useful statistical information can be calculated from these codes and their distribution over time.

RCM increases equipment and plant uptime while reducing costs through the performance of the right maintenance at the right time. It avoids the unnecessary and unwarranted use of well intentioned but misplaced maintenance activities that do not improve reliability, or worse, that result in increased failures.

A modern CMMS can be the foundation for effective RCM. It also can be the foundation for managing equipment reliability as part of normal maintenance management.

RCM is a one-time project that defines maintenance strategies that lead to maximum uptime of equipment at minimum cost. Management of equipment reliability is an ongoing strategy that requires the use of a CMMS with broad functionality that can analyze vast amounts of data collected as part of the maintenance management program. MT

Jim Picknell is a manager at Coopers & Lybrand Consulting, 145 King St., W., Toronto, ON M5H 1V8; (416) 869-1130. His company can facilitate the installation of a reliability-centered maintenance program. Keith A. Steel is senior industry consultant at Revere Inc., 3500 Blue Lake Dr., Suite 400, Birmingham, AL 35243; (800) 411-6614; Internet http://www.immpowerinfo.com. His company supplies the Immpower computerized maintenance information and asset management system.

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2:19 am
September 2, 1997
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Preventable Maintenance Costs More Than Suspected

Engineers reviewed more than 15,000 work orders in the quest to identify the extent of preventable maintenance for major corporations in North America.

The concept of preventable maintenance (“Focusing on Preventable Maintenance,” MT 10/95, pg 23) has matured into one of the most powerful factors used by HSB Reliability Technologies’ (HSBRT) engineers to drive the reliability improvement process and lead clients to manufacturing excellence.

As with most good ideas, the process has been enhanced with experience. In addition to improvements in the investigative process, significant progress has been made in the solutions arena. It is also clear that there is still room for improvement of the investigative process.

HSBRT engineers now review two more aspects of the extent of preventable maintenance. The accompanying pie charts, from a study of more than 1000 work orders in a large plant, depict preventable maintenance in three ways.

It is first expressed as a percentage of the total number of work orders reviewed. The next chart shows preventable maintenance as a percentage of total maintenance hours. The third chart depicts preventable maintenance costs as a percentage of total maintenance costs.

As a percentage of total work orders
The graph confirms the original assumption that reasonably preventable maintenance approximates half of the work accomplished in most organizations. In this case it was exactly 47 percent. In this plant, an overly simplistic conclusion would be that about $18 million of labor and material was wasted.

Number Of Work Orders

As a percentage of total hours worked
HSBRT engineers decided that it would be beneficial to carry the analysis one more step. When expressed in hours worked, preventable maintenance appears to be a larger piece of the pie, in this case, 63 percent. A possible conclusion is that the preventable work orders were more complex, or at least more time consuming.

Time Spent

As a percentage of expenditures
Using the findings of the previous exercise, we examined the preventable work orders on the basis of total maintenance expenditures to determine the nature of the materials component. The percentage climbed to 69 percent. It would be prudent to conclude that preventable maintenance is more costly in labor and materials. Theoretically, $26 million was wasted in the study plant instead of $18 million.

Maintenance Expenditures

HSBRT engineers are now working to capture the impact of preventable maintenance in dollars of lost opportunity, or profitability of a particular plant. This measure has proved to be somewhat more difficult to define. We will keep you posted on our progress.

We are also working on specific solutions in systems, procedures, processes, and practices to minimize the impact of preventable maintenance. We have found reliability-centered maintenance/solutions and root cause failure analysis to be effective tools in this venture.

Identifying and controlling preventable maintenance are critical activities for managers who are serious about improving reliability and reducing maintenance costs. That may well be the most important area of focus because of the leverage on cost and throughput. MT


Raymond J. Oliverson is executive vice president and general manager of HSB Reliability Technologies, Consulting Div., 800 Rockmead Dr., Kingwood, TX 77339; (281) 358-1477.

HSBRT engineers Greg Como and Harold Weimer contributed to the article. Continue Reading →

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