considerations for a multi-plant vibration monitoring program

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Emerson Process Management - CSI

DoctorKnow Application PaperTitle: Considerations for Multi-Plant Vibration Monitoring Program

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Author:

E.R. Bradbury

Product: GeneralTechnology: Vibration

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Considerations for a Multi-Plant Vibration Monitoring Program

E. R. Bradbury

Praxair, Incorporated

Tonawanda, NY

About the author

Gene Bradbury is a Vibration Analysis Consultant at the Praxair Technology Center in

Tonawanda, New York. In eighteen years with Praxair, Incorporated (formerly known as Linde

Division of Union Carbide Corporation), his responsibilities have included analytical and

experimental stress analysis, computer assisted analysis and testing, and the development of

remote vibration monitoring systems. He has been involved in the vibration analysis of high speed

turbomachinery for over twelve years and played a significant role in planning and implementing

the nationwide vibration monitoring system at Praxair. Mr. Bradbury received a 8S in EngineeringMechanics from Pennsylvania State University in 1975.

Abstract

In the mid 1980's, Praxair Incorporated began to implement a nationwide condition monitoring

strategy. The initial step of this effort consisted of augmenting the vibration monitoring capabilities

at facilities all over the country and then consolidating the individual plants into a comprehensive

vibration analysis network. Currently, more than one hundred domestic plant sites participate in the

vibration analysis program that forms the basis for this paper.

Introduction

Although Praxair (known as Linde Division of Union Carbide Corporation until June 1992) has

been active in the vibration analysis community for close to forty years, the 1990's ushered in

several new opportunities. New maintenance philosophies, new tools for equipment monitoring,

new diagnostic techniques, and computer-assisted analysis software programs are changing the

face of the industry. The availability of this new technology prompts a review of the methods used

to acquire, process, analyze, interpret, and even report vibration data. Like many other companiesin this time of innovation, Praxair found itself reviewing its vibration analysis practices.

In the decades after World War II, maintenance philosophy gradually evolved from a reactive

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mode (run-until-it-breaks) to calendar-based preventive maintenance. By the early 1970's,

literature [1,2] began to document the cost-savings potential ofpredictive maintenance - anew

philosophy asserting that monitoring the condition (or health) of operating machinery gives an

early indication of impending problems and is therefore a valuable tool for determining and

scheduling appropriate maintenance activities. Industry rapidly adopted the concepts of predictive

maintenance. Success stories and testimonials have populated trade magazines and professional

meetings ever since.

A good vibration monitoring program is the cornerstone of most predictive maintenance programs.

Properly implemented and run, such a program will yield benefits such as improved machine

reliability, longer production runs, shorter downtime, and general profitability in terms of reduced

maintenance costs and increased productivity. Successful implementation requires management

support, commitment of the necessary resources, well-trained personnel dedicated to the vibration

surveillance program, good organization, and goodrecord keeping practices. Programs lacking

these ingredients are frequently doomed to failure.

Air Separation Industry

Praxair, a world leader in air separation and purification techniques, is the largest industrial gases

supplier in North and South America, and has plants located all over the world. More than one

hundred facilities are strategically located across the United States to achieve an effective

distribution network. While these facilities are common in purpose, they vary significantly in

process, equipment, physical size, and staffing.

The complexion of the air separation industry is unique among major chemical businesses in many

ways. Air separation plants are typically smaller, both in physical dimensions and in the amount ofmechanical equipment present. Because on-site staffs are small, plant personnel are expected to

develop a diverse range of skills, limiting the time available for specialization in any single area,

such as vibration analysis.

The basic raw material, air, is free, although significant amounts of energy are consumed in the

process of separating and purifying the air into its constituents: nitrogen, oxygen, argon, etc. The

most familiar process involves the use of compressors and expansion turbines to achieve

refrigeration, liquefaction, and separation of the air. Other processes are also used and a few

facilities utilize an offgas or byproduct of another industry as the feed stream.

At a given location, plant design and equipment selection is dependent upon the quantity and

quality of the product required. In addition, plant designs have changed over the years as new

processes were developed and as improvements in compression and expansion equipment became

available. As a result, on a nationwide basis, Praxair owns and operates a wide variety of

equipment ranging in size from less than 100 HP to greater than 35,000 HP.

A typical facility operates 24 hours per day, 365 days per year. Major pieces of equipment are not

spared and when unexpected equipment failures occur, they can result in plant downtime. A highlyeffective condition monitoring program can provide the information required to maintain the

operating equipment and plan for the future maintenance activities.



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Praxair's Old Vibration Program

As a whole, Praxair plants run well; on-stream rates are relatively high, exceeding 95%. A portion

of the credit for this fact goes to the specifying engineering staff. A set of carefully defined,

detailed specifications, including vibration limits, has helped control the quality of equipment

purchased for use in Praxair plants. Credit also goes to the operations staff, who effectively

monitor and run the equipment on a daily basis.

A preventive maintenance program has been in place on all major equipment for many years. At

regular intervals, each machine was taken apart, certain components were replaced (regardless of

their condition), and the machine was reassembled. While this approach represented an

improvement over reactive maintenance philosophy, the required downtime, materials, and labor

were expensive, especially if the machine was "healthy". Furthermore, the procedure subjected the

equipment to the possibility of sustaining damage during the "repair" procedure or due to incorrect

reassembly. [Studies in the commercial aircraft industry [3] showed that most failures were not

calendar related, and that there was an unusually high correlation between failures and recently

performed maintenance work!]

Virtually every major piece of rotating equipment in the Praxair system has been purchased with

permanently installed Bently-Nevada [B/N] proximity probes. Although these probes were

installed primarily for machinery protection, it has been standard operating procedure to log the

overall vibration levels, as indicated on the B/N monitor. Plant maintenance personnel began to

regard the B/N monitoring system as an accurate barometer of machinery condition. In essence,

many plants were utilizing a form of predictive maintenance.

As spectral analysis tools became readily available, vibration practitioners began using the B/Nprobes to gain insight into the machine's health. Routine vibration data collection and analysis was

performed at many plant sites by roaming experts who visited on a periodic basis (typically 2-4

times per year). Spectral data was recorded on paper and sometimes on magnetic tape for

comparison to previous data sets. Between visits, plant operations would rely heavily upon

permanently installed B/N proximity probes to identify changes in the overall vibration levels of

the major pieces of rotating equipment. If changes were observed, the vibration experts were called

in to survey the situation.

All in all, the existing program suffered from several deficiencies.

q Spectra were acquired infrequently; the interval between spectra was too long for good

trending. Changes due to seasonal variation or weather conditions could not be separated

from a true change in the behavior of the machine. Rapidly developing situations were often

missed entirely.Early identification of problems occurred more by chance than by plan.

Furthermore, much plant equipment was reaching advanced ages on the bathtub-shaped life

cycle curves, and there is anticipation that the number of failures would soon begin to

increase.

q Manpower resources were not being used effectively. Highly trained vibration analysts

were spending more time traveling between plant sites than analyzing vibrations. Once at a

site, most of their time was spent gathering data from good machines, instead of analyzing



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data and solving machinery problems.

q Prox probe data portrays a limited view of the total machinery health picture. While the

proximity probes accurately monitored rotordynamic-related problems and other low

frequency phenomena, the location and the frequency response characteristics of these

displacement transducers simply did not facilitate the acquisition of high frequency

phenomena, such as gearmesh activity. Plant personnel had neither the tools nor the training

to acquire and analyze accelerometer data accurately.

q And moreover, the data management could have been much more effective. Although

duplicate machinery existed at plants located in different regions of the country, vibration

data and machinery histories were not shared. Vibration data were taken at different

measurement points, using different tools, and different spectral parameters. For example,

one group of vibration analysts routinely used peak hold spectra, while another group used

summation averaging.

q As mentioned before, several studies have been published supporting the conviction that

predictive maintenance philosophy represents a significant opportunity to reduce overall

maintenance COSTS. In one recent EPRI study [3], normalized costs for the three

maintenance philosophies were compared in terms of dollars per horsepower per year ($/HP/

year). Reactive mode costs were estimated at $17-18, preventive maintenance was $1 1-13,

while predictive maintenance was just $7-8/HP/year.

For all of these reasons, full implementation of a predictive program was preferable to purepreventive or the hybrid mixture of programs being used. It was decided that Praxair would pursue

the transition to a system-wide condition monitoring / predictive maintenance program. Simply

stated, the goals would be to reduce costs and improve profitability by early detection of

impending problems, increasing the interval between turnarounds, and improving problem

analysis, diagnosis, and correction capabilities by sharing information in an equipment database.

Overview of the New Program

The planners of the new vibration monitoring program envisioned a network of independent plantssharing support and advanced analysis resources, Each plant would collect and use its own

vibration data and then share the information with the rest of the network through a "national

database", To facilitate this plan, several global decisions were made to provide a uniform structure

for the vibration monitoring program at each plant location,

As an example, the instrumentation and analysis software was evaluated by a team of vibration

experts and plant maintenance personnel. Their group recommendation defined the universal

hardware and software selection for every plant in the network. Several direct benefits include:

improved data interchangeability, simplification of support issues, alignment of efforts, improvedinterplant communication about vibration issues, a single set of evaluation and development costs,

and last, but certainly not least, the ability to take advantage of quantity price breaks.



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in conveniently sized packages at relatively affordable prices. One popular tool for providing

monitoring and analysis capability at an affordable price is the portable vibration data collector.

Used in conjunction with analysis and trending software on a personal computer, this

instrumentation provides a versatile range of capability at an affordable price, yet it is simple

enough to use without years of training and experience.

The specifications of the portable machinery analyzers on the market today rival those of stand-

alone spectrum analyzers; averaged spectra with 400 or more lines of resolution can be obtained atfrequency ranges up to and surpassing 20 kHz. Used in route mode, the users can advance from

measurement point to measurement point while the device automatically controls all of the digital

signal analysis variables to assure that data taken at each defined measurement location is

consistent with previous data. The devices also possess the ability to store spectra and waveforms

from hundreds of measurement points - a function formerly handled by analog instrumentation

tape recorders and/or reams of plotter paper. Built-in battery features protect against the loss of

data. In addition, the hardware facilitates transferring the newly acquired vibration data to a

personal computer for subsequent analysis, trending, and reporting.

For the program envisioned, a portable data collector used in conjunction with personal computer

analysis software seemed an appropriate solution. Features such as spectra and waveform displays,

phase analysis capability, and the ability to run special downloadable programs were highly

desirable to help assure that the portable data collector would not inhibit the growth of the partners

in the first five years. The personal computer platform offered connectivity and access to database

programs, spreadsheets, word processing packages, etc.

Selection of a Data Collection System and Software

A three phase study of six portable vibration data collectors was undertaken in the third quarter of

1986. First, the evaluation team met with each of six equipment manufacturers for a detailed

review of capabilities and basic training on the use of each product. The units were subsequently

subjected to a field evaluation test at a Praxair production facility. The third and final phase

consisted of a software comparison of the qualifying packages to determine differences in both

quality and content.

A detailed spreadsheet was used to organize the data and evaluate the relative performance. The

hardware was judged in four general categories: Technical Specs (electronics, storage capacity,frequency response, FFT specifics),Design(physical, environmental,battery system, ergonomics),

Functionality (legibility, keypad layout and feel, user friendliness, and input sensors), and

Evaluation in Use (ease fo use, features, local diagnostics, and field performance). Each of the

subcategories listed above was further broken down, and the hardware was graded on a total of

about 150 separate items. Each subcategory was assigned an appropriate weighting factor, and a

grand total was determined on a scale of 0 to 100.

A similar approach was used to evaluate the software. The four general categories included:

Software capability (reports, spectral displays, trends, other features), Software use (userfriendliness, intuitive procedures, speed, adaptability), Computer hardware (memory and hard disk

requirements for program, video compatibility, database file requirements), and Support

(confidence factor, problem resolution, upgrade policy, training). As with the hardware, the



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subcategories were further broken down, individual items were graded, weighted, and contributed

to a composite score from 0 to 100.

The systems were ranked in order of their cumulative scores and one system was purchased from

the top-rated supplier for a plant pilot study. It was believed that any of the three best-scoring

systems could be successfully used to implement the envisioned condition monitoring program, so

the purchasing team began negotiating quantity pricing with all three contenders.

By December of 1988, when the pilot study was completed, there had been so much change and

improvement in the marketplace, another evaluation was undertaken. [It is pleasant to note that the

manufacturers had corrected most of the deficiencies which had been identified during the first

round of tests.] Interestingly, the finish order of the new study included the same three

manufacturers in the same order, but all scores were higher than the first time around and the

spread between the manufacturers was not as great. It is also noted that the products of all three of

manufacturers are still present in market today.

Consistent Implementation at all Plants

Implementation strategy at a plant site was designed to be relatively transparent to the plant. A

small team of vibration experts was responsible for an initial assessment of the plant to determine

measurement locations and set up the database. Another team installed accelerometer measurement

targets [4] to prepare the plant for data collection in a manner that would assure repeatable,

accurate data. At about the same time, the plant partners were scheduled to attend a one week in-

house training session. Individuals would receive the vibration analysis tools during training where

they would be taught why, where, and how to use the tool effectively.

Many of the steps toward uniformity and consistency helped to assure that the usual start-up

frustrations and mistakes would be eliminated, or at least kept to a minimum. Implementation and

execution at the plant were simplified and there was confidence that the machinery measurement

points were defined appropriately and consistently at all plants in the network, each plant database

was set up properly and consistently, and the plant partner was properly trained, equipped and

ready to begin acquiring valid data immediately.

The size of the total system and the limitation on resources made it necessary to utilize a staged

implement scheme, activating five or six plants at a time. In actuality this was a blessing, since thetelephone helpline activity soared for two to four weeks immediately following each training

session. After that initial surge, as the partners began to first exercise their newly developed skills,

telephone support activity would return to normal.

Central Support Services

The objectives of the central support organization are detailed in a previous section. The group

continues to handle issues that have a global impact upon the program. A few examples are

detailed below.

As mentioned before, the central support organization provides a one-week in-house training

session for each plant participant in the program. Utilizing in-house training provides the

opportunity to tailor the experience to specifically address the vibration monitoring program and



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maximize the productivity of the sessions. As an example, most similar introductory courses

include several hours of instruction on how to effectively set up analysis parameters and alarm

limit sets. Since experienced vibration experts preset the vibration parameters on each

measurement point at the plant, the concept is covered briefly and the time is utilized to cover

other topics of significance. In addition to practicing on rotor kits and other vibration instruction

tools, training includes a half-day of data acquisition at an operating Praxair plant.

Commercially offered courses have satisfied the needs for additional training, although anadvanced training program is being developed in-house to address the continuing needs of our

vibration partners.

The "vibration helpline" telephone line continues to ring and it has proved to be an effective

support tool for the program partners. In addition, the Praxair Maintenance Newsletter is used to

disseminate information, provide further education on new techniques, and celebrate success

stories.

Unsolved problems from each location are escalated to regional and then to the national centerwhere the pool of vibration analysis experience and machinery maintenance knowledge exist. In

essence, a tiered vibration support ladder exists, wherein problems are solved at the appropriate

level of expertise. Difficult problems rise to the top of the ladder where support is available for

even the most unusual problems.

Databases from each location funnel into the national centers where the information is rearranged

so that similar machines at different locations can be compared on a national basis. This concept,

the national database, is currently being implemented.

Other challenges currently being reviewed and planned in the Central Support Organization

include decisions on ISO standards and calibration issues.

Concluding Remarks

The methodology used to implement and support the vibration monitoring network described in

this paper has worked well at Praxair. While the particular circumstances that exist make every

installation unique, a few key observations may be drawn from this experience.

q Select tools that will make You successful, today and tomorrow. When deciding on

vibration analysis tools, plan for the future. Do not limit potential growth by buying solely

on today's needs, but rather anticipate tomorrow and purchase enough capability to bridge

to the future.

q Plan the implementation phase carefully.

Decisions on how to collect and manage

data should be made early, focusing upon the desired output of the program. This planning willboth simplify implementation and maximize the value of the program.

q Utilize a vibration expert.



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Years of vibration experience and judgment are required toproper/y implement a new vibration

program. If that talent is available in-house, use it; otherwise, purchase it. Many instrumentation

suppliers either offer start up services or can recommend an independent who can do the job

properly.

q Strive for continuous improvement.

Our system is nearly fully implemented, but the work list is now longer than when we started. With

each successfully completed challenge comes additional new and exciting opportunities.

q Enjoy the work.

The vibration industry is based upon a vibrant, rapidly changing technology. The work is exciting,

challenging, worthwhile, enjoyable, and gratifying. Enjoy it.

References

Hudachek, R. J. and Dodd, V. R., "Refinery-machinery surveillance and diagnostic program pay

off", Oil and Gas Journal, Oct. 18, 1976, pg. 70-81.

Blotzo, C., "Machinery Monitoring is Well Justified", Oil and Gas Journal, Nov. 22, 1976, pg. 144-

147.

Wowk, Victor, Machinery Vibration Measurements and Analysis, McGraw-Hill Inc., 1991.

Bradbury, E.R., and Jowdy, G. G., "Collecting High Frequency Vibration Data for a Condition

Monitoring Program", Vibration Institute Annual Meeting Proceedings, June, 1992.

All contents copyright 1998 - 2006, Computational Systems, Inc.

All Rights Reserved.

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