Sunday, April 15, 2018

Shaft Alignment Handbook Third Edition By John Piotrowski

Shaft Alignment Handbook Third Edition By John Piotrowski
Preface
Many of the material conveniences taken for granted in today’s society have been made possible by the numerous rotating machinery systems located in every part of the world. Virtually everything we use or consume has somehow been produced or touched in some way by rotating equipment. The multitude of industrial facilities that generate our electricity, extract and deliver our fossil fuels, manufacture our chemicals, produce the food we eat, provide our transportation, furnish the clothing we wear, mine and refine metals, manufacture the paper and printing products used for books, require millions of pieces of rotating machinery to create all the products we use.
It makes good sense to keep the motors, pumps, gears, turbines, fans, diesels, and compressors running for long periods of time to prevent financial losses due to decreased production and overhaul costs. Repair or replacement of this equipment is expensive and the loss of revenue when this machinery is is not in operation can spell the difference between continued prosperity or financial disaster for any company. Keeping these machines running requires a thorough understanding their design and operating envelope, careful attention during their installation and overhauls, the faculty to prevent or predict imminent failures, and the expertise to modify and enhance existing hardware to extend its operating lifespan. In the past 30 years, easily half of the rotating equipment problems I have experienced had something to do with misaligned shafts. Additionally, operating rotating equipment under misalignment conditions can be dangerous. I have seen a coupling burst apart on a 500 hp, 3600 rpm process pump that literally sheared a 10 in. pipe in half and coupling pieces landed
400 yards away from its point of origin. Keep in mind that rotor speeds above 100,000 rpm and drivers pushing 60,000? hp are now commonplace. With all of the rotating machinery in existence, you would think that shaft misalignment is well understood and that everyone who is involved with installing, maintaining, and operating this equipment is well versed in preventing this. When in fact, just the opposite is true. The information contained in this book is not taught in any high schools or junior colleges, is not a required course for mechanical engineers, is not discussed in business schools, and is typically not taught in trade schools for mechanics, millwrights, pipe fitters, or electricians. Over the past 100 years, hundreds of technical books and articles have been published on rotor balancing, flexible coupling design, vibration analysis, structural dynamics, and indus trial productivity. The first technical article on shaft alignment, on the other hand, was not published until after World War II and not until the late 1960s did anyone begin paying attention to this. I feel very fortunate to have been granted the opportunity to work in a wide array of different industries and the hundreds of different plant sites after studies at the University of Pittsburgh in 1974 as a bright eyed, eager, fledgling mechanical engineer. Back then, I had no idea how many talented, patient people I would have the pleasure working with over the next 32 years. It wasn’t clear, at least for the first few years working in industry, what exactly it was that I was destined to do or where I could make a contribution. My first experience with rotating machinery came working at a automotive tire plant. The tires were cured using hot water circulated through a closed loop piping system. The water was heated to 4008F and the pumps delivered it to the supply headers at 400 psi. Once you got the system up, everything seemed to work fine (generally). The problems usually appeared when the plant was shut down every Friday night at midnight and then started back up Sunday night at midnight. As the circulating water was heating up, the tremendous change in temperature from ambient to 4008F wrecked havoc on the piping and the pumps, causing many seal and bearing failures on both the pumps and the motors driving them. It was not uncommon to overhaul at least one of the pump drive systems every month. On one particular occasion, after rebuilding one of the pumps, I was working in the pump room on a control valve and a mechanic was working on finishing up the installation of the rebuilt pump. I noticed that he had a magnetic base attached to the motor shaft and a dial indicator touching the pump shaft. He would rotate the motor shaft so it would sweep around the perimeter of the pump shaft looking at what happened to the indicator as he rotated. I had never seen anyone do that before. I went over to ask if I could watch what he was doing. He glanced up and stared at me for about 30 seconds not saying a word. OK, I got the picture. I left him alone and went back to work setting up the control valve. I was there for about three hours and every so often, would glance over to see what he was doing. He would sweep the indicator around the pump shaft, stop, loosen the motor bolts, add some shim stock, tighten the bolts, and sweep the indicator around the pump shaft again. He would then loosen the motor bolts, push the motor sideways, tighten the bolts, and sweep
the indicator around the pump shaft again. He would then loosen the motor bolts, remove some shim stock, tighten the bolts, and sweep the indicator around the pump shaft again. Then he would then loosen the motor bolts, push the motor sideways in the opposite direction from the last sideways move, tighten the bolts, and sweep the indicator around the pump shaft again. After I saw this back and forth up and down iteration four times, it dawned on me that he was guessing. This went on for three hours and the level of his frustration began to show. I left for a few minutes and when I came back, he was gone, with the coupling guard in place. I have no idea if the alignment was correct. I thought to myself ‘‘Thank goodness I’ll never have to do that.’’ Six weeks later the bearings in the pump and motor failed. No one bothered to figure out what happened or why the bearings failed. It happened so often and for so long that the consensus was ‘‘that’s the nature of these beasts.’’ In 1977, I was interviewed for a job at an ammonia plant in Ohio. They were looking for a rotating equipment engineer. I had become somewhat proficient at instrumentation and attempted to convince them that’s why they needed to hire me. The engineer interviewing me indicated that they already had an instrumentation engineer and he was doing a fine job, what they really needed was a rotating equipment engineer. He asked ‘‘Do you have any experience with rotating machinery?’’ ‘‘I did order parts and oversee the rebuilding of some hot water circulating pumps at the plant I am currently employed at,’’ I explained. ‘‘Well then, we would like to offer you a job,’’ he said. ‘‘You are the eighth engineer we’ve interviewed and you are the first one who has some experience with rotating machinery.’’I took the job, expecting to convince them that I was their new instrumentation engineer
 but they had other plans. I still remember my first day. My supervisor gave me a plant tour. The ammonia plant had four major compressor trains and the acrylonytrile plant had three. ‘‘There are over 1500 pieces of rotating machinery in the plant ranging from 2 to 32,000 hp and speeds ranging from 150 to 126,000 rpm and they are now your responsibility,’’ he said to me. I got a lump in my throat and wondered what I had gotten myself into. To say the least, I was overwhelmed. Within the first three months the entire plant was shutdown twice due to rotating equipment failures one involving a 32,000 hp, 11,000 rpm steam turbine driving three barrel compressors that tripped off line due to high vibration. All of the major compressor trains had permanently installed proximity probe vibration sensors that were fed to the control room, which displayed the overall vibration levels and thrust positions. For those of you old enough to remember, vibration spectrum analyzers and laser alignment systems did not exist in 1977. We did eventually purchase a swept frequency analyzer and anoscilloscope. The alignment tooling consisted of custom Xmas tree brackets we made and
 some hand built alignment brackets for the machinery under 1000 hp. We also had an optical tilting level and a hp jig transit that no one knew how to use. I was also tasked with the job of maintenance training. I was asked to train the maintenance personnel in rotating machinery basics, pump overhaul, mechanical seals, basic vibration, and shaft alignment. Reference material and books on these subjects were few or nonexistent. I had never taught anyone anything before in a formal classroom setting and I had no visual aids or training equipment besides an overhead projector, a screen, a flip chart, and a training room. So I began preparing overhead slides with hand drawn sketches in pen and ink. For those of you old enough to remember, personal computers and software did not exist then so you either printed words by hand or if you wanted to be fancy, you could use a typewriter. That was the beginning of the contents of this book. As a farewell gift, my coworkers gave mea 35 mm camera,  which was used to take most of the photographs in this book. I left for another position in 1979 for a job at an aircraft engine plant where I managed a high-pressure high flow air compressor facility. I became involved with the Vibration Institute and we formed a local chapter in the Cincinnati, Ohio area. We had meetings every month where a guest speaker was invited to give presentations on vibration and other topics. We would solicit the attendees for future topics and one of the requests was for someone to do a presentation on shaft alignment. The other board members suggested that I do a presentation on alignment since they knew I had some material from the maintenance training I had done at the chemical plant. After I gave the presentation, which went much longer than the one hour allotted for the discussion due to questions from the audience, several people came up to me suggesting that I write a book on shaft alignment. I laughed. You must be kidding! Me? Write a book? I shrugged it off as a nice compliment and didn’t think anything about it until another presentation I gave a few months later when I was asked again. So, around 1981, I started writing trying to expand on the material I already had and writing down the things I was still learning. Three years passed and bit by bit I generated six chapters, working on the draft copy at night and for a little bit early in the morning before I went to work. I bought a typewriter transferring my hand written text and gluing my pen and ink drawing to the pages. I made five photocopies and sent them out to five publishers. I got five rejection letters. The letters were cordial and short. The general consensus in the letters was ‘‘We don’t think this material would be of any help or interest to anyone.’’ I put the manuscript into the closet and forgot about it. What a waste of time I thought. About a year later I gave another presentation at the annual meeting of the Vibration Institute and the director of the institute came up after the presentation and suggested that I write a book on alignment. I mentioned that I had and that it was rejected. He suggested that I contact a publisher called Marcel Dekker, Inc. who had approached him for anyone he might know who would be interested in writing engineering books. I resurrected the manuscript from the closet and submitted it one more time.
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