Operator’S Guide to Centrifugal Pumps: What Every Reliability-Minded Operator Needs to Know

By Robert X. Perez

We work in an industry where economic success is heavily dependent on the collective performance of our processing equipment and their operators. Without highly trained and confident operators we can never hope to realize the full potential of our complex processes. Formal and informal training must be provided regularly if continuous process and reliability gains are to be expected. There are no shortcuts to operational excellence.

One training topic essential to every operators education is that of centrifugal pumping technology. The ever-present centrifugal pump is one of the workhorses of the process world, tirelessly moving fluids, ranging from the innocuous to the toxic and flammable, from one stage of the process to the next. We would be hard pressed to find a processing unit inside our complexes without a few of these in service. Their shear numbers and variety can make their mastery a challenge.

This book was specifically written for process operators who regularly deal with centrifugal pumps, addressing principally those variables and factors under their control, while limiting design theory and mathematics to a minimum. The following topics and content are covered:
1. Importance of equipment reliability and what role operators play in this mission.
2. Centrifugal pump operating characteristics
3. Mechanical seals and their related seal flush plans
4. What operators should know about electric motors
5. Lubrication basics
6. Troubleshooting basics
7. How to start a pump reliability program
By the end of the book, the reader should possess a clear understanding of how to operate and monitor their pumps. Three handy references are also contained in the book to answer questions as they arise in the field: 1) Operators Guide to API Flush Plans, 2) Illustrated Glossary of Centrifugal Pump Terms, 3) Glossary of Electric Motor Terms, and 4) Useful Centrifugal Pump Formulas.

This book can be used as a self-paced, self-taught short course or as a companion to a live prepared short course for both inexperienced and seasoned operators. It can also serve as a handy field guide after completion of the course. The ultimate mission of this book is to provide the latest generation of operators a body of knowledge that is relevant, complete, and practical in an industrial setting for years to come.

• Language: English
• Publisher: Xlibris US
• Release date: Sep 22, 2008
• ISBN: 9781462803453

Robert X. Perez

Robert X. Perez has thirty years of rotating equipment experience in the petrochemical industry. He earned a BSME degree from Texas A&M University (College Station) and an MSME degree from the University of Texas (Austin), and he is a licensed professional engineer in the state of Texas. Mr. Perez served as an adjunct professor at Texas A&M University–Corpus Christi, where he developed and taught the engineering technology rotating equipment course. He authored Operator’s Guide to Centrifugal Pumps (Xlibris) in 2008 and coauthored Is My Machine OK?” (Industrial Press) with Andy Conkey in 2011. In 2013, he completed writing Illustrated Dictionary of Essential Process Machinery Terms (Diesel Publications) with the help of several other contributors. This dictionary has been well received by the community of rotating equipment professionals. In 2014, he coauthored Operator’s Guide to Rotating Equipment (Authorhouse) with Julien Lebeu. He has also written numerous machinery reliability articles for numerous technical conferences and magazines.

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Copyright © 2008 by Robert X. Perez.

Library of Congress Control Number:                           2008904945

ISBN:                   Hardcover                         978-1-4363-3985-8

                             Softcover                            978-1-4363-3984-1

                             eBook                                 978-1-4628-0345-3

All rights reserved. No part of this book may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without permission in writing from the copyright owner.

Any people depicted in stock imagery provided by Getty Images are models, and such images are being used for illustrative purposes only.

Certain stock imagery © Getty Images.

Rev. date: 06/27/2018

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CONTENTS

Preface

Acknowledgements

Chapter 1—The Operator’s Mission

Chapter 2—Centrifugal Pump Primer, Part I

Chapter 3—Centrifugal Pump Primer, Part II

Chapter 4—Centrifugal Pump Primer, Part III

Chapter 5—How to Protect Your Mechanical Seals

Chapter 6—Motors 101 for Operators

Chapter 7—Pump Lubrication in a Nutshell

Chapter 8—10 Ways to Protect Your Pumps

Chapter 9—How to Start-up a Centrifugal Pump, Part I

Chapter 10—How to Start-up a Centrifugal Pump, Part II

Chapter 11—Introduction to Field Troubleshooting

Chapter 12—The Road to Reliable Pumps

Appendix A—Illustrated Glossary of Centrifugal Pump Terms

Appendix B—Glossary of Electric Motor Terms

Appendix C—Basic Centrifugal Pumps Formulas

Dedication

To my mother and father for allowing me to attend the best engineering schools. I will never forget their sacrifice and encouragement.

Preface

We work in an industry where economic success is heavily dependent on the collective performance of our processing equipment and their caretakers. Without highly trained and confident operators, we can never hope to realize the full potential of our complex processes. Formal and informal training must be provided regularly if continuous process and reliability gains are to be expected. There are no shortcuts to operational excellence.

One training topic essential to every operator’s education is that of centrifugal pumping technology. The ubiquitous centrifugal pump is one of the workhorses of the process world, tirelessly moving fluids, ranging from the innocuous to the toxic and flammable, from one stage of the process to the next. We would be hard pressed to find a processing unit inside our complexes without a few of these in service. Their shear numbers and variety can make their mastery a challenge.

While working in industry, I have frequently been called upon to teach operators about pumping technology. This has forced me to think long and hard about what knowledge was needed for them to perform their jobs effectively. The more training I provided the clearer the vision of operator instruction became, until the outline for this book emerged. My goal soon became to write a book expressly for operators addressing principally those variables and factors under their control, while limiting design theory and mathematics to a minimum.

In the following pages, I will first explain the importance of equipment reliability and what role operators play in this mission. Then, I will cover centrifugal pump fundamentals, mechanical seals, electric motors, lubrication, and troubleshooting basics; and end with a few recommendations on starting a reliability program. By the end of the book, the reader should possess a clear understanding of how to operate and monitor their pumps. Four handy references are also contained in the book to answer questions as they arise in the field: 1) Operator’s Guide to API Flush Plans, 2) Illustrated Glossary of Centrifugal Pump Terms, 3) Glossary of Electric Motor Terms, and 4) Useful Centrifugal Pump Formulas.

This book can be used as a self-paced, self-taught short course or as a companion to a live prepared short course for both inexperienced and seasoned operators. It can also serve as a handy field guide after completion of the course. My hope is that this book provides the latest generation of operators a body of knowledge that is relevant, complete, and practical in an industrial setting for years to come.

Acknowledgements

This book would not have been possible without the support and assistance of my family and colleagues. I especially would like to wholeheartedly thank:

1. My wife, Elaine, for supporting and proofing this book. She never lost confidence in me.

2. Mike Riley, former editor for Pumps & Systems Magazine, for encouraging me to write this book and for helping me with some of the figures.

3. Joe Evans, Contributing Editor for Pumps & Systems Magazine, for reviewing the book and providing honest feedback and advice.

4. Bill Stark, Senior Instrument and Electrical Engineer with Bath Engineering, for contributing an insightful chapter on electric motors.

5. Dan Elwood, who works for A. W. Chesterton Company, for helping me with the text for all the API seal flush plans in this book and acquiring permission from Chesterton to use their API seal flush plan graphics.

6. Ronald J. Carlson, Leader of the Process Industry Practices Machinery Function Team Member API 610, 685, 686 committees, for his instructive contribution on pump design and installation pitfalls.

7. Dale Atwell, Manuel Pena, and Alan Flores of Celanese Chemicals, for their help developing the outline for the course that became the basis for this book.

Chapter 1

The Operator’s Mission

This in-your-face reminder was placed on expensive equipment in a south Texas chemical complex where I worked. It quickly drives home the point that we wouldn’t have jobs if not for the mechanical equipment at our sites that tirelessly power our processes.

To be gainfully employed, we need our processes to be profitable. This means that the revenue from products we manufacture has to exceed the expenses incurred. The way to maximize profits is to maximize the pounds, gallons, or barrels of product we make in a given reporting period, while minimizing equipment expenses.

To maximize production, production units must achieve a high level of process availability. Availability is whether (or how often) a system is available for use by its intended users. Since downtime (the opposite of availability) is usually very costly, this is a vital component of process reliability. The availability portion of the profit equations is controlled by what we call critical equipment. Typically these are unspared equipment that result in unit outages when they fail to function properly.

You probably are well aware of the critical pumps at your site. These are usually the pumps that get an inordinate amount of attention when they fail or begin to fail. Critical pumps may only represent less than 5% of your total pump population, but they are vital to your operation and your profits. These pumps definitely pay your salary.

The other pumps in your plant falling into the other two categories, essential and nonessential do not get near the attention as your critical pumps when they fail. Essential pumps are those pumps that can cause a major upset of your unit upon failure, due to switching delays; and nonessential pumps are pumps that represent little consequence when they fail. I recommend you compile a list of all your critical, essential, and nonessential pumps at your site for future reference.

Now let’s focus our attention to pumps and see what makes up pump-related expenses. They include:

• Energy costs—All centrifugal pumps need power to operate. You will learn that there are simple ways to reduce pump energy costs.

• Repair costs—All centrifugal pumps fail. However, not all pumps are created equal. Larger and more complex pumps cost more to repair. You may want to use relative repair cost as a means of prioritizing the importance of your pumps.

• Secondary damage—If a pump failure is severe enough, it can cause damage to nearby assets, such as piping, structures, vessels, etc.

• Fines due to environmental emissions.

• Lawsuits as a result of injuries and releases affecting nearby residents. Some pumps handle hot, flammable, toxic, and even lethal fluids that must be contained at all costs.

Pump repair costs usually get most of the press at your site due to their visibility. Pumps are constantly failing so they always show up on monthly and annual maintenance budgets. Each pump failure represents a cost of anywhere from $1000 to $50,000. An average repair cost for an ANSI pump is around $3000, while an average API pump repair runs about $6000. (Note these average repair numbers can vary widely depending on local labor rate, seal design utilized, and pump sizes.) For sites with 1000 pumps or more and an average pump life of four years, or 250 repairs per year, this equates to an annual repair budget of $750,000 for a population of ANSI pumps to $1,500,000 for a similar population of API pumps. If these pumps had an average mean life of only two years, or 500 repairs per year, these numbers would rise to $1,500,000 for ANSI pumps and $3,000,000 for API pumps. It’s no wonder site management is always interested in improving pump reliability.

Reliability Tracking

If you want to track how reliable your pumps are, you must have a means of analyzing your repair or failure records. Here are three simple means of tracking how your pumps are doing:

• Mean time between repairs

• Reliability growth

• Spending growth

The mean time between repairs (MTBR) metric is one of the most widely used metric for tracking centrifugal pump reliability by pump users throughout the industry. To calculate it, you simply need to know the number of failures in a given period of time and the total number of pumps in your population. The equation for MTBR is:

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Where M is the total pump count, T is the reporting time, and R is the total number of repairs during the reporting period. For example, let’s say we have 200 pumps in our population and you have 20 failures in 3 month period. This means your MTBR is 200x30/20 or 30 months between repairs.

To be useful, MTBR data must be trended over a significant period of time (12 months or more) and compared with similar populations of pumps. For example, it doesn’t make much sense to compare the MTBR for water pumps with those of pumps in hot oil service. Similarly, it doesn’t make sense to compare centrifugal pump MTBR with reciprocating pump data.

MTBR Data from Across the Industry

One of the first questions asked by management is: What benchmark should we compare our pump MTBR against? There are many factors to consider before answering this question, such as type of industry, pump type (API or ANSI), and average experience level of the operators and mechanics. Well-known author and machinery guru, Heinz Bloch, listed the following MTBF statistics for pumps in his March 2006 column in Hydrocarbon Processing Magazine as a guideline for pump users:

You can see a great deal of variability in the MTBR results across the industry.

Mr. Bloch went on to suggest the following MTBR targets for mechanical seals in refinery services¹, based on his experience and extensive failure data collected by the John Crane Company:

These suggested benchmarks may seem high, but keep in mind these are targets to shoot for. Only by knowing what is possible, can we attain world-class performance.

Other Tracking Tools

The reliability growth plot is another simple but useful tool for tracking the reliability performance of a single or set of similar pumps. It is constructed by plotting cumulative time on the abscissa (x-axis) and the cumulative number of failures (or repairs) on the ordinate (y-axis). (The term cumulative means you are continuously adding up the variable being evaluated. For example, if four pump repairs occur after 10, 11, 14, 9 months of operations, the