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- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Sprache: Englisch
Process machines are critical to the profitability of processes. Safe, efficient and reliable machines are required to maintain dependable manufacturing processes that can create saleable, on-spec product on time, and at the desired production rate. As the wards of process machinery, we wish to keep our equipment in serviceable condition. One of the most challenging aspects of a machinery professional or operator's job is deciding whether an operating machine should be shut down due to a perceived problem or be allowed to keep operating. If he or she wrongly recommends a repair be conducted, the remaining useful machine life is wasted, but if he or she is right, they can save the organization from severe consequences, such as product releases, fires, costly secondary machine damage, etc. This economic balancing act is at the heart of all machinery assessments. Troubleshooting is part science and part art. Simple troubleshooting tables or decision trees are rarely effective in solving complex, real-world machine problems. For this reason, the authors want to offer a novel way to attack machinery issues that can adversely affect the reliability and efficiency of your plant processes. The methodology presented in this book is not a rigid "cook book" approach but rather a flexible and dynamic process aimed at exploring process plant machines holistically, in order uncover the true nature the problem at hand.
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Seitenzahl: 220
Veröffentlichungsjahr: 2016
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Contents
Cover
Half Title page
Title page
Copyright page
Dedication
Preface
Acknowledgements
Chapter 1: Troubleshooting for Fun and Profit
1.1 Why Troubleshoot?
1.2 Traits of a Successful Troubleshooter
Chapter 2: An Insight in Design: Machines and Their Components Serve a Function
2.1 An Overview of the Design Process
2.2 Complex Machine Element Environments
Chapter 3: Machinery Design Issues and Failure Modes
3.1 Common Failure Modes
Chapter 4: Machinery in Process Services – The Big Picture
Chapter 5: Causes Versus Symptoms
5.1 Causal Chains
5.2 Summary
Chapter 6: Approach Field Troubleshooting Like a Reputable News Reporter
Chapter 7: The “What” Questions
7.1 What is the Problem or What Are the Symptoms?
7.2 What is Your Assessment of the Problem?
7.3 What is at Stake?
7.4 What Risk is at Hand?
7.5 What Additional Information is Required?
Chapter 8: Who Knows the Most About the Problem?
Chapter 9: When Do the Symptoms Show Up?
9.1 “When” Questions to Ask
9.2 Ways to Display Time Related Data
9.3 Timelines
9.4 Trend Plots
9.5 Constant Amplitude Trends
9.6 Step Changes
9.7 Gradual Versus Rapidly Changing Trends
9.8 Correlations
9.9 Speed-Related Issues
9.10 Erratic Amplitude
Chapter 10: Where Do the Symptoms Show Up?
10.1 Locating a Machine-Train Problem
10.2 Troubleshooting Problems Involving Multiple Machine-Trains
10.3 Multiple Versus Single Machine Train Examples
10.4 Analyzing Noises, Pings, and Knocks
10.5 Seeing the Light at the End of the Tunnel
Chapter 11: Why is the Problem Occurring?
11.1 Fitting the Pieces Together
11.2 Reciprocating Compressor Example
11.3 Troubleshooting Matrices
11.4 Assessing Machine with Multiple Symptoms
Chapter 12: Analyze, Test, Act, and Confirm (Repeat as Needed)
12.1 The Iterative Path to the Final Solution
Chapter 13: Real-World Examples
13.1 Case Study #1
13.2 Case Study #2
13.3 Case Study #3
13.4 Case Study #4
13.5 Case Study #5
Chapter 14: The “Hourglass” Approach to Troubleshooting
14.1 Thinking and Acting Globally
Chapter 15: Vibration Analysis
15.1 Vibration Analysis Primer
15.2 Identifying Machine Vibration Characteristics
Chapter 16: Applying the 5Qs to Rotordynamic Investigations
16.1 Introduction
16.2 Using Rotordynamic Results for Troubleshooting
16.3 Closing
Chapter 17: Managing Critical Machinery Vibration Data
17.1 Vibration Analysis Strategies
Chapter 18: Closing Remarks
18.1 Practice the Method
18.2 Provide Training on Fault Trees and Cause Mapping
18.3 Employ Team Approach for Complex Problems
18.4 Get Management’s Support
Appendix A: The Field Troubleshooting Process—Step by Step
Appendix B: Troubleshooting Matrices and Tables
Index
Troubleshooting Rotating Machinery
Scrivener Publishing100 Cummings Center, Suite 541JBeverly, MA 01915-6106
Publishers at ScrivenerMartin Scrivener ([email protected])Phillip Carmical ([email protected])
Copyright © 2016 by Scrivener Publishing LLC. All rights reserved.
Co-published by John Wiley & Sons, Inc. Hoboken, New Jersey, and Scrivener Publishing LLC, Salem, Massachusetts.Published simultaneously in Canada.
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Library of Congress Cataloging-in-Publication Data:
ISBN 978-1-119-29413-9
The authors would like to dedicate this book to their wives, Elaine Perez and April Conkey, for all their help and encouragement.
Preface
Troubleshooting is part science and part art. Simple troubleshooting tables or decision trees are rarely effective in solving complex, real-world machine problems. For this reason, the authors wanted to offer a novel way to attack machinery issues that can adversely affect the reliability and efficiency of your plant processes. The methodology presented in this book is not a rigid “cookbook” approach but rather a flexible and dynamic process aimed at exploring process plant machines holistically in order to understand and narrow down the true nature of the problem. Throughout this book, the term process machinery will be used to refer to rotating machinery commonly encountered in processing plants, such as centrifugal pumps and compressors, reciprocating pumps and compressors, fans, steam turbines, and electric motors.
Our first book in this series, Is My Machine OK? deals, in large part, with assessing process machinery in the field. This guide takes the assessment process to the next level by helping operators, mechanics, managers, and machinery professionals better troubleshoot process machinery in-situ, i.e., in the field. To cover the topic of troubleshooting, the authors will cover the following topics in this book:
What field troubleshooting means and entails
How to use this guide as a complement to
Is My Machine OK?
Using the “who, what, when, where, why” troubleshooting methodology
How to use cause maps to investigate possible causes
Real-world case studies
How to use machine-specific troubleshooting tables
To be successful, the troubleshooter must be persistent, open-minded and disciplined. Once field data is collected, an unbiased, logical approach to the finding is required to hone in on the most probable source of an observed symptom (or symptoms). Without a comprehensive and logical analysis of the findings, the investigator is only guessing, which wastes valuable time and resources. We hope those reading and using this guide will fully utilize the ideas and concepts presented to minimize maintenance cost and risk levels associated with machinery ownership.
Robert X. Perez and Andy P. Conkey
Acknowledgements
The authors would like to thank the following individuals for their help in reviewing this book and improving its contents with many useful suggestions. This book would not have been possible without their contributions, inspiration and support:
Ken Atkins, Engineering DynamicsDavid Lawhon, Shell OilJulian LeBleu, Machinery ConsultantCarol Conkey, Copy Editor
Chapter 1
Troubleshooting for Fun and Profit
Process machines are critical to the profitability of processes. Safe, efficient and reliable machines are required to maintain dependable manufacturing processes that can create saleable, on-spec product on time, and at the desired production rate. As the wards of process machinery, we wish to keep our equipment in serviceable condition.
One of the most challenging aspects of a machinery professional or operator’s job is deciding whether an operating machine should be shut down due to a perceived problem or be allowed to keep operating and at what level of operation. If he or she wrongly recommends a repair be conducted, the remaining useful machine life is wasted, but if he or she is right, they can save the organization from severe consequences, such as product releases, fires, costly secondary machine damage, etc. This economic balancing act is at the heart of all machinery assessments.
The primary purpose of this guide is to help operators and machinery professionals troubleshoot machines that are in a process service and operating at design process conditions. The reader may ask: What is the difference between field troubleshooting and other analysis methods such as a root cause analysis, failure analysis, and a root cause failure analysis?
Consider the following definitions:
Field troubleshooting is a process of determining the cause of an apparent machine problem, i.e., symptom, while it is still operating at actual process conditions. Troubleshooting efforts tend to focus on a specific machine or subsystem, using a proven body of historical knowledge. The body of knowledge may be in the form of troubleshooting tables and matrices or manufacturer’s information. Keep in mind that process machinery can only truly be tested and evaluated in service and under full load, i.e., in-situ. Very few testing facilities are available that can test a pump or compressor at full process loads and with actual process fluids. Field troubleshooting evaluates the mechanical integrity of a machine in process service in order to determine if symptoms are the result of an actual machine fault or a process-related problem.
Here are examples of troubleshooting opportunities:
Example #1: Pump flow has fallen well below its rated level.
Example #2: Compressor thrust bearing is running 20 °F hotter than it was last month.
Root cause analysis (RCA) is a broad analysis of a system made up of multiple components or subsystems or an organization made up of multiple processes. These complex systems may not have any historical failure information to reference and are not well understood. The overall complexity may require that the overall system be broken down and analyzed separately. Here are two examples of RCA opportunities:
Example #1: The finished product from a process unit went out of spec.
Example #2: Plant XYZ safety incidents for the month of May have doubled when compared to last year’s total.
One distinction between RCA approaches and troubleshooting is that RCAs tend to address larger problems that often require a team approach, while troubleshooting can normally be conducted by a single individual. As a general rule, maintenance and operations personnel normally participate more in troubleshooting activities than in root cause analysis activities due to the very nature of their jobs.
Failure analysis is the process of collecting and analyzing physical data to determine the cause of a failure. Physical causes of failure include corrosion, bearing fatigue, shaft fatigue, etc. Failure analyses can only be conducted after a component failure. A failure is defined as a condition when a component’s operating state falls outside its intended design range and is no longer able to safely, or efficiently, perform its intended duty.
Root cause failure analysis (RCFA) methodology attempts to solve complex problems by attempting to identify and correct their root causes, as opposed to simply addressing their symptoms. The RCFA methodology allows an organization to dig deeper into a failure or series of failures in order to uncover latent issues.
To further clarify the differences between these analysis approaches, we recommend the following line of questioning:
If the machine fails, either a failure analysis or root cause failure analysis must be performed, depending on the extent and cost of the failure. The failure analyst asks different types of questions depending on the level of detail desired:
All these approaches do have some common elements in their respective processes, and the information identified in one can be utilized in the other approaches. These are not necessarily competing activities, but are mutually supportive activities.
Figure 1.1 shows a simple decision tree that can be used to address machinery field problems. (Note: The RCA option is not considered in this chart because we have assumed the problem is confined to a specific machine and is within the troubleshooter’s level of ability.) The troubleshooter begins at the top of the tree when a symptom is first detected. At this point, the troubleshooter assesses the situation and then picks one of the possible path forwards:
Figure 1.1 Troubleshooting Decision Tree.Note: The dollar amounts shown here are based on the experiences of the authors. Each site may have its own trigger levels for repair costs. It goes without saying that these trigger levels need to be periodically modified for inflation.
If a repair is deemed necessary, the maintenance organization should then estimate the repair and outage costs. If the total cost (parts and labor) of the failure is less than $10,000, then a repair should be performed without any additional type of analysis. If the total cost of repair is estimated to be greater than $10,000 but less than $50,000, a failure analyses should be conducted on the failed parts in order to understand the nature of the failure. Finally, if the total cost of failure is greater than $50,000, then a root cause failure analysis is justified and should be executed.
The reader should note that the decision tree presented here is only one of many possible tools that can be used to address machinery field problems. Each organization can and should develop its own customized decision tree to satisfy its needs. For example, the cost breakpoints used in this example can be customized to satisfy your organization’s process and management goals.
The decision tree in Figure 1.1 clearly illustrates that all machine decisions usually begin with some sort of field troubleshooting or assessment effort. Field troubleshooting can therefore be considered a type of “gatekeeping” step for deciding which machines need to be repaired. If performed diligently and correctly, field troubleshooting can eliminate unnecessary machinery repairs and improve the overall site profitability and operating efficiency.
In the remainder of this book, we will concentrate on explaining a novel field troubleshooting method to those on the front lines and in the position to gather key performance and operating data. By acting quickly, perhaps the underlying problem can be identified, corrected, and the machine may be returned to normal operation in a timely manner. The reader should always keep in mind that field troubleshooting may be the first step in a series of analysis steps if machine conditions continue to deteriorate. This could also be the introduction to the two other analysis methods previously mentioned.
1.1 Why Troubleshoot?
Why should organizations care about field troubleshooting? You might ask: “Isn’t that why we have a maintenance department, so they can repair machines that are acting up?” The problem is that not all machines that act up have failed; they may simply be reacting to some external change. Distinguishing between a machine that is just acting up versus one that has failed or is failing is the goal of a troubleshooter.
Let’s consider this simple example: A pump bypass line was inadvertently left open after a start-up. This condition leads to a low forward flow condition. If the pump is overhauled, the same result will be seen, resulting in wasted maintenance dollars and frustration. If a diligent operator would have found the open bypass valve while troubleshooting, it would have been a very rewarding discovery. The subsequent accolades from management would have boosted the operator’s ego and spurred others to seek future troubleshooting opportunities.
While troubleshooting can be very rewarding and even fun at times, the main reason to consistently utilize a troubleshooting methodology is to add value to the organization. It has been demonstrated that a successful troubleshooting program can reduce machinery repair cost up to 20%. The savings come from:
Keeping equipment in service that are serviceable and eliminating needless repairs
Recommending required adjustments, such as balancing, before permanent damage occurs
Uncovering latent plant issues, such as fouling, flow blockage, etc.
Judiciously delaying repairs in order to properly plan work and get critical spare parts in stock before serious internal damage occurs
In a nutshell, troubleshooting allows maintenance and operating departments to better manage plant resources by maximizing the run lengths of machines, while avoiding major risks and consequences.
To realize the full benefits of field troubleshooting, all participants must possess adequate machinery experience and knowledge, be properly trained, and approach field problems wholeheartedly and with an open mind. What does being open-minded mean? An open mind means all participants have:
No preconceived idea to what the problems or solutions are
No hidden agendas
Willing to listen to everyone’s input
Participants with preconceived ideas are often doomed to failure because they are blinded to vital clues as to what’s really going on. Their nearsightedness will result in a big waste of time and resources. Furthermore, troubleshooting participants with hidden agendas are not being fair or honest to their organizations. Those that believe they are unable to investigate a problem faithfully, fairly, and with an open mind should let someone else in the organization investigate the problem.
1.2 Traits of a Successful Troubleshooter
We probably all know someone that is especially skilled at getting to the root of a problem. Instead of simply changing parts out or “shooting from the hip,” the skilled troubleshooter, weighs all the available field information and judiciously selects the optimal path forward. The correct decision may mean a simple adjustment, and sometimes a full-blown repair is in order. More often than not, successful troubleshooters identify and solve problems—they just don’t change parts! That is, they target the problem, not the symptom.
Questions that arise in critiquing the success of a diligent troubleshooter are:
What are the attributes that make a good troubleshooter?
Does experience make a good troubleshooter?
Does machine knowledge make a good troubleshooter?
It has been said that discovery comes to the prepared mind. We would like to build on this adage. We propose that for a troubleshooter to be successful they must have:
Prepared mind: The successful troubleshooter regularly studies to develop a working knowledge of machinery technology. It is impossible to troubleshoot machines without having a firm grasp on their inner workings as well as an understanding of their function. Self-study, seminars, trade magazines, webinars, online forums, and mentors can all help you master complex process machinery.
Open mind: The open-minded troubleshooter only follows actual clues that are uncovered during an investigation and ignores hunches or theories that are baseless. Such troubleshooters try not to have preconceived ideas when approaching a problem for the first time. They don’t assume that a machine is always going to fail a certain way or that all operators don’t understand machinery. Fact-driven investigations tend to be more successful than investigations fueled by preconceived notions.
There was a machinery engineer who would always jump to conclusions. This particular engineer loved to play the blame game. He would either blame the operators or the last mechanics that repaired the machine. This close-minded approach to troubleshooting rarely bears fruit. This particular machinery engineer never realized his full potential as a troubleshooter. Everyone soon realized his troubleshooting abilities were limited by his close-mindedness. Eventually no one trusted him to solve the more challenging problems in the plant.
Flexible mind: In days past, it was easier for individuals to become conversant in many facets of plant operations. Today, we all tend to become specialized as we progress through our careers. Try not to focus only on your area of expertise. (When you have a hammer, everything looks like a nail.) We should view our processes holistically, i.e., composed of numerous elements that interact with one another. Ask others for their opinion. They may provide a different view of the problem that could be vital to finding the true cause of the problem.
There was a time when technological changes in systems were usually gradual and not too radical. In contrast, today we are exposed to a dizzying barrage of incremental advances in manufacturing, materials, controls, and so forth. We are forced to either make a conscious effort to keep abreast of the new technological advances and understand how these advances affect our business or fall behind the knowledge curve. Those who make the effort to stay current in pertinent technologies will reap the rewards, i.e., better pay, advancements, and the enjoyment of a job done well. Those who fall behind due to conscious decision or indifference will eventually get left behind and replaced.
Years ago, a chess tournament director stated that he noticed that the better chess players, that is, the players that did the best in chess tournaments, seemed to use more clock than the others. Chess players that use “more clock” are taking more time to think about their moves. This suggests that those chess players that thought more about their moves probably discovered better moves than their opponents, which led to wins. Similarly, troubleshooters that think longer and deeper about the problem at hand have a better chance at uncovering the true nature of the problem.
Confidence in your abilities: With study, practice, and the occasional success comes confidence. Troubleshooters should keep score on their successes. It doesn’t matter how much analysis is done or how many plausible theories you generate; if the problem is not solved, you have failed. Be honest about your successes and failures. With failure comes humility and new insights. With success comes recognition and confidence.
There is no perfect troubleshooter. Every engineer, technical specialist, operator, etc., has shortcomings. We have to hope that by learning a little more every day we can become capable problem solvers and more efficient troubleshooters. It’s the challenge of the next problem that should keep us all studying.
Chapter 2
An Insight in Design: Machines and Their Components Serve a Function
Machines are put into service to serve a function. That is, they are there to do something, or perform an action. The majority of the machines installed in processing facilities are there to alter the energy of a fluid in the process stream. This is done by either pushing a fluid (liquid or gas) through the piping or by altering the thermodynamic properties of the fluid for a downstream process. The balance of the machinery in process facilities is there to provide power, such as motors, steam turbines and gas turbines.
A well-behaved process machine safely and efficiently converts some type of input energy into fluid energy at the proper flow and pressure that is required by the process. Degraded or malfunctioning process machines waste energy by converting some of the power into vibration, heat, and noise (see Figure 2.1). Fluid movers can waste additional power by converting input power into pressure pulsations and unwanted internal leakage. Heat, vibration, noise, pulsation, and leakage are sensible, or measureable, signs of inefficiency or distress that provide clues to the overall health of machines. Although all machines will exhibit these losses to some degree, it is the condition of excessive losses that would raise concern and merit a troubleshooter’s skill to assess the situation.
Figure 2.1 Machine energy losses.
Machines are systems that are composed of multiple elements that work together to perform a specific function. The manner in which these elements interact dictate how well the machine can perform its intended function. In troubleshooting a system it is necessary to be able to understand all the roles of all the working elements that make up the system so that they can be properly accounted for.
A list of the primary mechanical system elements are as follows:
