Solve the machinery failure problems costing you time and money with this classic, comprehensive guide to analysis and troubleshooting
- Provides detailed, complete and accurate information on anticipating risk of component failure and avoiding equipment downtime
- Includes numerous photographs of failed parts to ensure you are familiar with the visual evidence you need to recognize
- Covers proven approaches to failure definition and offers failure identification and analysis methods that can be applied to virtually all problem situations
- Demonstrates with examples how the progress and results of failure analysis and troubleshooting efforts can be documented and monitored
Failures of machinery in a plant setting can have wide-ranging consequences and in order to stay competitive, corporations across all industries must optimize the efficiency and reliability of their machinery.
Machinery Failure Analysis and Troubleshooting is a trusted, established reference in the field, authored by two well-known authorities on failure and reliability. Structured to teach failure identification and analysis methods that can be applied to almost all problem situations, this eagerly awaited update takes in the wealth of technological advances and changes in approach seen since the last edition published more than a decade ago.
Covering both the engineering detail and management theory, Machinery Failure Analysis and Troubleshooting provides a robust go-to reference and training resource for all engineers and managers working in manufacturing and process plants.
- Provides detailed, complete and accurate information on anticipating risk of component failure and avoiding equipment downtime
- Presents documented failure case studies and analyzes the procedures employed to define events that led to component or systems failure
- Includes numerous photographs of failed parts to ensure readers are familiar with the visual evidence they need to recognize
About the Author
Fred K. Geitner is a registered Professional Engineer in the Province of Ontario, Canada, engaged in process machinery consulting. He retired from Imperial Oil with 20 years of service as an engineer.
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Machinery Failure Analysis and TroubleshootingPractical Machinery Management for Process Plants
By Heinz P. Bloch Fred K. Geitner
Butterworth-HeinemannCopyright © 2012 Elsevier Inc.
All right reserved.
Chapter OneThe Failure Analysis and Troubleshooting System
Troubleshooting as an Extension of Failure Analysis 1 Causes of Machinery Failures 3 Root Causes of Machinery Failure 7 References 9
Troubleshooting as an Extension of Failure Analysis
For years, the term "failure analysis" has had a specific meaning in connection with fracture mechanics and corrosion failure analysis activities carried out by static process equipment inspection groups. Figure 1-1 shows a basic outline of materials failure analysis steps. The methods applied in our context of process machinery failure analysis are basically the same; however, they are not limited to metallurgic investigations. Here, failure analysis is the determination of failure modes of machinery components and their most probable causes. Figure 1-2 illustrates the general significance of machinery component failure mode analysis as it relates to quality, reliability, and safety efforts in the product development of a major turbine manufacturer.
Very often, machinery failures reveal a reaction chain of cause and effect. The end of the chain is usually a performance deficiency commonly referred to as the symptom, trouble, or simply "the problem." Troubleshooting works backward to define the elements of the reaction chain and then proceeds to link the most probable failure cause based on failure (appearance) analysis with a root cause of an existing or potential problem. For all practical purposes, failure analysis and troubleshooting activities will quite often mesh with one another without any clear-cut transition.
However, as we will see later, there are numerous cases where troubleshooting alone will have to suffice to get to the root cause of the problem. These are the cases that present themselves as performance deficiencies with no apparent failure modes. Intermittent malfunctions and faults are typical examples and will tax even the most experienced troubleshooter. In these cases, troubleshooting will be successful only if the investigator knows the system he is dealing with. Unless he is thoroughly familiar with component interaction, operating or failure modes, and functional characteristics, his efforts may be unsuccessful.
There are certain objectives of machinery failure analysis and troubleshooting:
1. Prevention of future failure events.
2. Assurance of safety, reliability, and maintainability of machinery as it passes through its life cycles of:
a. Process design and specification.
b. Original equipment design, manufacture, and testing.
c. Shipping and storage.
d. Installation and commissioning.
e. Operation and maintenance.
From this it becomes very obvious that failure analysis and troubleshooting are highly cooperative processes. Because many different parties will be involved and their objectives will sometimes differ, a systematic and uniform description and understanding of process machinery failure events is important.
Causes of Machinery Failures
In its simplest form, failure can be defined as any change in a machinery part or component which causes it to be unable to perform its intended function satisfactorily. Familiar stages preceding final failure are "incipient failure," "incipient damage," "distress," "deterioration," and "damage," all of which eventually make the part or component unreliable or unsafe for continued use.
Meaningful classifications of failure causes are:
1. Faulty design.
2. Material defects.
3. Processing and manufacturing deficiencies.
4. Assembly or installation defects.
5. Off-design or unintended service conditions.
6. Maintenance deficiencies (neglect, procedures).
7. Improper operation.
All statistics and references dealing with machinery failures, their sources and causes, generally use these classifications. And, as will be shown in Chapter 4, remembering these seven classifications may be extremely helpful in failure analysis and troubleshooting of equipment.
For practical failure analysis, an expansion of this list seems necessary. Table 1-1 shows a representative collection of process machinery failure causes. The table makes it clear that failure causes should be allocated to areas of responsibilities. If this allocation is not made, the previously listed objectives of most failure analyses will probably not be met.
Failure causes are usually determined by relating them to one or more specific failure modes. This becomes the central idea of any failure analysis activity. Failure mode (FM) in our context is the appearance, manner, or form in which a machinery component or unit failure manifests itself. Table 1-2 lists the basic failure modes encountered in 99 percent of all petrochemical process plant machinery failures.
In the following sections, this list will be expanded so that it can be used for day-to-day failure analysis. Failure mode should not be confused with failure cause, as the former is the effect and the latter is the cause of a failure event. Failure mode can also be the result of a long chain of causes and effects, ultimately leading to a functional failure, i.e. a symptom, trouble, or operational complaint pertaining to a piece of machinery equipment as an entity.
Other terms frequently used in the preceding context are "kind of defect," "defect," or "failure mechanism." The term "failure mechanism" is often described as the metallurgical, chemical, and tribological process leading to a particular failure mode. For instance, failure mechanisms have been developed to describe the chain of cause and effect for fretting wear (FM) in roller bearing assemblies, cavitation (FM) in pump impellers, and initial pitting (FM) on the surface of a gear tooth, to name a few. The basic agents of machinery component and part failure mechanisms are always force, a reactive environment, time and temperature. This important concept can be easily remembered by using the acronym "FRETT". Each of these agents can be subdivided as indicated in Table 1-3.
For our purpose, failure mechanisms thus defined will have to stay part of the failure mode definition: They will tell how and why a failure mode might have occurred in chemical or metallurgical terms, but in so doing, the root cause of the failure will remain undefined.
Root Causes of Machinery Failure
The preceding pages have shown us that there will always be a number of causes and effects in any given failure event. We need to arrive at a practical point—if not all the way to the beginning—of the cause and effect chain where removal or modification of contributing factors will solve the problem.
A good example would be scuffing (FM) as one of the major failure modes of gears. It is a severe form of adhesive wear (FM) with its own well-defined failure mechanism. Adhesive wear cannot occur if a sufficiently thick oil film separates the gear tooth surfaces. This last sentence—even though there is a long chain of cause and effect hidden in the adhesive wear failure mechanism—will give us the clue as to the root cause. What then is the root cause? We know that scuffing usually occurs quite suddenly, in contrast to the time-dependent failure mode of pitting. Thus, we cannot look for the root cause in the design of the lube oil system or in the lube oil itself—that is, if scuffing was not observed before on that particular gear set.
Sudden and intermittent loss of lubrication could be the cause. Is it the root cause? No, we still have to find it because we are looking for the element that, if removed or modified, will prevent recurrence or continuation of scuffing. Is it because this particular plant is periodically testing their standby lube oil pumps, causing sudden and momentary loss of lube oil pressure? Eventually, we will arrive at a point where a change in design, operation, or maintenance practices will stop the gear tooth scuffing.
Removal of the root cause of machinery failures should take place in design and operations-maintenance. Quite often the latter, in its traditional form, is given too much emphasis when looking for a sponsor or an agent of failure analysis and failure prevention. In our opinion, long-term reductions in failure trends will only be accomplished by specification and design modifications. We will see again in Chapter 7 that only design changes will achieve the required results. How then does this work? First, we must decide to find the failure cause. If we do not investigate, we have no other option than to allow the failure to repeat. After ascertaining the failure mode, we determine whether or not the failed machinery component could be made more resistant to the failure event. This is done by checking design parameters such as the ones shown in Table 1-4 for possible modification. Once a positive answer has been obtained, the root cause has also been determined and we can specify whatever is required to impart less vulnerability to the material, component, assembly, or system. As we formulate our action plan, we will test whether the mechanic's axiom holds true:
When in doubt Make it stout Out of something You know about.
We will keep in mind our inability to influence machinery failures by simply making the part stronger in every conceivable situation. A flexibly designed component may, in some cases, survive certain severe operating conditions better than the rigid part.
Table 1-5 concludes this section by summarizing machinery failure modes as they relate to their immediate causes or design parameter deficiencies.
Chapter TwoMetallurgical Failure Analysis
Types of Failures 15 Metallurgical Failure Analysis Methodology 15 Practical Hints 18 Failure Mode Inventory 18 Qualitative Tests 19 Failure Analysis of Bolted Joints 21 Why Do Bolted Joints Fail? 22 Use of Low-grade Cap Screws 22 Use of Mismatched Joint Components 24 Proper Joint Design 24 Failure to Apply Proper Preload 26 Carefully Consider Reusing Fastener Components in Critical Applications 26 Failure Analysis Steps 27 Shaft Failures 28 Causes of Shaft Failures 28 Fracture Origins in Shafts 29 Stress Systems in Shafts 30 Tension 30 Torsion 31 Compression 31 Stress Raisers in Shafts 40 Changes in Shaft Diameter 41 Press and Shrink Fitting 42 Longitudinal Grooves 42 Failures Due to Manufacturing Processes 43 Influence of Metallurgical Factors 44 Surface Discontinuities 44 Examination of Failed Shafts 45 Mechanical Conditions 45 Operating History 45 The Case of the Boiler Fan Turbine 46 Shaft Fracture 46 Analysis of Surface-Change Failures 48 Abrasive Wear 49 Adhesive Wear 49 Corrosive Wear 50 Effects of Corrosion 50 Fretting Corrosion 52 Cavitation Corrosion 53 Analyzing Wear Failures 56 Environmental Conditions 56 Analysis Procedure 57 Operating Conditions 57 Solving Wear Problems 58 Laboratory Examination of Worn Parts 58 Procedures 58 Taper Sectioning 59 Chemical Analysis 60 Recording Surface Damage 60 Preventive Action Planning Avoids Corrosion Failure 65 Corrosion Events Related to Research and Development 68 Preventive Action Plan 69 Case Studies 69 Summary 84 References 85
Failure analysis of metallic components has been the preoccupation of the metallurgical community for years. Petrochemical plants usually have an excellent staff of "static equipment" inspectors, whose services prove invaluable during machinery component failure analysis. The strengths of the metallurgical inspectors lie in solving service failures with the following primary failure modes and their causes:
1. Deformation and distortion
2. Fracture and separation
a. ductile fractures
b. brittle fractures
c. fatigue fractures
d. environmentally affected fractures
3. Surface and material changes
4. Stress-corrosion cracking
5. Hydrogen damage
6. Corrosion fatigue
7. Elevated temperature failures
b. stress rupture
Excerpted from Machinery Failure Analysis and Troubleshooting by Heinz P. Bloch Fred K. Geitner Copyright © 2012 by Elsevier Inc.. Excerpted by permission of Butterworth-Heinemann. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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Table of Contents
The Failure Analysis and Troubleshooting System Metallurgical Failure Analysis Machinery Component Failure Analysis Machinery Troubleshooting Vibration Analysis Generalized Machinery Problem-Solving Sequence Statistical Approaches in Machinery Problem Solving Sneak Analysis Formalized Failure Reporting as a Teaching Tool The Seven-Cause Category Approach to Root-Cause Failure Analysis Knowledge-Based Systems for Machinery Failure Diagnosis Training and Organizing for Successful Failure Analysis and Troubleshooting Appendices Index