root cause failure anal ysis

309 Pages·2005·4.23 MB·English

ROOT CAUSE FAILURE
ANAL YSIS
PLANT ENGINEERING MAINTENANCE SERIES
Vibration Fundamentals
R. Keith Mobley
Root Cause Failure Analysis
R. Keith.Mobley
Maintenance Fundamentals
R. Keith Mobley
ROOT CAUSE FAILURE
ANAL YSIS
~
R. Keith Mobley
Boston Oxford Auckland Johannesburg Melbourne NewDelhi
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Library of Congress Cataloging-in-Publication Data
Mobley, R. Keith, 1943-
Root cause failure analysis /by R. Keith Mobley.
p."tm. - (Plant engineering maintenance series)
Includes index.
ISBN 0-7506-7158-0 (alk. paper)
I. Plant maintenance. 2. System failures (Engineering)
1. Title. II. Series.
TS192.M625 1999
658.2'02-dc21 98-32097
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CONTENTS
io
Part I Introduction to Root Cause Failure Analysis I
Chapter 1 Introduction 3
Chapter 2 General Analysis Techniques 6
Chapter 3 Root Cause Failure Analysis Methodology 14
Chapter 4 Safety-Related Issues 58
Chapter 5 Regulatory Compliance Issues 62
Chapter 6 Process Performance 72
Part II Equipment Design Evaluation Guide 75
Chapter 7 Pumps 77
Chapter 8 Fans, Blowers, and Fluidizers 97
Chapter 9 Conveyors 112
Chapter 10 Compressors 123
Chapter 11 Mixers andAgitators 147
Chapter 12 Dust Collectors 153
Chapter 13 Process Rolls 164
Chapter 14 Gearboxes/Reducers 171
Chapter 15 Steam Traps 187
Chapter 16 Inverters 194
Chapter 17 Control Valves 202
Chapter 18 Seals and Packing 220
vi Contents
Part III Equipment Troubleshooting Guide 237
Chapter 19 Pumps 239
Chapter 20 Fans, Blowers, and Fluidizers 246
Chapter 21 Conveyors 251
Chapter 22 Compressors 254
Chapter 23 Mixers andAgitators 264
Chapter 24 Dust Collectors 266
Chapter 25 Process Rolls 269
Chapter 26 Gearboxes orReducers 271
Chapter 27 Steam Traps 276
Chapter 28 Inverters 278
Chapter 29 Control Valves 280
Chapter 30 Seals andPacking 282
Chapter 31 Others 285
List ofAbbreviations 288
Glossary 291
•. References 305
Index 306
Part I
INTRODUCTION TO ROOT
CAUSE FAILURE ANALYSIS
4 RootCauseFailureAnalysis
deviation modes. These tables list the common symptoms of machine and process-
related problems and identify the probable cause(s).
PURPOSE OFTHE ANALVSIS
The purpose of RCFA is to resolve problems that affect plant performance. It should
not be an attempt tofix blame for the incident. This must be clearly understood by the
investigating team and those involved in the process.
Understanding that the investigation is not an attempt to fix blame is important for
two reasons. First, the investigating team must understand that the real benefit of this
analytical methodology is plant improvement. Second, those involved in the incident
generally will adopt a self-preservation attitude and assume that the investigation is
intended to find and punish the person or persons responsible for the incident. There-
fore, it is important for the investigators to allay this fear and replace it with the posi-
tive team effort required to resolve the problem .
••
EFFECTIVE USE OFTHE ANALVSIS
Effective use of RCFA requires discipline and consistency. Each investigation must be
thorough and each of the steps defined in this manual must be followed.
Perhaps the most difficult part of the analysis is separating fact from fiction. Human
nature dictates that everyone involved in an event or incident that requires aRCFA is
conditioned by his or her experience. The natural tendency of those involved is to fil-
ter input data based on this conditioning. This includes the investigator. However,
often such preconceived ideas and perceptions destroy the effectiveness of RCFA.
It is important for the investigator or investigating team to put aside its perceptions,
base the analysis on pure fact, and not assume anything. Any assumptions that enter
the analysis process through interviews and other data-gathering processes should be
clearly stated. Assumptions that cannot be confirmed or proven must be discarded.
PERSONNEL REQUIREMENTS
The personnel required to properly evaluate an event using RCFA can be quite sub-
stantial. Therefore, this analysis should be limited to cases that truly justify the expen-
diture. Many of the costs of performing an investigation and acting on its
recommendations are hidden but nonetheless are real. Even asimple analysis requires
an investigator assigned to the project until it is resolved. In addition, the analysis
requires the involvement of all plant personnel directly or indirectly involved in the
incident. The investigator generally must conduct numerous interviews. In addition,
many documents must be gathered and reviewed to extract the relevant information.
Introduction 5
In more complex investigations, a team of investigators is needed. As the scope and
complexity increase, so do the costs.
As a result of the extensive personnel requirements, general use of this technique
should be avoided. Its use should be limited to those incidents or events that have a
measurable negative impact on plant performance, personnel safety, or regulatory
compliance.
WHEN TO USE THE METHOD
The use of RCFA should be carefully scrutinized before undertaking a full investiga-
tion because of the high cost associated with performing such an in-depth analysis.
The method involves performing an initial investigation to classify and define the
problem. Once this iscompleted, afull analysis should be considered only ifthe event
can be fully classified and defined, and it appears that a cost-effective solution can be
found.
Analysis generally is not performed on problems that are found to be random, nonre-
dlITing events. Problems that often justify the use of the method include equipment,
machinery, or systems failures; operating performance deviations; economic perfor-
mance issues; safety; and regulatory compliance issues.
2
GENERAL ANALYSIS mCHNIQUES
A flumber of general techniques are useful for problem solving. While many com-
mo,~ or overlapping, methodologies are associated with these techniques, there also
are differences. This chapter provides abrief overview of the more common methods
used to perform an RCFA.
FAILURE MODE AND EFFECTS ANALYSIS
A failure mode and effects analysis (FMEA) is adesign-evaluation procedure used to
identify potential failure modes and determine the effect of each on system perfor-
mance. This procedure formally documents standard practice, generates a historical
record, and serves as a basis for future improvements. The FMEA procedure is a
sequence of logical steps, starting with the analysis of lower-level subsystems or com-
ponents. Figure 2-1 illustrates atypical logic tree that results with aFMEA.
The analysis assumes a failure point of view and identifies potential modes of fail-
ure along with their failure mechanism. The effect of each failure mode then is
traced up to the system level. Each failure mode and resulting effect is assigned a
criticality rating, based on the probability of occurrence, its severity, and its delecta-
bility. For failures scoring high on the criticality rating, design changes to reduce it
are recommended.
Following this procedure provides amore reliable design. Also such correct use of the
FMEA process results in two major improvements: (1) improved reliability by antici-
pating problems and instituting corrections prior to producing product and (2)
improved validity of the analytical method, which results from strict documentation
of the rationale for every step in the decision-making process.
6