An Introduction to Failure Analysis

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An Introduction to Failure

Analysis Daniel Flores RomeroFlabio Cisneros VázquezIsaac Torres AnguianoEloy Encarnación Reyna ZamarrónNerio Albino Álvarez MartínezSaúl Chávez Salas

English Class



• The people we’ve worked with began doing failure

analysis on industrial equipment in the mid1960s.

• Their efforts were primarily linked with an interestin improving equipment reliability and production

capacity in chemical plants. Prior to that time, mostindustrial failure analyses merely involved trying tounderstand the physical roots of the problem. Fromtheir work and a manufacturing and processing

viewpoint, it wasn’t until the early 1970s that therealization began to develop that the true sources of our problems were much more complex.



• What is failure analysis? There are probably as

many definitions as people you ask the questionof, but we prefer to think of it as “the process of interpreting the features of a deterioratedsystem or component to determine why it nolonger performs the intended function.” Failureanalysis entails first using deductive logic to findthe mechanical and human causes of the failure,and then using inductive logic to find the latentcauses. In addition, it should also lead to thechanges needed to prevent the recurrence of failure.



• Many people in industry prefer not to use the termfailure analysis, and we have heard the statementmore than once that “We don’t want ourmaintenance improvement (or some similar)program being driven by concentrating on failures.”

• It’s easy to understand their words but impossible tounderstand their logic. What better and moreef ficient way is there to improve than to intelligently

look at our weaknesses and mistakes, learn fromthem, and try to do a better job the next time?



• This book is my attempt at a manual thatexplains how and why mechanical machinery fails.

• To do that, I have tried to explain how the basic failure mechanisms occur, the things we alldo to cause machinery problems, how torecognize those things, and what to do toprevent failures in the future.



THE CAUSES OF FAILURES



• Why are there premature equipment failures? When the people involved are asked this

question, the answer is almost always “the otherguy’s fault.” If one were to ask a plant millwrightor a maintenance mechanic, the most likely answer to that question would be “operator

error.”

• But if the same question were asked of anoperator who worked in the plant with that

millwright, his or her answer might be “it wasn’t properly repaired.” At times there is some validity to both these answers, but the honestand complete answer is much more complex



• It would be nice and neat if there were only one

cause per failure, because correcting theproblem would then be easy. However, in reality,there are multiple causes to every equipmentfailure.

• Unfortunately there are many people who

believe that there is only one cause for a failure.



• However, look at any well-studied major disasterand ask if there was only one cause. Was there only one cause for Three Mile Island? The Exxon Valdezmess? Bhopal? Chernobyl? A major airplane crash?Looking at these and other well-recognized andextensively studied failures, reports show that they

all have multiple causes.• Then why would an intelligent person believe a

typical pump or fan failure would be different? (Inthe case of Three Mile Island, there were three hugestudies, each commissioned by one of theresponsible groups. All three of the studies saidthere were numerous causes, but that it was“primarily the fault of the other organizations”.)



• At an international conference on failureanalysis, a presentation was made on the causesof aircraft equipment failures. The data from thepresentation is shown in the following:

• 30% — manufacturing errors• 26% — Design errors• 23% — Maintenance errors• 18% — Material selection

• 3% — Operation



• During the question-and-answer session after thepresentation, a member of the audience asked thespeaker why they had listed only one cause for each

failure when there were usually multiple causes. Thespeaker agreed with the questioner, then said “there wasonly one blank on the form.” This answer is a quote andan interesting testimony to the public’s lack of perception.

• They think about cases that have been carefully studied,such as those listed earlier, and agree that there areobviously multiple causes for each. Yet, when directly involved with a problem, many people still ignore reality and come up with data such as that shown in thepreceding study. They then ake this data, draw anattractive pie chart or bar graph, and point to a nice neatsingle cause for every failure — when simple and honestlogic clearly states that isn’t true.



• Two comments:

• At a later time in the session, another groupanalyzed the same basic data set and reached very different conclusions. They too sorted the data withthe idea of a single cause for each failure!

• One of the questions I find interesting is, “Why don’t they recognize that many failures have morethan one physical cause and all failures have morethan one human cause?” I suspect that there is an

innate human desire to neatly categorize problemsand answers but the answer to this lies with people who are more skilled than I am.



• Trevor Kletz has written a fascinating series of books detailing events leading to many of the

world’s major industrial disasters. In hisapproach to failures he uses a three-tieredsystem for classifying the causes; we shall use asimilar method. In this approach there are threegeneral classes of failure causes or roots, and,until the investigator understands each of theseclasses and their inevitable interaction, they do

not truly understand how and why the failureoccurred and don’t have the ability to preventanother.

An Introduction to Failure Analysis

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