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1Failure Analysis

1.1 Introduction

The abundant availability of raw materials in nature is the gift of God tohumanity. The invention of technologies to convert raw materials into usefulproducts is the contribution of science to modern civilization. Scientific prin-ciples and laws of nature broadly dictate the conversion of materials intocomponents and, thus, the performance of the components in an engineeredproduct. Disregard for these laws and principles leads to deficiencies indesign, manufacture and maintenance. The deficiencies may be flaws ordefects; these two faults are often incorrectly considered to be synonymous.While a flaw is a deviation from the perfect, a defect is a deviation from theacceptable. All the defective parts are flawed, but very few flawed parts aredefective. Similarly, all defects need not result in failure, but all failuresoriginate at defects. It is, therefore, necessary to identify the nature andsource of the defects, which ultimately cause failures in service.

An air crash in the Himalayas; a train accident down south; an unsched-uled shutdown of a power generation plant; immobilization of a tank in the

battlefield; a gun incapable of firing ammunition. There is something com-mon to these seemingly unconnected events: failure of an engineering com-ponent to function as its designer predicted. The term failure has negative

connotations and signifies malfunctioning, leading to unsatisfactory perfor-mance of an engineering system. Even in modern times, in spite of all ourtechnological advances, failures do occur, leading to loss of expensive equip-ment and invaluable human lives.

The consequences of premature failures are quite damaging to society andresult in loss of lives and materials. There are myriad reports quantifyingthe losses caused by material degradation processes such as corrosion andwear. The losses due to corrosion alone are estimated to be at 5% of the grossdomestic product (GDP) of any nation, and the loss is about $170 billion per

year in the U.S. The loss due to wear in the U.S. is estimated to be approximately1% of its GDP. If any such estimates of the direct and indirect losses due tounpredicted failures were made much before achieving the design lives ofsystems, the damages to the economy of any country would be mind-boggling.For example, the seemingly trivial failure of a boiler tube leads to the shut-down of an entire power generation unit. The direct consequence of the event

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is the loss of power generation. The indirect effects of the unavailability ofpower are loss of production in the manufacturing sector, stoppage of rail-way traction, immense inconvenience due to nonfunctionality of all electrical

gadgetry, etc. The total loss can be significant if one considers all the conse-quential damages of the power failure.

It is, therefore, imperative and customary to minimize losses by carefulfailure analysis and correct implementation of remedial measures. Thoughfinding the cause of failure has been a fascination of humans from the

beginning of history, the necessity of learning from mistakes continues to bethe driving force for failure analysis. Avoidance of failures or their recurrencethrough failure analysis is a sure way to minimize economic losses. Thus, afailure analyst has a significant role to play in society.

1.2 Qualities of a Failure Analyst

Failure analysis is a daunting and demanding task. The analyst has to takea comprehensive approach, covering a large spectrum of disciplines, to arriveat the correct cause of failure. He or she should also be endowed with certain

qualities to be successful: comprehensive knowledge of the field; adequateknowledge of related fields; knack for gathering information; ability to filterdisinformation; an eye for minor details; absolute honesty and integrity; andlots of common sense.

The failure analyst must possess adequate professional qualifications andhands-on experience in the relevant field and should strive to keep abreastof latest developments. Inadequacy in either the qualifications or the expe-rience of the failure analyst invariably leads to disastrous consequences. Itis not uncommon to hear of sulphate inclusions in steel purely because a

qualified chemist does the metallurgists job!The failure analyst should possess broad understanding of the operationof the system to which the failed component belongs. Though it is notpossible for any failure analyst to know about every system, adequate knowl-edge can be assimilated by discussing the functional aspects of the systemwith the users. It is absolutely necessary that the failure analyst be familiarwith the functional aspects of the system being analyzed, such as loads,operating conditions, etc., by thoroughly interacting with the shop floorengineers. Such an interaction with shop floor engineers not only helps indeveloping better understanding of the functional aspects of the system, butalso helps the failure analyst to win their confidence. While dealing with thefailure of complex systems, it is desirable to create a failure analysis team,drawing experts from design, production, operation, maintenance and mate-rials science.

The failure analyst should be able to seek complete information about thedesign, engineering and operational aspects of the system in which the failed

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component was a subsystem. Ideally, it is best to collect information fromdifferent interest groups, though there is an inherent danger of the failureanalyst becoming biased for or against the theories proposed. The information

channels should be kept open until completion of the investigation. Experiencesuggests that after preliminary tests, more specific queries can be put forth andcorrect information can be obtained in support of the line of investigation.

Like a forensic expert, the failure analyst must critically examine all theinformation. The failure analysts ability to filter out distorted informationfurnished by different agencies is of paramount importance. It is necessaryto remember that the culprits intentionally leave clues at the site of the crimeto mislead the sleuths. Though it is impossible to identify useful informationfrom the total collected a priori, it is relatively easy to differentiate between

a lie and the truth after the completion of a preliminary investigation. Theexpertise to look for seemingly insignificant scientific detail is the qualitythat differentiates successful failure analysts from the rest. When a researchmetallurgist examines the microstructure of a quenched and tempered low-alloy steel, he sees how nice the laths are, how fine the carbides are, andhow good the overall microstructure is. In contrast, when a forensic metal-lurgist examines the same sample, he not only observes the overall micro-structure but also looks for evidence of decarburization, grain size, inclusionmorphology and population, the presence of cracks and the path they take

in relation to the microstructural features, and so on. This in effect meansthat failure analysts look at all the good and bad features of a component.The process of finding out the correct cause of failure through a systematic

and scientific investigation centers around the scientific capability, honestyand integrity of the investigators. If the failure analyst lacks integrity, thescientific data generated on the failed component can intentionally be mis-interpreted by putting forth wrong reasoning. Once a wrong cause isreported, it is difficult to correct the damage even if the correct diagnosis ismade subsequently by more competent analysts, because of the usual ten-

dency of interested parties to use the findings to suit their convenience. Allsuccessful people are gifted with extraordinary common sense, and a suc-cessful failure analyst is no exception. The need for practical wisdom will

be felt by the failure analysts and the assisting team at every stage of thefailure analysis, be it in filtering out disinformation or in disregarding mis-leading experimental evidence.

1.3 Ethics in Failure Analysis

The efficiency of the solutions derived from the failure analysis to avoid recur-rence of failures depends on the ethics followed by the involved institutionsand honesty of the individuals associated with the investigation. To ensure

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that the investigation is undertaken without bias or prejudice, it is necessaryto

1. entrust the responsibility of failure analysis to a team whose mem- bers are endowed with sound technical judgment and irrefutableintegrity,

2. ensure independence of the investigation team,

3. avoid the presence of pressure groups in the investigation team, and

4. empower the investigation team to implement the remedial mea-sures and reassess the performance.

If the investigation team is not competent and honest, the findings tendto be ambiguous and do not address the critical issues, leading to no real benefit from the whole exercise. Intrainstitutional investigation teams aregenerally constrained and seldom exhibit the independence needed to recordthe facts. Failing to find relevant information and distorting the facts relatedto the failure is too common a practice to be ignored. It is, therefore, desirableto consider all of these factors while creating an investigation team.

2004 by CRC Press LLC