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Chapter-3 Failure Data Collection and Analysis

Introduction• Failure data are the backbone of reliability studies because

they provide invaluable information to concerned professionals such as reliability engineers, design engineers, and managers. In fact, the failure data of a product are the final proof of reliability related efforts expended during its design and manufacture.

• It would be impossible to have an effective reliability program without the collection, analysis, and use of information acquired through the testing and operation of products used in industrial, military, and consumer sectors.

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• The main purpose of developing a formal system of collecting, analyzing, and retrieving information acquired from past experiences is to allow design and development of better and more reliable products without repeating the previous efforts concerning research, design, and testing to achieve the current product reliability.

• Thus, the fundamental goal of a failure data collection and analysis system is to convert the relevant information accumulated in various sources into an effectively organized form so that it can efficiently be used by individuals with confidence in conducting their assigned reliability related tasks.

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In particular, the nature of the products and their intended applications are important factors in deciding the extensiveness, form, etc. of a failure data collection and analysis system. For example, a company stamping out stainless steel flatware will require a simple data system as opposed to a complex data system for a company manufacturing aircraft.

All in all, prior to deciding the size, type, etc. of a failure data system, consider factors such as individuals requiring information, information required by the individuals to meet their needs, and frequency of their need.

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• Failure data uses: There are many areas for the uses of failure data including conceptual design, preliminary design, test planning, design reviews, manufacturing, quality assurance and inspection planning, logistic support planning inventory management, procurement, top management budgeting, and field service planning.

• Nonetheless, some of the more specific uses of failure data are estimating hazard rate of an item, performing life cycle cost studies, making decisions regarding introduction of redundancy, predicting an item's reliability/availability, performing equipment replacement studies, recommending design changes for improving the product’s reliability, performing cost vs. reliability studies, determining the maintenance needs of a new item, and conducting preventive maintenance studies.

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Failure Data Collection Sources in Equipment Life Cycle and Quality Control Data

There are many sources of collecting failure related data during anequipment life cycle. Eight of these sources are as follows: 1. Warranty claims 2. Previous experience with similar or identical equipment 3. Repair facility records 4. Factory acceptance testing 5. Records generated during the development phase 6. Customers’ failure reporting systems 7. Tests: field demonstration, environmental qualification, and field

installation 8. Inspection records generated by quality control/manufacturing

groups

In order to maintain the required quality standards, the quality control groups within organizations regularly perform tests/inspections on products/equipment.

The important components of the quality control data are incoming inspection and test results, quality audit records and final test results, in-process quality control data, results of machine and process capability studies, and calibration records of measuring instruments.

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FAILURE REPORTING AND DOCUMENTATION SYSTEM DESIGN GUIDELINES AND FAILURE DATA COLLECTION FORMS

• A failure reporting and documentation system could be very effective if a careful consideration is given during its design. Some of the associated design guidelines are simplicity and clarity of the failure reporting form, effective and efficient documentation of the information on failures.

• The backbone of a failure data system is the failure data collection form. Such forms must be designed so that they require minimum effort to collect failure data and provide maximum benefits. Also, these forms must be tailored to meet the requirements of a specific organization or program effectively.

• Usually such forms are generally designed to include information such as form number, item description, location of the hardware, serial number of the failed item and manufacturer’s name, description of the failure, form completion date, dates on which failure occurred, was detected and corrected, operating hours from the previous failure, time taken for repair, repair cost, serial number and manufacturer of the replaced part, repair-person's name and appropriate signatures.

• Table 1 presents useful standard documents for failure data collection.

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Table 1: Selective standard documents for failure data collection

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External Failure Data Sources

There are a large number of organizations, data banks, and documents to obtain failure data related information. Some of these are as follows:

ORGANIZATIONS • Government Industry Data Exchange Program (GIDEP). It is probably the most

comprehensive source for obtaining data and is operated and funded by the U.S. government. A company must formally become a full or partial participating member of the GIDEP before making use of it. This means that the company must also submit its own data to GIDEP in order to receive data from it. The system is managed by the GIDEP Operations Center. Fleet Missile Systems, Analysis and Evaluation Group, Department of Defense, Corona, California 91720.

• National Technical Information Service (NTIS). This is also a good source for obtaining various types of failure data and the service is managed by the U.S. Department of Commerce. The address of the NTIS is 5285 Port Royal Road, Springfield, Virginia 22161.

• Reliability Analysis Center (RAC). RAC provides various types of information concerning reliability and is managed by the U.S. Air Force (USAF). In particular, the on electronic Parts Reliability Data (NPRD) reports are released periodically by the center. The address of the RAC is Rome Air Development Center (RADe), Griffiss Air Force Base, Department of Defense, Rome, New York 13441.

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• Defense Technical Information Center. This center is a useful source for obtaining various types of failure data related information, particularly concerning the defense equipment. The address of the center is Defense Logistics Agency, Cameron Station, Alexandria, Virginia 22314.

• Parts Reliability Information Center (PRINCE). This center is quite useful to obtain various types of data related to space systems. The address of the center is Reliability Office, George C. Marshall Space Flight Center, National Aeronautics and Space Administration ( IASA), Huntsville. Alabama 35812.

• Institute of Electrical and Electronics Engineers (IEEE). This is the largest professional body in the world and provides failure data concerning various electrical related items. The address of this organization is 345 East 47th Street, New York, New York 10017.

• National Electric Reliability Council (NERC). NERC publishes various types of failure data collected annually from the U.S. power plants. This organization is located in New York City.

• Insurance Information Institute (III). This organization provides data on disaster impacts and related matters. III is located at 110 William Street, New York, New York 10017.

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DATA BANKS • Nuclear Plant Reliability Data System (NPRDS). This system provides

various types of failure data on equipment used in nuclear power generation. NPRDS is managed by the South West Research Institute, San Antonio, Texas.

• Equipment Reliability Information System (ERIS). This system provides failure data on equipment used in electric power generation. The system is managed by the Canadian Electrical Association (CEA), Montreal, Quebec.

• SYREL: Reliability Data Bank. This data bank provides failure data Oil equipment used in power generation. The data bank is managed by the Systems Reliability Service, Safety and Reliability Directorate, United Kingdom Atomic Energy Authority (UKAEA), Wigshaw Lane, Culcheth, Warrington, Lancashire WA3 4NE, England.

• ESA Electronic Component Data Bank. This data bank provides data on various types of electronic parts, especially used in space environment. Its address is Space Documentation Service, European Space Agency (ESA), Via Galileo, 00044 Frascati, Italy.

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DOCUMENTS • MIL-HDBK-217, Reliability Prediction of Electronic Equipment, Department of

Defense, Washington, D.C. • Component Parts Failure Data Compendium, Engineering Dept., Electronic

Industries Association, II W. 42nd St., New York, New York 10036. • RADC-TR-85-194, RADC Non-electronic Reliability Notebook, Reliability Analysis

Center, Rome Air Development Center (RADC), Griffiss Air Force Base, Rome, New York 13441-5700, 1985.

• IEEE-STD-500-1977, IEEE Nuclear Reliability Data Manual, John Wiley & Sons, New York, 1977.

• WASH-1400 (NUREG 75/014), Appendix 3 and 4, Reactor Safety Study: An Assessment of Accident Risks in U.S. Commercial Nuclear Power Plants, U.S. Nuclear Regulatory Commission, Washington, D.C., 1975.

• Dhillon, B.S., Mechanical Reliability: Theory, Models, and Applications, American Institute of Aeronautics and Astronautics, Washington, D.C., 1988 (Chapter 9 contains failure data on various mechanical parts).

• RAC EMD 1 and 2, Electronic Equipment Reliability Data, Reliability Analysis Center (RAC), Rome Air Development Center, Griffiss Air Force Base, Rome, New York.

• NUREG/CR-1278, Handbook of Human Reliability Analysis with Emphasis on nuclear Power Plant Applications, U.S. Nuclear Regulatory Commission, Washington, D.C.

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Failure Data for Selective Items and Tasks

• For many decades, failure data on engineering items and various tasks performed by humans have been collected and analyzed. In order to demonstrate the type of analyzed and available failure data, Tables 1 and 2 present failure rates for some selected electronic and mechanical items, respectively, and Table 3 contains human error data for a few selective tasks.

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Table 2: Failure rates for some electronic items.

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Table 3: Failure rates for some mechanical items.

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Table 4: Human error rates for some tasks.

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Weibull Distribution and Parameters of Weibull distribution.

The Weibull Distribution This continuous random variable distribution is named after W. Weibull, a Swedish mechanical engineering professor. This distribution takes account of a non-constant hazard function. The Survival function is given by:

t

e)t(Rwhere β is the shape parameter and η is the scale parameter or characteristic life. The characteristic life is the life at which 63.2% of the population will have failed. When β = 1, the hazard function is constant and therefore the data can be modeled by an exponential distribution with η=1/λ . When β<1, we get a decreasing hazard function and When β>1, we get a increasing hazard function Figure 7, below, shows the Weibull shape parameters superimposed on the bath-tub curve. This distribution used to describe experimentally observed variation in the fatigue resistance of steel, its elastic limits etc.

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Figure 7 bath tub curve and the weibull distribution