Failure analysis and life assessment of structural components and Equipment Introduction LIFE ASSESSMENT of structural components is used to avoid catastrophic failures and to maintain safe and reliable functioning of equipment. The articles in the"Structural Life Assessment Methods"Section in this Volume are written to provide an overview of the prevalent life assessment methodologies for structural components. Because the failure analyst is often asked questions concerning remaining life, fitness-for-service inspection intervals, and reliability of structural components and equipment, it is necessary that the failure analyst be aware of life assessment methodologies to address the questions and concerns of the industry he or the serves. Life assessment method advances and changes in technologies for structural components and equipment will require the investigator to adapt to the need of the industry. Furthermore, the failure investigator role has expanded from providing accurate identification of life-limiting failure mechanisms and degradation phenomena to also providing the time for degradation or damage, and crack growth rate to be used in life assessment estimates. Thus, the failure investigator's input is essential for meaningful life assessment of structural components. This article provides an overview of the structural design process, the failure analysis process, the failure investigator's role, and how failure analysis of structural components integrates into determination of remaining life, fitness-for-service, and other life assessment concerns. The topics discussed in this article include Industry perspectives on failure and life assessment of components Structural design philosophies Life-limiting factors The role of the failure analyst in life assessment The role of nondestructive inspection Fatigue life assessment Elevated-temperature life assessment Fitness-for-service life assessment Probabilistic and deterministic approaches Industry Perspectives on Failure and life Assessment of Components As noted previously, life assessment of structural components is a means to avoid catastrophic failures and to maintain safe and reliable functioning of equipment. Catastrophic failures of structural components occur rather infrequently, but when they do, they take a heavy toll on human lives in addition to the cost of repairs, replacement power, and litigation costs. In 1982, the National Bureau of Standards commissioned a study to determine the direct and indirect cost of fracture in the United States. It was estimated that $120 billion are spent annually to cover direct costs and costs associated with fracture-related accidents(Ref 1). The estimates took into account the necessity of overdesigning to prevent failure, added inspections, repairs, and replacement of degraded materials. Needless to say, the costs and stakes for failure are high. In addition, the cost savings are reat if failure can be mitigated or prevented For the failure investigator, a failure is often defined as the rupture, fracture, or cracking of a structural member The industrial definition of failure is often quite different from the textbook definition. A component, in practice, is deemed to have failed when it can no longer perform its intended function safely, reliably, and economically. Any one of these criteria can constitute failure. For example, a steam turbine blade whose tip has eroded affects turbine efficiency and hence affects the economics of operation adversely. The blade should therefore be replaced even though it can continue to operate. Component failures are thus defined in terms of functional"rather than"structural failures. Replacement of parts can be based on economic considerations, reliability, and material properties. In the discipline of life assessment, equipment and structures are evaluatedFailure Analysis and Life Assessment of Structural Components and Equipment Introduction LIFE ASSESSMENT of structural components is used to avoid catastrophic failures and to maintain safe and reliable functioning of equipment. The articles in the “Structural Life Assessment Methods” Section in this Volume are written to provide an overview of the prevalent life assessment methodologies for structural components. Because the failure analyst is often asked questions concerning remaining life, fitness-for-service, inspection intervals, and reliability of structural components and equipment, it is necessary that the failure analyst be aware of life assessment methodologies to address the questions and concerns of the industry he or she serves. Life assessment method advances and changes in technologies for structural components and equipment will require the investigator to adapt to the need of the industry. Furthermore, the failure investigator role has expanded from providing accurate identification of life-limiting failure mechanisms and degradation phenomena to also providing the time for degradation or damage, and crack growth rate to be used in life assessment estimates. Thus, the failure investigator's input is essential for meaningful life assessment of structural components. This article provides an overview of the structural design process, the failure analysis process, the failure investigator's role, and how failure analysis of structural components integrates into determination of remaining life, fitness-for-service, and other life assessment concerns. The topics discussed in this article include: · Industry perspectives on failure and life assessment of components · Structural design philosophies · Life-limiting factors · The role of the failure analyst in life assessment · The role of nondestructive inspection · Fatigue life assessment · Elevated-temperature life assessment · Fitness-for-service life assessment · Probabilistic and deterministic approaches Industry Perspectives on Failure and Life Assessment of Components As noted previously, life assessment of structural components is a means to avoid catastrophic failures and to maintain safe and reliable functioning of equipment. Catastrophic failures of structural components occur rather infrequently, but when they do, they take a heavy toll on human lives in addition to the cost of repairs, replacement power, and litigation costs. In 1982, the National Bureau of Standards commissioned a study to determine the direct and indirect cost of fracture in the United States. It was estimated that $120 billion are spent annually to cover direct costs and costs associated with fracture-related accidents (Ref 1). The estimates took into account the necessity of overdesigning to prevent failure, added inspections, repairs, and replacement of degraded materials. Needless to say, the costs and stakes for failure are high. In addition, the cost savings are great if failure can be mitigated or prevented. For the failure investigator, a failure is often defined as the rupture, fracture, or cracking of a structural member. The industrial definition of failure is often quite different from the textbook definition. A component, in practice, is deemed to have failed when it can no longer perform its intended function safely, reliably, and economically. Any one of these criteria can constitute failure. For example, a steam turbine blade whose tip has eroded affects turbine efficiency and hence affects the economics of operation adversely. The blade should therefore be replaced even though it can continue to operate. Component failures are thus defined in terms of “functional” rather than “structural” failures. Replacement of parts can be based on economic considerations, reliability, and material properties. In the discipline of life assessment, equipment and structures are evaluated