necessary, then, to pay more attention to predicting and ensuring performance Predicting and ensuring performance is fundamentally a part of the design process for buildings, power plants, aircraft, refineries, and ships( Ref 16) For any given design, the mission and the intended use are established Predicting the performance and design life of a component depends on defining what life or performance is required for a given duration while the component operates generally in combinations of mechanical and chemical environments. Defining performance may involve defining end points such as: acceptable length of propagating cracks, maximum depth of propagating pits, acceptable remaining thickness of corroding pipes, maximum number of fatigue cycles or extent of cumulative damage, maximum number of plugged tubes, maximum number of failed circuits, maximum leakage, or appearance of a maximum area or number of rust spots. Defining such end points is a critical part of predicting life since prediction defines when these end points will be reached and therefore when"failure occurs Defining failure is also related to what is meant by the"design life. For example, for the aerospace industry, an airplane may be designed for 8000 flight hours and analyzed for two lifetimes or 16,000 flight hours. For the power industry, the design life of components is sometimes taken as 40 years. This means that the equipment is expected to perform satisfactorily at its rated output for 40 years. This is not to say that some maintenance is not necessary. However, to assert to a customer that a component has a 40 year design life it is necessary to develop bases for such a claim. Such bases are usually provided by analyses and by accelerated testing in the laboratory and with prototype and model testing As part of the life assessment process, it is important to understand how a structural component-whether a pressure vessel, shaft, or structural member-is designed in order to understand how it may fail and to perform meaningful life assessment. For example, the first step in the design of any pressure vessel is to select the proper design code based on its intended use. For example, a pressure vessel may be a power or heating boiler, a nuclear reactor chamber, a chemical process chamber, a hydrostatic test chamber used to test underwater equipment, or a pressure vessel for human occupancy. Once the intended use is identified, the appropriate design code can be selected. For example, pressure vessels use codes provided by many organizations and certifying agencies, such as the American Society of Mechanical Engineers(ASME), the American Bureau of Shipping(ABS), and European agencies have pressure vessel design codes Strict adherence to these codes for the design, fabrication, testing, and quality control and assurance allows the finished pressure vessel to be certified by the appropriate authorizing agency( ref 17) One of the first incentives to develop a pressure vessel code occurred after the Boston Molasses tank incident in 1919 when the tank failed by overstress, consequently releasing more than 2 million gallons of molasses and resulting in the loss of life and property(Ref 5 ). Even after that catastrophic failure and understanding the nature of the failure, another molasses tank failure occurred in New Jersey in 1973. Figure 2 shows the destruction caused by the molasses tank incident. These molasses tank incidences demonstrate how important it is to prevent failures, and it underscores that good designs consider the operating conditions and limitations of materials of construction Thefileisdownloadedfromwww.bzfxw.comnecessary, then, to pay more attention to predicting and ensuring performance. Predicting and ensuring performance is fundamentally a part of the design process for buildings, power plants, aircraft, refineries, and ships (Ref 16). For any given design, the mission and the intended use are established. Predicting the performance and design life of a component depends on defining what life or performance is required for a given duration while the component operates generally in combinations of mechanical and chemical environments. Defining performance may involve defining end points such as: acceptable length of propagating cracks, maximum depth of propagating pits, acceptable remaining thickness of corroding pipes, maximum number of fatigue cycles or extent of cumulative damage, maximum number of plugged tubes, maximum number of failed circuits, maximum leakage, or appearance of a maximum area or number of rust spots. Defining such end points is a critical part of predicting life since prediction defines when these end points will be reached and therefore when “failure” occurs. Defining failure is also related to what is meant by the “design life.” For example, for the aerospace industry, an airplane may be designed for 8000 flight hours and analyzed for two lifetimes or 16,000 flight hours. For the power industry, the design life of components is sometimes taken as 40 years. This means that the equipment is expected to perform satisfactorily at its rated output for 40 years. This is not to say that some maintenance is not necessary. However, to assert to a customer that a component has a 40 year design life, it is necessary to develop bases for such a claim. Such bases are usually provided by analyses and by accelerated testing in the laboratory and with prototype and model testing. As part of the life assessment process, it is important to understand how a structural component—whether a pressure vessel, shaft, or structural member—is designed in order to understand how it may fail and to perform meaningful life assessment. For example, the first step in the design of any pressure vessel is to select the proper design code based on its intended use. For example, a pressure vessel may be a power or heating boiler, a nuclear reactor chamber, a chemical process chamber, a hydrostatic test chamber used to test underwater equipment, or a pressure vessel for human occupancy. Once the intended use is identified, the appropriate design code can be selected. For example, pressure vessels use codes provided by many organizations and certifying agencies, such as the American Society of Mechanical Engineers (ASME), the American Bureau of Shipping (ABS), and European agencies have pressure vessel design codes. Strict adherence to these codes for the design, fabrication, testing, and quality control and assurance allows the finished pressure vessel to be certified by the appropriate authorizing agency (Ref 17). One of the first incentives to develop a pressure vessel code occurred after the Boston Molasses tank incident in 1919 when the tank failed by overstress, consequently releasing more than 2 million gallons of molasses and resulting in the loss of life and property (Ref 5). Even after that catastrophic failure and understanding the nature of the failure, another molasses tank failure occurred in New Jersey in 1973. Figure 2 shows the destruction caused by the molasses tank incident. These molasses tank incidences demonstrate how important it is to prevent failures, and it underscores that good designs consider the operating conditions and limitations of materials of construction. The file is downloaded from www.bzfxw.com