to determine if they are suitable, reliable, and economical for continual service. If deemed unreliable, the equipment or structure may be repaired, refurbished, or replaced any component the failure criteria need to be defined and established. Failure does not always involve acture or rupture. Progressive damage of structure and components under operating conditions leads to exhaustion of life, thus leading to failure. Damage may be defined as a"progressive and cumulative change acting to degrade the structural performance of the load-bearing component or components which make up the plant"(Ref 2). Life may be defined as the"period during which a component can perform its intended function safely, reliably, and economically"(Ref 3). With some modifications, the definitions used by Viswanathan and Dooley for fossil-fuel power steam plant components(Ref 3)can be used to define failure and life of components; that is, component life is expended when Design life has elapsed Calculations predict life exhaustion Service time has reached some arbitrarily chosen fraction of calculated or experimental failure life Previous failure statistics indicate high probability of failure Frequency of repair renders continued operation uneconomical Nondestructive inspection reveals cracking Surface degradation from corrosion, including coating degradation, is excessive Grain-boundary attack and/or pitting by oxidation/hot corrosion, is excessive Foreign object damage Destructive sampling and testing indicate life exhaustion Excessive deformation has occurred due to creep, causing distortion and unfavorable changes in Sudden and complete fracture occurs References cited in this section 1. J.J. Duga et al, The Economic Effects of fracture in the United States, Report to the National Bureau of Standards. Battelle Columbus Laboratories. March 1983 2. L.F. Coffin, Damage Evaluation and Life Prediction for High-Temperature Gas Turbine Materials 2382-3, Electric Power Research Institute, April 1986,p 1. 1-1/e Moterials,EPRI AP-4477,Project Proc. Conf on Life Prediction for High Temperature Gas Turbin 3. R. Viswanathan andR. B Dooley, Creep Life Assessment Techniques for Fossil Power Plant Boiler Pressure Parts, Proc. Conf on Life Prediction for High Temperature Gas Turbine Materials, EPRI AP 4477, Project 2382-3, Electric Power Research Institute, April 1986, p 2. 1-2.28 Structural Design Philosophies Historic Failures. It is often stated that history repeats itself. Yet, when it comes to structural components and equipment, structural designers, original equipment manufacturers (OEMs), and users do not want a repeat of history. The consequences and costs of fractured, cracked, corroded, and malfunctioned equipment are unwanted. Through the years, history has demonstrated that failures occur; history has also shown that the engineering communities have responded to prevent failure from occurring again. Table 1(Ref 4, 5, 6,7,8,9,10, 11, 12, 13, 14, 15)identifies some of the historic structural failures that have occurred in the 20th century. These historic failures as well as other failures have revolutionized design philosophies, inspection techniques and practices, material development, and material processing and controls and have redefined the criteria for failure. Furthermore, the pursuit of understanding how and why these ailures occurred have resulted in the development of structural-integrity programs, enhanced analytical modeling and prediction techniques, accurate life assessment methods, and a fortified commitment to avoid the recurrence of these failures through improved designs. The examples cited in Table I were serious and often tragic failures that had a great impact on structural designs and life assessment developments. However, not all failures or malfunctions of equipment is as pivotal in history as those mentioned in Table 1. Yet, it is emphasized that any failure, no matter how seemingly asignificant, should be investigated and the findings used to improve the design and increase the life and reliability of at component or equipment Thefileisdownloadedfromwww.bzfxw.comto determine if they are suitable, reliable, and economical for continual service. If deemed unreliable, the equipment or structure may be repaired, refurbished, or replaced. In any component the failure criteria need to be defined and established. Failure does not always involve fracture or rupture. Progressive damage of structure and components under operating conditions leads to exhaustion of life, thus leading to failure. Damage may be defined as a “progressive and cumulative change acting to degrade the structural performance of the load-bearing component or components which make up the plant” (Ref 2). Life may be defined as the “period during which a component can perform its intended function safely, reliably, and economically” (Ref 3). With some modifications, the definitions used by Viswanathan and Dooley for fossil-fuel power steam plant components (Ref 3) can be used to define failure and life of components; that is, component life is expended when: · Design life has elapsed. · Calculations predict life exhaustion. · Service time has reached some arbitrarily chosen fraction of calculated or experimental failure life. · Previous failure statistics indicate high probability of failure. · Frequency of repair renders continued operation uneconomical. · Nondestructive inspection reveals cracking. · Surface degradation from corrosion, including coating degradation, is excessive. · Grain-boundary attack and/or pitting by oxidation/hot corrosion, is excessive. · Foreign object damage is severe. · Destructive sampling and testing indicate life exhaustion. · Excessive deformation has occurred due to creep, causing distortion and unfavorable changes in clearances. · Sudden and complete fracture occurs. References cited in this section 1. J.J. Duga et al., The Economic Effects of Fracture in the United States, Report to the National Bureau of Standards, Battelle Columbus Laboratories, March 1983 2. L.F. Coffin, Damage Evaluation and Life Prediction for High-Temperature Gas Turbine Materials, Proc. Conf. on Life Prediction for High Temperature Gas Turbine Materials, EPRI AP-4477, Project 2382-3, Electric Power Research Institute, April 1986, p 1.1–1.17 3. R. Viswanathan and R.B. Dooley, Creep Life Assessment Techniques for Fossil Power Plant Boiler Pressure Parts, Proc. Conf. on Life Prediction for High Temperature Gas Turbine Materials, EPRI AP- 4477, Project 2382-3, Electric Power Research Institute, April 1986, p 2.1–2.28 Structural Design Philosophies Historic Failures. It is often stated that history repeats itself. Yet, when it comes to structural components and equipment, structural designers, original equipment manufacturers (OEMs), and users do not want a repeat of history. The consequences and costs of fractured, cracked, corroded, and malfunctioned equipment are unwanted. Through the years, history has demonstrated that failures occur; history has also shown that the engineering communities have responded to prevent failure from occurring again. Table 1 (Ref 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15) identifies some of the historic structural failures that have occurred in the 20th century. These historic failures as well as other failures have revolutionized design philosophies, inspection techniques and practices, material development, and material processing and controls and have redefined the criteria for failure. Furthermore, the pursuit of understanding how and why these failures occurred have resulted in the development of structural-integrity programs, enhanced analytical modeling and prediction techniques, accurate life assessment methods, and a fortified commitment to avoid the recurrence of these failures through improved designs. The examples cited in Table 1 were serious and often tragic failures that had a great impact on structural designs and life assessment developments. However, not all failures or malfunctions of equipment is as pivotal in history as those mentioned in Table 1. Yet, it is emphasized that any failure, no matter how seemingly insignificant, should be investigated and the findings used to improve the design and increase the life and reliability of that component or equipment. The file is downloaded from www.bzfxw.com