Useful life concepts

Corrosion likelihood describes the expected corrosion rates or the expected extent of corrosion effects over a planned useful life [14]. Accurate predictions of corrosion rates are not possible, due to the incomplete knowledge of the parameters of the system and, most of all, to the stochastic nature of local corrosion. Figure 4-3 gives schematic information on the different states of corrosion of extended objects (e.g., buried pipelines) according to the concepts in Ref. 15. The arrows represent the current densities of the anode and cathode partial reactions at a particular instant. It must be assumed that two narrowly separated arrows interchange with each other periodically in such a way that they exist at both fracture locations for the same amount of time. The result is a continuous corrosion attack along the surface. 

The life cycle cost of a process is the net total of all expenses incurred over the entire lifetime of a process. The choice of process chemistry can dramatically affect this life cycle cost. A quantitative life cycle cost cannot be estimated with sufficient accuracy to be of practical value. There is benefit, however, in making a qualitative estimate of the life cycle costs of competing chemistries. Implicit in any estimate of life cycle cost is the estimate of risk. One alternative may seem more attractive than another until the risks associated with product liability issues, environmental concerns, and process hazards are given due consideration. Value of life concepts and cost-benefit analyses (CCPS, 1995a, pp. 23-27 and Chapter 8) are useful in predicting and comparing the life cycle costs of alternatives. 

Our mission is to explore the molecular universe with an understanding of all of the local molecular environments and constrain possible chemical reactions using the concepts of physical chemistry. With such a wide brief we need a focus and I have chosen the origins of life on Earth and on all planets - astrobiology. 

In Chapter 3, it was noted that remarkably few biochemical pathways lead from Basic Integrated Metabolism into the pathways that serve to produce substances with Type 11 and Type 111 properties. Using the concepts discussed, it is possible to offer one evolutionary scenario to explain why a few, rather than many pathways flow from Basic Integrated Metabolism. As in the case of most evolutionary arguments, it is not difficult to produce a credible scenario but hard to find supporting evidence simply because the postulated events would have occurred early in the evolution of life and there are no known biochemical fossils . However, some computer modelling has at least provided some support for the approach adopted. 

Object-oriented systems use the concept of reusable entities that contain both the data and procedures relevant to the object, and thus eliminating the separation of knowledge and reasoning found in expert systems. In object-oriented systems computation is behavior simulation of real-life systems. Once certain classes of objects are created, they can be reused to create other objects and properties with interface and behavior. The self-contained character of objects is known as encapsulation. Inheritance allows derivation of new objects from existent ones, and encapsulation defines the limits of services an object can provide to other objects. An example of this system is provided by GENERA,31 and a schematic representation is given in Figure 5.2. 

How do engineers know how much of each reactant they need for a chemical reaction In this chapter, you will use the concept of the mole to calculate the amounts of reactants that are needed to produce given amounts of products. You will learn how to predict the amounts of products that will be produced in a chemical reaction. You will also learn how to apply this knowledge to any chemical reaction for which you know the balanced chemical equation. Finally, you will learn how calculated amounts deviate from the amounts in real-life situations. 

DOE 0 450.1, sec. 5.d.(6), CRD sec. 9 4.4.1.1 Based on the results of these assessments, contractors shall implement cost-effective P2 projects, using life-cycle assessment concepts and practices in determining their Retum-on-Investment (ROI). 

We support current legislative proposals to separate the capital recovery period from the traditional concept of permitting depreciation over the useful life of the asset. In order to Increase investment in new plant cuid equipment, it is necessary to permit a write-off more in keeping with replacement costs. 

The Control plug supports the 12 absorber drive mechanisms, sleeves which house thermocouples for measurement of outlet temperature of each fuel subassembly and three selector valves with sodium sampling from each fuel SA for failed fuel location. Use of bellows has been avoided for CSRDM to extend the life of the mechanisms and to enhance reactor availability, as bellows failure has been responsible for replacement of CRDMs in reactors using this concept. V-ring seals are used between the stationary sheath and mobile assembly of CSRDM. The core thermocouples are located at a fixed distance of 90 mm from the top of the SA during reactor operation and no Core Cover Plate Mechanism (CCPM) is provided as in FBTR. Thermohydraulic analysis indicates that the thermocouples are immersed in their respective streams at all power levels thereby ensuring adequacy of temperature measurement. 

Let us use the concept of a contradiction in discovering our next reason to learn inventive engineering. Imagine that you are in a hypothetical situation. As a student of engineering, ideally you would want to study as little as possible. Yet at the same time you also desire to make a lot of money after you graduate. We have here a clear contradiction. Usually a person s income in the engineering profession is proportional to the amount of knowledge acquired, not inversely proportional, as your dream would require. To succeed, you need to resolve this absolutely critical contradiction, which just may determine the course of your life. 

A product is at the end of its useful life when it no longer fulfils its technical function. But technical performance alone is not enough. To be useful, the product must continue to do its job in a cost-effective way. The criteria for cost effectiveness depend on the application and on the financial situation of the organization concerned, including its available investment capital and its perceptions of likely future return on capital. Such concepts are clearly outside our present terms of reference, but it is worthwhile to remind ourselves that cost effectiveness is inseparable from technical considerations, especially as energy saving features and low maintenance costs, rather than initial outlay, are so often mentioned as reasons for using reinforced plastics products. 

Farrar and Lieven (2006) define damage prognosis as the estimate of an engineered system s remaining useful life . They also introduce the concepts usage monitoring and structural health monitoring. 

The types of postpolymerization kinetic curves shown can be qualitatively explained using the conception of the three reactive zones proposed earlier. Up to the moment when the polymerizing system is in the liquid monomer-polymeric phase (MPPh), namely up to the moment of conversion = 0 5, only a weak post-effect is observed. MPPh is characterized by low concentration of free radicals with a short life time. A visible post-effect is observed in the autoacceleration stage Po > Py , that is, at the beginning of polymer-monomeric phase elimination and formation of the interface layer at the phase division boundary between MPPh and the polymer-monomeric phase PMPh, which are new reactive zones. In such reactive zones the translational and segmental mobilities of the macroradicals are sharply decreased and the life times are sharply increased. This explains the essential post-effect. 

Keeping things simple, we will basically use two financial mathematical equivalences and the concepts of net present value (sometimes called net present worth) and annual equivalent benefits (or annual equivalent cost) (Sect. 12.6) to do all calculations for real-Ufe problems and project evaluations. Although it represents a limitation (not using more concepts and equations), you will be amazed at the wide variety of real-life and engineering problems that can be solved with these few rather elementary tools. Thus, we continue to meet our objectives, which are to (a) teach just a few concepts and (b) captivate you with the diversity of problematic situations that arise in process and bioprocess engineering. 

Solve problems using the half-life concept. 

The bathtub curve is a longstanding concept and describes a graph of maintenance levels versus maintenance costs (see Fig. 7.1). These costs normally gradualfy decrease as equipment is bedded in, stay steady for the projected lifetime of equipment and then start to show a distinct climb again as equipment reaches the end of its useful life. 

With respect to some hidden costs in environmental cost accounting that often are not considered, it seems that tracing flow of material could avail more information. Jasch (2003) evaluated environmental costs by using the concept of product life cycle and MFCA. 

In the different LCA studies, the investigated fuel cell systems vary in their system boundaries. While some studies focus exclusively oti the stack itself, others also include the Balance-of-Plant into the investigations. Major impacts on the results can also be identified due to the variation of fuels used and the end-of-life concept considered in the analysis. 

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