Economic Factors Affecting Material Choice

The first requirement must be to specify carefully the operational requirements of the item to be produced and of the material(s) to be used in its construction. This is seldom easy and is usually the most difficult part of the selection process. The most common factors to be considered are  

Once such criteria have been established and a shortlist of possible materials drawn up, it will be important to consider  

In most instances there will be more than one material that will meet a technical specification, and choice will then be largely a matter of economics. Since parts 

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In general, the following items are considered vital in plant location proximity to market, raw materials, transportation, labor supply, water supply, power supply, economic interrelation with other industries, and specific plant requirements. There are other plant and process location matters that are of real importance to, and exist as real responsibilities of, the chemical plant design engineer of commercial plants for the manufacture of chemicals and chemical formulations, such as land, local ordinances, public improvements, utilities, waste disposal, and climatic conditions. All the factors that enter into the problem of plant or industry location also affect the choice of local sites and must be considered by the design engineer (see Chap. 7). 

The choice of the moderator material for a central-station powerplant is generally based on the economics involved. Obviously, many factors other than the cost per unit weight or volume, per se, enter into the economics. The neutron slowing-down capability of the material has an important effect on the size of the reactor core and, therefore, the capital cost of the plant, because of the investment in moderator, pressure vessel, shielding, etc. Containment requirements for the moderator (particularly liquid moderators) can affect both the capital cost of the plant and the fuel cycle economics, the latter because of possible neutron losses. Integrity and stability of the moderator material can, of course, have important implications on other aspects of the reactor design. The neutron absorption behavior of the moderator itself affects the potential conversion ratio of the reactor and, therefore, the fuel cycle economics of the reactor. The properties of the more important moderators and the implications of these properties on the choice and performance characteristics of gas-cooled reactors will be reviewed in this section. 

Whilst it may not always be possible to estimate the actual money cost of equipment, it is possible to make the relevant economic decision with the help of the relative costs for comparison. This applies especially to equipment for which the price quotations vary greatly and are influenced by many factors. Thus it is more meaningful to examine the ways in which the choice of materials may affect primarily the initial cost and then future expenses. 

The materials engineer has control over three factors that affect the cost of a product (1) component design, (2) the material(s) used, and (3) the manufacturing technique(s). These factors are interrelated, in that component design may affect which material is used, and both component design and the material used influence the choice of manufacturing technique(s). Economic considerations for each of these factors are now briefly discussed. 

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