Selection of materials

Materials should meet the standards and requirements for their design and fabrication. The design lifetime of the materials should be determined considering the effects of operational conditions (e.g. radiological and chemical environment, single and periodic loads). In addition, effects of design basis accidents on their characteristics and performance shonld be considered. 

For materials whose adeqnacy is based on testing, all test results should be documented. 

Materials in contact with radioactive efQnents shonld have anticorrosion properties against relevant corrosion mechanisms and resistance to chemical reactions under operational conditions. Contact of carbon steel with radioactive products should be avoided as much as possible. Polymer materials should be radiation resistant if used for systems containing radioactive effluents. 

Control of halogen elements in materials (e.g. pipe insulation) in contact with stainless steel components should be ensured by design in order to avoid intergranular stress corrosion cracking (IGSCC). 

Particular attention should be given to compatibility of the materials used with regard to the water chemistry in order to prevent corrosion phenomena. For all equipment exposed to damp steam or to fluids which can cause severe erosion, corrosion and erosion resistant materials should be used. Low alloy steel containing chromium (Cr 0.5%) may be used. 

Materials should be selected to be suitable for the service conditions expected in all operational states and under design basis accident conditions. 

If the materials selected do not meet the specifications, they should be qualified by means of analysis, testing, the feedback and analysis of operating experience, or a combination of these. 

A layer (lamina or ply) of fiber reinforced composite is strong along the fiber direction, but considerably weaker in all off-fiber directions. Hence, in practice, it is necessary to use a number of layers oriented in different directions to withstand loadings from multiple angles. 

A lay-up notation is used to specify a laminate structure [zhota ip %c]ds where a, p, % are the angles of the UD fiber in relation to a reference axis the integers a, b, c indicate the number of layers, d is the number of times the bracketed construction is repeated and s, when present, indicates that the whole lay-up is symmetrical about a center plane. 

There are about 70,000 engineering materials available. Selecting the most suited material for a given application out of this large variety is a daunting task. Only a systematic selection method will help in this, and a number of such methods have been developed [1-11]. 

Many engineering plastics are selected on the basis of other properties (mouldability, stiffness, temperature performance, etc.) and the suitability for adhesive bonding is unlikely to be considered in the first instance. Polyetheretherketone (PEEK), for example, is a very good engineering plastic with some excellent properties but, for the adhesive engineer, this is one of the most difficult materials to bond and will 

Just as there is no universal plastic for every application, there is no universal adhesive and so the bonding process should be treated as an integral part of the entire design and assembly operation. 

Plastics and elastomers that have a low surface energy and are therefore more difficult to bond are listed below  

The bonding of these low-surface-energy plastics is discussed in more detail in Section 6.3. 

The beads are designed to be deformable to effect the seal and a rubbery material is thus required. 

The urethane systems used in this application are essentially casting systems. In these, prepolymers are reacted with low molecular weight glycols or diamines to give chain-extended copolymer with alternating rigid and flexible segments. 

The prepolymers are polyols (polyesters or polyethers) which have been reacted with isocyanate by the chemical manufacturer, to have isocyanate endings. In the final copolymer they comprise the flexible segments. 

The glycol or diamine extends the chain by linking together polyol segments, with urethane or urea linkage respectively. These links are the rigid segments of the final copolymer. 

By selection of appropriate polyols and chain extenders a wide range of properties is available for selection. 

---

A unique capability of induction heating is apparent in its abdity to heat the surface of a part to a high temperature whde the interior remains at room temperature. Proper selection of material, high frequency, and high power density can produce a thin surface hardness with a heat unaffected core (3). Figure 4 shows the cross section of a typical automotive shaft heated with 10 kH2 at various power densities. The required hardness depth is selected to... 

Design parameters as a function of temperature and design temperature limits are set forth in the ANSI/ASME B31 Piping Codes for a very broad range of materials. These codes, and the additional information available from manufacturers, vendors, and technical societies such as the National Association of Corrosion Engineers provide ample data for the selection of materials for piping systems (1—13). 

For a viable commercial process, the selection of materials and the choice of synthetic route is governed primarily by cost, not by overall yield. The selection of starting material is dictated usually by the desked C-3 substituent. For cephalosporins containing 3-acetoxymethyl or 3-(substituted)methyl such as 3-thiomethyl and 3-aminomethyl derived moieties, the most dkect synthetic route is from cephalosporin C, whereas pencillin V or G is the preferred starting material for the synthesis of the C-3 methyl cephalosporins. The three chemical transformations (2), (5), and 6) can potentially be carried out in a variety of ways, the precise sequence being determined by a balance of competing factors such as cost and optimization of yield (87). 

Fatty acids are corrosive at high temperatures and selection of materials of constmction for distillation systems is critical. Stainless steels with various contents of molybdenum have proved satisfactory. For example, 316 L has 2% Mo and is satisfactory for service up to 260°C 317 L has 3% Mo and can be used satisfactorily up to 285°C, whereas 904 L can be used up to 310°C (31). 

Bending. The smallest radius over which strip of a particular alloy can be formed without failing is important in the selection of materials for a given appHcation. The industry tests formabiHty using samples cut from strip material to rank materials and thereby indicate whether a particular alloy/temper is suited for an appHcation (15). Performance of the material in actual stamping is the best final judge of suitabiHty. 

S. H. Butt andj. M. PoppleweU, "Corrosion Considerations on the Selection of Materials ia Automotive Terminal Systems," S.A.E. Paper 700031, Automotive Engineering Congress, Detroit, Mich., Jan. 1970. 

The selection of materials of construction for rotaiy pumps is critical. The materials must be corrosion-resistant, compatible when one part is running against another, and capable of some abrasion resistance. 

The selection of material to resist deterioration in seivdce is outside the scope of the B31.3 code (see Sec. 23). Experience has, however, resulted in the following material considerations extracted from the code with the permission of the pubhsher, the American Society of Mechanical Engineers, NewY ork. 

In the selection of materials of construction for a particular fluid system, it is important first to take into consideration the characteristics... 

The selection of materials to be used in design dictates a basic understanding of the behavior of materials and the principles that govern such behavior. If proper design of suitable materials of construction is incorporated, the eqiiipment should deteriorate at a uniform and anticipated gradual rate, which will allow scheduled maintenance or replacement at regular inteivals. If localized forms of corrosion are characteristic of the combination of materials and environment, the materials engineer should still be able to predict the probable life of equipment, or devise an appropriate inspection schedule to preclude unexpected failures. The concepts of predictive, or at least preventive, maintenance are minimum requirements to proper materials selection. This approach to maintenance is certainly intended to minimize the possibility of unscheduled production shutdowns because of corrosion failures, with their attendant possible financial losses, hazard to personnel and equipment, and resultant environmental pollution. 

External corrosion Implement mechanical integrity program of high-energy, Implement proper selection of material of equipment. Loss construction of containment and damage due to flying debris. CCPS G-23 CCPS G-29 CCPS G-39... 

In this chapter we illustrate, using a variety of examples, how the designer selects materials so that they provide him or her with the properties needed. As a first example, consider the selection of materials for a... 

Selection of materials of construction compatible with the chemical(s) in use, properly cleaned and passivated... 

Several materials react with pure oxygen so care in selection of materials in contact with oxygen including cleaning agents is crucial. 

Because any material may be characterized by some desirable and nondesirable properties with respect to a specific application, the selection of materials is reduced to a reasonable compromise. In so doing, one strives to select materials so that properties correspond to the basic demands determined by the function and operating conditions of the equipment, tolerating some of the undesirable properties. 

---