Steel Selection Criteria

The selection of appropriate steel grades is made aiming for the lowest cost while satisfying all necessary design conditions such as 

In addition to the purely technical considerations of the steel selection, also regulatory compliance must be observed. The requirements depend on the national laws of the country where the high-pressure components are to be used. Only approved steels within the limitations of the pressure vessel code (or piping code) may be used [3, 4]. 

Steel type (typical grades) Yield strength at 20 °C (MPa) Steel type (typical grades) Yield strength at20°C (MPa)  

Austenitic stainless (1.4429, 316LN) 300 Fine-grain and high-temperature structural steel (1.6368) 450 Weldable 

Austenitic-ferritic duplex (1.4462) 450 Cr-Mo H2-resistant steel (1.7779) 500 Weldable 

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That is, ttcr is directly proportional to K c/cry) since oh is a fraction of Oy. Thus, the larger the value of acr, the more attractive is the material, since cracks can be easily detected without the use of sophisticated equipment. The Ashby plot of fracture toughness versus density (Figure 8.10) indicates that of the three classes of materials selected with Criterion 1, only the engineering composites and engineering alloys provide suitable possibilities for Criterion 2. Again, of the alloys, titanium, steel, nickel, and copper alloys are the best here. 

The real power of the Ashby diagrams comes when we realize that we can combine Figures 8.9 and 8.10 to yield one, more useful diagram (Figure 8.11), namely a plot of fracture toughness versus strength. This plot shows unequivocally that the steel, nickel, and titanium alloys are the best classes of materials to select for this application. We will use Criterion 3 to narrow this field even further. 

Though there are many possibilities of the engineering alloys, let us consider three common alloys from different classes a steel, an aluminum alloy, and a titaninm alloy. The three alloys and their appropriate design properties are listed in Table 8.3. The values that are the most favorable in each category are listed in bold typeface. On the basis of Criterion 1, the best material is maraging steel, but from the viewpoints of Criteria 2 and 3 the titanium alloy is obviously superior. Cost is an additional factor that could influence the final selection. 

Structure-to-electrolyte potential measurements are analyzed to determine whether a structure is cathodically protected these measurements are made by the use of cathodic protection criteria. Unfortunately, no one simple criterion has been accepted by all cathodic protection engineers that can be practicably measured in the field under all circumstances. Guidelines for selecting the proper criterion under various circumstances will be provided below. Guidance concerning the criteria of cathodic protection for external corrosion control on underground structures is found in two recommended practices (RPs) published by the National Association of Corrosion Engineers (NACE). These are RP-01-69 and RP-02-85. A summary of the criteria for steel and cast iron structures follows [8]. 

A high temperature Pd/Stainless Steel H2 separation membrane manufactured by CRI-Criterion by deposition of Pd on sintered porous metal support with permeable dimensions of 1 inch OD and 6 inches length is shown in Figure 11.7. An SEM cross section of the top layers of the membranes showing the porous stainless support, the inter-metal diffusion barrier, and the selective Pd layer. Note that the picture lack pinholes in Figure 11.8. 

For FE simulations of experimental joints with UHM-CFRP, failure can be either adhesive-related (i.e. as in the previous point) or fibre-related (i.e. pure UHM-CF rupture at the central gap between both steel plates, as in Fig. 10.5(e)) therefore both cases should be assessed to find out the critical one (i.e. the case that satisfies its failure criterion at a smaller time increment). For the pure UHM-CF rupture, the FE maximum principal stress of the fibres is plotted with time increments for a selected integration point within the vicinity of the central gap and since the fibre material is modelled as brittle elastic, its assumed mpture (i.e. failure) onset is predicted at the time increment when the fibre s experimental tensile strength is slightly exceeded in the aforementioned curve. The above method for ultimate stress, joint capacity and failure pattern predictions has been successfully validated in Al-Shawaf (2010). 

Although it is a matter of common knowledge that stainless steel is quite prone to corrosion in fuel cells, bare substrates of different alloys were tested in past material investigations. In 1998, Hornung and Kappelt (1998) selected different iron-based materials for Solid Polymer Fuel Cell bipolar plates by using the pitting resistance equivalent (PRE = %Cr + 3.3%Mo + 30%N) as corrosion resistance criterion. The authors exposed that some iron-based materials with PRE >25 (the material compositions are not given... 

The dimensions of plain steel pipes, their pressure ratings, and relative roughness are presented in Table 2-2. It is obvious that steel pipes are limited in pressure rating to 3000 psi. This criterion is essential when considering location of booster pump stations or chokes. In the case of slurry pipelines, the thickness of the pipes is selected on the basis of... 

Cost puts a constraint on material selection. In simple cases, the cost per unit property can be used as a criterion for selecting the optimum material. Because of the changing cost of materials in the market, inflation, supply and scarcity, the cost of materials is measured as a relative cost (Cr) where the cost of material is normalized to the cost of mild steel. 

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