Carbon steel corrosion material factors

Flow sheets of the chemical plant were prepared with a pre-design of the main equipment. For the capital cost assessment, the factored estimate has been chosen because it considers characteristics of the process corrosive products, high temperature (up to 850°C for Section II) and high pressure (up to 50 bar for the helium coolant). The factored method is essentially based upon charts and formulas developed over 30 years in the petroleum and chemical industries in France (Chauvel, 2000). It consists of estimating costs of basic equipment (generally carbon steel) and correcting them for materials factors. 

From the practical and economic point of view atmospheric corrosion is closely associated with centers of population. Three factors here coincide high pollution level, high density of population, which in turn means great use of materials. The rate of atmospheric corroion decreases sharply with increasing distance from the emission source. This may be illustrated by the corrosion of carbon steel as function of the distance from the stack of a polluting industry in Kvarntorp, see FIG.8 (26). 

On the basis of the risk factors and economics coated carbon steel with a supplemental corrosion inhibitor was preferred over the duplex stainless steel in spite of higher risk of the coated steel. The material selected for flow lines and trunk lines is shown in Table 4.43. 

The pressure factor for horizontal and vertical process (pressurized) vessels of diameter D meters and operating at a pressure of P barg is based on the ASME code for pressure vessel design [5]. At base material conditions using a maximum allowable stress for carbon steel, S, of 944 bar, a weld efficiency, E, of 0.9, a minimum allowable vessel thickness of 0.0063 m (1/4 inch), and a corrosion allowance, CA, of 0.00315 m (1/8 inch) gives the following expression ... 

CEPCI (Chemical Engineering Plant Cost Index), 186. 188 corrosive environments, 202-204 cost data, sources of, 182 equipment cost attribute, 182 equipment summary, PFD, 19-20 inflation adjustment, 186-187 manufacturing vessels, 207-208 Marshall and Swift Equipment Cost Index, 186. 188 MOCs (materials of construction), 202-208 module costing technique, 192-193 pressure factors, 197-202 relative costs of metals, 206 weld efficiency, 198 Capitalized cost, 314 Capitalized cost method, 314-316 Carbon steels, equipment cost, 205 Carnot efficiency, 235 Cascade diagrams... 

In a new chemical process, it is prudent to determine the factors that affect the corrosion and then run tests on various materials in order to select the most suitable one. Figure 4.1 shows an example of a heat exchanger used in city water service. The corroded tubesheet is made of carbon steel and the un-conoded tubes are made of copper. Another example shown in Fig. 4.2 is a titanium tubesheet after exhibiting crevice corrosion. 

Friction factor in long steel pipes handling wet (saturated with w ater vapor) gases such as hydrogen, carbon monoxide, carbon dioxide, nitrogen, oxygen and similar materials should be considered carefully, and often increased by a factor of 1.2 to 2.0 to account for corrosion. 

Compared with ferritic carbon and low-alloy steels, relatively little information is available in the literature concerning stainless steels or nickel-base alloys. From the preceding section concerning low-alloy steels in high temperature aqueous environments, where environmental effects depend critically on water chemistry and dissolution and repassivation kinetics when protective oxide films are ruptured, it can be anticipated that this factor would be of even more importance for more highly alloyed corrosion-resistant materials. 

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