Corrosion Considerations

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. 

When using alloy pipe with greater tensile strength than carbon steel, the schedule numbers still apply, but may vary, because it is unnecessary to install thicker walled alloy pipe than is necessary for the strength and corrosion considerations. Schedules 10 and 20 are rather common for stainless steel pipe in low pressure applications. 

Noise generation and erosion/corrosion considerations limit the maximum water velocity in pipework systems. Noise is caused by the free air present in the water, sudden pressure drops (which, in turn, cause cavitation or the flashing of water into steam), turbulence or a combination of these. 

Corrosion can, however, be a factor in another type of assessment, which is arguably more important. It could influence important decisions about the whole project, taken at an early stage in the overall design process, which are concerned with the fundamental basis of the project rather than with corrosion aspects directly. In a major project, feasibility assessments in the initial stages are used to decide between possible alternatives, later effort being concentrated on one or two preferred options. If corrosion considerations are relevant they can influence the economics of the project as a whole, and have a much larger effect than in the first type of assessment. 

An example where reactant concentration is solely governed by corrosion considerations is in the production of concentrated nitric acid by dehydration of weak nitric acid with concentrated sulphuric acid. The ratio of HN0j H2S04 acid feeds is determined by the need to keep the waste sulphuric acid at > 70 Vo at which concentrations it can be transported in cast-iron pipes and stored after cooling in carbon-steel tanks. 

Various ceramic membranes, for example, possess differing degrees of acid/base resistance, depending on the pH value, particular phase of the membrane material, porosity, contact time and temperature. However, no quantitative data are available on the kinetics of chemical dissolution of ceramic membranes as a guide for chemical corrosion considerations. 

Important characteristics determining the quality of a feedstock are the C/H ratio as determined by elemental analysis and the BMC Index [4.7] (Bureau of Mines Correlation Index), which is calculated from the density and the mid-boiling point resp. the viscosity. Both values give some information on the aromaticity and therefore the expected yield. Further characteristics are viscosity, pourpoint, alkaline content (due to its influence on the carbon black structure), and sulfur content, which should be low because of environmental and corrosion considerations. 

Corrosion Considerations. Corrosion rates are dictated by the properties of the brine being used. Pilot-plant testing with an electrochemical corrosion rate probe indicated corrosion rates of less than 5 mils/year for emulsions flowing in pipes. The corrosion rate declined over time, presumably because of formation of an oil layer on the metal. In all pilot and fleld tests that we conducted, pipe walls have always shown a thin (approximately 0.001-in.) layer of crude oil on the wall after emulsion runs. 

The choice of cathode materials is less restricted by corrosion considerations than the choice of anodes so few metals react readily with the medium that their use is impractical. Some of the most popular electrode materials are mercury, lead, tin, copper, iron, aluminum, platinum, nickel, and carbon. 

Choose materials of construction based on corrosion considerations. Column diameters are determined by specifying linear velocities for the two phases. Column heights are determined by estimating the actual number of stages based on the theoretical stage requirements and average stage efficiency. Internals in pulse columns are very similar to those in distillation towers, especially for sieve trays. Therefore, distillation correlations can be used to estimate FOB purchased and installed costs for continuous differential contactors, if they are assumed to be pulse columns. 

Electrochemical Corrosion-Rate Measurement Methods and the Uniform-Corrosion Consideration... 

Absorption and stripping are usually conducted in packed columns or in trayed towers. Packed columns are preferred when (1) the required column diameter is less than 60 cm (2) the pressure drop must be low, as for a vacuum service (3) corrosion considerations favor the use of ceramic or polymeric materials and/or (4) low liquid holdup is desirable. Trayed towers are preferred when (1) the liquid/gas ratio is very low, and (2) frequent cleaning is required. If there is no overriding consideration, cost is the major factor to be taken into account when choosing between packed columns and trayed towers for absorption or stripping. 

In part I above, c. Wagner s theory of mixed conduction was reviewed in terms of an equivalent circuit approach. The implications of mixed conduction theory for parabolic scaling of metals in high temperature atmospheres were also detailed. It was pointed out, however, that current interest in mixed conduction theory is no longer motivated by corrosion considerations because far too few systems of practical interest conform to the conditions required for pareibolic oxidation. 

Corrosion considerations are critical in many applications. For instance, the chemical industry uses very aggressive environments for synthesis, and purity is usually extremely important. Therefore, the reactors and vessels must be essentially inert and resist the aggressive attack of the process environment. Corrosion resistant alloys have wide usage in this industry. Microelectronics is another area in which corrosion is important even though the environment is typically not very aggressive. In this case, the size of the structures is such that the smallest amount of corrosion could cause a failure, for example, a short in a submicron-sized conductor line. Other corrosive environments and industries in which corrosion is critical include oil and gas recovery and processing, marine and seawater applications, underground... 

CORROSION CONSIDERATIONS 11.3.1 Corrosion—Basic Concepts Revisited... 

Bologna, D. J. and Page, H. T., Corrosion Considerations in Design of Automotive Fuel Systems, Designing for Automotive Corrosion Prevention, SAE P-78, Warrendale, PA, 1978,... 

It is also expected that corrosion considerations wiU be more emphasized in the steam cycle design and material selection so that all materials of construction of the steam system will be compatible with the water treatment used. In design component integrity monitoring and failure analysis, the combination of the effects of corrosive environment, stress, flow velocity, and thermal conditions must be considered. 

If one is changing the product, check materials compatibility - one of the advantages of some PI unit operations is their flexibility, but normal corrosion considerations come into play if the nature of the throughput is changing. 

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