Corrosion effects, modeling

VFO works well in gas turbines. In a nine-month test program, the combustion properties of VFO were studied in a combustion test module. A gas turbine was also operated on VFO. The tests were conducted to study the combustion characteristics of VFO, the erosive and corrosive effects of VFO, and the operation of a gas turbine on VFO. The combustion tests were conducted on a combustion test module built from a GE Frame 5 combustion can and liner. The gas turbine tests were conducted on a Ford model 707 industrial gas turbine. Both the combustion module and gas turbine were used in the erosion and corrosion evaluation. The combustion tests showed the VFO to match natural gas in flame patterns, temperature profile, and flame color. The operation of the gas turbine revealed that the gas turbine not only operated well on VFO, but its performance was improved. The turbine inlet temperature was lower at a given output with VFO than with either natural gas or diesel fuel. This phenomenon is due to the increase in exhaust mass flow provided by the addition of steam in the diesel for the vaporization process. Following the tests, a thorough inspection was made of materials in the combustion module and on the gas turbine, which came into contact with the vaporized fuel or with the combustion gas. The inspection revealed no harmful effects on any of the components due to the use of VFO. 

In cases where dynamic effects must be considered, the problem is typified by A and b matrices that are parametrized, say, by time or other quantities. One such example involves modeling corrosion effects where time, acidity, and material thickness and age might be relevant dynamical parameters. In most cases one calculates a sequence of static solutions at time steps t that are then pieced together to fit initial (and final) conditions. 

Other methods include use of intelligent pigging as well as corrosion prediction models developed by C. De Waard and some other modifications that have been published and commercialized by several other investigators. However, after prediction and/or detection of corrosion incidents inside the pipelines, the most cost-effective method of control is the use of corrosion inhibitors. These are usually amine based and are thus water dispersible. They are usually blended with vapour phase inhibitors and probably some flow enhancers. 

Although there is little evidence for auto-catalysis in dechlorination by Fe , it is still possible that localized corrosion contributes to the remediation of contaminants in environmental applications. Various investigators have postulated that localized corrosion contributes through increased surface area (44) and creation of corrosion cell domains (49-51). The corrosion cell model works on the same principle as the electrochemical model described above (Figure 3), but invokes additional effects such as the reduction of protons as the major cathodic reaction, and the creation of an electrical double layer between the anode and cathode that permits transport due to electrical migration as well as diffusion. Although many aspects of these models are plausible, there are not yet any data that specifically support them, and a study that systematically addresses the role of localized corrosion in remediation applications of Fe remains to be done. 

The first barrier to sea water ingress is the bitumen which covers the whole SGI. This bitumen is assumed to degrade linearly in 100 years from full to zero effectiveness, modelled by the bitumen factor k(, = O.Olt (t 100 years). The fuel, and hence the fission products and actinides, is surrounded above and below by at least 300 mm of solidified Pb-Bi coolant, and multiple layers of SS. Using the most pessimistic estimates of corrosion rates and thicknesses, the minimum time for water ingress to the fuel via corrosion directly from above or below is over 40 000 years. This timescale is much longer than that of ingress through the EPR tubes and ECTs hence, this method will be assumed to be the primary means of release and is studied in more detail below. 

Effective modeling of complex electrochemical processes of corrosion in the systems based on iron required the use of a more complex equivalent electrical circuit, i.e., circuit containing CPE - constant phase elements. Constant phase element (CPE) is characterized by a constant angle of phase shift. Impedance of the CPE is described by the following expression Zcpe = l/Yo(jffl)", where Yo and n are parameters related to the phase angle. The more heterogeneous the corrosion processes occurring on the metal surface the smaller value of the parameter n. 

First is the blunt crack school by whom the laws of stress concentration at the tips of rounded cracks are believed to apply. As a result, great attention is focused on the blunt tip radius. This model is easily used in the interpretation of increased strength on aging because corrosion effects are seen to increase the tip radius and so decrease the stress concentration. 

Corrosion is an irreversible surface modification of a material due to chemical reaction with the environment that results in the formation of metal ions dissolved in the liquid (material loss) and, in the case of passive metals, of surface oxide films. A preliminary attempt to include particle flow in tribocorrosion was already proposed by Stemp [11] and Mischler et al [9] to explain the discrepancy mentioned above between first body degradation and mechanical wear. This paper is aimed at developing a phenomenological model of tribocorrosion by combining electrochemical corrosion effects with the third body concept of wear. The approach is applied to three electrochemically controlled wear situations, i.e. wear under cathodic protection (absence of corrosion), wear in presence of passive films and wear combined with metal dissolution. The proposed concepts are compared to already published results concerning carbon steel and stainless steels and their merits are discussed. 

Adsorption and Film Formation. Inhibition of HC1 corrosion by organic compounds is a complicated multi-step process. Nevertheless, the effect of an inhibitor on corrosion of a metal is often treated mathematically with an equilibrium adsorption model for displacement of water (19,20) ... 

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