Cash flows are important in engineering economy since they form the basis for evaluating alternatives. The Present Worth (PW) method is popular because all future cash flows are converted into present dollars and makes it easy to determine the economic advantage of one alternative over another. The PW is determined by using the equation PW = FW(1+r)−N, where PW : present worth, FW : future worth, r : discount rate, N : compounding period. The factor (1+r)−N is known as the present worth factor. If discount rates remain constant at r% for the PW, FW, AW, all three values are equivalent. Hence, the AW and FW values can be easily computed for a project from the equivalent PW value. In this report, the relationship between the PW factors and time for different rates, the examples of equivalence calculation of the FW and AW values from the PW value, and the examples of the application of the PW method to port structures are shown.
Recently, a pulverized coal firing boiler is getting large capability; therefore, it should take a further effective environmental measure. As a facility aspect, it takes a measure to inhibit the amount of generation of NOx and, in operation aspect; it is operated by low O2 combustion. As a result, in the combustion chamber, it becomes to low O2 atmosphere because of lack of oxygen and also the sulfide corrosion becomes actualized because of H2S. In addition to that, it is recognized that it accelerates damages by multiple influences from erosion damage by steam blast from the wall blower to remove slag. The damage behavior around wall blower in the investigated boiler is as follows. (1) Steam erosion by direct collision of high temperature and high pressure steam. (2) The coal ash that was caught in the current of steam injection and collided on the tube surface causes the ash erosion. (3) The steam that is lower temperature than the tube temperature collides onto the tube surface which is exposed by high temperature combustion gas and that causes the thermal collision. The synergistic result of those 3 physical collisions causes a crack and delamination in the scale. Moreover, because of the above results, when the nascent metal aspect is exposed it is directly contacted with combustion gas. And that prompts the high temperature corrosion response and it is accumulated. For that result, it was concluded that the damage has been accelerated.
It is well known that nitric acid and nitric acid+chromate solution have been applied effectively for surface treatment or passivation treatment of stainless steels. However, recent regulation of waste water quality demands that nitrogen from nitric acid and Cr(VI) ion from chromic oxide have to be removed in the waste water. This study aims to develop alternate effective surface treatment method for passivation treatment of stainless steel. H2O2 and O3 might be candidate chemicals, because they decompose to oxygen and water after reaction which are non toxic to the environment. Effect of concentration of H2O2 and O3 and temperature on the treatment potential was examined. After the treatment, pitting potential was measured to evaluate corrosion resistance of passivated stainless steels. Passivation treatment condition using H2O2+O3 solution to increase pitting potential of SUS 304 and SUS 430 stainless steel was found.
In order to characterize the corrosion products near the shear cut edge of the 55 mass% Al-Zn alloy coated steel sheet, galvanized steel sheets with scratch exposing substrate steel and galvanic couple electrodes composed of steel and Al-Zn alloy were subjected to atmospheric corrosion test using artificial seawater simulating the marine atmospheric environment. The corrosion products formed on Al-Zn coating, exposed steel and the coating near the exposed steel were analyzed by EDS, XRD and FT-IR. NaZn4(SO4)(OH)6Cl·6H2O, CaCO3 and Mg(OH)2 were identified on the exposed steel. Precipitation of these corrosion products was rationalized by thermodynamic analysis considering solubility products. Furthermore, it was concluded that the corrosion products exhibit a high electrical resistance to depress electrochemical reactions and also act as a barrier for oxygen diffusion, resulting in suppressed corrosion rate.