The total length of expressways in Japan has reached to approximately 9,200 km at the present moment. About 40% of the total length has been in service for more than 30 years. The structures on the expressways are exposed under severe environments such as increase in vehicle weight and the number of large vehicles and the scatter of anti-freezing agent (NaCl). As a result, the structures have been seriously deteriorated. This report explains the various efforts in West Nippon Expressway Company Limited towards the long-term bridges maintenance to permanently maintain expressways in a good condition.
The purpose of this study is to improve the life of sensors used to monitor the internal temperature of a coal gasification furnace, which has a strong reducing atmosphere. This paper reports the results of a comparison study of corrosion between protection tubes made from chromium, known for corrosion resistance, and iridium, commonly used in this application. It was confirmed during this study that the pure chromium tube had a life at least 2.5 times longer than that of a pure iridium tube.
The aim of this study is to investigate the effect of different types of an organic acid on morphology of copper corrosion. We conducted immersion and exposure tests of copper tubes using three types of an organic carboxylic acid; formic, acetic and propionic acid. Randomly-branched pores developed after immersion tests in the formic and acetic acid solutions. A layered corrosion occurred after the immersion test in 1000 ppm propionic acid solution. Ant nest corrosion was detected on the copper tube under the formic acid atmosphere, whereas a hemispherical pit was detected under the acetic acid atmosphere. A layered corrosion developed under the propionic acid atmosphere. SEM inspection and EPMA analysis revealed that constituents of the hemispherical pit developed under the acetic acid atmosphere were metallic copper with sponge-like pores and cuprous oxide infilled the pores.
In addition to salt deposition methods prescribed in ISO 16539:2013, we have developed a simple salt deposition method for multiple specimens. This method also includes the possibility to suppress the variations of the amount of salt deposition. Not only the salt deposition characteristic, but also the influence on corrosion was examined experimentally. The newly developed method provided salt deposition that was approximately equivalent level of the quantity prescribed ISO 16539:2013. The results of corrosion test with this new salt deposition method showed good agreement with those of other salt deposition methods prescribed in ISO.
The galvanized anode system, which is often used for the cathodic protection of aluminum panels, was applied to reinforced concrete specimens of variable chloride concentration. The primary objectives of this study are the specification of the variation factor on a polarizing current and the evaluation of the steel’s corrosion rate for the natural (open-circuit) corrosion and cathodic protection conditions. As a result, the polarizing current decreased as the cathodic polarization resistance and concrete resistance increased. Despite the variable chloride concentration in concrete, the corrosion rate of the natural corrosion condition was reduced compared with that of the early period. The corrosion rate of steel under cathodic protection was assumed to be equivalent to the passive current density.
The mechanism of corrosion inhibition of Mannich-modified phenolic resin coating which is one of the alternatives to chromate conversion coating on the electrogalvanized steel sheet was investigated by cross-section analysis and electrochemical measurements of the coating film. The 200ºC cured coating film which has good corrosion inhibition has the higher charge transfer resistance (Rct) and the higher film resistance (Rf) calculated by electrochemical impedance measurement than the 80 ºC cured coating film. The increase of these resistances is due to decrease of water absorption property of the film caused by crosslinking reaction. Namely the film resistance is enhanced by reduction of ionic conductivity of the film, and the charge transfer resistance is enhanced by reduction of the supply of the water containing dissolved oxygen to interface between the film and substrate. The phosphoric acid added to coating solution forms an insoluble zinc phosphate coating layer at the coating / material interface. The zinc phosphate coating layer, which is formed in close contact with the complex surface shape of the substrate by chemical interaction with the substrate surface by chemical interaction with the material surface, enhances the barrier effect to obstruct the contact of substrate with the water containing dissolved oxygen. Consequently the corrosion inhibition of the coating film is excellent. On the other hand, the 80ºC cured coating film without phosphoric acid, which has no chemical interaction with the substrate, has some voids (defects) at film /substrate interface and its corrosion inhibition is inferior.