Development of corrosion engineering of social infrastructures and buildings in the past half century has been reviewed in connection with the changes and resulting requirements of society. It was intended to pass down the historical background of the present technology to the new generation. Following a brief historical review, an account of ten important topics was given in more details. Included are the use of unpainted weathering steel, cathodic protection of buried pipelines in the early days, quality control of concrete to avoid corrosion of steel reinforcements, mitigation against delayed failure of high-strength bolts for structural bolting, development of groove-corrosion resistant welded water pipe, prevention of premature corrosion of buried utility piping, application of heavy-duty paint coating systems for long-span bridges over straits, various linings for splash-zone protection, instructive impact by a book “America in Ruins” authored by P. Choate and S. Walter, and use of rust-proof stainless steel and titanium for exterior of buildings for amenity.
Before the development of the accelerated corrosion testing method simulating the actual environment of electrical appliances, the actual corrosion of the surface treated steel sheets used in electrical appliances was investigated. The electrical appliances were collected from four domestic regions in Japan. In addition, the amount of deposited sea salt of the electrical appliances and the temperature and humidity of the environment for which the electrical appliance was used was measured. For the air conditioner outdoor units, the distance from the seashore and the host site influenced it for the corrosion rate. Moreover, the amount of deposited sea salt was confirmed as the main corrosion factor in the air conditioner outdoor units and the washing machines. On the other hand, the corrosion of the refrigerators was minor. The amount of deposited sea salt and the temperature and humidity of the environment were different by the kind of the electrical appliances. It is thought that the difference of the environment used influences the difference of the corrosion of the surface treated steel sheets of the electrical appliances. It is important for the development of the accelerated corrosion testing method simulating the actual environment of electrical appliances to control the amount of deposited sea salt widely and to evaluate the corrosion rate. Moreover, it is desirable that the temperature and humidity is changed keeping absolute humidity constant and that the time of wetness of the testing environment sets to 50% or less.
In order to reduce hazardous substances in electrical appliances, the chromate coating used in zinc-coated steel sheets is being changed to chromate-free coating. The objective of this study was to develop a new accelerated corrosion test method for zinc-coated steel sheets based on the actual environment of electrical appliances, for appropriately evaluating the corrosion resistance of zinc-coated steel sheets with the chromate-free coatings that will be used from now on. The conventional accelerated corrosion tests, which are the salt spray test (SST) and the combined cyclic corrosion test (JASO M609-91), have been widely used in evaluating the corrosion resistance of zinc-coated steel sheets for electrical appliances. However, these tests showed a low correlation with the actual corrosion behavior of electrical appliances from the perspective of corrosion morphology and the ranking of corrosion resistance. It is suggested that the conventional accelerated corrosion tests (SST, JASO M609-91) cannot be used for appropriately evaluating the corrosion resistance of zinc-coated steel sheets with the chromate-free coatings. Based on the actual corrosion behavior of electrical appliances and inadequacies of the conventional accelerated corrosion tests, a new accelerated corrosion test for electrical appliances, “ACTE” (ACTE: Accelerated Corrosion Test for Electrical appliances) was developed. A good correlation between ACTE and corrosion in actual environments was demonstrated. ACTE consists of a salt deposition process and cyclic wet/dry process. As distinctive features of ACTE, the test conditions simulate actual environments (use of artificial seawater, constant absolute humidity), and it is possible to estimate the corrosion life of materials in a wide range of use environments by obtaining dependency data on the main corrosion factors (amount of deposited sea salt, etc.) by varying the test conditions. ACTE makes it possible to appropriately evaluate the corrosion resistance of zinc-coated steel sheets with chromate-free coatings.
This paper discusses the mechanism of environmental assisted cracking (EAC) of an austenite/ferrite duplex stainless steel in a 35 mass % MgCl2 solution at 363 K by measuring both the acoustic emission (AE) and corrosion potential fluctuation (CPF). We utilized a new fracture toughness testing device and measured the growth characteristics of macroscopic crack. The duplex stainless steel was found to suffer delayed fracture through the ferritic grains in this solution rather the active path corrosion (APC) type SCC in austenitic grains. We detected no clear CPF but strong AEs during the test. AE sources were located at the zone 1-3 mm from of crack tip or at the zone with high hydrostatic pressure at which micro crack of delayed fracture took place. Source wave analysis of AE revealed the fast brittle micro fractures. Fractographic study supported the brittle fracture of ferritic phase by hydrogen and subsequent ductile fracture of the austenitic phase.