The codes and standards that have implication for corrosion engineer are looked over. But most of Japanese standards are made for keeping qualities of materials at production and fabrication. To maintain aged equipments in chemical plants, post construction standards that provides the procedures of fitness for service are strongly required. And very limited qualified corrosion resistant data based on fully standardized test of various charges of materials is available. At the corrodion design and corrosion life control, more reliable and statistically analyzed data including long term trends is also needed. Only the contributions and efforts of corrosion engineers can construct practical engineering bases and standards of corrosion services in industry for themselves.
The maintenance and management of plant materials are very important to keep safe and steady operations in chemical process industry. In this paper, recent topics of the analytical techniques on problems related to corrosion of materials are reviewed, and part of the management activities of our company to protect the materials from chemical corrosion are introduced.
A new corrosion and protection database system, which stores a large amount of documents and informations about corrosion and protection, such as case histories, materials data, fabrication methods and repairing methods, has been developed. Users of the database system can be accessed using WWW browser via Intranet. This database can be operated by easy handling with only click and drug. The database system is expected to offer a wide knowledge for corrosion related engineers and to decrease corrosion troubles.
A questionnaire investigation about the present situation, current problems and countermeasure to be discussed with by material technology groups in the eight chemical companies was carried out. It has become clear from the analysis of answers obtained that the roll of material group has been changing under the diminishing construction of new plant and the increased needs of stable and sustainable plant operation. The present major subjects of material groups, which are pointed out in the answers, are such new technological problems as the plant life estimation, the dissemination and handing down of material technology and the upbringing of technology successors. The countermeasures to meet those requirements made clear are such technology developments as a new monitoring system, preparation of database on material technology and closer cooperation with related associations. It is hoped for that the findings of this study would lead to further and more detailed identification of common problems to be solved and development of practical countermeasures therefor.
This comprehensive paper, based on about 30 earlier papers and presentations of the present author and his associates, deals with case studies of localized corrosion of carbon steel. Included are localized corrosion in water and hot water pipes, steam return lines, electric resistance welded pipes, underground pipes, pipes in concrete and under dewcondensation protective coverings, and in many other systems. The rates of penetration observed in the case studies are reported and explained in terms of corrosion situations. The results of experiments to reproduce various types of localized corrosion in the laboratory are also shown. It is demonstrated that the theoretically possible highest penetration rate at areas of preferential attack is given by the potentiostatic anodic current density for the oxide-free surface by comparing the current density with the highest penetration rate observed in case studies. Some cases of unusual corrosion in terms of the penetration rate, form of attack, and mechanism are also reported.
Sulfidation behavior of a nickel-base superalloy, AISI 685, was investigated in N2-H2-H2S mixtures within a temperature range of 673 to 873K. Pure Ni and Cr, which are two main components of AISI 685, were also tested as references. Uniform internal sulfidation occurred on AISI 685 at a lower sulfur-partial-pressure than the dissolution pressure of Ni3S2 whether stressed or not. On the other hand, grain boundary sulfidation occurred on AISI 685 at a higher sulfur-partial-pressure than the dissolution pressure of Ni3S2 at 873K under a static stress. Whereas no grain boundary sulfidation was observed at or below 773K even under a stress of 588MPa. The grain boundary penetrations were brought by sulfidation of Ti, Mo, Al and Cr near the alloy grain boundaries. The time dependence of the grain boundary sulfidation length followed a parabolic rate law.
It is well known that the corrosion of steel occurs by sea salt particle near seashore environment. However, it is not understood that the shape of sea salt particle and whether sea salt particle is the liquid or solid status when it attaches the steel. The morphology of attachment of sea salt particle has a large influence on corrosion of steel. It is very important to understand the morphology and composition of sea salt particle. The morphology and composition of sea salt particle was studied by using an AFM and an optical microscope under relative humidity control conditions. As the result, it was found that the sea salt particle attached the specimen with circular figure and that the thin liquid film of MgCl2 with thickness of 10nm existed. Small sea salt particles with diameter of 50nm were found around the big sea salt particle.
Corrosion of carbon steel has been investigated for 200h in concentrated aqueous solution of mixed LiBr-LiNO3-KCl-LiOH salts at elevated temperatures as functions of temperature and concentration of LiNO3 and Li2MoO4O. The structure and composition of the surface films were analyzed by XRD, SEM and XPS. At 463K, addition of LiNO3 (>0.0125mol/kg) decreased the total amount of iron corroded (WT), amount of iron ions in the oxide (WF) and amount of Fe2+ ions dissolved into the water (WD) drastically, however pits were observed. At LiNO3=3.01mol/kg, WT and WF increased as temperature rises, whereas WD decreased as temperature rises. Pit was observed at LiNO3=3.01mol/kg between 363K and 463K. Below 403K, pit depth was less than 15μm, while above 433K the pit depth was more than 80μm. These corrosion behavior did not depend on the addition of Li2MoO4. Outermost parts of oxide films formed at LiNO3=3.01mol/kg, were composed of γ-Fe2O3 and the decrease in the LiNO3 concentration changed the composition from γ-Fe2O3 to Fe3O4. The role of surface film in the corrosion behavior was discussed in terms of its ion-selectivity and OH- ion stabilizing ability.
For long term durability evaluation of the reprocessing facility equipment made of zirconium, the fatigue crack propagation behavior of zirconium in heat affected zone (HAZ), weld metal (DEPO), and base metal (BASE) was investigated. Fatigue crack was propagated in room temperature atmosphere and in the boiling nitric acid solution. The crack propagation behavior of zirconium was evaluated by the measurement of crack propagation rate and the fracture surface analysis. The fatigue crack propagation was accelerated in the boiling nitric acid solution. Moreover the fracture surface caused in the boiling nitric acid solution was fluted one. It was guessed that acceleration factor of the fatigue crack propagation was the stress corrosion cracking (SCC). Crack sensitivity in the boiling nitric acid environment of welded joint (HAZ and DEPO) and BASE was almost the same.