Yasuyoshi Tomoe

Corrosion of iron by iodide-oxidizing bacteria isolated from brine in an iodine production facility.

Elemental iodine is produced in Japan from underground brine (fossil salt water). Carbon steel pipes in an iodine production facility at Chiba, Japan, for brine conveyance were found to corrode more rapidly than those in other facilities. The corroding activity of iodide-containing brine from the facility was examined by immersing carbon steel coupons in “native” and “filter-sterilized” brine samples. The dissolution of iron from the coupons immersed in native brine was threefold to fourfold higher than that in the filter-sterilized brine. Denaturing gradient gel electrophoresis analyses revealed that iodide-oxidizing bacteria (IOBs) were predominant in the coupon-containing native brine samples. IOBs were also detected in a corrosion deposit on the inner surface of a corroded pipe. These results strongly suggested the involvement of IOBs in the corrosion of the carbon steel pipes. Of the six bacterial strains isolated from a brine sample, four were capable of oxidizing iodide ion (I−) into molecular iodine (I2), and these strains were further phylogenetically classified into two groups. The iron-corroding activity of each of the isolates from the two groups was examined. Both strains corroded iron in the presence of potassium iodide in a concentration-dependent manner. This is the first report providing direct evidence that IOBs are involved in iron corrosion. Further, possible mechanisms by which IOBs corrode iron are discussed.

Influence of Chloride Ions on Corrosion of Modified Martensitic Stainless Steels at High Temperatures Under a CO2 Environment

The influence of chloride ion concentration on the passivation film and corrosion product film of martensitic stainless steels (SS) (13% Cr, modified 13% Cr-1% Mo, modified 13% Cr-2% Mo, and 15% Cr...

Corrosion of 304L stainless steel in CO2 removal units using high concentration DGA aqueous solution : Concentration differences of metallic ions in deposits along the different flow streams

The general corrosion of 304L stainless steel has been found in CO 2 removal units using a high concentration DGA solution in a natural gas processing plant. Deposits precipitated in the DGA units were sampled during annual inspections and were analyzed for metallic ions and their compounds. It was found that Fe and Cr were rich in the deposits along the lean DGA lines and Ni was rich along the rich DGA lines. Fe and Cr precipitated as oxides and Ni precipitated as sulfides. This uneven distribution of metallic ions in the units was interpreted due to the differences in metal chelate stability with DGA and/or DGA carbamate and also due to the trace amount of H 2 S in the raw natural gas. Although there has not been reported any direct proof of corrosive roles of carbamates in actual amine units, this uneven distribution of metallic ions is one of indirect evidences that DGA carbamate plays some roles in corrosive systems in actual DGA units.

Effect of environmental and material factors on SSC property of super 13Cr steel for OCTG.

The susceptibility of pitting and cracking of super 13Cr steels in light sour environment was systematicaly investigated by a notched bent beam test using autoclave. In mild condition such as chloride free solution at 25°C, the steels presents the passive state with no pitting and no cracking. With increase in chloride concentration, corrosion morphology changes from passive state into either pitting or general corrosion allowing hydrogen entry into steel so that SSC can occur. In higher temperature condition, passive film also becomes unstable to cause either pitting or general corrosion, however, cracking susceptibility decreases. These events suggest that a principal mechanism of SSC of super 13Cr steel is hydrogen embrittlement in condition that some breakdown of passive film undergoes.The major environmental factors affecting the pitting and cracking susceptibility are H2S partial pressure, temperature and chloride concentratoin, while pH effect is relatively small. The pitting and cracking resistance depends on alloy composition especially Mo content, but hardly influenced by strength of material.

Corrosion problem on high-density clear brines.

In recent years, solid-free, hight-density brines such as CaBr2-CaCl2 or NaBr-NaCl conc. solution, became to be used as completion fluid.Generally, the advantages using the brines are recognized, i.e, they are chemically stable, and their corrosivity are not high. However, as is usual at pure system, it was concerned about that the circumstanes should change if some contaminant come into those brines, owing to lack of their buffer action.Several laboratory corrosion tests were carried out in those brines using L-80 test coupons.In case of oxidizing agent coexisted, the corrosivity of the brines increased drastically. For example, 1% of NaClO3 added into NaBr-NaCl brine, pushed up the corrosion rate more over 80 times as compared with solution of, 1% NaClO3 only. Organic and inorganic inhibitors were tried to control the corrosion, but the performance of both inhibitors were unsatisfactory in the very severe conditions. This phenomenon is considered to be induced from hydration of high concentrated electrolyte, which restricts free water molecules.The interpretation was supported by analytical research of 1H-NMR measurements of thebrines.