[en] The 19th annual conference being hosted by NACE International Gateway India Section (NIGIS) CORCON 2011 will feature technical symposia, interactive technical sessions and an expo. By promoting awareness and knowledge related to corrosion and its control through its educational programs and annual conferences, NIGIS reflects the mission and objectives of NACE International in India. The annual conference branded as 'CORCON', has emerged as the premier forum in India for Indian and overseas professionals wishing to interact on matters related to corrosion and its prevention. The technical symposia comprise a wide array of corrosion - related topics such as: Paints Coating and Lining, Materials and Composites, Inhibitors, MIC, Cathodic Protection, Failure Analysis, Inspection and Testing and covers sectors such as RCC and Infrastructure and Electric Power and Utilities. Papers relevant to INIS are indexed separately

[en] Stress corrosion cracking (SCC) of non sensitized 304L stainless steel (SS) in boiling water reactors worldwide is of concern. SCC is a surface phenomenon and the susceptibility to SCC essential depends on the protective nature of surface film. The present study aims to bring out the difference in the protective nature of the surface film formed on SS with different surface conditions under high temperature and high pressure aqueous condition. Solution annealed SS grade 304L was subjected to two kinds of surface finishing operations a) machining and b) grinding. The SS having different surface conditions together with solution annealed condition was exposed to high temperature and pressure (300C, 100 bars) high purity (conductivity < 0.1 Scm^-1) demineralised water. The oxide film thus formed was monitored and electrochemically characterized in-situ by electrochemical impedance spectroscopy by controlled distance electrochemistry (CDE) which is a novel technique to electrochemically characterize the surface film from a distance of 10 m. Microstructural characterization of the surface film was done using scanning electron microscopy (SEM). The results discussed in the paper to bring out the effects of surface working on the oxidation behavior of 304L SS. (author)

[en] Gram-negative pseudomonas sp. was used as the test organism for the biofilm formation and growth on 316 LN stainless and electrochemical noise (EN) monitoring studies, since this genus has been identified as the major biofilm former on stainless steels. EN studies were conducted for 21 days on the galvanically coupled specimens exposed to the dilute nutrient culture with pseudomonas sp. The visual records of the current potential EN, analysis of statistical and power spectral density (PSD) parameters of current and potential along with shot-noise parameters showed increase in the localized corrosion during initial 2-11 days exposure; thereafter the specimens showed passive behaviour. Raman spectra taken inside the pit for the specimen exposed for 21 days showed the peak corresponding to Cr³⁺ ions signifying repassivation process. Similarly, Raman spectra on the surface outside the pits on the specimens exposed for 7, 10 and 15 days showed steady growth of the peak corresponding to Cr³⁺ ions. This implied steady enrichment of Cr on the surface of the specimen which accounted for the gradual passivation with increased exposure time. (author)

[en] Micro laser Raman technique was used to analyse the corrosion products on the surface of the failed components received from different plants of DAE. The corrosion of active-passive materials generally occurs due to the failure of the passive film which protects the surface. The paper currently deals with two case studies. Case study I: Al-brass condenser tubes which failed due to erosion corrosion and also due to pitting as these condenser tubes had sea water as the coolant. The failure of the tube was a result of a poor passive film formation on the surface. The remedial measure was to subject these tubes to ferrous sulphate dosing. The Raman analysis was carried out after these tubes were subjected to ferrous sulphate dosing which is essentially done to get a γ-FeOOH layer on the surface. The results showed that a 7 cycle treatment gave an adherent and protective layer but in case of field treatment the concentration of γ-FeOOH was very less as established from the Raman spectrum thereby indicating that the treatment was improper. Case II: The carbon steel column in a heavy water plant showed excessive thinning. The cause for this thinning was attributed to reactive species in the column which reacts with Fe to form a non-adherent layer on the surface. The H₂S passing in the column generally results in the formation of an adherent FeS₂ coating which is desirable. The Raman analysis carried out on these samples showed the presence of FeCO₃ which is an undesirable product along with Fe-oxides. Formation of these products resulted in the consumption of Fe from the surface resulting in thinning of the column. These analyses on the failed samples have shown the importance of surface film on the corrosion resistance of these alloys. The micro laser Raman is a powerful tool in analysing the corrosion surface compounds without disturbing the surface since it doesn't involve any sample preparation. The paper illustrates the importance and application of Raman spectroscopy in establishing root cause of corrosion failures in plants. (author)

[en] The investigation is primarily aimed at the high temperature corrosion behavior of different grain sizes of 2.25 Cr-1 Mo steel at SO₂+O₂ (mixed oxidation and sulfidation). The various grain sizes (18 μm,26 μm, 48 μm, and 72 μm) are obtained by different annealing treatment. Isothermal corrosion studies are carried out in different grain size specimens at 973K for 8 hours. The corrosion growth rate and the reaction kinetics are studied by weight gain method. The external scales of the post corroded specimen are studied in Scanning Electron Microscope (SEM) to examine the corrosion products morphology on the scale. X-ray mapping analysis of the different elements (Fe, O, Cr and S) is carried out by Energy Dispersive Spectroscopy (EDS) attached with SEM. The X-ray Diffraction Analysis (XRD) is also carried out to identify the corrosion products in the external scale. Finally, it is concluded that that the corrosion rate of 2.25 Cr-1 Mo steel strongly depend on grain sizes of the specimens. The corrosion rate increases with the decreases of grain size. The finer grain (18 μm) show higher corrosion rate than the coarse grains (72 μm). The weight gain kinetics follows the parabolic growth rate which further indicates that the corrosion process is diffusion controlled. The scale analysis shows the thicker scale and extensive scale cracking and spallations in case of finer grain size specimen (18 μm), whereas the coarse grain specimen (72 μm) shows compact and adherent layer. The XRD analysis shows that the corrosion products consist of mixtures of iron oxides( Fe₃O₄ and Fe₂O₃) and iron sulfides (FeS). The details mechanism of the corrosion is discussed to explain the difference in corrosion rate for different grain sizes. (author)

[en] The sea water cooled condensers have to resist severe corrosion as marine environment is the most corrosive natural environment. Copper alloys are being phased out due to difficulties in water chemistry control and Titanium base alloys are extremely expensive. Austenitic stainless steels (SS) remain prone to localized corrosion in marine environments hence not suitable. These heat exchangers operate at temperatures not exceeding 50 deg C and at very low pressures. The tubes of these heat exchangers are joined to the carbon steel tube sheets by roll expansion or by roll expansion followed by seam welding. These conditions are expected to affect the localized corrosion resistance of the tube in roll joined region due to cold working and in the tube-tube sheet welded joint due to thermal effects of welding. In this study, the localized corrosion behaviour of a Hyper Duplex Stainless Steel (HDSS) has been evaluated, and compared with other materials e.g. types 304L SS, 316L SS, Duplex SS 2205, Titanium grade - 2, and Al Brass. The evaluation is done in three metallurgical conditions (a) as received, (b) cold rolled and (c) welded condition in synthetic sea water at room temperature and at 50 deg C to assess the resistance to crevice, pitting and stress corrosion cracking using standard ASTM exposure and electrochemical techniques. The results provide comparative assessment of these alloys and show their susceptibility in the three metallurgical conditions as encountered in condensers. Hyper-duplex SS has been shown to be highly resistant in sea water for the condenser tubing application. (author)