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A grade TP-316LN austenitic stainless-steel pipeline was found to undergo microbiologically influenced corrosion after 3 months of being hydrotested using demineralized water. The demineralized water was left half-filled in the pipeline for the mentioned 3 months after the hydrotest. Fine and deep pits were found to develop at the weld zone and at the far HAZ. SEM investigation showed that the corrosion was caused by bacterial colonies of rod-like bacteria. The cause of the corrosion was investigated by means of EDS analysis which showed that the corrosion was caused by selective leaching of Cr, Ni and Mo into the water phase. The type of corrosive attack was found intergranular rather than transgranular. [ABSTRACT FROM AUTHOR]

[Display omitted] • The corrosion was observed as a weight loss due to Fe dissolution activity. • The corrosion rate was found to be 1.3 times higher with the increasing OA. • The intergranular corrosion was observed to the CS surface. The corrosion behavior of Carbon Steel (CS) SA106 Gr. B in an organic condition of oxalic acid (OA) was elucidated under the anticipated conditions of a Pressurize Heavy Water Reactor (PHWR) during the chemical decontamination. CS specimens were exposed in the acidic medium for 18 h at 95 °C to evaluate the corrosion activity. Atomic Absorption Spectrometry (AAS) was employed to analyze the dissolved Fe concentration and found to be 276.5 and 401.3 ppm in 10 mM and 20 mM OA solution, respectively. Corrosion rates were assessed using the weight loss method. The CS specimens dissolved in 20 mM exhibited a corrosion rate of 6.3 mm/y, while that dissolved in 10 mM OA has 4.6 mm/y. The corrosion products were characterized by Electron Probe Microanalysis (EPMA). The intergranular corrosion (IGC) was observed prior to the formation of corrosion products and oxalate passivation, potentially providing pathways for contaminant diffusion into the bulk substrate. [ABSTRACT FROM AUTHOR]

This technical note provides some considerations for the metallographic observation of intergranular attack (IGA) in Alloy 600 steam generator tubes. The IGA region was crazed along the grain boundaries through a deformation by an applied stress. The direction and extent of the crazing depended on those of the applied stress. It was found that an IGA defect can be misevaluated as a stress corrosion crack. Therefore, special caution should be taken during the destructive examination of the pulled-out tubes from operating steam generators.

Fe–18Cr–21Mn-0.65 N austenitic stainless steel was pre-exposed at intermediate temperature, from 400 to 700 °C, for different durations, up to 100 h. Corrosion behavior of the samples, unexposed as well as exposed, at different temperatures, was assessed in seawater (0.5 M NaCl) through potentiodynamic polarization. It was found to decrease with an increase in the temperature of exposure. Corrosion resistance of the passive layer formed, evaluated by EIS, showed that it decreased with increase in the temperature of exposure. The corroded samples were characterized by X-ray photoelectron spectroscopy (XPS) and Scanning electron microscopy (SEM-EDS). XPS analysis revealed the presence of oxides and hydroxide of Cr+3, Mn+3, and Fe+3. The pitting mechanism was prominent in the specimens exposed from room temperature to 500 °C, whereas a mixed-mode of corrosion (intergranular combined with accelerated pitting) was there in the samples exposed at higher temperatures of 600 and 700 °C. Precipitation of Cr 2 N along grain boundaries and within the matrix was the leading cause of the deterioration in the corrosion resistance. • Increase in temperature of exposure decreases the resistance of passive film in aqueous chloride medium. • With increases in time and temperature of exposure corrosion rate increases. • Pitting upto 500℃ and intergranular attack combined with pitting at 600-700℃ was the corrosion mechanism. [ABSTRACT FROM AUTHOR]

Highlights: [•] This research presents a case study of accelerated local corrosion of water supply system pipeline. [•] Presence of weld decay on AISI 304 steel was shown and its consequences were revealed. [•] Formation of galvanic cells related to chromium depletion as a result of sensitisation was studied. [Copyright &y& Elsevier]

High-resolution characterizations of intergranular attack in alloy 600 (Ni-17Cr-9Fe) exposed to 325°C simulated pressurized water reactor primary water have been conducted using a combination of scanning electron microscopy, NanoSIMS, analytical transmission electron microscopy, and atom probe tomography. The intergranular attack exhibited a two-stage microstructure that consisted of continuous corrosion/oxidation to a depth of ~200 nm from the surface followed by discrete Cr-rich sulfides to a further depth of ~500 nm. The continuous oxidation region contained primarily nanocrystalline MO-structure oxide particles and ended at Ni-rich, Cr-depleted grain boundaries with spaced CrS precipitates. Three-dimensional characterization of the sulfidized region using site-specific atom probe tomography revealed extraordinary grain boundary composition changes, including total depletion of Cr across a several nm wide dealloyed zone as a result of grain boundary migration. [ABSTRACT FROM PUBLISHER]

Abstract: Optical and electron microscopies and EBSD were used to study the early stages of corrosion propagation during stable pit formation on AA2024-T3. Polished AA2024-T3 developed large scale rings of corrosion product, typically a few hundred microns in diameter, within 2h of exposure to 0.1M NaCl at room temperature. These features were sectioned using diamond ultramicrotomy and substantial subsurface attack, in the form of intergranular corrosion was observed beneath these sites with virtually no grain etchout. A model is proposed for the mechanism of stable pit progression which involves extensive grain boundary attack, followed by grain etchout leading to open pit formation. [ABSTRACT FROM AUTHOR]

The objectives of the present investigation were to characterize ammonia-producing bacteria ( Bacillus sp.) and study its impact on biodeterioration of cupronickel alloy 90:10. in a nitrogen free environment. It is well known that iron sulphate and molybdenum are good inhibitors when used in a cooling water system. The interactions between inhibitor and ammonia producing bacteria on the corrosion of cupronickel 90:10 were studied. The predominated ammonia producing bacteria Bacillus sp. (AG1-EU202683; AG2-EU202684; AG3-EU202685 and AG4-EU202686) were identified by 16S rRNA gene sequencing from the biofilm. These bacteria fixed with atmospheric nitrogen for their cell protein synthesis and converted into ammonia. Ammonia enhanced pH and ammonical solution were formed in the presence of Bacillus spp. which acted as an etchant. The presence of some anodic spots in the presence of bacteria was affected by ammonia and then underwent pitting corrosion. The present study reveals that Bacillus spp. encourage intergranular attack without any stress in the cooling water system. [ABSTRACT FROM AUTHOR]

Type 304 stainless steel and carbon steel are extensively used as structural materials in the reactor coolant systems of nuclear power plants. The corrosion of these structural materials during normal operation and the subsequent neutron activation of their corrosion products leads to the build-up of radiation on the out-of-core surfaces of the coolant systems. The Dilute Chemical Decontamination (DCD) process is one of the methods used to remove the activity that becomes embedded in the oxide layers formed over these structural materials. Permanganate based oxidising reagents are generally used to dissolve chromium from oxide films containing iron, chromium and nickel on the surfaces of Type 304 stainless steel and other chromium-containing alloys. This study has investigated the behaviour of carbon steel in oxidising permanganate based acidic media. The corrosion/decomposition rate varied with temperature. With permanganate concentrations above 1·5 mM for permanganic acid and greater than 6 mM for nitric acid and potassium permanganate (NP), passivation of carbon steel surfaces occurred with negligible loss of weight of the carbon steel and insignificant decomposition of the permanganate. The effects of additions of chromate to permanganate on the passivation of carbon steel have also been evaluated. In the case of permanganic acid, the presence of even 50 ppm of chromate was sufficient to protect the carbon steel surface whereas a minimum of 150 ppm of chromate was required for passivation in the NP medium. Electrochemical polarisation experiments were also carried out to support these observations. When the concentration of permanganic acid was above 200 ppm, the open circuit potential of carbon steel in permanganic acid was +1·0 V (SCE) and it was observed to be passive whereas at lower concentrations the carbon steel was actively corroding at a potential of -0·695 V (SCE). [ABSTRACT FROM AUTHOR]

In this work, observations of the corrosion on a failed copper U-shaped tube, of 1 mm nominal thickness, are presented. This tube was subjected to severe corrosion and subsequent cracking after a month of operation as the heating element of an electrical boiler. Morphological and microstructural observations of the failure area as well as cross sections of the corroded copper tube are presented. Moreover, the chemical composition of the material and the principal physicochemical characteristics of the tap water used for boiler operation were determined in the context of the failure investigation. The quality of the water used for boiler operation was a significant factor influencing the heating element efficiency and reliability. Hard water with high electrical conductivity accelerated salt precipitation and led to the corrosion and premature failure of the components. [ABSTRACT FROM AUTHOR]

Abstract: The thermowell inside the post combustion chamber in an incineration plant failed due to severe high temperature oxidation. The failure was caused by deep intergranular oxidation attack and surface scaling of the component. The intergranular oxidation attack is more damaging to the material integrity. Inconel 600 was improperly used as the thermowell material due to insufficient Cr content for formation of a continuous protective Cr2O3 layer on the alloy surface, and the high operating temperature 950 °C nearly approaching its upper temperature limit (1000 °C). Replacement of Inconel 600 by more corrosion- and heat-resistant materials is strongly recommended. [Copyright &y& Elsevier]

Abstract: Currently, dental bleaching and fluoride treatment agents are popular for esthetic purposes and prevention of plaque and caries formation. The corrosive effect of these agents on dental metallic materials has not been well documented. It was an objective of this in vitro study to evaluate and compare chemical and electrochemical corrosion behavior of seven metallic dental materials in commercially available fluoride and bleaching agents. Fluoride treatment agents were tested on Ti–6Al–4V and 17-4 stainless steel. Discoloration on these alloys was examined by a colorimeter and the naked eyes. Bleaching agents were tested on commercially pure titanium, Ni–Co–Mo alloy, type IV gold alloy, and amalgam. Electrochemical corrosion tests were also conducted for these materials, using each treatment agent as an electrolyte. All tested materials suffered from discoloration, which mostly disappeared after brushing. The fluoride-treated 17-4 stainless steel indicated severe intergranular attack, causing localized Cr depletion. The bleaching agents made the passivation layer on the metallic materials unstable. Within the limitations of this study, although these treatments are indicated for patients (enamel), it is proven that these agents are contraindicated for dental metallic materials. [Copyright &y& Elsevier]

The susceptibility to stress corrosion cracking (SCC) in 0.01 M Na2S2O3 of alloy 690 under different heat treatments has been investigated using slow strain rate tests. Double-loop electrochemical potentiokinetic reactivating tests in 0.5 M sulfuric acid+0.0001 M potassium thiocyanate was used to evaluate the resistance to intergranular attack (IGA). Alloy 690 was solution annealed at 1100 °C for 30 min and water quenched (WQ), followed by sensitization at 700 °C for 5, 12, 24, 36, 48 and 72 h and then WQ. The susceptibility to IGA and intergranular stress corrosion cracking (IGSCC) in 0.01 M Na2S2O3 at 90 °C increased with increasing the aging time, reaching a maximum value at the aging time of 48 h, and then, it decreased again for the specimen sensitized during 72 h. The chromium-depletion profile was deeper also for the specimen aged for 48 h. These results are discussed in terms of consumption of carbon during sensitization, and a continuous diffusion of chromium, ‘back-filling’ the prior depletion profile, recovering the IGSCC resistance. Also, it is suggested that the presence of a continuous network of grain boundary carbides in the specimen sensitized during 72 h, rather than discrete carbides, as in the one aged during 48 h, is another reason for the increased SCC resistance. [Copyright &y& Elsevier]