1. Depassivation and repassivation of stainless steels by stepwise pH changeEmir Mujanović, Bojan Zajec, Andraž Legat, Tadeja Kosec, Janez Kovač, Gregor Mori, Stefan Hönig, Gerald Zehethofer, 2020, original scientific article Abstract: Immersion tests with different stainless steels have been performed, while the pH was stepwise decreased and then increased again. During 8.5-day exposure, the depassivation and repassivation pH values as a function of pitting resistance equivalent number were determined. There is always a gap between both pH values (depassivation and repassivation), indicating that for every steel, there are conditions where an existing passive layer can be maintained but cannot be rebuilt after depassivation. In such environments, the passive layer is thicker, consisting mainly of molybdenum and iron rich oxides, while chromium is dissolved. Usually, depending on conditions, the passive layer is more chromium-rich, especially the inner layer. This is relevant, for example, for acidizing jobs in oil and gas industry, proving that repassivation after acidizing will happen promptly, when the pH is increased again.
Keywords: stress corrosion cracking, surface finish impact, tapered tensile specimen, autoclave, accelerated testing, light water nuclear reactor, critical threshold stress
Published in DiRROS: 30.08.2023; Views: 301; Downloads: 156
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2. Stress corrosion crack initiation testing with tapered specimens in high-temperature water - results of a collaborative research projectRik-Wouter Bosch, Stefan Ritter, Matthias Herbst, Renate Kilian, Grace Burke, Jonathan Duff, Fabio Scenini, Yuchen Gu, Alice Dinu, Ulla Ehrnsten, Aki Toivonen, Radek Novotny, Oliver Martin, Francisco Javier Perosanz, Andraž Legat, Bojan Zajec, 2020, original scientific article Abstract: The applicability of an accelerated test technique using tapered tensile specimens for investigating the stress corrosion crack (SCC) initiation behaviour of structural materials in high-temperature water was assessed in the framework of a European collaborative research project (MICRIN – MItigation of CRack INitiation). The main advantage of using a tapered geometry is, that in a single test a stress gradient is obtained through the gauge length, and therefore a stress threshold for SCC initiation can be determined in a reasonable timeframe. This method was used to investigate two different materials that were known to be susceptible to SCC in light water reactor environment: a high-Si stainless steel and a Ni-base weld metal (Alloy 182). The results of the international test programme confirmed that the tapered specimen test methodology could be used to identify a SCC initiation stress threshold, albeit that significant scatter was present in the data.
Keywords: stress corrosion cracking, surface finish impact, tapered tensile specimen, autoclave, accelerated testing, light water nuclear reactor, critical threshold stress
Published in DiRROS: 28.08.2023; Views: 278; Downloads: 152
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3. Distribution of chemical elements in surface waters from the Strumica River Basin, North MacedoniaKaterina Trajanova, Robert Šajn, Trajče Stafilov, 2023, original scientific article Abstract: In this work, the distribution of chemical elements in samples of surface water from the Strumica River Basin, North Macedonia, was studied. The water samples were collected from a total of twelve sites. In addition to the Strumica River, samples were collected from its tributaries: Bansko, Dabile, Turija, Vodoča, Radoviška, and Injevska. The determination of the concentration of 21 elements (Ag, Al, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Mo, Na, Ni, P, Pb, Sr, V, and Zn) was performed by inductively coupled plasma - atomic emission spectrometry (ICP-AES). All detailed information on the studied items was statistically processed using Stat Soft, 11.0 software. Using the obtained data on the concentration of the studied elements, descriptive statistical analysis of the values for the concentration of the elements was performed. A map of spatial distribution was obtained for each element. The obtained results show that the concentrations of the studied elements in the surface water samples are relatively low and the distribution of most of the elements follows the lithology of the study area.
Keywords: rivers, surface water, heavy metals, Strumica River Basin, North Macedonia
Published in DiRROS: 20.07.2023; Views: 344; Downloads: 110
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4. Effect of surface machining on the environmentally-assisted cracking of Alloy 182 and 316L stainless steel in light water reactor environments : results of the collaborative project MEACTOSMariia Zimina, Stefan Ritter, Bojan Zajec, Marc Vankeerberghen, Liberato Volpe, Anna Hojna, Rik-Wouter Bosch, Fabio Scenini, Zaiqing Que, Alberto Sáez-Maderuelo, P. Jill Meadows, Michael Grimm, Matthias Herbst, Andraž Legat, Agostino Maurotto, Radek Novotny, Karl-Heinz Seifert, 2023, original scientific article Abstract: The main objective of the EU-funded project mitigating environmentally-assisted cracking through optimisation of surface condition (MEACTOS) was to gain knowledge on the ability of different surface machining procedures to mitigate environmentally-assisted cracking (EAC) in typical light water reactor structural materials and environments. Surfaces of cold-worked (CW) type 316L austenitic stainless steel and nickel-based weld metal Alloy 182 flat tapered tensile specimens were machined using different processes. EAC initiation susceptibility of these specimens was evaluated using constant extension rate tensile (CERT) tests under simulated boiling water reactor (BWR) and pressurized water reactor (PWR) conditions and assessed using constant load experiments. More than a hundred tests were performed covering about 10 years of autoclave testing time. Only minor or no measurable improvements in EAC initiation susceptibility as a function of surface treatments (grinding or advanced machining) compared to the standard industrial face milling were demonstrated. In most cases, the stress thresholds for EAC initiation determined in constant load tests confirmed the trend obtained from CERT tests. This paper summarises the most important results and conclusions concerning the EAC initiation behaviour for the CW 316L and Alloy 182 under reducing PWR and oxidizing BWR conditions.
Keywords: crack initiation, environmentally-assisted cracking, Alloy 182, AISI 304 stainless steel, surface treatment, light water reactor, open access
Published in DiRROS: 30.05.2023; Views: 330; Downloads: 189
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5. Investigation of surface treatment effects on the environmentally-assisted cracking behaviour of Alloy 182 in boiling water reactor environmentZaiqing Que, Bojan Zajec, Stefan Ritter, Tommi Seppänen, Timo Saario, Aki Toivonen, Aleksandra Treichel, Valentin Lautaru, Fabio Scenini, 2022, original scientific article Abstract: Surface treatments of primary circuit components in light water reactors are regarded as possible ways to mitigate environmentally-assisted cracking (EAC). To date, it is not fully conclusive which surface condition is suitable to reduce the EAC initiation susceptibility. Constant extension rate tensile (CERT) tests were performed by several labs using flat tapered tensile specimens with different surface conditions (ground, industrial face milled, advanced face milled and shot peened), exposed to a boiling water reactor normal water chemistry environment at 288°C. Despite some scatter in the results, the CERT tests revealed that the EAC initiation susceptibility seems lowest for the advanced face milled surface and highest for the shot peened surface. However, it must be emphasised that the differences were moderate and that the surprising behaviour of the shot peened surface can be explained. The mechanical grinding of the surface did not significantly retard EAC initiation compared to industrial face milling.
Keywords: crack initiation, environmentally-assisted cracking, Alloy 182, surface machining, boiling water reactor, open access
Published in DiRROS: 05.05.2023; Views: 360; Downloads: 151
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