Intermittent operation is common in industrial processes where stainless steel components undergo repeated cleaning cycles. In such conditions, the durability of passive films plays a central role in controlling tribocorrosion. Here, the tribocorrosion behavior of AISI 316L stainless steel in 5 wt% NaHCO3 solution was examined under ball-on-plate reciprocating sliding at 25 N load, 10 mm stroke, and 5 Hz frequency, with four sliding sequences (1000 s each) separated by rest intervals of 15 min, 1 h, 2 h, and overnight for a total test duration of 20 h. A similar to 50% reduction in the coefficient of friction occurred within the first 180 s, followed by a stable lowfriction regime (similar to 0.4) that persisted regardless of rest duration. This response correlated with open circuit potential recovery during pauses, evidencing rapid repassivation. A total wear volume of 0.28 mm(3) was measured, giving a wear rate of 1.12 x 10(-4) mm(3)/N.m. After an initial transient stage, the wear curve stabilized, showing that the tribofilm arrested further degradation. Post-test surface analyses revealed a chemically complex tribofilm composed of iron/chromium oxides and hydroxides enriched with carbonate species, with localized metallic nickel enrichment in chromium-depleted areas. These results provide quantitative evidence that sodium bicarbonate promotes the formation of durable self-healing tribofilms, capable of suppressing wear and maintaining low-friction conditions in stainless steel components subjected to intermittent sliding in diverse industrial cleaning alkaline environments.
Openings (nozzles, branch connections) located in the knuckle region of pressure vessel heads represent a major design challenge, particularly when neighboring nozzles induce stress concentrations in the ligament separating them. Current construction codes, such as CODAP and ASME BPVC.VIII.1-2, do not provide explicit rules for these configurations, often leading to lengthy and costly finite element (FE) analyses. The objective of this study is to develop a simple and parsimonious analytical envelope formula linking the maximum equivalent stress to geometric and mechanical parameters, in order to derive design rules (minimum reinforcement thickness, allowable pressure) ensuring an adequate level of safety. The methodology is based on a parametric FE database (Abaqus) covering several thousand configurations of neighboring and isolated nozzles. An original algorithm constructs an ordinal correlation matrix to identify critical zones and establish an objective hierarchy of local stresses. An incremental weighting, called ordinal regularization, applied to the ratio D-e/E , leads to an explicit envelope formula for the Tresca equivalent stress, expressed as 2p D-e/E ring: E-ring >= 2pD(e) /sigma(adm) - E-head.
Sheet metal forming processes are widely used in many industries, with blanking being one of the most common operations. The blanking process is highly sensitive to controlled parameters, such as clearance, and uncontrolled factors, like tool wear, which can significantly affect cut-edge quality and process stability. This study presents a numerical investigation of the blanking of a high-strength steel sheet commonly used in automotive applications, with particular emphasis on accurate material modeling. Experimental tests were conducted to characterize the elastoplastic behavior and fracture response of the sheet metal. The material behavior was modeled using J2 plasticity coupled with a Modified Mohr–Coulomb fracture criterion calibrated from experimental data. Finite element simulations were performed under different tool wear conditions and validated against experimental blanking force measurements. The results demonstrate good agreement between the predictions and the measurements with a maximum error of 11.2
Stress corrosion cracking (SCC) in austenitic stainless steel (SS) welds remains a complex challenge due to the interplay of metallurgical heterogeneities and environmental parameters. This study proposes a new accelerated SCC test designed to evaluate the SCC susceptibility of 316L SS welds under conditions that better simulate in-service environments. The newly designed test is a uniaxial tensile test which incorporates incremental loading combined with anodic polarization cycles in a 1 M NaCl solution acidified to pH 4 at 60 degrees C, i.e., a solution more representative of in-service applications than the usual boiling MgCl2 often used in the literature. Tensile specimens were machined to align the weld axis with the loading direction, and 1-mm diameter stress concentrators (i.e., holes) were strategically located between the fusion zone (FZ), heat-affected zone (HAZ), and base metal. When the tensile loading was incrementally increased to 450 MPa, fracture of the tensile specimen was observed. Fractographic analysis confirmed crack initiation in the HAZ and unstable propagation toward the FZ. Two reference tests were performed for comparison. For one reference test, the same methodology was used, but without stress concentrators: only microcracks were observed, primarily intergranular in nature and concentrated in the HAZ, validating this zone as the most susceptible to SCC. Another reference test used the tensile specimen with stress concentrators, but it was conducted at open-circuit potential (OCP) for one month. This long-term test demonstrated similar failure patterns and corrosion mechanisms as the newly designed test, confirming its representativeness despite anodic polarization. The newly designed test successfully accelerates SCC while preserving the relevance of observed damage modes, bridging the gap between traditional accelerated methods and actual service conditions. The findings emphasize the critical role of the HAZ in SCC initiation, as well as the influence of microstructural features and stress and deformation gradients. This methodology offers a robust framework for screening SCC resistance in welded SS components and for further mechanistic studies under controlled but representative conditions.
This study examines how sliding frequency governs the tribocorrosion behavior and surface durability of AISI 316L stainless steel used in food-processing equipment and volumetric pumps subjected to cyclic alkaline cleaning. Although AISI 316L exhibits high corrosion resistance, its passive film can be degraded under combined mechanical loading and chemical attack during cleaning-in-place operations, leading to accelerated material loss and reduced component lifetime. To clarify the role of dynamic operating conditions, tribo-electrochemical tests were performed in an eco-friendly 5 wt.% sodium bicarbonate solution representative of industrial cleaning environments, coupling in situ monitoring of the coefficient of friction and open-circuit potential with post-test surface characterization. The results show a clear frequency dependent transformation of the passive film. At low sliding frequencies (2–5 Hz), the surface is enriched in metallic nickel and chromium hydroxide–carbonate species, forming a self-healing, hydroxide–carbonate-rich layer that favors repassivation, stable friction, and limited wear. At higher frequencies (8–10 Hz), these protective hydroxides are progressively replaced by brittle oxides such as iron(III) oxide and chromium(III) oxide, leading to unstable electrochemical response, higher wear rates, and surface embrittlement. These findings identify sliding frequency as a critical operational parameter for stainless steel components exposed to repetitive contact in alkaline media and provide a mechanistic basis for adjusting motion conditions and cleaning protocols to reduce tribocorrosion damage and extend service life.
