For the purpose of contributing to sustainable machining, the aim was to investigate the turning of martensitic stainless steel X20Cr13 under alternative cooling and lubrication techniques. The minimum quantity lubrication technique in combination with the vortex tube cooling, as the determined optimal cooling method using the Taguchi-based entropy weighted grey relational analysis (compared to emulsion and minimum quantity lubrication technique) in previous research when turning martensitic stainless steel X20Cr13, were applied in this research in accordance with the Box–Behnken design. The aim is to investigate, when applying the optimal cooling condition (minimum quantity lubrication + vortex) with the Box–Behnken design, which parameters have a significant influence on reducing the surface roughness parameters Ra and Rz and also on the tool life (T). The cutting speed (v_c = 260, 290 and 320 m/min), feed rate (f = 0.3, 0.35 and 0.4 mm/rev) and depth of cut (a_p = 1, 1.5 and 2 mm) were selected as cutting parameters. An exponential model for Ra, Rz and T was obtained. According to the ANOVA results, it can be seen that only the feed rate had a significant influence on Ra and Rz. For tool life, according to the ANOVA results, it can be seen that all three parameters (cutting speed, feed rate and depth of cut) have significant influence on the tool life (T). Experimental results were compared with the results of the exponential mathematical model and presented in diagrams. A new nozzle was designed for this research to allow micro-droplets from the MQL unit and chilled compressed air from the vortex tube to be connected in one stream (single-channel system) before entering the cutting zone, thus allowing for simultaneous lubrication and cooling. For the used vortex tube system with an air flow of 708 L/min and the inlet air pressure of 0.69 MPa, a temperature drop of −29 °C can be achieved in regard to the inlet air temperature of 21 °C. Therefore, the minimum quantity lubrication technique with vortex tube cooling can be recommended for turning of martensitic stainless steel X20Cr13.

Surface cracks in butt-welded joints usually occur in places with increased stress concentrations. The stress concentration factor (SCF) can be calculated using an empirical equation, with five geometric parameters of a butt-welded joint (thickness of the base material, toe radius, weld toe angle, weld width, and reinforcement height). However, in an industrial environment, it is impractical and sometimes even impossible to measure all five geometric parameters with sufficient accuracy. In this study, eight experiments on butt-welded joints were performed. All samples were scanned with a 3D scanner, and the geometric sizes of the welded joints were measured using computer software. A modified empirical expression proposed by Ushirokawa and Nakayama was used to calculate the SCF; the expression was adjusted in such a way that the SCF was calculated by knowing only the toe radius. In addition, four new expressions were proposed for the calculation of the SCF by knowing the toe radius in relation to the weld toe angle; the expressions were then compared and analyzed. Additionally, the values of the stress concentrations in the butt-welded joints were obtained using a finite element method (FEM). The SCFs calculated using the four methods were compared and further discussed. Our data suggested a new accurate and straightforward approach for calculating the SCF by knowing only the weld toe radius.

Maintenance of process plants such as refinery plants requires implementation of good maintenance practices due to the presence of high complexity. With regard to the aspect of refinery plants maintenance, the most significant undertaking is the turnaround (TAR) carried out through a project task with a long duration of planning and a very short duration of realisation period, which makes it one of the most complex maintenance projects in general. Such maintenance is based on multidisciplinarity that must be implemented through a quality management system at all levels of maintenance management. This paper will define and test factors in turnaround refinery project management process, which also represent the quality factors inherent to the turnaround refinery project. Research findings point to the importance of evaluating leadership, team, policy and strategy in the turnaround refinery project management process.

Maintenance of process plants requires application of good maintenance practice due to a great level of complexity. From a plant maintenance point of view, the most significant activity is turnaround, an activity carried out through project task with long planning process period and very short execution period, which makes it one of the most complex projects of maintenance in general. It is exactly this kind of maintenance that is based on multidisciplinarity which has to be implemented through the system of quality management on all levels of maintenance management. This paper defines the most significant factors determining the process of turnaround projects quality management and its efficiency. Such relation is observed through moderating influence of complexity on process management efficiency in the turnaround project. The empirical research was conducted based on the survey of turnaround project participants in five refineries in Croatia, Italy, Slovakia and Hungary. For exploring the influence of research variables testing of the target relation is carried out by applying logistical regression. Research results confirm the significance of complexity as variable that significantly contributes to the project performance through the moderating influence on success of the project, as well as the influence of an efficient management on a plant turnaround project key results. Beside theoretical indications, practical implications that arise from this research study mainly refers to management process of the industrial plant maintenance project.