This paper presents the analysis of the behavior of welded joints made of 9–12% Cr-Mo steel SA-387 Gr. 91. The successful application of this steel depends not only on the base metal’s (BM) properties but even more on heat-affected-zone (HAZ) and weld metal (WM), both at room and at operating temperature. Impact testing of specimens with a notch in BM, HAZ, and WM was performed on a Charpy instrumented pendulum to enable the separation of the total energy in crack-initiation and crack-propagation energy. Fracture toughness was also determined for all three zones, applying standard procedure at both temperatures. Results are analyzed to obtain a deep insight into steel SA 387 Gr. 91’s crack resistance properties at room and operating temperatures. Results are also compared with results obtained previously for A-387 Gr. B to assess the effect of an increased content of Chromium.

This paper presents the analysis of the temperature and exploitation time impact on the resistant measure to brittle fracture of welded joint constituents of the new and exploited low-alloyed Cr-Mo steel A-387 Gr. B from the aspect of application of the parameters obtained by tensile testing and parameters obtained by fracture mechanics testing. The exploited parent metal is a part of the reactor mantle which has been exploited for over 40 years and is in the damage repair stage, i.e. in the stage where the part of the mantle is being replaced with new material. Basic characteristics of the material strength, as well as the stress-elongation curves required for stress analysis are obtained by tensile testing. The testing of plane strain fracture toughness is conducted in order to determine the critical stress intensity factor, K_Ic, that is, assessment of behavior of the new and exploited parent metal, welded metal and heat affected zone from the side of the new parent metal and from the side of the exploited parent metal in the presence of the crack type error. Based on the research results, the analysis of the resistance to brittle fracture represents the comparison of obtained values for characteristic areas of welded joint and justification of the selected welding technology.

The reliability study is the most important part of the engineering design process, as it is the basis of analysis and assessment of future product performance in exploitation. Since performance cannot be predicted with absolute certainty, the application of reliability theory includes probability theory and unreliability modeling. The proposed approach has been applied to assess the reliability of gear planetary power transmissions. The assessment of system reliability was determined on the basis of the block diagram method, as a function of the reliability of individual components, calculated by statistical analysis. Using the Weibull model, the reliability of the planetary gear was defined on the basis of the probability of failure of the gear teeth and the results were interpreted to assess the reliability of the component and the entire planetary train. For a more precise assessment of reliability and to avoid modeling every failure and mode of occurrence, a competitive risk model was developed. The reliability assessment study was conducted with a “bottom-up” approach. Reliability has been assessed, for instantaneous, estimated and assigned failures rate of planetary train and component.

The facture and fatigue behaviour of welded joints made of A516 Gr 60 was analysed, bearing in mind their susceptibility to cracking, especially in the case of components which had been in service for a long time period. With respect to fracture, the fracture toughness was determined for all three zones of a welded joint, the base metal (BM), heat-affected zone (HAZ) and weld metal (WM), by applying a standard procedure to evaluate K_Ic via based on J_Ic values (ASTM E1820). With respect to fatigue, the fatigue crack growth rates were determined according to the Paris law by the standard procedure (ASTM E647) to evaluate the behaviour of different welded joint zones under amplitude loading. The results obtained for A516 Gr. 60 structural steel showed why it is widely used in the case of static loads, since the minimum value of fracture toughness (185 MPa√m) provides relatively large critical crack lengths, whereas its behaviour under amplitude loading indicated a need for further improvement in WM and HAZ, since the crack growth rate reached values as high as 4.58 × 10⁻⁴ mm/cycle. In addition, risk-based analysis was applied to assess the structural integrity of a pressure vessel, including comparison with the high-strength low-alloy (HSLA) steel NIOVAL 50, proving once again its superior behaviour under static loading.

Gear tooth side wear in planetary gearboxes represents one of the main reasons for damage occurring in these gears. Wear magnitude is unpredictable and depends on temperature, lubrication, load, material and other random variables. Wear...

In this paper, the behavior of the basic material of low-alloy carbon steel A516 Gr 60 under tensile and impact loads at different temperatures was analyzed. The test results are presented in tabular and graphical form, where the influence of the test temperature on the tensile and impact properties is clearly visible.