In the paper the reasons for steam pipeline’s elbow material rupture, made of steel 13CrMo4-5 (15HM) that is being used in the energetics. Based on the mechanical properties in the ambient temperature (Rm, Rp0,2 and elongation A5) and in the increased temperature (Rp0,2t) it was found, that the pipeline elbow’s material sampled from the ruptured area has lower Rp0,2 i Rp0,2t by around 2% than it is a requirement for 13CrMo4-5 steel in it’s base state. The damage appeared as a result of complex stress state, that substantially exceeded the admissible tensions, what was the consequence of considerable structure degradation level. As a result of the microstructure tests on HITACHI S4200 microscope, the considerable development of the creeping process associates were found. Also the advances progress of the microstructure degradation was observed, which is substantial decomposition of bainite and multiple, with varied secretion size, and in most cases forming the micro cracks chains. With the use of lateral micro sections the creeping voids were observed, that creates at some places the shrinkage porosities clusters and micro pores.

The paper presents the results of microscopic examinations of the growth of primary silicon crystals in hypereutectic A390.0 (AlSi17Cu5Mg) silumin. A diagram of the growth of primary silicon crystals in the melt without overheating and superheated to a temperature of 920°C has been presented. From the experimental results obtained on crystal morphologies of primary silicon, different sequences of crystal growth of the primary silicon can be expected. In the silumin without overheating, five-pointed star-shaped particles form, after superheating, the crystals of primary silicon take more compact shapes. This structure provides better mechanical properties and thus increases the area of application of alloys with hypereutectic silicon content.

The specific heat capacity was calculated by DSC and the kinetics of oxidation was determined for alloys from the NiAl, FeAl and TiAl phase equilibrium system. The Ti48Al alloy contained an addition of 2 at.% of chromium and niobium. The highest value of heat capacity had the Ti-Al and Fe-Al alloys. At temperatures above 673K, the Ti48Al alloy showed an anomaly, that is, a lower value of the heat capacity. The change in heat capacity was related with an exothermic reaction. The oxidation of alloys was running according to either parabolic or cubic law. Alloys characterised by high thermal capacity showed a higher gain in weight. The slowest to oxidise was the Ni3Al intermetallic phase.

The paper presents results of calorimetric studies of foundry nickel superalloys: IN100, IN713C, Mar-M247 and ŻS6U. Particular attention was paid to determination of phase transitions temperatures during heating and cooling. The samples were heated to a temperature of 1500°C with a rate of 10°C⋅min -1 and then held at this temperature for 5 min. After a complete melting, the samples were cooled with the same rate. Argon with a purity of 99.99% constituted the protective atmosphere. The sample was placed in an alundum crucible with a capacity of 0.45 cm 3 . Temperature and heat calibration was carried out based on the melting point of high-purity Ni. The tests were carried out by the differential scanning calorimetry (DSC) using a Multi HTC high-temperature calorimeter from Setaram. Based on the DSC curves, the following temperatures were determined: solidus and liquidus, dissolution and precipitation of the γ' phase, MC carbides and melting of the γ'/γ eutectic. In the temperature range of 100-1100°C, specific heat capacity of the investigated superalloys was determined. It was found that the IN713C and IN100 alloys exhibit a higher specific heat while compared to the Mar-M247 and ŻS6U alloys.

The paper presents a research method concerning the application of statistical prognostic models for assessment of material durability and operational reliability of steel for steam pipelines, whose operation has exceeded the working time of 100,000 h. Decisions on the admission of long-lived materials to work for power industry results from extensive diagnostic examinations are based on the results of tests of mechanical properties, microstructure degradation, and corrosion processes. Considering the economic reasons and available data published in diagnostic reports, the determination of failure-free operating time of steam pipelines is based on the results of static tensile tests—tensile strength (Rm); conventional yield point (Rp); elongation (A) and Vickers hardness (V), correlated with the operating time and the media type (fresh steam and secondarily super-heated steam) for the most sensitive element of a pipeline, namely the elbow. The results of changes in strength properties during operation are presented in the form of graphs of the analyzed material feature vs. operating time in the range from zero hours (for a new material) to 300,000 h, taking into account the impact of random and systematic disturbances within the adopted tolerance limits. It has been found that because of the R2 factor and significance level in the t-Student test for regression and correlation coefficients, exponential, hyperbolic and quadratic models are best fitted to empirical points. Based on the tensile strength results (Rm), it has been found that the forecast time of the steam pipeline ranges from 193,400 to 258,300 h. Taking the yield strength (Rp) into account, it has been ascertained that the time ranges from 225,000 to 293,000 h, and for the working time forecast of steam pipelines based on Vickers hardness results, it ranges from 192,100 to 246,800 h.