Study of the effect of test parameters on the assessment of steel resistance to carbon dioxide corrosion

Carbon dioxide (CO2) corrosion is one of the most dangerous types of destruction of metal products in the oil and gas industry. The field steel pipelines and tubing run the highest risk. Laboratory tests are carried out to assess the resistance of steels to carbon dioxide corrosion. However, unified requirements for certain test parameters are currently absent in the regulatory documentation. We present the results of studying the effect of the parameters of laboratory tests on the assessment of the resistance of steels to CO2 corrosion. It is shown that change in the parameters of CO2 concentration, chemical composition of the water/brine system, the buffer properties and pH, the roughness of the sample surface, etc., even in the framework of the same laboratory technique, can lead in different test results. The main contribution to the repeatability and reproducibility of test results is made by the concentration of CO2, pH of the water/brine system, and surface roughness of the samples. The results obtained can be used in developing recommendations for the choice of test parameters to ensure a satisfactory convergence of the results gained in different laboratories, as well as in elaborating of a unified method for assessing the resistance of steels to carbon dioxide corrosion.

The use of carbon nanotubes to increase the sensitivity of the antibiotic determination with a piezoelectric immunosensor

Conditions for the preparation of carbon nanomaterials for embedding into the discerning layer of a piezoelectric immunosensor are described. The effect of the oxidation method, temperature, and the duration of treatment of nanomaterials with an oxidizing agent on the surface concentration of active functional groups is demonstrated. It is shown that the use of carboxylated carbon nanotubes (CNT) increases the efficiency of their binding to biomolecules and increases the stability of the discerning layer of a piezoelectric sensor when measurements are carried out in liquid media. Conditions for the determination of antibiotics using piezoelectric immunosensors modified with carbon nanomaterial were studied including the choice of immunoreagent concentrations and assessment of the selectivity of antibiotic determination. The CNT-based piezoelectric immunosensors providing rapid, highly sensitive, and selective determination of the analyte at the MRL level and below it in food products and biological fluids are proposed.

Validation of the expert methodology «Detection of condensed traces of the gunshot residue containing heavy metal compounds on various objects by scanning electron microscopy and X-ray microanalysis»

We present and discuss the results of the validation of a forensic qualitative testing technique which consists in the detection of condensed traces of the gunshot residue (GSR) in the form of individual microparticles on the objects under study and their identification by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) using a scanning electron microscope Mira III (Tescan, Czech Republic) equipped with a system of X-ray microanalysis INCA GSR 450 (Oxford Nanoanalysis, Great Britain). The procedure for detecting GSR particles containing heavy metal compounds, systems of their classification and interpretation of test results are described. The suitability of the methodology for solving forensic problems has been confirmed. The validation procedure consists in assessing the reliability by comparing the test results obtained by experts (A and B) in two laboratories at different times using the same device, and in confirming the competence of experts proceeding from the results of blind tests. A standard sample ENFSI GSR PT 2018 A-03-07 is used. Each of the experts determined the number of particles classified as GSR present in control samples taken in a ballistic laboratory during a full-scale experiment: from the hands of the shooter; from the hands of a person who did not shoot; without microparticles (clean stage of an electron microscope). The reliability of the technique is characterized by the index (probability) of correct results of detecting GSR particles in the standard sample of at least 95.8% and by a small proportion of false results (no more than 5.4%). The competence of the experts is proved by the consistent results of «blind» testing of control full-scale samples, containing and not containing GSR particles obtained in different laboratories. The results of the validation indicate the suitability of the method for obtaining reliable and valid information about the presence of GSR particles on the objects under study.

Study of the destruction of the chassis main cross member made of VT22 alloy

The reasons for the destruction of the chassis main cross member made of alloy VT22 are considered and analyzed in bench test conditions. The chemical composition, mechanical properties, as well as macro- and microstructure of the material were studied. The tests of the cross-arm material for crack resistance and low-cycle fatigue (LCF) with the determination of the durability were carried out. The results of analysis proved that material meets the declared performance characteristics. A fractographic study of the traverse fracture showed that the fracture occurred from several foci according to the fatigue mechanism. The length of the longest fatigue crack was 1.7 mm and the critical stress intensity factor KIc was thus attained. Proceeding from the dimensions of the part at the site of fracture, the maximum crack length and the value of the critical stress intensity factor obtained experimentally KIc = 56.5 MPa • m1/2, we have calculated the nominal tensile stress at the moment of fracture. The calculated value of the nominal stresses is 1022 MPa, which is comparable to the yield strength of the material (1100 MPa). A high level of tensile stresses in the loading cycle is considered the most probable reason for the destruction of the chassis main cross member in the conditions of bench tests.

Extraction concentrating of the acid-soluble forms of rare earth elements from oils of the Volga-Ural oil and gas province using rotating coiled columns

Trace elements in oils are the natural markers of the oil origin of and the mechanism of oil genesis. Direct determination of rare earth elements (REE) in crude oils is rather difficult due to their low concentrations (10–6 wt. %). Information about the forms of trace elements in oils is of particular interest. The goal of the study is determination of the content of acid-soluble forms of REE in oils from various fields of the Volga-Ural oil and gas province. Six samples of oils of heavy and medium density and viscosity were analyzed. Extraction of acid-soluble forms of REE was carried out using rotating coiled columns in 0.5 M aqueous solution of nitric acid. Toluene was used to dilute the oils up to the necessary values of the density and viscosity providing the possibility of extraction in the system aqueous acid solution – oil. The content of REE was determined by inductively coupled plasma mass spectrometry on an Agilent 7900 spectrometer. Their content in an acid-soluble form in oil samples under study ranged within 172 – 2173 ng/kg. Such a wide range of values is attributed to the difference in the geology and age of deposit formation. The highest content of acid-soluble forms of REE (2173 ng/kg) was observed in the oil sample from the Novo-Elkhovsky field, whereas the lowest value (172 ng/kg) was measured in the oil sample of the Pioneer field. It is shown that the content of acid-soluble forms of REE depends on tectonic zoning, productive horizons and layers, as well as on the physical and chemical properties of oils. The distribution of acid-soluble forms of light and heavy REE was evaluated. Most of the REE (75 – 99%) determined in the analyzed oil samples are light REE. It is noted that systematization of the data on the properties of oils, geological and geochemical characteristics of the deposits will provide reliable forecasting of the various forms of REE present in oils.

Study of Ti – Al based high-temperature cermet filters

Operation in corrosive media and/or at high temperatures requires improved characteristics of the performance and durability of filtering equipment. The Ti – Al intermetallic system combines low density with high strength and exhibits high resistance to oxidation and corrosion at elevated temperatures. We present the results of studying high-temperature Ti – Al cermet products (filters) with nanoscale pores. Filters were obtained from a mixture of Ti and Al powders (mass ratio 40:60) by thermal explosion. XRD methods showed that the synthesized material consists of two main phases: TiAl3 and Al2O3. The microstructure analysis revealed the presence of large-sized TiAl3 structures and spherical Al2O3 aggregates enveloped by nanostructured TiAl3. Moreover, nanoscale fibrous TiAl3 compounds forming a multilevel developed cobweb-like structure are observed in the entire volume of the pore space of the material. The open porosity of the material was 48%, the pore size was 0.1 – 0.2 μm, the efficiency of the porous material was 99.999%, the resistance to gas flow was 100 mm of water column, and the filtration index was 0.062. Thermal tests revealed the possibility of effective use of filters under conditions of elevated (up to 800°C) temperatures and corrosive media due to the chemically stable and heat-resistant binary structure of the material. The results obtained can be used to improve the methodology of the development and operation of high-temperature cermet filters based on Ti – Al.

Selective determination of rhodium and iridium in the urban environment using the catalytic method

The problem of studying the level of technogenic pollution of the environment with platinum group metals is attributed first to the release of platinum metals into the environment together with the exhaust gases of cars using afterburning catalysts containing Pt, Pd, Rh. The pharmaceutical, electronics and jewelry industries the waste of which contains PGMs also contribute to the pollution of the environment. A number of studies have shown the toxic effects of PGM on humans. The goal of the study is to obtain new information about the level of technogenic pollution of the environment with platinum group metals (such as water-washings from roads, bio-collector plants, roadside dust), which necessitates developing of the method for sample preparation and determination of rhodium and iridium. A technique of sample opening and determination of rhodium and iridium in environmental objects, water-washings from roads, bio-collector plants, roadside dust is proposed. To increase the selectivity of rhodium determination, the samples were treated with a mixture of concentrated perchloric acid and sodium periodate when heated to boiling, which provided more than 5-fold increase the rhodium signal. Moreover, the permissible excess of iridium and ruthenium was increased by 5 and 20 times, respectively, due to the conversion of other PGMs into catalytically inactive forms. The indicator reaction of sulfarsazen oxidation by periodate was used in the kinetic determination of rhodium and iridium. The correctness of the results obtained by the developed method was confirmed by the ETAAS method. The determined content of Rh and Ir: in roadside waters (μg/liter) up to 0.015 and 0.005; in collector plants (g/ton) up to 0.030 Rh and 0.022; in street dust (g/ton) up to 0.05 and 0.025, respectively. The standard deviation of the repeatability of the determination results does not exceed 0.07 (Rh) and 0.12 (Ir). The developed method of opening samples and determining rhodium and iridium in environmental objects provided a great bulk of information about the content of rhodium and iridium in water-flushes from Moscow roads, bio-collector plants, roadside dust, which correlate fairly well with the scarce data from other geographic regions available in the literature and our earlier results on rhodium content in dust. The developed technique made it possible to obtain data on the level of technical pollution of the environment with PGMs in places with different traffic density in Moscow.

Study of the heat capacity of VZhM4 nickel superalloy using differential scanning calorimetry, adiabatic and mixing calorimetry

An increase in the operating temperatures of assemblies and parts of modern aircraft is a key task for the aviation industry which entails developing of new materials that meet the increased requirements for their operational characteristics. A high level of the accuracy and reliability of the determined properties is one of the most important factors in designing high-temperature metal, ceramic and heat-shielding materials. The features of a particular measurement procedure, as well as their hardware design, do not always ensure the specified accuracy of experiments over the entire temperature range. We present the results of studying the heat capacity of VZhM4 nickel superalloy in the temperature range 100 – 1360° C by the methods of differential scanning calorimetry (DSC), adiabatic and mixing calorimetry. The data of the DSC analysis of the alloy, the temperatures of phase transformations and temperature dependences of the specific heat of the material are analyzed along with the assessment of their accuracy at different temperature intervals. A comparative analysis of the studied measurement procedures complements the research. The results obtained can be used in the development of new materials and in the study of the specific heat capacity of metal products in a wide temperature range.

Procedure for determining the constants of JH-2 (Johnson – Holmquist) dynamic fracture model for brittle materials

A simplified method for evaluating the constants in the JH-2 (Johnson – Holmqvist) model of the dynamic fracture for brittle materials is presented. The classical procedure suggests the use of 21 independent parameters describe the material, and the problem of their determination entails a large number of calculations experiments which hamper the use of the JH-2 model. The proposed technique requires fewer complex calculations and experimental data to determine the parameters of the material thus making it more feasible in use. In this work, the technique is used to search for the parameters of aluminum oxide (Al2O3) with a density of 99.5%, which is the material of a ceramic barrier subjected to high-speed interaction with the impactor. We present the results of three tests for penetration of a corundum plate: two of them are used to determine the constants of the model, and the third is used to verify the obtained values. Note that, the results obtained using the presented approach match quite accurately the experimental data, which is demonstrated in the course verification of the procedure.

Evaluation of the threshold for the development of fatigue cracks in a railway steel under harmonic and operational loading

The results of experimental studies of the fatigue crack development in 20GFL steel specimens cut from a cast bolster of a freight car are presented. The ratio of the threshold stress intensity coefficient Kth determined from the kinetic diagram of fatigue fracture and from the average parameters of the operational loading process is considered using the experimental results with a simulation of operational loading. Tests were carried out upon the development of permanent blocks of crack opening in the specimen (in a rigid loading mode). The operational process is presented in the form of a block of consecutive loading cycles recorded during the test of the car frame in conditions typical for a straight section of the railway track. The threshold operational level is determined by the algorithm of gradual reduction of the loading similar to the original process. The regularities in a decrease of the rate of crack development and corresponding decrease in the load were determined. Subsequent extrapolation of the obtained experimental regularities to zero value of the crack propagation rate provided estimation of the threshold loading level, similar to the initially specified value. It is shown that the value of the threshold level of the fatigue crack development in low-alloy steel 20GFL obtained from the fatigue fracture diagram (i.e., under harmonic loading) is significantly higher than that obtained from the estimate based on the average values of the operational loading process. The considered model of operational loading gives greater damage compared to harmonic loading, on the basis of which the survivability of structural elements is usually assessed.