Ilya Vlasov

Structural levels of the nucleation and growth of fatigue crack in 17Mn1Si steel pipeline after long-term service

AbstractThe majority of modern gas pipelines in Ukraine, Lithuania and Russia have been operating for more than 30–40 years. The problem of forecasting residual life-time of materials comprising such gas pipelines calls for study of their degradation kinetics as well as requires to determine its relationship with the strain-force loading parameters. The aim of the paper is to study the kinetics of fracture in order to range mechanisms of cyclic deformation of 17Mn1Si steel at nucleation and growth of a fatigue crack. Flat specimens were cut out from a fragment of 17Mn1Si steel pipe after 40 years of service. Microstructures of specimens were examined. In the paper, an attempt was made to apply the combined approach to study of deformation and fracture based on the following research parameters from nonlinear fracture mechanics: physical mesomechanics and numerical fractography.

Fatigue life enhancement by irradiation of 12Cr1MoV steel with a Zr+ ion beam. Mesoscale deformation and fracture

The structure and properties of 12Cr1MoV steel irradiated with a zirconium ion beam were studied by optical microscopy, scanning electron microscopy, and micro- and nanoindentation. It is shown that the modification covers the entire cross-section of the irradiated specimens to a depth of 1 mm. The data on irradiation-induced structural changes are used to interpret the changes in mechanical properties of the irradiated specimens under static and cyclic loading. Particular attention is given to analysis of strain estimation by the digital image correlation method.

Effect of temperature-force factors and concentrator shape on impact fracture mechanisms of 17mn1si steel

The influence of the notch shape on the impact fracture of 17Mn1Si steel is investigated at different temperatures with the focus placed on the low-temperature behavior. An approach towards fracture characterization has been suggested based on the description of elastic-plastic deformation of impact loaded specimens on the stage of crack initiation and growth at ambient and lower temperatures. The analysis of the impact loading diagrams and fracture energy values for the pipe steel 17Mn1Si revealed the fracture mechanisms depending on the notch shape. It was found that the testing temperature reduction played a decisive role in plastic strain localization followed by dynamic fracture of the specimens with differently shaped notches. A classification of fracture macro- and microscopic mechanisms for differently notched specimens tested at different temperatures was proposed which enabled a self-consistent interpretation of impact test results.

Structural and mechanical defects of materials of offshore andonshore main gas pipelines after long-term operation

Abstract The study has established the main regularities of a fatigue failure of offshore gas steel pipes installed using S-lay and J-lay methods.We have numerically analyzed the influence of preliminary deformation on the fatigue life of 09Mn2Si steel at different amplitudes of cyclic loading. The results have revealed the regularities of formation and development of a fatigue crack in 17Mn1Si steel after 40 years of underground operation. The quantitative analysis describes the regularities of occurrence and growth of fatigue cracks in the presence of a stress concentration.

Increasing the fatigue life of 12Cr1MoV steel by surface nanostructuring with a Zr+ ion beam. Structure, properties, and fracture pattern

The paper presents the results of static and cyclic tensile tests and alternate cyclic bending tests of 12Cr1MoV specimens in the initial state and after surface nanostructuring with a Zr+ ion beam. Examination by optical and scanning electron microscopy and interference profilometry revealed differences in the formation of the deformation relief and in the character of cracking of the modified surface layer. The changes occurring in the modified surface layer were estimated by nanoindentation, X-ray analysis, and fractography. The nanostructure formed in the treated surface layer was analyzed by transmission electron microscopy. The difference in deformation is interpreted using the multiple cracking concept. The effect of substantial enhancement of fatigue strength is associated with retarded plastic deformation and fatigue crack propagation in the modified surface layer.

Influence of notch shape on deformation mechanisms and energy parameters of fracture of 12Cr1MoV steel under impact loading

Impact loading curves and fracture energy of the notched 12Cr1MoV ductile steel specimens are analyzed. The qualitative description and quantitative parameters are obtained for major stages of ductile and brittle fracture depending on the shape of the notch and the stress stiffness ahead. It is shown that a zone with enhanced plasticity is formed in the vicinity of V-, U-, and I-shaped notches at 20°C testing temperature, giving rise to ductile fracture. The stress stiffness at the notch tip increased with testing temperature reduced to –40°C. Using the quantitative description of fracture surfaces, a physical-mechanical scheme of the specimen fracture was suggested for the case of enhanced and localized (constrained) plasticity near the stress concentrator tip.

Structure and mechanical properties of coatings formed by detonation spraying of titanium powder

The paper studies the structure and properties of coatings formed by detonation spraying of titanium powder when varying the deposition parameters including nature of carrier gas, spraying distance, O2/C2H2 ratio, and volume of explosive mixture. It is shown that when the air is used as a carrier gas the primary strengthening by the titanium oxide phases is implemented. When nitrogen is introduced into the explosive mixture, a more complicated scheme of hardening is executed due to the formation of titanium oxides, carbides, oxynitrides and carbonitrides. The authors consider the aspects of employing the revealed “rational” modes of the detonation spraying to form protective composite coatings based on titanium possessing a complex of improved physical and mechanical properties.

Study of fracture toughness of ZrO2 ceramics

The fracture toughness characteristics of ZrO2ceramics were determined experimentally using an original technique of wedging small-sized chevron notch specimens developed at the Institute of Strength Physics and Materials Science SB RAS (Russia) in the laboratory of physical mesomechanics of materials and non-destructive testing. Measurements have shown that inelastic displacements can be more than 22% of the total displacement of the consoles by the time of the specimen failure. The effect of the Y2O3 stabilizer on the critical stress intensity factor KIc was verified. It was shown that an increase in the Y2O3 stabilizer content from 3 to 8% significantly decreases the fracture toughness. The stress intensity factor KIc falls within the range from 5.7 to 2.35 MPa m1/2.The fracture toughness characteristics of ZrO2ceramics were determined experimentally using an original technique of wedging small-sized chevron notch specimens developed at the Institute of Strength Physics and Materials Science SB RAS (Russia) in the laboratory of physical mesomechanics of materials and non-destructive testing. Measurements have shown that inelastic displacements can be more than 22% of the total displacement of the consoles by the time of the specimen failure. The effect of the Y2O3 stabilizer on the critical stress intensity factor KIc was verified. It was shown that an increase in the Y2O3 stabilizer content from 3 to 8% significantly decreases the fracture toughness. The stress intensity factor KIc falls within the range from 5.7 to 2.35 MPa m1/2.

Influence of stress concentrator shape and testing temperature on impact bending fracture of 17Mn1Si pipe steel

INTRODUCTION A common tendency in transportation pipeline development, particularly, for main gas and oil pipelines, is a gradual increase in their service life and performance [1]. The problem is particularly acute since the pipelines often operate in unfavorable weather conditions, e.g., at low temperatures. A challenging task in this respect is to extend the service life of pipe steels by improving their mechanical properties [2]. Specifically, the fracture toughness – the major characteristics of crack resistance has to be increased. Main detrimental factors affecting the strength and crack resistance of pipe steels are attributed to tensile stresses and corrosion of the outer surface of pipes arising in underground conditions due to delamination or rupture of protective coating and localized corrosion of the inner surface [3]. Currently available approaches to characterizing the base metal ductility allow estimating the dynamic crack initiation conditions that are crucial for the prevention of gas and oil pipeline failure [4]. It requires development of robust methods for the fracture energy determination in pipe steels with account of the shape of stress concentrators. These data can be used to account for the influence of embrittlement factors on the impact deformation resistance of pipe steels. Furthermore, modern low-carbon steels produced by thermomechanical processing of the initial sheet have different sensitivity to the concentrator shape and temperature/force loading parameters. It is therefore important to understand the fracture mechanisms operating at different stress stiffness values. The present paper is aimed at obtain a deeper insight into the influence of the notch shape on the impact fracture of 17Mn1Si steel at different temperatures with a focus on the low temperature fracture behavior.

Effect of vacuum arc ion beam treatment on the structure and mechanical properties of 30CrMnSiNi2A steel

The paper reports on a study of the structure and mechanical properties of 30CrMnSiNi2A high-strength steel irradiated with a Zr+ ion beam. The effect of irradiation on the steel was assessed by optical, transmission, and scanning electron microscopy as well as by X-ray di ITraction analysis of its irradiated and non-irradiated specimens 1 mm thick under static and cyclic tension, showing an increase in the fatigue life of the steel after irradiation. The deformation behavior and the mechanical properties of the specimens were compared, and the factors responsible for the increase in fatigue life were analyzed.