Increasing the construction strength of petroleum pipes operating in agressive environment

Purpose. Questions about ways to increase the structural strength of oil country tubular goods are considered. Alloying and heat treatment of medium-alloy steels should ensure: pro-carbonization to the structure of martensite and lower bainite with a minimum carbon content (C ≤ 0.3 %), high resistance to brittle fracture and hydrogen embrittlement, the formation of uniformly distributed finely dispersed carbides and sulphides of a round shape to reduce diffusion mobile hydrogen is absorbed by steel. Propose modes of thermal treatment of casing pipes that provide the required level of mechanical and operational properties. Methodology. We used standard techniques for determining the mechanical properties in tension, dynamic bending tests and fracture studies. Results. The modes of heat treatment of casing pipes of strength category E, L are proposed, which provide the required level of mechanical and operational properties and an increase in structural strength. Originality. A systematic analysis of the influence of various factors on the structural strength of oil country tubular goods operating in an aggressive environment has been carried out. The highest degree of correlation between the value of the impact toughness and the tough component in the fracture is shown. Cooling of pipes with a nozzle sprayer of the design of the Department of Heat Treatment of Metals of NMetAU, which provides high resistance to brittle fracture by increasing the proportion of the viscous component and changing the microrelief of the cup fracture. Practical value. The proposed technology of heat treatment of oil pipes, working in an aggressive environment, provides the required level of mechanical properties and resistance to hydrogen sulfide cracking. Keywords: structural strength; oil country tubular goods; alloying; heat treatment; strength categories;temperature and deformation parameters; hydrogen sulfide cracking; brittle fracture resistance

On the Methods for Assessing the Resistance of Steels to Brittle Fracture

The problem of assessing steels durability, their resistance to brittle fracture in the structures used in various branches of industry, remains relevant at the development of the new equipment and control of the old equipment. Standard strength calculations do not give a complete picture of the ability of steels due to their physical and mechanical properties to resist the formation and further development of defects and cracks under the action of actual stresses. The correct choice of a structural material for technical devices operating at low temperatures, knowledge of its characteristics of resistance to brittle fracture, understanding of brittle fracture mechanism at low temperatures and research in this area are of great importance. Since 1980s, JSC IrkutskNIIkhimmash systematically conducts the research works related to impact strength characteristics. These works are carried out in connection with the need for assessing the resistance to brittle fracture of metal of the equipment for storing oil products, vessels and pipelines, drill pipes and tubing, etc. As a result of many years of research, the authors accumulated significant experimental material in the form of temperature dependences of impact strength - both for the material of various types of blanks (sheets, pipes, forgings) in the state of delivery, and for the metal of technical devices elements after their operation of various duration. The main objective of the article is to assist specialists in establishing the correct choice of steel for the new or old structures in terms of their resistance to brittle fracture without conducting special studies. Specialists can select the closest steel analogue (on chemical composition, mechanical properties, and the type of product without making cuts from the structure or blanks for additional research), and set the numerical value of the impact strength, critical temperature of brittleness and the stress intensity factor for any temperature in the range from –40 to 20° С in order to use them in further calculations.

Modifying and Micro-Alloying Effect on Carbon Steels Microstructure

Small additives of elements exhibiting high chemical activity with respect to iron and impurities, included in its composition, have a complex effect on the structure and properties of steel. Moreover, as a result of the modifying and refining effect of micro-additives, the amount, dispersion and morphology of nonmetallic inclusions change, and when alloying the matrix, hardenability, uniformity of structure and resistance to brittle fracture of steels change, too. The article presents a metallographic analysis of carbon steel deoxidized by a complex Са – Ва alloy. Deoxidation of steel using the complex Са – Ва alloy allows significant reducing the content of nonmetallic inclusions, modifying residual nonmetallic inclusions into favorable complexes with their uniform distribution in the volume of steel, and significant increasing the mechanical properties of steel. The high surface activity of barium makes it possible to consider barium as a rather effective modifier. The use of barium in alloys leads to grinding of non-metallic inclusions, homogenization of liquid metal, lowering the liquidus temperature, grinding of primary grains of cast steel, and increasing technological ductility.

Analysis of Methodological Framework for Computer Strength Justification of Steel Structures at Operating NPP Units

Over the last decade, new national regulatory documents on the design and assessment of the technical state of building structures, in particular steel ones, have been put into force in Ukraine to replace relevant former USSR regulations. The experience of applying new national regulatory documents indicates certain incorrect provisions, which can potentially cause catastrophic consequences in case of failure of steel building structures of corresponding facilities and(or) hazardous production capacities. The paper presents the analysis of Ukrainian regulations to check compliance of available methodologies for computer strength justification of steel structures. It is established that current regulatory documents of Ukraine do not contain a description of methodologies and procedures (formulae) with regard to calculations of steel structures on resistance to brittle fracture and cyclic crack resistance. The analysis of a number of publications was performed to define methods for the calculation of steel structures to check endurance, cyclic crack resistance and resistance to brittle fracture.