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

RESEARCH OF THE METAL WORKING IN THE ENVIRONMENTS CAUSING SODIUM HYDROGEN CRACKING

The results of a study of a metal working in environments causing hydrogen sulfide cracking are presented. The previously studied steels were induced in a hydrogen sulfide-containing medium under the action of tensile stresses in the metal of the samples. It has been established that characteristic defects in the form of bubbles and blisters are formed on the surface of metals. A study of microstructures showed that cracks originate at the boundary between pearlite and ferrite grains and on the streaked sulfide phase of the FeS · MnS type. Disclosure of the boundary of pearlitic and ferrite grains is due to their surface contamination with microimpurities. The results of the analysis for inclusions show that 20YuCH steel is much cleaner in inclusions than American steel of the type steel 20, and sulfides are more dispersed and coagulated, while a significant part of the sulfur is bound by cerium. This explains the best resistance of steel 20YUCH against hydrogen sulfide cracking.