Orenburg State University, Orenburg, Russia:

V. S. Repyakh, Cand. Eng., Associate Prof., Dept. of Materials Science and Technology (MS&T), e-mail: podval2004@mail.ru
V. M. Kushnarenko, Dr. Eng., Prof., Dept. of Mechanics of Materials, Structures and Machines, e-mail: vmkushnarenko@mail.ru
Yu. A. Chirkov, Dr. Eng., Prof., Dept. of Mechanics of Materials, Structures and Machines, e-mail: chirkov_ura@mail.ru
S. V. Boyko, Cand. Eng., Associate Prof., Director of Engineering Center, e-mail: boikosv61@mail.ru

The article provides the results of studies to determine the causes of failure of the check valve body. The fracture analysis of fractures resulting from the formation of cracks on the body of the check valve is described, with the determination of the fracture site. Also, based on the data of the process documentation for the check valve, an analysis was carried out on the manufacture, heat treatment and mechanical properties of the material of the check valve body. As a result of studies, possible defects obtained both as a result of valve operation and during manufacture as a result of heat treatment of the valve body material are determined, the microstructure of the main metal of the valve body, the results of mechanical tests, the causes of destruction are considered. In the structural elements of the tubing string (tubing) there are defects that cause their failures. For example, a fracture of the pipe body or nipple end occurs during corrosion-sorption cracking of steel, sulfide cracking in a hydrogen sulfide-containing aqueous medium; failure of the wall integrity during corrosion-sorption mechanical wear; disturbance of thread turns during fretting corrosion and cracking of steel; narrowing of internal section due to formation of solid deposits. Influence of mode of heat treatment of metal of check valve body and working loads, under conditions of complex stressed state, creates considerable concentration of stresses in area of thread hollows and corrosive sores of metal of check valve body, which in case of short-term action of inducing hydrogen sulfide-containing working medium leads to development of microcracks and destruction of metal of check valve body.

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