Vol. 7 є 3, 2017 p 24-31

Pages

Article name, authors, abstract and keyword

24-31

On the role of construction and metallurgic defects in destruction failure of main pipelines

Airat R. Khafizov a, Maria N. Nazarova b, Andrey N. Tsenev b, Nikolay K. Tsenev a, c

a Ufa State Petroleum Technological University, 1, Kosmonavtov St., Ufa, 450062, Russian Federation

b The Mining University, 2, 21st Line, St Petersburg, 199106, Russian Federation

c Research and Development center of pipeline transportation Transneft R&D LLC (STC Transneft R&D), 144/3 Oktyabrya prospect, 450055, Ufa, Bashkortostan, Russian Federation

https://doi.org/10.28999/2541-9595-2017-7-3-24-31

Abstract: Introduction. The paper considers typical examples of depressurization of coils of long-operated sections of pipelines.
Materials and methods. To determine the causes and conditions that led to the incidents, various modern research methods were used: Mechanical tests, metallographic and fractographic analysis, finite-element computer complex ANSYS 6.0.
Experimental results and their discussion. An example of an incident was considered when, during the construction of a pipeline, crowns of excavator teeth left impact on the coil. Despite such a construction and installation defect, the coil was operated for almost 40 years. There were defined conditions for fatigue fractures by means of experiments and with the use of two-dimensional calculated finite element model of 6016 PLANE 2 elements, designed to analyze stress distribution in regions with significant gradients. Thus, the samples cut from the places of local plastic deformation made by the excavator teeth crowns had the number of cycles before failure at an average cycle stress of σ1 = 0,9σт more than two times less than in the samples cut from the body of the coil. It is shown that if a 2 mm deep defect is located on the outside of the pipe wall, the level of tensile stress at a pressure of 2.68 MPa at the defect tip reaches about 407 MPa, which is noticeably higher than the yield strength (350 MPa). It is obvious that a plastic zone is formed in this place, and there is an active accumulation of crystal grating defects in the pipe wall under the influence of variable loads, which lead to the nucleation and development of a crack.
The features of the crack process development were investigated in the case of formation of an extended cavity in the zone of the pipe welded butts displacement and with a use of a reinforcing cover as the coil repair element.

Keywords: construction defects, repair defects, metallurgic defects, pipeline destruction

Reference for citing:
Khafizov A.R., Nazarova M.N., Tsenev A.N., Tsenev N. K. On the role of construction and metallurgic defects in destruction failure of main pipelines. Naukatekhnol. truboprov. transp. neftiinefteprod. = Science & Technologies: Oil and Oil Products Pipeline Transportation. 2017;7(3):24Ц31.

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