Determination of the limiting sizes of crack-like defects in a wall of steel vertical tanks

UDK: 621.64:539.4

DOI: 10.24887/0028-2448-2017-3-104-107

Key words: vertical steel tank, surface cracks, finite element method, stress intensity factor

Authors: G.H. Samigullin, AA Lyagova (Saint-Petersburg Mining University, RF, Saint-Petersburg)

This paper presents the results of numerical investigation of stress-strain state of the vertical steel tanks with longitudinally oriented cracks. The paper studies the cracks in the wall of vertical steel tanks with specified volume of 5000, 10000, 20000 and 30000 m³. Surface non-through cracks are one of the main causes of tank failure. The prognostication of the crack critical dimensions requires analytical expression for the K-calibration function. K-calibration function is the dependence taking into account the change in dimensions of a defect and defect orientation angle relatively to generatix of the tank. The calculation of the stress-intensity factor (SIF) of a surface longitudinally oriented crack located in the tank wall was performed using finite element method. The cracks with various dimensions were studied by generating global finite-element model of the tank and a sub-model of the tank ring with a crack. Curve Fitting Toolbox Matlab software was implemented to derive analytical expressions for K-calibration function of cracks with different shape located in the wall of vertical steel tank. All expressions for the K-calibration function are described by a polynominal function that allows estimating the critical size of a defect. The new program is created for calculation critical and threshold crack depth. The work results could be interesting for oil industry engineers.

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