PSI - Issue 48

Udaya B Sathuvalli et al. / Procedia Structural Integrity 48 (2023) 207–214 Sathuvalli and Suryanarayana/ Structural Integrity Procedia 00 (2019) 000–000

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Fig. 1. Schematic illustration of tension collapse

In the preceding operations, the casing experiences “displacement controlled” loading, either by transfer of geomechanical strain (Fig. 1a) or the suppression of thermal strain (Fig. 1b). Though casing collapse mechanisms have been studied extensively, a simple and expedient method to determine the structural limit of casings in these situations has not been explicitly addressed in the literature. Our paper tries to fill this gap. The number of studies on collapse of tubulars is too numerous to attempt a full survey here. We refer the reader to chapter 8 of Pattillo (2018), and the references therein for a thorough discussion. Other important studies are listed in Madhavan et al. (1993). They present experimental results on the effects of tension and material anisotropy on load controlled collapse of thick-walled cylinders, and compare them with a plasticity model. 2. Tension Collapse Load on a Thick-Walled Cylinder Fig. 2 shows a pressurized hollow cylinder subjected to axial strain. In this illustration, the plasticized inner circular core is constrained by the outer elastic zone. Since plasticization in an unbent cylinder begins at the ID, the combination of pressures and axial strain that causes yielding at the cylinder ID can be found from elastic considerations. By using Lame equations for the radial and hoop stresses in a cylinder, we can show that the ID yields when the following condition is satisfied, ( ) ( ) ( ) 2 2 2 2 int int 1 2 . 3 s z i ext o ext o yp EA P A P A P P A F ε ν − − − + − =     . (1) where F yp denotes the pipe body yield strength, (2) Further increase in any of the load parameters ( P int , P ext , ε z ), increases the area of the plastic zone. Because of axisymmetry, the elastic plastic boundary that demarcates the plastic and elastic zones is a circle of radius ρ ( a ≤ ρ ≤ b ). , yp T s A σ = . yp F

Fig. 2. Progressive plasticization of a pressurized cylinder