PSI - Issue 42

Chmelko et al. / Procedia Structural Integrity 42 (2022) 315–320 Chmelko, V./ Structural Integrity Procedia 00 (2019) 000–000

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The burst pressure can be considered as the pressure at such a stress-strain state in the region of a corrosion defect that allows the development of plastic deformation into fracture (plastic collapse) [10] (Fig. 5). The additional bending was modelled by prescribing displacements along a defined length of pipe. The corrosion defect of dimension 30x30 mm was oriented in the line of maximum stress from bending. The depth of the defect was progressively increased from 0 to 60% of the wall thickness. Pipe centerline displacements were prescribed in increments for each defect depth so that the condition corresponding to the destruction could be determined. The effect of axial forces on the pipe is represented by the force F 0 calculated as the resultant of the axial stresses in the cross section generated by the internal pressure (Fig. 6).

Fig. 6. Simulation of the additional bending on the pipeline using FEM.

For the following simulations, a pressure magnitude of 7 MPa was considered on a DN500, t=10 mm pipe with a progressive corrosion defect of dimension 30x30 mm. The material model used was represented by the following parameters: Yield stress Re=380MPa, Ultimate stress-true Rm, true =663 MPa (recalculated from conventional σ - ε tensile diagram under condition of constant volume: σ true = σ (1+ ε )), strengthening modulus M=2162.5 MPa. The results of a large number of simulations can be interpreted graphically as the dependence of the maximum stress in the corrosion defect on the magnitude of the pipe axis deflection. Such a way of interpreting the results for an axis buckling length of 4.25 m is shown in Fig. 7. From an operational point of view, it is more appropriate to use an interpretation expressed as the dependence of the safety margin against failure on the size of the axis deflection for a defined length, as documented in Fig. 8

Fig. 7. Effect of additional bending on maximum stresses in the pipe as a function of axis deflection (DN500, t=10 mm, deflection length 4.25 m, defect 30x30 mm).