PSI - Issue 60

Dhanesh N. et al. / Procedia Structural Integrity 60 (2024) 456–470 Dhanesh et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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In the FE model, the 95 m length of the plain pipeline is modeled and meshed using 20 node quadratic hexahedral continuum elements with reduced integration (C3D20R). This includes the entire length of the pipeline inside the casing and also the dented region (Appx. 8 m away from the casing end) outside the casing. The sufficient length of the pipeline is modeled beyond the dented region to capture the global bending behavior under the embankment and traffic loads. A 72 m long 18” steel casing is provided for the pipeline at the highway crossing. The casing is 4. 78 mm thick and of Grade CR-X42. The full length of the casing is included in the model and meshed using 8-node quadratic quadrilateral shell elements with reduced integration (S8R). The FE mesh generated in ABAQUS for native soil, embankment, pipeline, and casing is shown in Fig.6.

(a) Native soil and embankment

(b) Pipeline

(c) Casing

Fig. 6. FE mesh model

3.3. Material Models The standard material properties of pipeline and casing as per API 5L are presented in Table 2. A true stress-true strain curve (Fig.7) based on the Ramberg and Osgood model (Richards and Andronicou 1990) is generated. To reduce the computational requirement, the nonlinear material model is applied only for the fine-meshed dented region as plasticity is expected only in this portion of the pipeline. For the remaining length of the pipeline and casing, the elastic material model is used. Table 2. Properties of Pipeline and Casing

Item

Pipeline

Casing

Material of Construction (MOC)

X60 415 520 207

X42 290 414 207

SMYS (MPa)

SMTS (MPa)

Steel Young’s Modulus (GPa)

Steel Poisson’s Ratio Steel Density (kg/m 3 )

0.3

0.3

7850

7850

In ABAQUS, the soil layers are modeled using the Mohr-Coulomb Plasticity model (ABAQUS 2019). The Mohr-Coulomb criterion assumes that failure is controlled by the maximum shear stress and that this failure shear stress depends on the normal stress. The properties of native soil considered for the study are presented in Table 3. For the present study, the Youngs’s Modulus (E) value of the embankment is selected as 20 MPa.