PSI - Issue 60

11

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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Fig.11. Geostatic stress state of the native soil and old embankment.

In the next step, the pipeline (without dent) is introduced in the model, activating its interaction between the casing and the trench bed. Further, the 3D profile of the pipeline dent generated using spline interpolation is introduced in the FE model as described in Section 4.1. In the next step, the trench is gradually filled with soil. To simulate the gradual backfilling of the pipeline trench, the trench soil is activated in five layers. Further, the embankment corresponding to the new highway lanes is activated. To realistically simulate the embankment construction, the activation of the new embankment is done in four layers. Fig.12 shows the deformation profile of the native soil and full embankment under gravity load. This state of the dented pipeline and soil system under the gravity load is taken as the base state for further assessment under different load cases such as internal pressure, highway vehicle load, etc.

Fig.12. Deformation profile of the native soil and full embankment under gravity load.

5. API 579-1/ASME FFS-1 Level 3 Assessment The API 579-1/ASME FFS-1 (2021), Part 12, Level 3 Assessment procedures involve simulation of the deformation process that caused the damage (i.e. dent). The following assumptions have been made for the Level 3 assessment. • No degradation of material properties (yield strength, ultimate strength, % elongation, fracture toughness, etc.) due to local large plastic strains and aging. • There is no crack or other geometrical anomaly present at the location of the dent. • Dent has occurred over an uncorroded pipeline. However, considering the design condition the analysis is performed with uniform corrosion allowance. • Pressure cycle data provided for the 1 year are taken as representative for both past and future operations