PSI - Issue 60

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

459

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Design Temperature

-26 to 65 0 C

Design factor Native soil type

0.576 (Zone – II)

Silty medium dense sand

2.2. Operational History Fatigue due to pressure cycles is a comparatively major risk component of the overall spectrum of threats to pipeline safety. The pressure variation data for the pipeline at the nearest valve location for a duration of approximately 1 year was collected from the pipeline operator. The most widely used cycle-counting algorithm “Rain flow counting” method is used to convert the fluctuating variable pressure spectrum into a pressure loading histogram. The maximum pressure range in 1 year is found to be 34 kg/cm 2 with a single cycle. On the other hand, the maximum cycles of 145 nos. for a pressure range of 1.6 kg/cm 2 . For the present assessment, the pipeline is assumed to have operated previously in a similar manner, and to continue operating similarly in the future.

Fig. 2. Histogram of internal pressure data

2.3. Details of Dent Damage The dent was identified during a routine ILI survey of the considered gas pipeline. The ILI was carried out using Electronic Geometric Pigging (EGP) method, which is a type of smart or intelligent caliper (geometric) inspection. The device has 12 sensors equally spaced around the circumference. The maximum dent depth reported was 16.2 mm (5% of diameter). The worst affected area of the pipeline is located between 4:30 and 7:30 and over about a length of 325 mm. The ILI does not report metal loss/crack/other geometrical anomaly at the location of the dent. The dent has occurred over an uncorroded pipeline thickness. Hence a uniform internal corrosion equal to the specified corrosion allowance is only considered for the integrity assessment of the dented pipeline. 3. Modeling and Assessment Methodology API 579-1/ASME FFS-1 (2021), Part 12 gives procedures for the integrity assessment of the pipeline featuring dents, gouges, and dent-gouge combinations. The Level 1 and Level 2 assessment procedures given in the above standard do not apply to the present pipeline due to complex loading conditions and the shape of the dent. Therefore, a Level 3 assessment of the dented pipeline has been carried out. Level 3 assessment involves numerical stress analysis of the dented pipeline system which should simulate the deformation process that causes the damage and evaluate the magnitude of permanent plastic strain developed. To simulate the distortion process, the analysis shall include geometric and material non-linearity as well as the contact interaction between the original undeformed pipeline and the contacting native soil. The nonlinear FE analysis has been carried out to replicate the dent using