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  • Nadirsha Shahabudeen

Under Ground Pipelines (Pipe stress Analysis)

Updated: Feb 1

We know in the process industry a substantial part of the piping system runs underground. Oil and gas pipelines are entombed in the ground for complete protection and aid. Nonetheless, buried or underground piping is commonly used to carry fluids for long miles.

Because of relative ground displacements along their length, these deposited pipelines experience a substantial load. Inorder to address the static as well as dynamic loading, which results from the temperature changes, effects of gravity, internal and external pressures, piping stress analysis offers an easing hand for underground piping. This stress analysis assures the safety of piping, piping components, linked equipment and supporting structure.

The analysis of a buried pipeline is absolutely different from plant piping analysis. The exceptional characteristics of this kind of pipeline oblige some unique problems like code requirements and techniques in the underground pipeline stress analysis.Not only that but also, the analysis elements consist of anchorage force, pipe movements, lateral soil force, soil friction, and soil pipe interaction. CAESAR II software does piping flexibility analysis, as well as the stress analysis for the underground piping system. It provides sufficient flexibility to assimilate thermal expansion, displacement aroused in the buried piping system, and code conformity for stresses.

It is necessary to differentiate the pipeline from plant piping to endorse the pipe code prerequisites and foresee the problems associated in the buried pipe stress analysis.

Here we are detailing some unique essences a pipeline acquires :

1. High Allowable Stress: A pipe has a circular shape and usually stretches several miles before turning. Most accurately , the calculation of stress is through simple static equilibrium formulas. As the provided stresses are foreseen, the acceptable stress for the plant piping is substantially higher.

2. High Yield Strength Pipe: The first stumbling block to develop is the allowable yield strength.The yield strength does not devise the complications of structural integrity, it can induce objectionable deformation and chances of strain follow-up even though the pipeline operates above. Therefore, for the construction of pipelines, a high test line with the very high ratio of yield to utmost strength is used. All the allowable stresses have yield strength as the only basis.

3. High-pressure Elongation: The movement of a pipeline is commonly because a very long line’s development has a low-temperature variation. The pressure elongation is imperceptible in a plant piping, granting much to the total movement and hence should constitute the pipe stress analysis.

4. Soil-pipe Interaction: As a huge part of a pipeline is buried underground, any unrest in the pipe has to conquer the soil force, commonly divided into two categories: (i) Friction Force Organized by Sliding, and (ii) Pressure Force deriving from Pushing. The most compelling task of underground pipe stress analysis is to inspect the soil-pipe interaction, which does not matter in the plant piping analysis.

The penetraty study of a buried piping system is chiefly done using (ASME 31.1), the power piping code whereas the CAESAR II platform supports in modeling and analyzing the piping system. Revised layouts can be then reviewed through CAESAR II for the same operating and environmental plights to select the most optimized piping system layout

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