Pipeline Stress Analysis: How To Get it Right?

Pipeline Stress Analysis differs from standard plant piping stress analysis. Pipelines usually have long-distance transportation (kilometers in length) of a liquid and gas. There are various types of pipelines in operation as transportation systems around the world. Let us dig deeper to understand the considerations to perform complex stress analysis for buried and above-ground pipelines.

ASME B31.4 is the design standard for transporting liquids such as natural gas liquids, liquefied petroleum, crude oil, natural gasoline & more. At the same time, ASME B31.8 covers gas distribution and transmission pipeline design. IT includes gas metering and regulation stations, gas pipeline, gas mains, and more.

General Pipeline Design Considerations

The long length of the pipeline is the main difference between plant piping and pipeline. In most cases, the design temperature for pipes is lesser than piping systems. Pipeline thicknesses are usually lesser compared to plant piping. A reasonable estimate of the material moment and its interface with the connected piping and equipment resistance force is vital in designing a pipeline.

The elongation of the pipe due to internal pressure can have a considerable effect on pipeline stress analysis. A large number of pipeline movements are caused by pressure elongation or the bourdon effect.

Total Elongation of Pipelines = Temperature Elongation + Pressure Elongation

The hydro-test pressure for pipeline stress analysis is nearly 1.25 times the design pressure.

Pipeline Stress Analysis Software

Software for pipeline stress analysis consists similar list as plant piping stress analysis. The software can change design code and run the analysis. Some of the popular pipeline stress analysis software are as follows:

CAESAR II by Hexagon

Auto-Pipe by Bentley

Caepipe

Critical points for Pipeline Stress Analysis

The most basic type of loads considered during pipeline stress analysis includes:

Sustained Loads

Occasional Loads

Expansion Loads

The features for pipeline modeling are as below:

Bend radius should be provided as pipelines dimension has very long radius elbows i.e., 25 D to 60 D

The cover of the pipeline must be adequately buried into the soil parameters. As pipelines usually run on uneven surfaces, different pipeline segments come with different buried depths.

If sleeves are used for buried parts of the pipeline, then it needs to be modeled. It becomes above-ground parts with spacer supports at even distances.

For above-ground pipeline: Expansion loops are provided at 500 m distance from the other loop.

Pipelines turn at various angles, unlike 45° or 90° in-plant piping. So, it needs to be molded appropriately from GA drawing.

The pipelines for above ground and buried applications have different design temperatures.

Proper soil data entry should be done from soil reports by the civil team for buried pipelines.

There are no Sh values like B 31.3. Pipelines run several km without fittings.

The default value for Fac is 0.0.

There is nothing like liberal stress in pipeline stress analysis.

Soil parameters are essential for stress analysis. The stress engineer should avoid following an approach that leads to over-design in stress analysis.

Anchor blocks are necessary to support pipeline stress analysis.

Pipelines are always connected via piping systems. So, both piping and pipeline codes are used as and when needed.

There are different challenges associated with pipeline stress analysis. But the biggest one is not planning for action. Are you looking for pipe flexibility analysis services for your process industry? If yes, then consider hiring a reliable engineering partner that adheres to international codes and standards.

Judith Morrison is an expert in the field of industrial engineering and writes articles related to piping, civil, equipment engineering related articles.