How to Limit Permanent Pipeline Deformation when Conventional Methods Can’t be Applied
Ground movements or constrained thermal expansion can cause stresses in a pipeline or other structure to exceed the yield strength of the pipe material, resulting in permanent deformation of the pipe.
Conventional stress-based design methods would suggest that higher strength materials and thicker pipe walls are required to limit the stress in these pipes; however, in many cases, these designs become impractical due to the cost or size of the pipe.
A design approach is required to provide cost effective designs for the desired service life in cases where large deformations are anticipated.
Using Strain Based Design to Limit Strain and Deformation
C-FER uses a new design method that is based on limiting the strain, or amount of deformation, in a pipe rather than focusing on the stress as in conventional design methods.
The strain-based design approach recognizes that a pipe retains a large portion of its structural capacity even after being deformed to some degree.
The approach is based on determining the level of strain that would lead to a catastrophic failure such as a rupture (termed the strain capacity) and compares this to the amount of strain that is expected to occur due to ground movement or other mechanisms (termed the strain demand).
When the amount of deformation is expected to continuously increase over time, this method can be used to specify an explicit design life for a pipeline that meets the operational and economic requirements of the asset.