What Does Buckle Mean?
Buckle is an alternating pattern of bulges and hollows recurring along the length of a flat product, with the edges remaining relatively flat. Buckle can also refer to a geometrical defect in submerged pipeline originating from external mechanical impact, which can cause localized corrosion and fracture of the pipeline.
Corrosionpedia Explains Buckle
Buckle can be considered either regular or sharp. Regular buckle is the residual deformation of the interior of a pipe wall without a sharp edge extending over an area. Sharp buckle is the residual deformation of the interior of a pipe wall with a sharp edge extending over an area. A common cause for both these types of buckle is external mechanical impact.
Pipelines that transport oil and natural gas in deep ocean wells are designed to withstand very high hydrostatic pressure. Pipelines may sometimes develop a local buckle due to accidental collisions, and if the hydrostatic pressure is high enough, this buckle propagates along the pipeline, flattening the pipeline in a dog-bone shape. The steady-state buckle propagation pressure is the smallest pressure at which a buckle, once initiated, propagates along the entire length of the pipeline. A propagating buckle only stops if the external hydrostatic pressure falls below the propagation pressure or if the bending rigidity of the pipe is suddenly increased by a buckle arrestor.
Internal corrosion alters the buckling behavior of a pipeline due to changes in the flexural rigidity, submerged weight and axial force. Large deformations may take place during pipeline buckling. Corrosion causes the strain at the buckle apex to increase. Large scale uniform corrosion around the circumference reduces the flexural rigidity of the pipe. If the submerged weight and axial force remains unchanged, this would result in a concentration of the buckle. Subsea pipelines operating at high temperature can buckle vertically and laterally. The curvature and high strains in buckled pipelines can cause ovalization, wrinkling and fracture.