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Strain Limit of Large Diameter Pipe

The Industry Challenge:

Slope movement or heave/subsidence during annual freeze thaw cycles results in bending and tensile strains that can permanently deform pipe affecting its serviceability and, in extreme circumstances, leads to a pipeline rupture.

The ability of the pipe to withstand these deformations (termed the strain capacity) is determined by a variety of factors including the base pipe material behavior, the girth and long-seam weld strengths, the potential for imperfections and the pipe geometry.

The complexity of these factors make it difficult to accurately predict the strain capacity of pipes; therefore, conducting large-scale loading tests is necessary.

How We Help:

Tension tests using large coupons called curved wide plates were conducted to observe the growth of simulated cracks in pipe girth welds to determine critical flaw sizes that lead to rupture of the girth weld.

These tests are typically cooled to the expected pipeline operating temperature to ensure faithful reproduction of the material toughness in service.

Full-body, biaxial tension tests, that include both axial tension and hoop tension imposed by internal pressure are performed to evaluate weld flaw performance.  

Full-body, biaxial compression tests are run by subjecting a pipe specimen to internal pressure and pure bending.

To complete these tests, C‑FER constructed testing systems that can accommodate pipe diameters up to 1.2 m (48 in) with tensile loads up to 72 MN (20 million pounds).

To achieve pure bending in the compression tests, a large compression load frame must be used to react the axial tension loads imposed by the internal pressure. Tests are often run with various weld configurations, pipe segment alignments (hi/lo) and orientations between the long seam weld the bending axis to understand how these factors can influence the pipe performance.

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