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PRCI PR-276-9905
- Strain Criteria for the Assessment of Girth Weld Defects
- Report / Survey by Pipeline Research Council International, 08/01/2001
- Publisher: PRCI
$148.00$295.00
L51842e
Engineering Mechanics Corporation of Columbus
Need: Most girth weld defect assessment procedures are stress-based. Many geometry and material specific parameters can be neglected to conduct a reasonably accurate stress-based defect assessment. The simplicity of this method is typified by the widely used Level 2 assessment procedure in BS 7910:1999 [1] (successor to PD6493:1991) in the oil and gas industries. However, there are some situations where stress-based defect assessment may not be appropriate. The longitudinal strains can greatly exceed the yield strains in pipelines through discontinuous permafrost, soil or seismic instability, and in offshore pipe laying. The stress-based assessment procedures are incapable of providing safe strain limits for such high strain conditions.
Result: This is the first project in a multi-year effort intended to develop alternative defect acceptance criteria for pipelines experience high longitudinal strains. The strain capacity of girth welds containing welding defects is investigated using numerical analysis with comparison to experimental data. The key deliverables of this project are (1) a three-region strain design diagram, and (2) a set of parametric equations allowing the computation of allowable strains with the input of defect depth, defect length, CTOD (Crack Tip Opening Displacement) toughness, and weld strength mismatch. The three-region strain design diagram provides a quick method to determine if a large strain design is possible. The parametric equations can be used to provide a rough estimate of strain limits for a given set of input parameters.
Benefit: The results of this project should help the pipeline industry in setting up safe and economical girth weld defect acceptance criteria in new constructions. The defect acceptance criteria have a direct impact on field welding repair rate. In addition, the technology developed in this effort allows the assessment of in-service pipeline integrity when high longitudinal strains are expected.
Engineering Mechanics Corporation of Columbus
Need: Most girth weld defect assessment procedures are stress-based. Many geometry and material specific parameters can be neglected to conduct a reasonably accurate stress-based defect assessment. The simplicity of this method is typified by the widely used Level 2 assessment procedure in BS 7910:1999 [1] (successor to PD6493:1991) in the oil and gas industries. However, there are some situations where stress-based defect assessment may not be appropriate. The longitudinal strains can greatly exceed the yield strains in pipelines through discontinuous permafrost, soil or seismic instability, and in offshore pipe laying. The stress-based assessment procedures are incapable of providing safe strain limits for such high strain conditions.
Result: This is the first project in a multi-year effort intended to develop alternative defect acceptance criteria for pipelines experience high longitudinal strains. The strain capacity of girth welds containing welding defects is investigated using numerical analysis with comparison to experimental data. The key deliverables of this project are (1) a three-region strain design diagram, and (2) a set of parametric equations allowing the computation of allowable strains with the input of defect depth, defect length, CTOD (Crack Tip Opening Displacement) toughness, and weld strength mismatch. The three-region strain design diagram provides a quick method to determine if a large strain design is possible. The parametric equations can be used to provide a rough estimate of strain limits for a given set of input parameters.
Benefit: The results of this project should help the pipeline industry in setting up safe and economical girth weld defect acceptance criteria in new constructions. The defect acceptance criteria have a direct impact on field welding repair rate. In addition, the technology developed in this effort allows the assessment of in-service pipeline integrity when high longitudinal strains are expected.
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