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PRCI PR-185-9432
- Investigation of Fatigue Properties of Girth Welds with Root Imperfections Allowed by API 1104
- Report / Survey by Pipeline Research Council International, 01/09/1997
- Publisher: PRCI
$325.00$649.00
L51762e
Edison Welding Institute
Need: Fatigue analysis of welded components and structures according to established codes is based upon either S-N design curves or fracture mechanics principles. Fatigue damage in nominally sound joints is commonly estimated using an appropriate S-N curve in conjunction with a linear cumulative damage rule (i.e., Miner's rule). By comparison, fracture mechanics is used to assess the growth of an imperfection during a period of cyclic loading, or to assess whether an imperfection will remain dormant under the applied cyclic loading condition. Thus, the S-N approach is used mostly during initial design, while the fracture mechanics approach is used mostly to justify the continued operation of existing structures. As the aim of this investigation is the rationalization of certain features of API-1104, an initial design code, the S-N approach was used here.
Benefit: The work described in this report was aimed at determining the effect of root imperfections allowed by API 1104 on the fatigue properties of girth welds, and to recommend a S-N curve appropriate for girth welds in pipelines. S-N curves were developed for single-sided girth welds without a backing strip using pipe strip specimens containing various sizes of incomplete root penetration and lack-of-root sidewall fusion.
Result: The results from the baseline weld pipe strip specimens were compared to the full pipe section results available from the literature. It was concluded that the results from the baseline pipe strip specimens adequately represent the fatigue performance of full pipe sections loaded axially or in bending. Therefore, a baseline weld design curve was developed using both the pipe strip specimens and full pipe section data. All test results for axial or bending loads lie above the proposed fatigue design curve. The lack of definitive data on pipes subjected to fluctuating internal pressure confounds attempts to extend the applicability of the proposed fatigue design curve to this important loading condition.
Edison Welding Institute
Need: Fatigue analysis of welded components and structures according to established codes is based upon either S-N design curves or fracture mechanics principles. Fatigue damage in nominally sound joints is commonly estimated using an appropriate S-N curve in conjunction with a linear cumulative damage rule (i.e., Miner's rule). By comparison, fracture mechanics is used to assess the growth of an imperfection during a period of cyclic loading, or to assess whether an imperfection will remain dormant under the applied cyclic loading condition. Thus, the S-N approach is used mostly during initial design, while the fracture mechanics approach is used mostly to justify the continued operation of existing structures. As the aim of this investigation is the rationalization of certain features of API-1104, an initial design code, the S-N approach was used here.
Benefit: The work described in this report was aimed at determining the effect of root imperfections allowed by API 1104 on the fatigue properties of girth welds, and to recommend a S-N curve appropriate for girth welds in pipelines. S-N curves were developed for single-sided girth welds without a backing strip using pipe strip specimens containing various sizes of incomplete root penetration and lack-of-root sidewall fusion.
Result: The results from the baseline weld pipe strip specimens were compared to the full pipe section results available from the literature. It was concluded that the results from the baseline pipe strip specimens adequately represent the fatigue performance of full pipe sections loaded axially or in bending. Therefore, a baseline weld design curve was developed using both the pipe strip specimens and full pipe section data. All test results for axial or bending loads lie above the proposed fatigue design curve. The lack of definitive data on pipes subjected to fluctuating internal pressure confounds attempts to extend the applicability of the proposed fatigue design curve to this important loading condition.
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