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PRCI PR-185-9430
- Development of Modeling Procedures for Branch Welds
- Report / Survey by Pipeline Research Council International, 11/06/1995
- Publisher: PRCI
$75.00$149.00
L51737e
Edison Welding Institute
Need: One major difficulty in developing fitness-for-purpose based flaw acceptance criteria for pipeline branch connections is the calculation of the stress distributions in the vicinity of the welds. Even with the latest computer-aided modelling technologies, finite element modeling of branch connections using three-dimensional (3-D) solid elements is the only way to accurately determine the stress distributions local to the weld toes of branch connections.
Benefit: This report describes work to access the applicability of linear elastic fracture mechanics (LEFM) principles to a saddle-pad reinforced branch connection modelled using 3-D elements, The effort concentrated on determining the amount and location of plastic zones resulting from different combinations of service loadings. Loadings considered include pressurization to 72% of the specified minimum yield strength with the addition of main pipe end tension or compression. The effect of contact and different material models were also quantified.
Result: In the end, none of the modelling strategies investigated were found to be suitable for LEFM evaluations due to excessive plasticity in the weld toe crack planes for almost all loadings. The only loading found to be acceptable for LEFM evaluation was that of main pipe compression, which is not of particular interest for a pressure containing geometry. Hence, for this geometry and loadings, LEFM is deemed inappropriate. In summary, the results of these analyses indicate the following: Contact has a negligible effect on the weld toe crack plane stresses. Significant plasticity has occurred at all main weld toe crack planes for all loadings except main pipe end compression. Significant plasticity has occurred at all reinforcement weld toe crack planes for all combined loadings. Incorporating a more realistic pipe yield strength value and branch pipe wall thickness did not sufficiently reduce the plastic zone size enough to make LEFM applicable. These analyses indicate significant plasticity even for the simplest loading conditions. If a 3-D crack is to be evaluated it would need to be incorporated into the model to permit calculation of the driving force to fracture. This driving force could then be compared with the fracture toughness of X52 to assess the appropriateness of a particular design.
Edison Welding Institute
Need: One major difficulty in developing fitness-for-purpose based flaw acceptance criteria for pipeline branch connections is the calculation of the stress distributions in the vicinity of the welds. Even with the latest computer-aided modelling technologies, finite element modeling of branch connections using three-dimensional (3-D) solid elements is the only way to accurately determine the stress distributions local to the weld toes of branch connections.
Benefit: This report describes work to access the applicability of linear elastic fracture mechanics (LEFM) principles to a saddle-pad reinforced branch connection modelled using 3-D elements, The effort concentrated on determining the amount and location of plastic zones resulting from different combinations of service loadings. Loadings considered include pressurization to 72% of the specified minimum yield strength with the addition of main pipe end tension or compression. The effect of contact and different material models were also quantified.
Result: In the end, none of the modelling strategies investigated were found to be suitable for LEFM evaluations due to excessive plasticity in the weld toe crack planes for almost all loadings. The only loading found to be acceptable for LEFM evaluation was that of main pipe compression, which is not of particular interest for a pressure containing geometry. Hence, for this geometry and loadings, LEFM is deemed inappropriate. In summary, the results of these analyses indicate the following: Contact has a negligible effect on the weld toe crack plane stresses. Significant plasticity has occurred at all main weld toe crack planes for all loadings except main pipe end compression. Significant plasticity has occurred at all reinforcement weld toe crack planes for all combined loadings. Incorporating a more realistic pipe yield strength value and branch pipe wall thickness did not sufficiently reduce the plastic zone size enough to make LEFM applicable. These analyses indicate significant plasticity even for the simplest loading conditions. If a 3-D crack is to be evaluated it would need to be incorporated into the model to permit calculation of the driving force to fracture. This driving force could then be compared with the fracture toughness of X52 to assess the appropriateness of a particular design.
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