API 579 G-factors for K Calculations and Improvements For Assessment of Crack-like Flaws in Pipelines
API 579-1/ASME FFS-1 2007 gives a complete guideline of Fitness-For-Service (FFS) assessment of cracklike flaws in structural components based on the Failure Assessment Diagram (FAD) method. The assessment is carried out in FAD using a non-linear relationship between the load ratio (Lr) and the toughness ratio (Kr) where the toughness ratio (Kr) is defined as the ratio of the Mode I stress intensity factor (KI) to the toughness of the material (Kmat). One of the methods for Mode I stress intensity factor (KI) calculation in API 579-1/ASME FFS-1 2007 is FEA based, which correlates five influence coefficients, namely Go to G4, for KI calculation. These influence coefficients are dimensionless and are tabulated for a range of two ratios; the wall thickness to the internal radius (t/Ri) and the flaw depth to the wall thickness (a/t) for infinite cracks and three ratios (crack depth to half crack length (a/c) besides a/t and t/Ri) for finite cracks. API 579-1/ASME FFS-1 2007 allows interpolation of the influence coefficients, Gs for intermediate values. Even though it is not explicitly mentioned about the method of interpolation, a linear interpolation is generally considered. Another possible method is explored here with the polynomial function fitted by the FEA data provided in the table given in API 579. A detail discussion on obtaining the influence coefficients for an intermediate value is outlined here. Case studies are provided to illustrate the advantages and disadvantages of the linear interpolation and the fitted polynomial function.
Stress Intensity Factor Influence Coefficients Gi G Interpolation FAD Level 2 Limiting Pressure
Shaikh Rahman Ming Gao Ravi Krishnamurthy
Blade Energy Partners,Houston,TX,USA
国际会议
北京
英文
1-10
2013-06-16（万方平台首次上网日期，不代表论文的发表时间）