Validation of BS 7910; Assessing the integrity of pipes containing axial flaws

The results of hundreds of large scale fracture tests have been collected from various sources and analyzed in accordance with the latest version of the BS 7910 fitness for service (FFS) standard and, in selected cases, with R6 and/or the API 579-1/ASME FFS-1 fitness for service standard. This analysis aims to provide further validation of BS 7910 and identify where modification is needed. The tests cover a wide variety of materials, flaw geometries (surface, embedded, through thickness) and loadings (pressure, bending, residual stress), thus validating the standard over a wide spectrum of applications. All the tests are analyzed with the use of the basic assessment option (Option 1), which requires only the basic tensile properties and fracture toughness of the component, and selected tests are re-analyzed using more advanced methods. During the analysis, close attention was paid to the results of 173 tests on pipes with axial flaws, where an apparently arbitrary safety factor on reference stress is included in BS 7910, but not in other standards, leading to apparently lower defect-tolerance when BS 7910 is used. The history of this part of the standard, along with approaches used in other standards, was investigated. A modified equation, without this safety factor, was used in the analysis of the tests, where applicable, and compared with results from other standards. The comparison between the approaches shows the BS 7910 safety factor to be unnecessary, with all test results falling outside the failure assessment diagram (FAD), but with less conservatism, as they lie closer to it.