PSI - Issue 13

Konstantinos Kouzoumis et al. / Procedia Structural Integrity 13 (2018) 868–876 K. Kouzoumis et al. / Structural Integrity Procedia 00 (2018) 000–000

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Fig. 3: Assessment of 1602-API X100 specimen

It is apparent that all points, apart from a single one, lie in the potentially unsafe zone of the FAD. This single point, designated “1602”, concerns one of the full scale burst tests conducted on X100 steel by Demofonti et al. (2002). Separate assessment of this specimen, illustrated in Fig. 3, with the FALs having been based on the speci men’s mechanical properties, places the BS 7910 modified solution-point outside both continuous and discontinuous yielding FALs. Overall, the modified BS 7910 equation predicts failure with higher accuracy while ensuring safety, thus rendering the omission of the 1.2 factor justifiable.

5. Conclusions and Summary

A central objective of this work was to study the history and purpose of a 1.2 multiplication factor included in the reference stress solution of axially flawed pipes in the BS 7910 procedure. The initial step was to explain its origin and set the layout of the solutions provided by other extensively used procedures (R6 and API 579-1 / ASME FFS-1). After the description of the formulae that each procedure provides for this purpose, a comparison between them followed, with an additional solution, which assumes the omission of the factor of 1.2 in BS 7910. It was apparent from the comparison that the 1.2 factor produces higher L r values, regardless of the geometrical features of the specimens assessed, i.e. thick or thin cylinders. After the comparison, which generated the initial incentive to investigate this factor, the modified BS 7910 so lution was validated against experimental data. The validation process, which included 173 pipe test data collected from various sources in the literature, gave su ffi cient proof that such a factor is not necessary in BS 7910. It is there fore recommended that this factor is omitted in the forthcoming editions of the standard for higher accuracy in the assessments.

Acknowledgements

This publication was made possible by the sponsorship and support of the industrial members of TWI as part of the Core Research Programme and of the UK Research and Innovation centre (Engineering and Physical Sciences Research Council - EPSRC) through the Doctoral Training Programme grant awarded to the University of Bristol for partial financial support for this research. The work was enabled through, and undertaken at, the National Struc tural Integrity Research Centre (NSIRC), a postgraduate engineering facility for industry-led research into structural integrity established and managed by TWI through a network of both national and international Universities.