Wed, 09 January, 2019
December 2018 saw the publication of a new version of the fracture toughness testing standard BS 8571 for carrying out Single Edge Notch Tension (SENT) tests [1]. Dr Philippa Moore from TWI has chaired the BSI committee that has drafted the new version of the standard, which incorporates some significant changes. The main differences in the 2018 version in comparison to the 2014 version are:
- Calculation of J for clamped specimens is now the same for specimens with all W/B ratios [2]
- Inclusion of informative annexes on ‘Guidance for stable crack path deviation during ductile crack extension’ and ‘Guidance for using non-fatigue pre-cracked specimens’.
- Extension of the Annex giving a worked example calculation to include CTOD as well as J.
- The formula to calculate of the elastic component of CTOD has been updated.
- The crack length to specimen width ratio range is now narrowed 0.3 to 0.5 (but shallower notches can be used on agreement of all parties)
- Validity of the shape of the initial and final crack shapes is now the same as those given in BS EN ISO 15653
Plus other typographical and formatting changes, additional clarifications, and guidance notes. TWI is UKAS accredited to perform fracture toughness testing to BS 8571.
The BS 8571 standard has become the industry accepted method for performing SENT testing, being required by DNV-GL for subsea pipeline design and pipeline girth weld assessment to DNV-GL ST F101 and DNVGL RP F108 [3-4].
[1] BS 8571:2018 ‘Method of test for determination of fracture toughness in metallic materials using single edge notched tension (SENT) specimens’, British Standards, December 2018.
[2] MOORE P., HUTCHISON E. Comparison of J Equations for SENT Specimens. In: Proceedings European Conference of Fracture, ECF-21, Catania, Italy, 20-24 June 2016. https://www.twi-global.com/technical-knowledge/weldasearch/270195
[3] DNVGL-ST-F101 STANDARD ‘Submarine pipeline systems’, December 2017
[4] DNVGL-RP-F108 RECOMMENDED PRACTICE, ‘Assessment of flaws in pipeline and riser girth welds’, October 2017