An article written by staff at TWI has been named in the top four of the most popular technical pipeline papers for 2013 in the Journal of Pipeline Engineering. Written by Philippa Moore and Henryk Pisarski, the paper discusses the most widely-used fracture-toughness parameter within the oil and gas industry, crack-tip-opening displacement (CTOD), in an article titled 'CTOD and pipelines: the past, present, and future'.*
An abstract for the paper can be seen below and the full article is available here.
CTOD and pipelines: the past, present, and future
Dr Philippa Moore and Dr Henryk Pisarski
CRACK-TIP-OPENING displacement (or CTOD) has been the most widely used fracture- toughness parameter within the oil and gas industry for nearly 50 years. Originally developed from research at TWI in the UK during the 1960s, CTOD was an ideal parameter for characterizing the fracture toughness of medium-strength carbon manganese steels used in pressure vessels, offshore platforms, and pipelines where the application of linear-elastic fracture mechanics was insufficient to account for their ductility.
Once fracture-toughness testing (CTOD testing) became standardized within BS 7448, ASTM E1290, ISO 12135, and ISO 15653, the CTOD concept enjoyed an established international reputation. The development of standardized fitness-for- service assessment procedures, initially through the use of the CTOD design curve, and then to use of the failure-analysis diagram approach described in BS 7910, also allowed CTOD to be used directly to determine tolerable flaw sizes to assess the structural integrity of welds.
In more recent times, single-edge-notched tension specimen (SENT) testing has been enthusiastically adopted by the pipeline industry in place of the traditional single-edge-notched bend (SENB) specimen used for standard CTOD tests. However, currently there is no national standard describing SENT testing, although this is being developed. SENT testing is particularly advantageous when pipeline girth welds are subjected to plastic straining, and a number of assessment procedures based on CTOD have been and are being developed to define strain capacity and flaw-acceptance criteria.
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*Since this paper was written, a British Standard draft for public comment on SENT testing has been issued; TWI have been heavily involved in drafting the document. The title is "Method of test for determination of fracture toughness in metallic materials using single edge notched tension (SENT) specimen" BS 8571:2014. It can be examined and commented upon via the BSI website.