CTOA Testing of Pipeline Steels Using MDCB Specimens
Robert L. Amaro, Jeffrey W. Sowards, Elizabeth S. Drexler, Joseph D. McColskey, Christopher N. McCowan
Crack tip opening angle (CTOA) is used to rank the relative resistance to crack extension of various pipeline steels. In general, the smaller the CTOA value, the lower the resistance to crack extension. It is unclear, however, whether CTOA is a material property that is valid for all thicknesses and rates of crack growth. Historically, drop weight tear tests (DWTT) and modified double cantilever beam (MDCB) specimens have been used for measuring CTOA. Tests using either specimen may be conducted at quasi-static and dynamic rates. The fastest displacement rates achieved in our laboratory were near 14 m/s, resulting in crack extension rates near 30 m/s for high-toughness linepipe steels. In-service crack extensions for ductile crack fracture can be more than 100 m/s. The failure mode at this rate is plastic collapse, and it is uncertain if correlations can be drawn between in-service failures and laboratory tests conducted on thinner material tested at slower rates. We describe the evolution of our test method using MDCB specimens from 2006 to 2012 and the direction we anticipate for future CTOA research.
, Sowards, J.
, Drexler, E.
, McColskey, J.
and McCowan, C.
CTOA Testing of Pipeline Steels Using MDCB Specimens, Journal of Pipeline Engineering, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=914141
(Accessed December 7, 2023)