A representative range of duplex and super duplex stainless steels (different grades, product forms and thicknesses) and their weldments (different processes and notch location) was studied and/or analysed to derive appropriate toughness requirements for this type of steel. With the exception of deliberately ‘sigmatised’ weld metal specimens, none of the materials investigated exhibited brittle fracture events during CTOD testing carried out at temperatures between –20 and –100°C. Correlations were developed between Charpy energy and CTOD for different thicknesses. These were shown to be safe for use in fracture mechanics calculations by analysing a series of full-scale tests on parent steel, weld metal and HAZ specimens with thickness ranging from 2.8mm to 40mm. For readily detectable surface and embedded flaw dimensions, the appropriate CTOD and Charpy requirements are 0.1mm and 40J, respectively, at the minimum operating temperature. The marked effect of the presence of intermetallic precipitation on Charpy and fracture toughness has been confirmed. It has been shown that the correlation between Charpy and CTOD is not affected by the presence of intermetallics which means that the Charpy requirements developed are also applicable to super duplex steel joints which may contain intermetallic precipitation.