SEDL / STP / STP1325-EB / STP13866S

The Ductile-Brittle Transition Behaviour of Submerged-Arc Weldments Following High Temperature Exposure

Beere, WB
Research Officer, Magnox Electric plc, Berkeley Centre, Berkeley, Gloucestershire

Fidler, RS
Research Officer, Nuclear Electric Ltd, Barnwood, Gloucester

Bolton, CJ
Research Officer, Magnox Electric plc, Berkeley Centre, Berkeley, Gloucestershire

Fenton, ST
Research Officer, Nuclear Electric Ltd, Barnwood, Gloucester

Jones, RB
Research Officer, Magnox Electric plc, Berkeley Centre, Berkeley, Gloucestershire

Pages: 10    Published: Jan 1999

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Abstract

The paper analyses data derived from surveillance specimens withdrawn periodically throughout the life of Magnox reactors with the objective of establishing a predictive equation for the end of life Charpy impact properties of the submerged-arc welds in the ferritic steel pressure vessels. Theoretical arguments and experimental data show that the transition temperature shifts in welds exposed in high temperature (360°C and above) low irradiation dose (∼0.4 mdpa) locations are controlled by thermally-induced intergranular fracture due to phosphorus segregation. The available data have been analysed as a function of time-at-temperature and a trend curve has been developed, taking into account both the time and temperature of exposure before and after a temperature decrease early in life. Data analysis showed that a threshold time condition should be allowed for, which must be exceeded before a shift in transition temperature is observed. This was interpreted as a threshold level of phosphorus segregation which had to be reached before intergranular fracture could take place in preference to cleavage fracture.