The development of steels for the end fittings of CANDU pressure tubes

The toughness of our present end fittings do not consistently meet the requirements of Section III of the ASME Boiler and Pressure Vessel Code and a number of developments to improve their toughness and irradiation response have been undertaken. In the laboratory the toughness can be improved by the new double austenitizing heat treatment but it is difficult to apply to end fittings industrially, and end fittings still do not consistently meet the toughness requirements of the ASME code. The change of toughness with irradiation can be decreased by lowering the copper concentrations. However, the tests have shown that the present end fittings are more than adequate to serve their designed purpose and the decision to change composition or heat treatment becomes an economical one. An improved end fitting would be far more costly and we believe the additional cost is not warranted