Behaviour of steam generator bolted flange joints at elevated temperatures

Manholes with flanged joints are provided in the sodium heated once through straight tube steam generators of Prototype Fast Breeder Reactor (PFBR). The material of construction of steam generator is modified 9Cr 1Mo grade steel with studs made of 1 Cr 0.5 Mo steel. During the commissioning of model steam generator, the flanged joint lost its leak tightness at elevated temperature due to differential thermal expansion between flange and stud. A design modification incorporating sleeves of higher thermal expansion coefficient is discussed in this paper.

► Steam generator of prototype fast breeder reactor is made of modified 9Cr 1Mo steel.
► Flanged joint in the steam generator lost its leak tightness at high temperatures.
► Differential thermal expansion was the reason for the leakage.
► Sleeves were provided to compensate the differential thermal expansion.
► The leak tightness was achieved at high temperature with the action of sleeves.