Finite element analysis of residual stresses in a letter-box excavation repair weld for Chapelcross Power Station

A routine inspection on the heat exchanger 6 boiler in Chapelcross Nuclear Power Station revealed the existence of a crack in the bottom dome of the boiler. A 'letter-box' repair procedure was developed to repair the damage and justify the return to service of the boiler. Due to the location of the repair, it was undesirable to conduct post weld heat treatment (PWHT) because this could result in damage to neighbouring components. A full residual stress programme was conducted in order to justify a non-PWHT repair to the boiler using a temper bead technique on a boiler shell section of up to 44 mm. This paper describes the work conducted during the project and subsequently regarding residual stresses in letterbox excavation repairs.