Life extension of hot steam piping after 200 000 h of service

The units 2 and 3 of Naantali power plant have been successfully operated for more than 200 000 h, and it is of interest to ensure the eligibility of the units for continued production. For this purpose and to assist in the related life assessments, the condition of the high temperature piping has been subjected to long term inspection and monitoring programs. Inspections have been concentrated on sites of earliest indications of creep damage or highest rates of damage accumulation as observed from monitoring and repeated measurements. Particular locations of interest are found at the welded branches of the high pressure steam mixing headers. With these example components, two traditional solutions of directly welded and wrought branch connections are compared in terms of observed creep damage and expected life.