Creep analyses of a steam pipe system

Elastic pipe stress analyses are frequently performed to check that the stresses in pipe systems are allowed. For operation in the creep range such analyses may describe the stress distribution in the beginning but not after creep relaxation starts to take place. In the present work effects of creep are considered. A pipe system of P22 material that had been analysed by software for elastic analysis was also modelled for creep. By use of tabled creep data the following was studied: - Creep stress relaxation in the pipe system, - The effects of starts and stops on stress and strain distributions, - Creep in T-pieces with super imposed system stresses from the pipe system creep analysis. The creep properties of a virgin weld and a service exposed weld were determined by impression creep testing. The tests were performed in the parent metal, different parts of the HAZ and the weld metal. A weld was included in the model and analysed with these data. Resulting creep strain distributions from analyses with tabled and present creep test data were compared to each other and also to actual creep damage that was observed in components from the system.