Damage Analysis And High Temperature Failure Assessment For SS Main Steam Pipelines

For the SS main steam pipelines serviced for 100,000 hrs in alkene plant of Yangzi Petrochemical Company, the microstructure examination, the uniaxial tensile test and creep test at high temperature were carried out in the dissertation. The damage cumulation and mechanical properties degradation degree of the serviced pipeline material were investigated. Thermal stress and creep of the pipeline during serviced period were analyzed by using finite element codes ABAQUS and stress distribution of the pipeline was obtained. Based on compiled user subroutine computing damage for pipe element, damage analysis was carried out for the SS pipelines, and the maximum damage location was find out. Finally, by means of establishing high temperature failure assessment diagram of the pipe material serviced 100,000 hrs and 200,000 hrs, the structural integrity assessment was done for the pipe containing defects. The main contents and conclusions of the dissertation are summarized as follows:(1) The microstructure degradation of the pipe material was studied by microstructure examination. The examination results show that the material microstructure is ferrite and pearlite, dispersive carbide is precipitated at inner and boundary of grain, pearlite spheroidization isn't serious, and the degradation degree of outer-wall structure is more serious than inner-wall structure, which is consistent with the damage rule of the main steam pipeline at high temperature.(2) The results of short-term tensile test at high temperature shows that the mechanical properties of STPA23 steel serviced for 100,000 hrs is decreased, but it still has enough high temperature strength to service. After serviced for 200,000 hrs, the mechanical properties of the pipe material further decreased, which is caused due by accumulation of damage with the serviced time increasing.(3) The creep curves were obtained by creep test at serviced temperature, and the creep and fracture constants of the pipe material were obtained by fitting the creep test data. The thermal stress and creep of the SS pipelines were analyzed by means of...