Prediction of High Temperature and High Pressure Pipes with Defects

Lianyong Xu*, Lei Zhao, Hongyang Jing

Tianjin University, Tianjin, 300350, China

ABSTRACT: Advance power generation systems with high efficiency and low emissions have been widely developed in China. Improvements in temperature and pressure of power plants lead to the stringent requirements for high temperature welded pipes, particularly high stress concentration, defects, embedded cracks and Type IV cracks in the fine-grained heat-affected zones likely occurring in the weakest welded joints. Hence, the effects of three mainly issues: stress condition of defects, variation of material properties with stress and t high temperature on the life prediction accuracy for high temperature and high pressure pipes with large thickness and defects were introduced. Then, new developed accurately life prediction approaches by considering the combine effect of constraint loss, residual stress relaxation and stress-dependent creep properties on the creep initiation times and crack growth rates under pure creep and creep-fatigue interaction conditions were given. Furthermore, a new creep interaction method to characterize multiple cracks interaction at elevated temperatures was proposed. To evaluate the performance and microstructures degradation of in-service components, a miniature creep testing equipment and a micro-damage sampling machine were developed. Finally, the framework of the life prediction standard for high temperature and high pressure pipes with defects in China was introduced.    

 Figure 1.  Schematic of crack prediction of the standard specimen

Keywords: High temperature and pressure pipes; Defect; Creep; Life prediction