The Residual Life Prediction Of Cr9Mo Main Stem Pipes With Online Nondestructive Methods Under Creep Condition

Heat and power are strong demanded for electric power, petrochemical and other industries. The steam pipeline is one of the most important carriers of energy transmission medium, and it will directly affect the operation safety. Due to long-term work in high temperature and pressure conditions, the steam pipeline’s structure may be changed. Especially the over temperature could exacerbate the creep damage of steam pipeline, and shorten its service life. Therefore, it is important to analyze the creep damage and study on-line nondestructive residual life evaluation methods of steam pipelines.In this work, Cr9Mo steam pipes’mechanical properties and high temperature enduring strength were studied by work using aging experiment simulating the creep damage process of materials. And the microstructure, hardness, and resistance change law in the aging process were also investigated. On the basis of the above work, the online, nondestructive residual life evaluation was realized by using hardness method and resistance method. Furthermore isothermal method, L-M method and corrected L-M method were employed to predict the conventional residual life.Main work and results are as follows:(1) Macroscopic examination and chemical composition analysis show that, the 14 years old steam pipeline is in good condition overall, and its chemical composition meets JIS3467 and ASTM A235 standards.(2) Mechanical performance tests and creep sustained experiments show that the steam room temperature mechanical properties meet the standard requirements, but high temperature mechanical properties of tensile strength and elongation are not in conformity with the requirements, the creep rupture strength degradation is serious.(3) High temperature aging experiment shows that the microstructure, hardness and resistance have been changed a little in the process of ageing. The microstructure is the main reason that results in the change of hardness HV, and resistance R. The relationship between hardness HV, resistance R and heat strength parameter P was established, and it illustrates that the high temperature aging experiment could simulate creep damage.(4) Based on the creep sustained experiment, the isothermal method, L-M method, the adjusted L-M method, hardness, and resistance method were used respectively to evaluate steam pipeline’s residual life, and each result was analyzed. So an online nondestructive pipeline’s residual life evaluation method was established. The adjusted L-M, hardness, and resistance methods predicted that the steam pipe lifespan is 144326h,42563h,46299h respectively, under the working condition of 500℃ and 1.7MPa only considering the creep damage.