Limit Loads Of High Temperature Pipes With Local Wall Thinning

Based on the previous researches on the limit load for pipes with local wall thinning in room temperature, the limit loads of the pipes which serviced for long time at high temperature in this thesis, considering local wall thinning due to corrosion were investigated.Firstly, based on Ramberg-Osgood elasto-plastic constitutive equation and creep damage mechanics, the creep damage coupled elasto-plastic constitutive equation was derived in the paper. Creep tests were performed on 10CrMo910 to different time periods to yield different creep damages. High temperature tensile tests were then carried out on the damaged materials to obtain the stress-strain curves corresponding to different damages. A comparison of the experimental stress-strain curves with the ones described by damage coupled with elasto-plastic constitutive equation showed that they are in reasonable agreement.Secondly, creep damages may gradually occur in the pipes serviced at high temperatures. Under the control of maximum principal stress, damage increased from the inner wall to outer wall of pipes. On the contrary, damage decreased in the case that the equivalent stress was dominant. Damage coupled elasto-plastic constitutive equation was then used to analyze the limit load of the pipes with constant damage across the wall. The relationship between the damage and the limit load of the pipes was obtained. Furthermore, the limit load of pipes with distributed damage varying from inner wall to outer wall was analyzed. A linear relationship between the limit load and the maximum damage of the pipes was obtained.Finally, damage coupled elasto-plastic constitutive equation was used to analyze the limit load of the pipes with local wall thinning and damage varying from the inner wall to outer wall. A relation among limit load, maximum damages and the defect sizes in the pipes was obtained.