Experimental Study And Life Evaluation Of High Temperature Creep Damage Of P91 Steel

As a kind of high temperature resistant martensitic steel,P91 steel is the main material of the main steam pipeline of thermal power plant.Once damage or even fracture occurs,it will cause huge economic losses and even casualties.Creep is one of the main failure modes of the main steam pipeline of thermal power plants.It is of great significance to study the creep of P91 steel.Constitutive equation is an important method to establish mathematical-physical model.In this paper,three creep constitutive equations of Norton creep power law equation,Kachanov-Rabotnov model and sinh model of P91 steel at 620 ℃ equation.The study found that all three constitutive models can characterize creep,and the Norton creep power law equation cannot describe the third stage of creep.Through the comparison of creep life,Norton and K-R model creep curves,K-R and sinh creep model damage evolution process:(1)The creep life of three creep models of Norton,K-R and sinh.The error between different creep models and experimental data does not exceed 8.9%,which is within the error tolerance.(2)The Norton creep model cannot fully describe the creep process,and the Norton creep curve is lower than the test curve,which is easy to get a more optimistic evaluation;the K-R creep curve can completely describe the whole creep process,especially in creep.In the middle and late stages,the KR creep model has an advantage over the Norton creep model.(3)There is a mutation in the third stage of the damage evolution process of K-R creep model,and the damage variable of K-R creep model at the same moment is smaller than that of sinh creep model,and the sinh creep model is more moderate than the damage evolution process of K-R creep model.This article uses damage theory to characterize the creep behavior of P91 steel at620 ° C to understand the damage of the material.It is found that the experimental value of P91 steel breaking damage can not reach the theoretically derived value,and the damage is generally around 0.4.The effects of life fraction and creep on the creep damage of P91 steel were analyzed:(1)The creep damage of P91 steel increases with the increase of stress and the damage of the same material is not much different.(2)The creep of the creep damage of P91 steel is about 0.028 at the beginning of the creep and the damage increases linearly with the increase of material creep.In this paper,the lifetime of P91 steel at creep temperature of 580 ° C ～ 620 ° C was evaluated by LM and MH parameters method,and the error of the two was evaluated by ECC(European Creep Collaborative Committee)creep life.The conclusions show that the LM parameter method is very sensitive to creep data,which leads to an increase in error as the prediction duration increases.Since there is no long-term creep test to support,the error of the LM parameter method is doubled the error of the MH parameter method;Because the MH parameter method is different from the LM parameter method,it does not have too strong laziness to the data.Therefore,the error of the MH parameter method is relatively stable,and the breaking life of the P91 steel can be accurately predicted.