Creep lifetime prediction method for P92 main steam pipeline welded joint

A creep lifetime prediction method for a P92 main steam pipeline welded joint, comprising:

• collecting a microstructure of a P92 steel welded joint after service, and determining an area with a most significant degradation of the P92 steel welded joint by performing grading processing on the microstructure, wherein in a process of determining the area with the most significant degradation, a quantity of creep voids, a size of the creep void, and a size of a Laves phase of the microstructure are obtained, and grading processing is performed on the microstructure through a dichotomy method to determine the area with the most significant degradation of the P92 steel welded joint;
• grading standards of the microstructure are:
• a level I:
• the creep voids begin to appear in a critical area or a fine-grained area in a heat-affected area of the P92 steel welded joint, and the creep voids only appear individually at grain boundaries of individual grain, wherein a quantity of the creep voids on each of the grain is not greater than 1, an average size of the creep voids is 4 to 5 μm, and an average length of the Laves phase is less than 0.85 μm;
• a level II:
• the creep voids appear at a plurality of grain boundaries of a grain in the critical area and the fine-grained area in the heat-affected area of the P92 steel welded joint, wherein a quantity of the creep voids on each of the grain boundaries of each of the grain is not greater than 1, the average size of the creep voids is 5 to 7.5 μm, and the average length of the Laves phase is 0.85 to 1 μm;
• a level III:
• the creep voids appear at the plurality of grain boundaries of the grain in the critical area and the fine-grained area in the heat-affected area of the P92 steel welded joint, the quantity of the creep voids on each of the grain boundaries of each of the grain is greater than or equal to 2 and the creep voids do not aggregate, and a distance between adjacent creep voids is greater than a diameter of the creep void, wherein the average size of the creep voids is 7.5 to 10 μm, and the average length of the Laves phase is 1 to 1.15 μm;
• a level IV:
• the creep voids aggregate at the grain boundaries of the plurality of grains in the critical area and the fine-grained area in the heat-affected area of the P92 steel welded joint or micro-cracks appear at the grain boundaries, wherein the average size of the creep voids is 10 to 15 μm, and the average length of the Laves phase is 1.15 to 1.3 μm;
• obtaining a maximum main stress of the P92 steel welded joint based on an actual service pressure of the P92 steel welded joint and according to a finite element technology;
• establishing a creep lifetime prediction model to predict a creep lifetime of the P92 steel welded joint under service conditions under a premise of considering a service environment temperature and according to the microstructure after grading and the maximum main stress, wherein the creep lifetime prediction model is expressed as:
• PLM=(T+273.15)[C+lg(tr)]=a0+a1·lg(σ)+a2·[lg(σ)]2;
• in the formula, PLM is a Larson-Miller coefficient;
• T is the service environment temperature;
• C, a0, a1, and a2 are material constants;
• tr is a creep rupture time;
• and σ is the maximum main stress;
• in a process of obtaining the creep lifetime, based on the grading standards of the microstructure, lifetime prediction is performed through the creep lifetime prediction model, and the creep lifetime generated according to the grading standard is obtained;
• in a process of generating the creep lifetime according to the grading standards, a lifetime of the P92 steel welded joint of the microstructure under the level I is 60% of a lifetime predicted of the creep lifetime prediction model;
• the lifetime of the P92 steel welded joint of the microstructure under the level II is 45% of the lifetime predicted of the creep lifetime prediction model;
• the lifetime of the P92 steel welded joint of the microstructure under the level III is 20% of the lifetime predicted of the creep lifetime prediction model;
• and
• the lifetime of the P92 welded joint of the microstructure under the level IV is 5% of the lifetime predicted of the creep lifetime prediction model.