Estimation Method Of J-integral And Failure Assessment Curve Of Nuclear Power Plant Pipe Contained Internal Circumferential Surface Crack

As the development of nuclear power plant in our state, the safety of nuclear power plant pipes are concerned, especially coolant pipes which transmit radiant liquid are more focused by people. Because of manufacture problem and influence of service condition, nuclear power plant pipes can't avoid defects within 60 years'service, thus structural integrity assessment method should be used to assess the safety state of cracked pipes. Estimation of J-integral and failure assessment curve is the core of structural integrity assessment. But now, there is no established integrity assessment method system for nuclear power plant equipments in our country. From this point, this thesis studied estimation method of J-integral and failure assessment curve for internal circumferential surface cracked coolant pipes. The study conducted as follow:(1) Established finite element (FE) models of internal circumferential surface cracked coolant pipes under different loading condition, such as pure pressure, pure bending, and combined pressure and bending(λ=0.2,0.5,1,2,5), with various material (n=1,2,5,8,10) and crack geometries (θ/π=0.1,0.2,0.3,0.4,0.5,a/t=0.1,0.3,0.5,0.75), and calculated the J-integral to obtain full plastic solutions H1 for complement of EPRI ductile handbook, as well supplying FE analysis dates for the coming study.(2) Considering of the problem that EPRI-J estimation method is non-conservative for pipes under pure bending or mainly bending conditions, explained the reason of non-conservation for EPRI-J estimation method based on FE analysis; induced the distribution of H1a/H1a* and concluded the rule that H1a/H1a* are independent of the crack geometry, based on which, improved EPRI-J estimation method which called functionΦcontained EPRI-J estimate method were given; compared of FACs which established by the improved EPRI-J estimation method, EPRI-J estimation method and FE method to proof that the improved EPRI-J method is more accurate than EPRI-J estimation method.(3) Based on the given improved EPRI-J estimation method, analyzed the distribution of H1/H1(n=1), and applied the law that ln[H1(n)] and n are almost linear relationship to transform H1/H1(n=l) to xo factors, as well functionΦto functionΓ, then redefined abscissa to obtain improved option 2 FAC. Compared the FACs which established by improved option 2, R6.option 2 and option 3 (FE) method used true material 316L, to proof that the modified option 2 offer more accurate results than R6 option 2. Finally, gathered some material property dates of nuclear power plant pipes to establish improved option 2 FACs, and the lower envelope of which was fitted as special FAC of coolant pipes.(4) For further validation of the advantage of the given modified option 2 FAC and special FAC of coolant pipes, the published experimental fracture property dates are used to validate the given FACs to impersonally assess the accuracy of them.