The Parameter Optimization And Flaw Sizing Of TOFD Testing For Thick-walled Pressure Vessel

To ensure safe and reliable operation of thick-walled pressure vessel, it is required that positioning and sizing flaws which may occur in the weld accurately. Time of Flight Diffraction (TOFD) is a non-destructive testing method which is particularly suitable for the thick-walled weld. This article relied on a foundation project in the national defense program during the twelfth five-year plan period "The research on TOFD testing technology for the weld of reactor thick-walled pressure vessel". By means of experiment combined with numerical simulation, TOFD testing technique for the weld of pressure vessel whose thickness is larger than1OOmm was studied. Firstly, TOFD testing parameters optimization of thick-walled weld was researched by both theoretical analysis and experiment. And on this basis, methods to improve the height and length sizing precision of TOFD testing for thick weld were explored. The main contents were as follows:(1)160mm-220mm thick reference blocks of45#steel were tested, the preferred parameters of TOFD testing were researched by both theoretical analysis and experiment. Parameter optimization of thick-walled weld in TOFD testing was studied and summarized systematically.(2) The height resolution of220mm thick reference block in TOFD testing was analyzed theoretically, and the function curve of flaw height resolution which was changed with the flaw depth was drawn. When the flaw height was smaller than the system height resolution, a method based on spectrum analysis to size the flaw height was proposed. The heights of2.0mm～3.0mm height,22.5mm～182.0mm buried flaws were quantified with the method. The results showed that, when the flaws were22.5mm and182.0mm buried, the height resolution can be improved from5.1mm to1.0mm,4.5mm to1.1mm respectively,(3) Given the current pointer that commonly used TOFD parabolic law may import large error of flaw length,6dB drop technique was applied to TOFD testing. A numerical simulation models were constructed to verify the feasibility of the method theoretically. Better sizing precision was achieved when applying the method to D scanning results of22.5mm～200.0mm buried flaws. In addition, the synthetic aperture focusing technology (SAFT) was used to process numerical simulation results of D scanning of flaws with lengths range from5mm-45mm, and the absolute errors were less than0.6mm.(4) Using the parameter optimization conclusion and sizing methods of TOFD testing for thick-walled pressure vessel,160mm～220mm thick reference blocks were tested, and the sizing errors were analyzed.