At present, in the fracture resistance analysis of pressure vessels, safety assessment 6 of pressure vessels with defects is used for calculation and assessment. The criteria are based on the straight forward propagation of the crack. The research so far has shown that the actual crack of the catalytic cracking device is not straight, but is irregularly bent and expanded forward. It is believed that the crack has fractal characteristics and is a fractal curve. The use of crack fractal can quantitatively describe the stress intensity factor. The fluctuation range and the change of fatigue crack growth rate In engineering practice, the size of the pressure vessel, the size of the defect and the material performance parameters are not definite values, but fuzzy values, which are distributed according to a certain distribution law.

In addition, there are still many deviations in the pressure vessel fracture criterion, which limits the reliability of the literature application to a certain extent. To this end, the author compares the relevant theories of fractal theory, fuzzy theory and reliability design with the conventional evaluation of plane defects in the literature.Combined, calculation and analysis evaluation are performed in the fracture design of pressure vessels, which will greatly improve the reliability and level of fracture evaluation. Petrochemical equipment 1. Effect of fractal crack propagation on fracture Determination of fractal dimension When fractal analysis of material cracks is performed, the fractal dimension D is an important parameter.

Fractal crack stress intensity factor When the length effect and bending effect of fractal crack are considered, in the conventional evaluation of plane defect fracture, the fractal effective stress intensity factor is: In the fatigue evaluation, the fractal effective stress intensity factor is not considering the fractal effect. The I-type stress intensity factor at the time, the fuzzy reliability calculation of the pressure vessel fracture is carried out by the literature, the conventional assessment of the plane defect is carried out by the method of the general failure assessment diagram, that is, in the safe area, due to the influence of various objective factors, it is random. Variables and fuzzy variables, the principle of fuzzy probability must be used to discuss the fracture ratio probability distribution of pressure vessels. Fuzzy reliability combines the probability distribution with the membership function, and the integration can be used to obtain the general formula of fuzzy reliability: The crack propagation can be regarded as a fractal curve, and the stress intensity factor calculation model of fractal crack is established. Combining the randomness of fracture ratio, the ambiguity of material fracture ratio and the conventional evaluation of plane defects, the fuzzy fractal fracture of pressure vessel is calculated and analyzed. Reliability, the fractal fuzzy reliability safety assessment of pressure vessel fracture is realized.