Abstract: For accurate evaluation of the safety of pressure vessels with complex structure containing defects beyond tolerance, this paper takes the alkylation reactor with planar defects beyond tolerance in the weld of the inclined pipe and cylinder as an example and makes qualitative and precise quantitative analysis of defects and failure modes by using new technologies such as the phased array. Combining with finite element analysis method, it also carries out research on fitness-for-service assessment. The research results indicate that the potential failure mode of the alkylation reactor was the elastoplastic fracture failure; the evaluation points were located in the safety zone of the failure evaluation diagram which was calculated by adopting conventional planar defect evaluation method. This study provides a scientific basis for the safe operation of the reactor and is of reference and significance for similar engineering projects.

Key words: reactor, finite element, phased array, defects beyond tolerance, fitness-for-service assessment