Abstract: Plastic collapse failure is one of the key failure modes for pressure vessels under the condition that load is applied once. A dual evaluation criterion for plastic collapse is introduced in this paper. The criterion integrates the design concept of strength criteria based on ASME code and deformation criteria based on EN standard, and also borrowing the ideas of determining allowable stress. It can prevent both plastic collapse and excessive plastic deformation. The evaluation of the criterion can be carried out by the load-resistance coefficient method based on elastic-plastic analysis. Elastic-plastic analysis shall use the real stress-strain curve of the material and consider the geometric nonlinear effects. Taking the large opening nozzle on cylindrical shell as example, this paper introduces the realization method of this criterion in finite element software and evaluation steps in detail. Compared with the result of stress classification, it is found that the evaluation criteria by stress classification method for plastic collapse failure may be too conservative for some structures. The dual criterion is more advanced and accurate, and can provide a more reasonable solution.

Key words: plastic collapse failure, pressure vessel, dual evaluation criterion, elastic-plastic analysis, stress classification method