Papers by Author: Jun Si

Abstract: Overage service pressure vessels are widespread in China. These pressure vessels may be suffered from some forms of material deterioration and damage with an increasing possibility of failure. However, some of the potential damage mechanism couldn’t be found if the inspection strategies were carried out in according with traditional inspection regulations. Through identifying the damage mechanism of these pressure vessels, the risk evaluation would be carried out by use of RBI technology in company with the structure integrity assessment. The procedure of inspection for overage service pressure vessels was developed, and some of the reasonable inspection and testing requirements and basic principles also were proposed. The three levels evaluation methods of residual safe-service life for these pressure vessels were proposed. At the same time, the risk supervision method of these pressure vessels was established by use on the risk basic theory.

Abstract: The creep rupture behavior of weld joint of modified 9Cr-1Mo martensitic heat-resistant steel is investigated by conducting creep tests. The creep strain-time curves of 838K under different stress levels are obtained. The effects of different stress conditions on the creep rupture lifetime are analyzed. Based on the creep test data, the relationship between minimum creep rate and stress, creep rupture time is analyzed. The test results show that the creep rupture occurred in the fine-grained heat-affected zone. The microstructure evolution during creep process is studied by metallographic analysis and fracture analysis.

Abstract: Inspection strategy is an important activity in processing plants, and one of the key tools used for such strategy is the risk-based inspection (RBI) methodology. Risk-based inspection is a methodology for optimization of inspection strategy. Based on principle of the risk-based inspection methodology in API 581, the risk assessment for vessels and pipelines in olefins conversion plant is carried out. The main failure modes and damage mechanisms of vessels and pipelines are identified. All vessels and pipelines in this plant are prioritized based on the level of risk. Risk reduction measures and optimal inspection strategy are proposed. This application of risk-based inspection will provide reference for the inspection of the olefins conversion plant.

Abstract: The interaction behavior of two non-aligned through-wall cracks in flat plates is investigated by the finite element method (FEM) under extensive creep condition. The time-dependent fracture parameter C*-integral along the crack tips are calculated and compared to the results of a single crack of the same size. For comparison purpose, the interaction of stress intensity factors (SIFs) is also examined in the study. The results indicated that interaction of multiple cracks is different between the time- dependent fracture characterized by C*-integral and linear elastic fracture noted by SIF. The magnifying factors of time-dependent fracture are obviously larger than that of the linear elastic fracture cases. Therefore, the current re-characterization rule for multiple cracks developed from linear elastic fracture analysis may lead to a non-conservative result and should be modified when it is used in the assessment of time dependent failure.