The effect of fastening stress on hydrogen diffusivity behavior and numerical finite element simulation research analysis of hydrogen brittle process for bolt
A number of bolts fastening blade of vessel under sea fail by cracks after service time of 43800h.Firstly,the paper presents that fastening stress and hydrogen environment produced by electrochemical protection project are the mainly causes to the failure of bolt.In order to research the hydrogen brittle process induced by stress and hydrogen diffusivity,the model of numerical finite element simulation is set up to analyze the stress field,the effect of it on hydrogen diffusivity,and hydrogen content distribution dependent on time.It is inferred that the hydrogen diffuses to high stress region with the effect of stress gradient,and the longer the diffusivity time,the higher hydrogen content on stress concentration.Furthermore,the bolt fractures by hydrogen brittle with hydrogen content of 7.0ppm after service time of 43800h.The simulation results are consisted with actual fracture time,failure position and experiment of hydrogen content,therefore,the numerical FE simulation can be used to predict the hydrogen brittle failure process of engineering components provided that the simulation with correct setting of model and boundary conditions of stress and hydrogen diffusivity.Key word: hydrogen diffusivity; stress gradient; hydrogen brittle The fastening bolts for blade in the marine crack induced by hydrogen,and the main hydrogen source are cathodic protection.In order to avoid the corrosion of marine material subsea,the electronic chemical circuit composed by anode,sea,and marine should be checked to be stable.Hydrogen induced stress cracking from cathodic protection is a result of interconnected mechanisms involving electrochemistry,diffusion,metallurgy,fracture micro mechanisms and external load.For martensite stainless component part with large size,the time from beginning to fail of service induced by hydrogen may be a very long as the low hydrogen diffusivity of material and strained region a bit far from the diffusivity interface,therefore,it is hard to make experiment simulation by the lab.Up to present,only simple component parts such as thick1 or thin plate are hydrogen simulated by experiment2,3 or calculation4,5.It is presented1 that hydrogen content is 4.9 ppm after hydrogen diffusivity time of 2000 days (about 5.48 years)at the distance of 10 mm far from hydrogen penetrating interface with content of 30 ppm when the diffusion coefficient is.It proved that the Fick’s second law can be used for the hydrogen diffusivity of thick plate.Hydrogen distribution can be affected by the stress gradient,and it is reported6 that there is higher hydrogen content in stress concentration area than other regions.The fastening bolts in the marine is working in the environment of stable cathodic protection and preloading stress during the long time service,which is a good research sample for hydrogen diffusivity induced by stress both for experiment and calculation.And the numerical modeling results can be verified by comparing with the hydrogen content experiment.
Zhong Zhenqian Zhu Yanyong Tian Zhiling
Central iron & steel research institute,Beijing,100081 Beijing University of Science and Technology,Beijing,100083
国际会议
Asia Steel International conference 2012(第五届亚洲钢铁大会)
北京
英文
1-8
2012-09-23（万方平台首次上网日期，不代表论文的发表时间）