Estimation Of Multiaxial Fatigue Life For The Key Parts In Air Seperation Equipment

Though great progress has been achieved in design and manufacturing of nationals’air separation equipment industry in the decades, there is a certain distance with the international advanced level. Problems, such as the market demand is huge, the manufacturing level is small, the products energy consumption is higher, and the working stability is low, must be solved at once. A systems analysis must be done for the large scale air separation equipment, and a reaserch in depth must be underway to the load of the key parts. A fatigue life estimation method can be established to predict the life of the air separation equipment key parts.In this paper, the low-middle pressure cylinders of a 40k air compressor were selected as the subject investigated. Estimation of faigue life for the impellers and shafts has been finished with the corresponding load spectrum that based on the load-time histories, which acquired from the analysis of the working condition and load for the impellers and shafts of the low-middle pressure cylinders. The main works of this paper are as follow.(1) Estimation models of high cycle (HCF) and low cycle (LCF) multiaxial fatigue life were summarized according to the materials and loading condition of the key parts. In order to compare the fatigue life estimation accuracy of different modles by using the experimental data from the references, which demonstrate that the Crossland criterion and the Matake criterion are sutible for 30NCD16 steel similar to FV520B which makes up the impellers, and Brown-Miller criterion is sutible for 1050 middle steel which makes up the shafts.(2) According to air compressor units design parameters, load conditions and their influence factors,9 working conditions for impeller and 2 working conditions for shafts are divided. Three-dimensional models of the impellers and shafts were worked out by using the Solidworks and static structure analysis for the modles were compelted with the Workbench from ANSYS. Given points were selected according to the stress and strain nephogram. Load-time histories for the impellers and shafts were acquired by applying the FSI method and transient structural method with the Workbench.(3) Rain flow matrix and load spectrum of the key parts were obtained by taking full use of theMATLAB with simulation method. As a result, the small load filter standar from 3% to 5% is reasonable when applying on such situation in this paper, by taking a discussion about the filter standars (3%,5%, and 8%) for rain flow matrice.(4) The S-N cruve of FV520B were revised by taking four fatigue factors into acount, they are stress concentration coefficient, size coefficient, surface condition coefficient and the mean stress coefficient. Nominal stress method and local stress-strain method were used to estimation the fatigue life of the impellers and shafts. The prediction results show that the fatigue life of the impelles and shaft are all above 106, belongs to the infinite life.