The Safety Assessment Of Bolt Flanged System Under Thermo-mechanical Loadings

Due to repeated disassembly, easy installation, low cost, bolted flanged system is widely applied in industry, electric power, aerospace and other fields. This paper is studied three aspects, such as the influence of different heating styles on bolted flanged strength, the effect of dimension and material on gasket stress, and the influence of bolted expansion on thread elastic shakedown loads.Based on finite element analysis method, this paper is analyzed the stable temperature and transient temperature, and obtained test point’s temperature, and further acquired stable time. In heating mode second(inner wall temperature gradually arise to target temperature), the relationship between the stable time and the heating time is linear. Such as1 T ?0.89 T ?3.996, T1 is stable time, and T is heating time.Based on the stress field which calculated from temperature field, the third heating mode is the reasonable heating style. Based on Tresca yield criterion, this paper is analyzed several stress field and obtained shortest heating time. The better heating mode in this paper is 0~150~300~400℃ which is calculated from heating slope, holding period and total heating time. The better heating mode is flange inner temperature heating to 150℃, and holding 1200 s, and heating to 300℃ with 1300 s, and holding 1200 s, and heating to 400℃ with 1700 s. The total heating time is 1.5h.The effect of factors, such as bolt flanged materials, gasket compression-resilience characteristics, gasket inner diameter and gasket outer diameter,on gasket stress were studied. According to the analysis results, the varieties of the elastic modulus and poisson ratio have little effect on gasket stress. The more left the compression-resilience characteristic curve is, the harder the gasket will be. Meanwhile, the difference between inner and outer diameter of the gasket stress is greater The more right the compression-resilience characteristic curve is,the softer the gasket will be. Meanwhile, the difference between inner and outer diameter of the gasket stress is amaller The average gasket stresses are all 55 MPa under 3 different kinds of compression-resilience characteristics, and it proves average gasket stresses have no relation to compression-resilience characteristic. When gasket width exceeds 59 mm, gasket stress does not decrease. And the gasket average stress is inversely proportional to gasket width.The elastic shakedown of bolt during cyclic thermo-mechanical loadings were analyzed by Abdalla method. Internal pressure has no influence on elastic shakedown loads. It is good for bolt’s elastic shakedown when linear coefficients of expansion are close in flange and bolt.