PSI - Issue 22

Yufei Li et al. / Procedia Structural Integrity 22 (2019) 43–50 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

48 6

(c) Point of load 5B

(d) Point of load 6B

(e)Point of load 7B

Fig. 6. Von Mises stress of premium connection with bending load in series B test

5.2. Results of sealing performance of premium connection for ISO 13679 thermal cycle test Fig. 7 shows Von Mises stress of a premium connection at critical moment in a complete thermal cycle test. Fig. 7(a) is Von Mises stress after the first tension/internal pressure cycle at room temperature for five times. The maximum Von Mises stress appears on the sealing surface of the connection, which is 716 MPa, and does not exceed the yield strength of the material. The maximum Von Mises stress appears in the middle of the coupling, which is 779 MPa (see Fig. 7(b). Compared with the maximum stress at room temperature, the maximum Von Mises stress increases by 8.8%. It can be seen that temperature has a great influence on the stress of premium connections. After 50 times thermal cycles, the Von Mises stress of the connection remained basically unchanged. The Von Mises stress distribution of the connection after five load cycles at 180℃ is similar to that at room temperature. Stress concentration occurs on the sealing surface and shoulder. The maximum Von Mises stress is 676 MPa, and the threaded section is still in good condition. Fig. 7(e) is Von Mises stress of the premium connection after the second thermal cycle 50 times. Compared with the first thermal cycle 50 times, the overall stress level of connections significantly decreased. The maximum Von Mises stress appeared at the sealing surface of connections, which decreased by 16.6%. Compared with Fig. 7(f) and Fig. 7(e), the Von Mises stress of premium connections will increase even if the temperature is decreased due to the plastic deformation of the contact surface. The maximum Von Mises stress will occur at the sealing surface of the connections. After the second tension/internal pressure cycle at room temperature, the stress shows that the overall stress level of the connection decreases compared with all the load cycles at the first room temperature, but the stress distribution is similar. The maximum Von Mises stress occurs on the sealing surface of the connection, which is 700 MPa. From the previous analysis, it can be seen that the stress of incomplete threaded section and sealing surface of premium connections varies greatly during thermal cycling test. The stress value of coupling at the middle surface is greater during high and low temperature cycling process. Yield occurs and there is a risk of failure. Temperature has great influence on stress and distribution of premium connections. When designing premium connections, the influence of temperature should be taken into consideration.