PSI - Issue 22

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

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2.2. Sealing mechanism of premium connection Different to traditional API connection, which is sealed by thread, premium connections are sealed by metal/metal interference on the main sealing surface and assisted by torque shoulder. The local resistance generated by the fluid is related to the length of the leakage path and the cross-sectional area of the clearance as follows (Mo et al. (2018)): R pdl    (1) Where P is the contact pressure, Pa. By studying the sealing ability and contact stress of metal/metal sealing surface, Murtagian et al. (2004) put forward the criterion of sealing ability of threaded connection as follows:

  0 L n W p l dl  

(2) Where, L is the sealing length, m; n is the correlation index, with sealing grease, n=1.2; without sealing grease, n=1.4.

3. Introduction of Loads during the simulation 3.1. Introduction of the loads in CAL IV B-series test

The purpose of the load envelope test in ISO 13679 is to evaluate whether the sealing ability of threaded connection is within safe limits under high and complex loads. There are 9 common load points and 5 bending load points in the test load path. The sequence of the load applied is counterclockwise-clockwise-counterclockwise. When the compression efficiency of the connection is the same as that of the pipe body, the load point 8 coincides with the load point 9. Fig. 3 shows the loading path of CAL IV B-series test when bending load is considered, where path 1, path 2 and path 3 are 100%VME envelope, 95%VME envelope and test load path respectively. Bending load equivalent tensile/compressive load is the minimum among 40% yield strength of pipe body, 40% connection yield strength and 19.7 ° / 30 m wellbore curvature.

Fig. 3. Loads in series B test of ISO 13679.