Experimental tests of the vacuum sealing performance of the ConFlat flange 25 for the HL-2M divertor pipeline circuit

Abstract

A collection pipeline is designed to connect the divertor with the cooling and the baking systems in HL-2M. The ConFlat flange 25 used as the connecter in the pipeline is one of the feasible schemes. According to the requirements of the leak rate, the helium leak detector is used to research on the vacuum sealing performance of the flanges with the heating rate of 35 °C/h, 50 °C/h, 65 °C/h, 80 °C/h and 95 °C/h. The results show whatever the heating rate is, the leak rate increases as the temperature rises. When the temperature rises from 250 °C to 350 °C, the leak rate increases very rapidly. Moreover, the faster the temperature rises, the greater the fluctuation of the leak rate is. And the influence of helium pressure in the pipeline on the leak rate is very small. When the initial torque applied on the bolts is10 N m, the maximum leak rate is 7 × 10−10 Pa m3/s in the first heating process but is greater than 1.0 × 10−6 Pa m3/s in the second heating process which exceeds the acceptable leak rate of 1.0 × 10−9 Pa m3/s. So if we don't pre-tighten the bolts again in the heating cycles, the initial torque must be larger than 10 N m.