Overview

Ultra-low temperature butterfly valves are mainly used in pipeline systems of liquefied natural gas and liquid nitrogen to control the opening and closing or adjustment of the pipeline equipment. The product adopts a double offset structure and an elastic metal sealing structure. The double offset structure can greatly eliminate unnecessary overloading and scraping of the disc and sealing ring during the opening and closing process of the butterfly valve. The elastic metal sealing structure can effectively compensate for the deformation caused by temperature changes. The application of these two structures can effectively improve the sealing performance of butterfly valves under ultra-low temperature conditions.

Material selection

At low temperatures, the strength and hardness of metallic materials increase while the ductility and toughness decrease, exhibiting varying degrees of low-temperature brittleness, which seriously affects the performance and safety of butterfly valves. In order to prevent brittle fracture of materials at low temperatures, pressure-bearing components such as valve bodies and butterfly plates are made of austenitic stainless steel (such as 304L, 316, 316L), among which 316L has the best stability and no apparent low-temperature brittle transition temperature. It can still maintain relatively high toughness under low-temperature conditions. Therefore, pressure-bearing components such as valve bodies and butterfly plates are made of 316L material.

Test

Referring to relevant low-temperature valve test standards such as BS6364 and JB/T7749, the sealing performance of butterfly valves is tested through combined operations of pressure reducing valves and shut-off valves. During the test, the temperature of the valve body, valve cover, and butterfly plate are monitored using a thermocouple. After reaching the required test temperature, the sealing performance of the butterfly valve is tested using a low-temperature test medium, helium gas.

Epilogue

Through the study of the double eccentric butterfly plate, combined with factors such as the required compression of the sealing components in the sealing structure and the additional static hydraulic torque generated by the double eccentric butterfly plate, the structural dimensions of the double eccentric butterfly plate can be determined better. The proposed elastic metal sealing structure can effectively reduce the impact of material thermal expansion and contraction caused by temperature changes on the sealing performance. The use of 316L material as the material for valve bodies, butterfly plates, and other components is suitable for ultra-low temperature conditions.