Investigation of the mechanical behavior of a flexible solid metal seal for a cryogenic butterfly valve |
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Authors: | Ahn Jun Tae Lee Kyung Chul Lee Kwon Hee Han Seung Ho |
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Affiliation: | 1.Department of Mechanical Engineering, Dong-A University, Busan, 618-270, Korea ;2.Quality Management, Dukwon Valve, Busan, 618-270, Korea ; |
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Abstract: | Seat tightness at the fully shut position should be a consideration in the development of a butterfly valve for use in a liquefied
natural gas (LNG) vessel. A flexible solid metal seal offers sufficient tightness of the butterfly valve and meets the specifications
for cryogenic temperature. In the present study, characteristics for a cryogenic butterfly valve, such as the flow coefficient
and the pressure loss coefficient, were estimated by numerical fluid analysis carried out to simulate 3-D flow and to study
performance as it was affected by the opening angles of the valve disc. A design criterion to ensure the seat tightness of
the butterfly valve at the fully shut position was proposed, in which the contact pressure between the metal seal and the
valve disc would be compared with the fluid pressure. Numerical structural analysis showed that the contact pressure can be
calculated by simulation of the frictional contact behavior on the surface of the metal seal and the valve disc. As a result,
an adequate flexibility of the metal seal and the valve disc was required in order to accomplish a contact pressure that would
be high enough to satisfy the seat tightness requirement. Under cryogenic temperature, thermal shrinkage caused the metal
seal to adhere closely to the valve disc periphery at both sides and raised the contact pressure to a relatively high value,
though there was no contact across a small area at the center position, which is susceptible to leakage. An additional displacement
of the metal seal and the valve disc appeared at an operating fluid pressure of 6.9 bar and produced sufficient contact pressure
at the no-contact area. This was verified by experimental leakage tests performed at room and cryogenic temperatures. |
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