Molten glass conduit structure, and device and method using conduit structure

Provided are: a molten glass conduit structure, in which the erosion of a solid heat insulating material constituting a backup of a conduit can be prevented by a molten glass that exudes from a joint part between electrocast bricks constituting the conduit, without using any cooling means, and which can be manufactured at a reduced cost; a vacuum defoaming device using the conduit structure; and a method for vacuum defoaming a molten glass using the vacuum defoaming device. The molten glass conduit structure, said conduit structure comprising a conduit and a backup provided on the periphery of the conduit, is characterized in that: the conduit is a hollow tube having electrocast bricks disposed in the longitudinal direction and circumferential direction thereof; the backup comprises a refractory layer provided on the outside of the conduit and a heat insulating material layer provided on the outside of the refractory layer; the refractory layer comprises a refractory brick layer consisting of refractory bricks disposed in the longitudinal direction and circumferential direction of the conduit and a monothilic refractory layer that is formed by laying a monothilic refractory, said monothilic refractory containing, in terms of mass percentage of oxide(s), 30-100% of Al2O3 and 0-70% of SiO2, and then sintering the monothilic refractory; the heat insulating material layer comprises a solid heat insulating material layer comprising a solid heat insulating material disposed in the longitudinal direction and circumferential direction of the conduit; and the electrocast bricks constituting the conduit, the monothilic refractory constituting the monothilic refractory layer and the refractory bricks constituting the refractory brick layer are selected in such a manner that, when the molten glass passes through the conduit, a site being at the same temperature as the pour point of the glass is positioned within the heat insulating material layer.