The porous section at the bottom of ceramic lined composite pipes prepared by the gravitational SHS method and the influence of additive were investigated. The controlling measures were given by analyzing the formation of porous section. The results reveal that the formation of porous section is attributed to the existence of SiO2 particles

where the porous section can be increased with the increase of SiO2 particles. In addition

additive can be helpful to creating porous section. The volume of porous section can be obviously reduced by adding proper fluoride with the SiO2 particles content less than 2%.