Web3D has gradually become the mainstream online 3D technology to support Metaverse. However, massive multiplayer online Web3D still faces challenges such as slow culling of potentially visible set at servers, networking congestion and sluggish online rendering at web browsers. To address the challenges, in this paper we propose a novel Web3D pipeline that coordinates PVS culling, networking transmitting, and Web3D rendering in a fine-grained way. The pipeline integrates three key steps: establishment of a granularity-aware voxelization scene graph, fine-grained PVS culling and transmitting scheduling, and incremental & instanced rendering. Our experiments on a massive 3D plant have demonstrated that the proposed pipeline outperforms existing Web3D approaches in terms of transmitting and rendering.