Consider using CSG to create your model. Create a mesh of the pipe that will be outer thickness. Then an inner mesh that represents the center to be removed.
const pipeCSG = BABYLON.CSG.FromMesh(outer);
const centerCSG = BABYLON.CSG.FromMesh(center);
pipeCSG.subtractInPlace(centerCSG);
var pipe = pipeCSG.toMesh("pipe");