You may also want to check the tesselation values of your pipes (assuming they are NURBS). You may be able to lower them, especially the ones not so close to the camera.

FYI, mayabatch handles memory differently that the render window within Maya. By differently I mean better. think of it this way, Maya is sucking up RAM to display and manage your file so it has less to work with for rendering.

I would try setting up your render globals they way you want them, quit out of Maya, right click on your file and select "render".

Setting up render layers is a great idea for flexibility, but it likely won't help your RAM problem.

You could also buy more RAM, but Maya doesn't seem to recognize anything more than 2 GB.

Good luck.