How do I attach a shelf to an existing kitchen unit?
Wall studs should be every 16". If you measure from the start of the wall where the pipes are, you should be able to hit a stud every 16" behind the backing board. I'm not sure what the pipes are that you have in your kitchen - venting maybe, but I would look for shelves that would be supported via studs through the backing board wall instead of trying to screw into the wall with the pipes.