Concept of spares procurement

I would like to know what is the standard process of spares procurement as per SAP. I understand that materials will be consumed through Storage Loacations as against Maintenance orders. So unless there is a breakdown or preventive maintenace job done the materials cannot be consumed. So the value of inventory rises. Materials procured under Non Stock type donot have provision for materials not being charged for long. So ideally should they come under Stock materials?Please advise