Approval for material return issued against the Work Order

Hello,

We are using PM module and issuing materials against the work order. Many times users are returning the un-used material back to stores. This un-used material may come back <b>with or without</b> work order reference. i.e. Sometimes they just return bunch of material but don't know the work order # against it was issued initially.

We need to control this flow of un-used return material through proper system approval.

How can do this.

Thanks,