Recovery of duty where concessional goods are not used for intended purpose requires payment of differential duty with interest. Recovery of duty applies when concessional-rate goods are not used for the intended purpose: the recipient manufacturer must pay the difference between the duty otherwise leviable and any duty already paid, with interest, and recoveries follow the provisions of the Central Excise Act; defective, damaged, unsuitable or surplus goods may be returned to the supplier and will be added to the supplier's non-duty paid stock; loss or destruction by natural causes or unavoidable accidents in transit, handling, or storage is treated as non-use for intended purpose.