It shall be capitalised as equipment – tank (not sure is this the correct description) and depreciate over 2 years (50% per year). For tax purpose, no capital allowance will be claimed under replacement basis (not allowed to claim for the first time purchase). When the company purchase additional tank in future to replace the old one, it will be charged out immediately as expense under tax treatment. While for accounting, the replacement purchase will be capitalised again and charge out as gradually as depreciation.