Any plant which performs one of the following functions: removing liquefiable hydrocarbons from wet gas or casinghead gas (gas processing); removing undesirable gaseous and particulate elements from natural gas (gas treatment); removing water or moisture from the gas stream (dehydration). Also, the original cost of property, plant and equipment owned and used by the utility in its gas operations and having an expectation of life in service of more than one year from the date of installation.