(6)The Chief Inspector shall, on registration of the boiler, order the grant of a certificate to the owner in such form as may be specified by regulations, authorising the use of the boiler for a period not exceeding twelve months, at a pressure not exceeding such maximum pressure as he thinks fit:Provided that where an economiser or an unfired boiler forms an integral part of such processing plant in which steam is generated solely by the use of oil, asphalt or bitumen as a heating medium, the Chief Inspector may authorise the use of such boiler for a period not exceeding twenty-four months.
