Section 32(2)(b) in The Merchant Shipping (Cargo Ship Construction And Survey) Rules, 1974
(b)all boilers including exhaust gas or steam heated steam generators, economisers and domestic boilers, other than domestic boilers having a heating surface of 4.65 sq. metres or less and a working pressure of 3.52 k. gms. per sq. centimetre or less, shall be examined internally and externally at intervals not exceeding two years until they are eight years old and thereafter annually :