Answer
When extensive repairs (e.g., replacement of generating/water-wall tubes, combustion chamber plating repairs, or furnace re-welding) are completed, a strict protocol under Class and national rules (Indian MS Act, 2025) must be followed before recommissioning.
Class Requirements & Surveys
Approved Welder & Materials: Ensure all welding was conducted by a Class-certified pressure vessel welder using Class-approved low-hydrogen electrodes with matching material test certificates (MTC).
Non-Destructive Testing (NDT): Prior to any pressure testing, Class mandates Radiographic Testing (RT) or Ultrasonic Testing (UT) of the newly executed structural welds to verify zero internal volumetric defects or inclusions.
Hydraulic Test (Hydro-test):
Class requires the boiler to undergo a hydrostatic pressure test.
Test Pressure: Typically conducted at 1.5 times the maximum allowable working pressure (MAWP) of the boiler.
Conditions: Water temperature must be maintained above the brittle fracture threshold (typically between 30C and 40C). The pressure must be held steady for at least 30 minutes while the Class Surveyor examines all tubes, welds, and tube plate expansions for distortion or weeping.
Duties of the Chief Engineer
Accumulation Test Verification: If safety valves were overhauled or disturbed during the repair, perform a formal accumulation test under the surveyor’s supervision to confirm that the valves can vent excess steam without the boiler pressure rising more than 10% above the MAWP.
Refractory & Inspection: Inspect the internal refractory lining of the furnace to ensure it is correctly cured and free from major cracking. Ensure all internal foreign objects, scale, and welding rods are cleaned out.
Refitting and Boxing Up: Supervise the refitting of the internal deflector plates, dry pipe arrangements, and verify that the main manhole door gaskets are brand new and properly torque tightened.
Chemical Treatment & Boil-Out: If extensive new tubes were fitted, coordinate a mild chemical "boil-out" using alkaline compounds to remove storage oils and anti-rust coatings from the new metal surfaces before normal operation.
Statutory Logging: Make precise technical entries in the Engine Room Logbook, Boiler History Record, and ensure the Class Survey report is attached to the ship's statutory portfolio.