|Back to Main Page ----- Back to Chapter 2|
2.16 TANK INSPECTIONS
Inspections in cargo tanks are part of the ship's preventive maintenance program. The structure and all of the equipment each tank contains are vital to the work of the tanker. Information on condition of the tanks and cargo equipment is essential to preparation of requirements for shipyard or underway repairs. For tank inspection information to be useful to the crew and owners, the vessel must have a program for keeping tank inspection records and for filing tank inspection reports.
2.16.1 Tank structural inspection
Port wing tank looking forward.
Because of the flexing and stresses imposed on the hull structure during every voyage, the structure must be routinely inspected for early detection of defects. Defects can be impact damage, corrosion, cracks, buckling or distortion. Reporting defects requires a clear description of the size and type of defect and its exact location in the tank. Figure 2.16.1 is a diagram of a typical wing tank. Owners should provide a book of such diagrams (laminated), including one diagram of each tank, to provide the officer responsible for tank inspections with a convenient way of accurately indicating defects. Examples of recorded defects might be:
1 'No.3 port cargo oil tank, frame 67, inboard, aft side, bracket stiffener weld to longitudinal is cracked for 9 cm, 7th longitudinal from bottom.'
2 'No.5 port cargo oil tank, frame 60 to 61, bottom, in way of main longitudinal, bottom set in about 6 cm, for length of 2 meters and breadth of 1.3 meters; longitudinal buckled and weld cracked at connection to frame 60.'
3 'No.5 port ballast tank, Frame 60, deckhead, coating deteriorated and severe corrosion to longitudinal and transverse framing from main longitudinal inboard to longitudinal bulkhead.'
Each of these defects is described with enough detail to enable the
owner's repair engineer or a shipyard foreman to locate the defect.
Each defect could be recorded more quickly by use of a copy of the diagrams
suggested above. Using the diagram it is only necessary to circle the
defective area or location and make a note such as '9 cm crack in weld'.
The defect can be marked with erasable pen on the laminated copy (which
constitutes the ship's running record of tank defects) and a photo copy
of the diagram sent to the owner's office as the defect report.
2.16.2 Tank inspection checklist
Cargo tanks are not frequently gas free, and the chief officer should make the best of every opportunity to verify that a cargo tank and its equipment are in good order. A chief officer who returns frequently to the same vessel can take the opportunity of a shipyard period to photograph the critical equipment in each cargo tank. An album of these photographs is an invaluable reference when problems with in-tank equipment occur.
2.16.3 Testing heating coils
Whenever the heating coils are placed in service, the vent should
be opened and the water which is ejected for the coils (as the steam
begins to fill them) tested for oil content. The test can be as simple
as the feel and odour of the water. Or a sample can be captured in a
glass container, allowed to settle and examined for oil contamination
on the surface. If a coiled cargo tank is entered for inspection, the
heating coils should be filled with water and enough pressure placed
on the coil to provide an effective leak test. Every decimetre of the
heating coils should be visually examined. Any leaks detected should
be repaired by clamping or isolated until permanently repaired at the
earliest opportunity. A tank defect report must be prepared and submitted
to the owner's port engineer.
2.16.4 Cargo and ballast piping tests
2.16.5 Tank gauge repairs