Fracturing of the Structural members of a transverse bulkhead of a Bulk carrier are:-
- Side Shell Plating
- Connection of Bulkhead plating to side shell.
- Connection of side shell frame & end brackets to the shell plating and hopper side tank plating by close-up inspection.
- Connection of side shell frame & end brackets to the shell plating and topside tank plating.
Actions to control structural stresses and fatigue:-
- Routing Planned Maintenance & Inspection of Structural members of cargo holds & hatch covers.
- Identification of susceptible areas prone to Fatigue & Stresses.
- Ensure accessibility of the area to be surveyed with due regards to the area under inspection shall be clean and will lit.
- Careful planning of the surveys to be undergone with all personnel involved.
- Where a fracture which not been caused by contact damage is found in the main hull structure on one side of a ship, corresponding structure on the opposite side should be examined to see if a similar fatigue has occurred. Fractures of this nature are of concern, especially where corrosion is associated with failure & may have been contributing factor
Structural Surveys include:
- Routine Inspections.
- Planning Surveys
- Surveys of known defects.
- Classification surveys.
- Annual surveys
- Intermediate Surveys
- Special surveys
- Condition Surveys
- CAP Surveys
- Life extension surveys, etc.
Fatigue cracking of steel structures:-
- Fatigue cracking occurs at points such as hatch covers where stresses are locally high.
- Such cracking is the result of cumulative damage caused by cyclic loading of structure & invariable starts at welded joints.
- The fatigue life is the time required in service for the structure to experience enough stress cycles for a crack to occur. A bulker is so designed that with proper maintenance cracking should not occur until a fatigue life span of 20 years.
- Fatigue life span once used up cannot be regained except by complete replacement of welded joints.
- Therefore, it is very essential that the welded joints of an overstressed structure are replaced, before proceeding with life exterior surveys/ programmes.
- Fatigue cracking have been most frequently observed in the bracket toes at the connection of the main frames to the hopper and topside tanks and in the boundaries of the vertically corrugated transverse bulkheads with upper stools, lower stools and topside tanks.
Corrosion / Structural Deterioration:-
- The major barrier preventing structural deterioration on ships, especially in very corrosive environment of Water Ballast Tanks and to a slightly lesser extent cargo holds is the tank/ hold coating. Since the establishment of ESP water ballast tanks and CH of all new ships must be fully coated. Such coatings should be hard coating & preferably light in colour.
- To maintain a good and efficient standard of coating is an important part of structural condition management. If coatings are kept in good condition the structure will be effectively protected and the original scantlings will be available to resists ―service loads‖ & ―stresses‖.
- Sea staff therefore should meaningfully report the condition of tank/ hold coatings during routines inspections and same to be documented in the company PMS system.
- The most effective method of protecting a structure of a bulk carrier is to maintain coatings and carry out repairs of coating breakdown in good time.
- Installation of Anodes, subject to the tank being regularly ballasted is an effective back-up that will prevent accelerated corrosion in the way of local coating breakdown.
- The most effective time to carry out coating repairs in the tanks i.e. freshwater washing, surface preparation and coating application, can be done during a routine repair period of reasonable duration.