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 over stressed 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.