Cracks at side-frame bracket toes on bulk carriers

#Where they appear

In single-side-skin bulk carriers, the side shell between the hopper tank and the topside tank is stiffened by vertical hold frames, ended by brackets at both ends. The toes of those brackets — where the bracket meets the hopper or topside sloping plate — concentrate stress. Add corrosion from cargo and ballast and impacts from grabs and bulldozers, and the toe becomes a classic place for fatigue cracks.

#Why it matters

Hold frames carry the loads of the side shell into the double bottom and the deck structure. A cracked or detached frame lets the shell work, and failing side structure is one of the scenarios behind the losses that led to the IACS requirements for bulk carriers: UR S12 for the strength of side frames and UR S31 for their renewal criteria on older ships.

#Finding them

• Close-up survey of frames and brackets in the holds, cleaned where needed.
• Magnetic particle testing on suspect toes, which shows cracks too fine for the eye.
• Thickness measurement of webs, flanges and brackets — wasted frames crack sooner.

#Repairing them

A crack is not repaired by running a weld over it. The repair:

1. locates the ends of the crack by NDT;
2. gouges or grinds the crack out along its full length, down to sound metal;
3. welds the groove with a qualified procedure, in passes, with controlled heat input;
4. grinds the toe to a smooth profile where the design allows, to reduce the stress concentration;
5. tests the repair again by magnetic particle testing.

Where the web or flange of the frame is wasted beyond the class limits, the right repair is to renew the frame and its brackets, not to weld it.

#Removing the cause

If a toe has cracked once, it will crack again unless something changes: a better bracket shape, a soft toe, a renewed member of the right thickness, protection against grab damage. That decision is taken with the owner and class, and it belongs in the repair plan from the start.