Wednesday, 28 December 2011

Structural failure in a Panamax

The Antipodean Mariner has been reviewing a report on structural failure on a Panamax bulk carrier. The ship in question is nothing special, one of many standard bulk carriers built in the mid-1990's at a reputable Japanese Yard. She has traded without problems until now and had just completed Special Survey which entailed a lot of close-up attention of the hull structure by her Managers and Class.

The problem came to the crews' attention when she arrived at a terminal to load. Water was seen gushing from a crack in the hull where a ballast tank and cargo hold bulkhead joined the shell plating. The area of the shell plating was cropped out and replaced, and the welded seam sent away for metallurgical analysis.

Analysis of the weld found a flaw in the welded seam which had been undetected for over 15 years. An asymmetric weld profile on the two sides of the hold bulkhead, combined with impurities in the weld, had lead to a crack propagating into the shell plating and the cracking of the hull.

Worse was to come when the vessel's hull cracked in adjacent frames on the next laden leg of the same voyage. More repairs were done and the ship sits awaiting the outcome of the inevitable legal dispute between the Owners and Charterers.

The moral of this posting is that despite computer aided design, fatigue analysis and close-up inspections, inherent defects can take years to manifest themselves. It was fortunate for the crew that this defect didn't lead to a catastrophic failure in the single hull bulk carrier.

The Antipodean Mariner

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