Fatigue problem avoidable, says DNV
Tuesday January 23 2007, From Lloyd's List
FATIGUE cracking of the type which caused the water ingress and subsequent abandonment of the MSC Napoli has been recognised as a problem of which operators of larger containerships need to be aware.
Long, narrow vessels such as containerships flex more than many types of ship in a seaway and care needs to be taken with the weight distribution in the cargo holds and tanks to minimise stresses.
They are also subject to torsional stresses in a quartering sea or with a swell on the bow that can contribute to fatigue stresses and even structural failure. Cracking in longitudinals, which have propagated to neighbouring structure and shell plates, have occurred to a number of large container vessels — not necessarily old ships.
Alerting owners to such problems, classification society Det Norske Veritas last October pointed out that side shell fatigue “had been of concern for some time”, with fatigue life on some designs found to be less than 10 years on some ships operating in particularly harsh conditions.
In its regular Container Ship Update, DNV, which happens to be the class society for the stricken British ship, suggests that regular visual inspection by ship staff, in areas where fatigue cracking is most likely, is a sensible precaution.
The society has developed a scheme, the Planned Inspection and Maintenance System, under which a ship-specific hull inspection manual would be produced for a containership, while ship’s staff would be trained to identify the first signs of fatigue cracking, along with a reporting system.
Using this system, a fatigue crack was discovered on a ship less than five years old. It is pointed out that such an inspection regime can be critical, as by the time a crack visibly manifests itself, some 90% of the fatigue life of the structure has elapsed.
Investigation into the causes of the incident are also expected to inquire whether the full sea speed grounding of the vessel on a coral reef in 2001 under its previous CMA CGM ownership might have some bearing on the subsequent structural problems.
The vessel, which was severely damaged in its forepart after being ashore on a pinnacle for nearly two months, was repaired in Vietnam and was bought by Zodiac soon after.
FATIGUE cracking of the type which caused the water ingress and subsequent abandonment of the MSC Napoli has been recognised as a problem of which operators of larger containerships need to be aware.
Long, narrow vessels such as containerships flex more than many types of ship in a seaway and care needs to be taken with the weight distribution in the cargo holds and tanks to minimise stresses.
They are also subject to torsional stresses in a quartering sea or with a swell on the bow that can contribute to fatigue stresses and even structural failure. Cracking in longitudinals, which have propagated to neighbouring structure and shell plates, have occurred to a number of large container vessels — not necessarily old ships.
Alerting owners to such problems, classification society Det Norske Veritas last October pointed out that side shell fatigue “had been of concern for some time”, with fatigue life on some designs found to be less than 10 years on some ships operating in particularly harsh conditions.
In its regular Container Ship Update, DNV, which happens to be the class society for the stricken British ship, suggests that regular visual inspection by ship staff, in areas where fatigue cracking is most likely, is a sensible precaution.
The society has developed a scheme, the Planned Inspection and Maintenance System, under which a ship-specific hull inspection manual would be produced for a containership, while ship’s staff would be trained to identify the first signs of fatigue cracking, along with a reporting system.
Using this system, a fatigue crack was discovered on a ship less than five years old. It is pointed out that such an inspection regime can be critical, as by the time a crack visibly manifests itself, some 90% of the fatigue life of the structure has elapsed.
Investigation into the causes of the incident are also expected to inquire whether the full sea speed grounding of the vessel on a coral reef in 2001 under its previous CMA CGM ownership might have some bearing on the subsequent structural problems.
The vessel, which was severely damaged in its forepart after being ashore on a pinnacle for nearly two months, was repaired in Vietnam and was bought by Zodiac soon after.
Etiquetas: maritime incident
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on martes, enero 23, 2007 at 9:58 a. m..
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