The NTSB finally released it's report on the SS Norway's boiler failure.
You can read the full report at
http://www.ntsb.gov/publictn/2007/MAB0703.htm
Summary:
The Safety Board determined that the following factors contributed to the rupture of boiler No. 23 on the Norway:
*Lack of adherence to water chemistry composition limits and procedures by both the water chemistry subcontractors and NCL during wet lay-up periods, leading to pitting from oxygen corrosion.
*Failure to take number of boiler cycles into account during maintenance.
*Severe thermal transients from heating and cooling the boilers too quickly and from constraints created by frozen boiler support feet.
*Use of questionable weld repair procedures.
*Lack of appropriate nondestructive testing by the BV surveyors and NCL inspectors to determine whether cracks were present.
*Inadequate survey guidance from BV to its surveyors.
*Failure to repair cracks into which copper had been inappropriately introduced.
Probable Cause
The National Transportation Safety Board determines that the probable cause of the boiler rupture on the Norway was the deficient boiler operation, maintenance, and inspection practices of Norwegian Cruise Line, which allowed material deterioration and fatigue cracking to weaken the boiler. Inadequate boiler surveys by Bureau Veritas contributed to the cause of the accident.
