Corrosion in Down-Flooding Ducts

Lloyd’s Register has recently issued an inspection alert applicable to all passenger and passenger ro-ro ships fitted with down-flooding ducts. The subject ducts are formed as enclosed spaces on the ship’s side and provide for the necessary down-flooding in the event of serious collision damage. An investigation following a recent incident on a passenger cruise ship has revealed that, in certain conditions, accelerated corrosion can occur to the inner hull structures and shell plating around which the down-flooding ducts are constructed.

In particular, ducts in close proximity to galleys and laundry rooms have been affected. In some cases, internal inspection of these enclosed spaces has been restricted due to the carriage of permanent ballast in the tanks below and the limiting size of the ducts themselves. All down-flooding ducts are recorded in the damage stability criteria, on the damage control plan and in the instructions to the ships’ master. It is recommended that checks are made to determine that arrangements in place are satisfactory for inspection of these enclosed spaces. Consequently, access panels may need to be installed and also, confirmatory thickness measurements taken.All operators of Lloyd’s Register classed ships that have been identified as having down-flooding ducts, will be separately advised of new arrangements for survey of these items. Some operators may have installed such features for damage stability purposes under flag state jurisdiction and they are requested in such cases to contact their local Lloyd’s Register office with details.