Position-related difference in surface salinity on board ro-ro vessels - A field study of corrosion sensitive cargo exposed to marine salts in the North Sea

Abstract: The marine atmosphere is one of the most corrosive environments due to its high content of wind-transported salts and high relative humidity. Transporting vehicles with corrosion sensitive parts on open decks is advised against in cargo handling manuals however this recommendation contravenes with the transporter’s need for flexibility regarding cargo placement on board. There is also a strong suspicion that regarding exposure to marine salts, some areas on the open decks can actually be compared to the fully closed main deck, where the vehicles are being transported today. The purpose of this study is to examine if this theory can be confirmed through surface salinity measurements, in order to provide the transporter with the knowledge needed as a ground for decision-making of whether it is possible to start shipping corrosion-sensitive cargo placed in such areas or not. This report contains results from a field study made during September-November 2015 on ro-ro vessels transporting vehicles in the North Sea. Using the Bresle method the surface salinity at predetermined cargo spaces is measured before departure and after arrival. These values are then compared to evaluate if there is a difference pre and post the sea voyages and if there are any variations between the cargo space areas. The measured salinity values are supplemented by results from weather observations during the voyages for the purpose of identifying eventual relationships. The results show that most of the areas on board that were considered for shipping of the vehicles have a very small increase in surface salinity. These areas are deemed as suitable for transportation under calm weather conditions. During more severe weather conditions most areas appeared to be unsuitable for transportation as they had a high increase in surface salinity.